MegaSquirt Carb to EFI Conversion

Part 1: TBI Fuel Only

Objective of this Article

This article will walk you through the process of installing a MegaSquirt EFI system on a classic carb’d vehicle attempting to go the least expensive route possible using junkyard parts and DIY ingenuity.  We’ll be using an MegaSquirt-II v3.57 ECU.  We’re converting the car over to an EFI ‘fuel only’ setup leaving control of the ignition in the hands of the old school distributor for now.  We’ll take control of ignition in a separate article, but like we recommend to first time EFIer’s, it’s easier to take control of fuel first, then ignition.  Fuel control is fairly easy and rewarding.  After this taking control of ignition isn’t that hard either and will continue the EMS (Engine Management System) learning process and the rewards of using an EMS.  That will come in part two.

We chose a 1977 Chevy Nova with a 350 small block as our subject, but the principles laid out here can be used just the same on a big block Chevy, or a Ford, Dodge small or big block engine, inline engine, a foreign motor…  a motor is a motor is a motor.  The only trick becomes finding a suitable intake and/or TBI and/or TBI adapter.  Or fabricating your own.  For the more common engines, off the shelf adapters and intakes abound.  For owners of the more obscure stuff, well, you’re probably a pretty good fabricator by now anyways eh?

Note that though this is one example of a Carb-to-EFI conversion using a MegaSquirt-II this system can be used on just about any vehicle, using TBI or Multi-Port injection, even Central Port injection if you so choose.  We’ll be doing further articles (MPFI soon) but you’ll certainly find the MSExtra Manuals an invaluable resource that our guides are meant to supplement and not replace.

Installing the Electronics

Mounting the ECU, Relay Board, and Fusebox

First things first.  I found a good spot under the hood on the firewall for the Relay Board, and another inside the cabin on the kick panel for the MegaSquirt.  I chose very visible spots for both boxes, you can be more stealthy of course though I had no reason to be ;).  I physically mounted the two boxes.  Drilled a hole out in the firewall and passed the relay cable through using a grommet to protect the cable.  I had also installed a couple of Innovate TC-4’s in this car for individual cylinder (all 8) EGT monitoring.  That’s really only needed in full on race conditions or tuning a motor for such conditions, or on R&D projects such as this car where I intend to swap several different EFI systems on and measure the differences in individual cylinder air/fuel distribution.

Wiring Main Power to the Fusebox

Next I installed a 70amp Main Power Relay and Fuse Block that I would be using to power all of the engine management and datalogging  goodies I had planned for this car.  The fuse block gets a 10ga ground directly from the engine block (battery (-) would have been good too).  It gets it’s 12v feed via another 10ga wire directly to the Positive terminal of the battery with a 60a MAXI type fuse right at the battery, then the 10ga wire is routed to and through the 70 amp relay so the entire fuse block is switched 12v.  I ran a trigger wire to the relay from the factory fuse block near the drivers feet.  There’s conveniently a spade terminal on the fuse block labeled ‘IGN’ that’s hot in crank and run, just like I needed.  You may not have this, but what’s important is that  the Relay Board and therefore the ECU/Fuel pump/Injectors, etc have power both when cranking, and when running.  Some circuits may be powered in one or the other but not both, you need both.

Note– This wiring above is really all additional to what is normally required.  This is what we did to support the additional goodies in this car, the two TC4 EGT amplifiers, the LC-1, and allowing a bit of room to grow.  Had we not needed the TC-4s or the ‘room to grow’, we would have done something simpler.

Like this:

Here in this simplified approach, which is really all most will need, you see the Relay Board’s main power is wired directly to battery 12v and Ground.  The 12v Switched position for the relay board’s power is run a switched 12v source that’s hot in accessory, crank and run positions of the key.  That’s important or you might not have power when cranking, so test it!  If you’re not installing a wideband yet, that’s it, you’re done with your power wiring.  If you are, then the above shows simple wideband wiring too.  You ALWAYS want to ground your wideband (and any analog wideband gauge) at the same point as your ECU to prevent what’s known as a ground offset which can effect the accuracy of your readings.  In this case that’s the battery where we’ve grounded the Relay Board, so bring the ground back there.  The 12v supply is less picky, but you’ve probably already found a good switched source for 12v so as long as it can handle the load (maybe 5a) then you can use it for your wideband too.  Then final wire is the signal wire out from the wideband and back to the MegaSquirt.  This would be the brown wire on the LC-1, to the ‘o2’ terminal on the Relay Board.

Wiring Power to the Relay Board

Next, power and ground were wired up to the relay board.  This required the third and final hole in the firewall that I drilled large enough for my EGT wiring an anything else I’d be passing through as well, also using a grommet of course.  The relay board was wired to the main fuse block’s ground and 12v switched supply.  I started with a 5amp fuse in this circuit, though I expect to have to increase that.  So that covers the ground for the Relay Board, and the Switched 12v for the Relay Board.  The final connection is the permanent 12v connection, this should go straight to the battery 12v post just on the ‘protected’ side of that 60A MAXI fuse.  I did this by connecting it together with the Main power input to the 70A Relay as can be seen in the above picture of the relay.

Getting a TACH Signal

Next I wired up the tach signal to Relay board from the distributor’s ‘TACH’ terminal.  I used some of our shielded wiring for this as there will be a ton of high voltage/current induced noise around the distributor and wires and I wanted to avoid that if possible.  This is a convenient pickup point on the 4-pin HEI distributors to grab a tach signal for a fuel only EMS installation, though you should try and avoid direct contact of your tach wire with the plug wires.  Crimp a spade terminal on the center conductor of the shielded wire.  Strip back the shielding from this end and cut it off so that it doesn’t contact the crimp.  Heat shrink this connection to protect it.  Use split loom to cover the wire to prevent direct contact, route it away from the plug wires as much as possible, and at the relay board side, connect the center conductor to the TACH terminal, and connect the shielding to one of the sensor return terminals to ground the shielding.  You only want the shielding grounded on one end, not both.

The following diagram I could have put in many places in this article, but I’ll go ahead and put it here where I’m discussing the first of the wiring that would need to go back to the relay board from the engine (tach signal).  You’ll refer to this for all of the later components as well though, sensors, injectors, IAC, etc.  Everything you see here:

Note the above wiring diagram shows one difference from how I wired things up– this shows how to use a 2-wire narrowband o2 sensor.  I highly recommend a wideband o2 sensor such as the AMP Wideband as when it comes to tuning time nothing else but a wideband will do.  Use the information in the ‘simplified power wiring’ diagram above for wideband wiring. 

MAP/Vacuum Signal to the ECU

Next I routed the MAP signal hose (vacuum line) to the MegaSquirt through a small hole drilled in the firewall just next to where I passed the relay cable through.  I connected this to the MegaSquirt and made sure I had enough loose vacuum line in the engine compartment to reach the TBI’s vacuum port I’d be using.

Should I play or should I go?

At this point, you can still drive the car around on the carb, but you can connect to your MegaSquirt with the tuning software and see your RPM and manifold pressure.  You can also datalog this if you want and play with the software a bit just getting a feel for things.  You don’t have much info yet as you’ve only wired up two inputs, but it’s a start.  Pretty cool eh?

Wiring up the CLT Sensor

Ready for more?  Install and wire in the CLT sensor.  Many intake manifolds have a boss just in front of the thermostat opening where they’re either already tapped, or where you can drill and tap them for a CLT.  The Coolant Sensors we offer use a 3/8″-NPT thread.  Wire this back to the relay board’s CLT and CLT RET terminals.  You can’t wire this particular sensor backwards as it will work either way, but if you run a black wire back on one side go ahead and run it to CLT RET to avoid confusion, that is the ground side of the circuit.

Wideband Oxygen Sensor

Next install and calibrate your wideband o2 system.  Though installing a dedicated wideband in the car is optional, it’s highly recommended.  We recommend and sell the Innovate Motorsports LC-1, it’s affordable, easy to install if you can follow a few simple directions, easy to calibrate, and does a great job.  We use the common fuse block for power and ground, however if you’ve gone a simplified path like many will and wired your relay board straight to the battery then you can wire your wideband just like we did in the diagram above titled “Simple Relay Board Power Diagram with LC-1”.

IAT/MAT – now or later

You could go ahead and wire up an intake air temp sensor too if you want and keep playing around with the software and datalogging, learning a bit about how the car ran on the carb before going any further.  Or for that matter I’ve had customers wire up our systems about this far along and use them as datalogging systems only for longer terms, knowing some day they wanted to go EFI but happy to just collect data for the time.

Here’s an easy way to add an MAT/IAT sensor to your stock carb-style air cleaner:   (note:  the terms MAT and IAT are used interchangeably, meaning Manifold Air Temp, or Intake Air Temp)

So now your MAT/IAT sensor just screws into the bottom of your otherwise stock looking carb-style air cleaner.  As it’s internally the same type of sensor as a CLT the wiring polarity doesn’t matter, wire one side to the MAT terminal on the Relay Board, and the other side to the MAT Ret terminal on the relay board.  Again, if you choose black for one of the wires, it just makes sense to use that on the return side.

So now what?

At this point, you’re able to datalog all, or nearly all (if you didn’t install the IAT yet), of the inputs required for EFI to function on your car.  Again, drive it this way it is for a bit if you’d like and get used to the computer interface and datalogging tools, or just dive into the next section and go EFI!

Installing the TBI System

Finding the TBI bits

Remember our goal here is cheap and as easy as possible.  So I hit up the junkyard, found a 1992 GMC 2500 Van with VIN ‘K’ indicating it had a 350 in it, and grabbed the TBI system including the air cleaner, injectors, and a couple feet of the fuel hardlines.  Also make sure to get several inches of all wiring and all connectors.  Make sure you get the mounting bolts.  Cost me $33-34 total.  Here’s what I got for that:

Preparing and installing the TBI

I then slapped a TBI adapter plate on my Torker II intake Manifold and bolted the TBI to it.  I found the stock mounting bolts were a touch too long.  I could have either cut them shorter, or used washers, so I sortof used washers.  I found some nuts in my spare jar that were just big enough to slip over the bolts and act as thick washers.  Works like a champ ;).  Lastly I cut both fuel lines down short leaving just enough that I could clamp the feed and return onto them.  Check your o-rings and if they’re in bad shape then replace them (parts store), mine weren’t perfect but were holding together, and they’ve been fine though I may grab some replacements next time I visit the parts store.  Make sure you de-burr that fuel line so it won’t damage the hose you clamp to it later nor release any loose metal in the lines at a later date.

Throttle Linkage

So now I’ve got my the TBI bolted up to the manifold, I’ll go ahead and work out my throttle/kickdown linkage before I wire it up.  I re-used the stock carb linkage from the Quadrajet, but had to build a spacer to move it back just a bit.  The pics below show me holding the throttle wide open with the cable in the WOT position as well, I then measured the difference in the hookup versus hole alignment and made a spacer to move it back that far.  Easy enough right?

Fuel Injector Wiring

Next, wire up the injectors.  Run 12v Power to each of the injectors on one side, I chose the White and Red wires for this.  You can actually crimp these together to a single larger gauge (14-16ga) wire and run that back to one of the ‘Injector 12v’ Terminals on the Relay Board.  Then wire the Blue wire up to the INJ1 terminal, and the Green wire up to the INJ2 terminal, both on the Relay Board.

True, if you look closely above there’s only one injector wire run back to the relay board in that picture.  OK you caught me with a bad picture.  Here’s another pic further along in the process where you can see both run back, one to INJ1 (Blue) and the other to INJ2 (Green).  You can also see the Injector 12v wire run back to the relay board here.

Throttle Position Sensor Wiring

Next, wire up the 3-pin Throttle Position Sensor connector on the TBI to the Relay Board.  This is simple.

  • Grey wire goes to VREF terminal on the Relay Board.
  • Blue wire goes to TPS terminal on the Relay Board.
  • Black wire goes to TPS RET terminal on the Relay Board.

*You’ll need to calibrate your TPS in the tuning software later.  We’ll go over that but I figured I’d mention it here.

Installing and Wiring the IAT/MAT Sensor (if you didn’t already)

Here are a couple of ideas for installing an IAT sensor in a GM TBI system:

First option> In the stock GM TBI collar with the stock GM TBI Air cleaner/snorkel.  Very clean appearance, hides the TBI system well, breathes fairly good but not as good as putting one of the other two cleaners (below) on top of the collar.  In my case it didn’t quite clear my hood so I tried something else.

Second option> Alternately, you can put the IAT sensor right into the bottom of a carb style air cleaner like so.  Then you can set it directly on top of the TBI without the collar, BUT, you will likely loose some top end power without the collar in there.  You will gain in the ‘stock-carb-like-appearance-factor’ as the carb-style air cleaner will practically hide the TBI system when sitting that low.  But you might suffer a bit in airflow at high RPM.  See the next section ‘What to use for an air cleaner?’ for more info.

So now the IAT just screws into the bottom of the otherwise stock looking carb-style air cleaner.

Third Option>  So I’ve found I need the collar there.  So I’m putting the IAT back in that GM TBI Collar similar to Option 1, and under an air cleaner.  Either a stock carb-style round air cleaner, or an aftermarket low profile air cleaner for more hood clearance.

On our 77 Nova I was about 1/2″ short on hood clearance to fit the GM TBI air cleaner sitting on top of this collar.  I similarly didn’t have quite enough clearance for a 3″ tall round carb-style cleaner.  So since I didn’t want to go to a raised cowl hood, my final solution was a low profile aftermarket foam filter.  Cheap and easy, though sacrifices appearance a bit.  If I was a bit more determined I could have shortened that collar 1/2″ and used that 3″ carb style cleaner for the best of both world, breathing and appearance.

Back to the original focus of this section, the IAT.  When wiring the IAT/MAT sensor, it’s internally the same type of sensor as a CLT so the wiring polarity doesn’t matter, wire one side to the MAT terminal on the Relay Board, and the other side to the MAT Ret terminal on the relay board.  Again, if you choose black for one of the wires, it just makes sense to use that on the return side.

What to use for an air cleaner?

I found in dyno testing that you absolutely want to use the riser collar that comes with the TBI unit under your air cleaner.  It’s amazing the difference it makes if you pull this puppy out, and it’s a difference most won’t like.  This serves more purpose than just raising the filter up, but it also straightens out the path of the airflow as it enters the throttle body.  On our test car this was worth only about 4-6whp up at the peak(around 4000rpm), but an amazing 40whp, yes four-zero wheel horsepower near redline at 5300-5400rpm.  The air just can’t enter the stock GM throttle body at a right angle like that fast enough to keep up and it severely hinders the flow of the TBI unit without this collar in place.

So what worked the best?  Using the collar, with the stock carb-style air cleaner on top and paper filter seemed to work the best, and provides the most carb-like appearance.  However with the hood clearance I was working with I’d have to find a seriously short filter to allow me to close the hood this way.  I tested both 3″ and 4″ tall filters on the dyno and saw no HP difference, though neither would fit under my hood without surgery.

Pretty much identically following the hp/torque curve of the above was the Edlebrock low profile foam filter.  This is short enough to clear the hood, and breathes nearly as well as the tall paper filters above.  It may have averaged 1 whp less if that.  IMO well worth solving the hood clearance issues unless you like the idea of installing a cowl hood or cutting a hole for a scoop.  This is the route I ended up choosing.

The stock ‘black snorkel’ TBI air cleaner came in third– it breathes fairly good up until 5000rpm or so and then fell off loosing horsepower rapidly.  Still much better than the final option.

The last option, removing the collar from the TBI and sitting an air cleaner all the way down on the TBI looks fairly carb-like stock, and around town, under 4000rpm will perform very good, but above 4000rpm it’s going to hinder performance significantly.  HP/TQ fell way off from about 4000rpm all the way to redline.

Fuel System

Installing and Wiring the Fuel Pump and Filters

I chose a location just in front of the fuel tank and above the wheel well.  I first determined where I wanted to place the pump based on easy inlet and outlet as well as mounting considerations, and then I marked the stock hardline to cut a section out of it where I’d be patching the fuel pump in.  I then unbolted and removed the factory hardline from the fuel tank leading up towards the engine bay, drained the fuel out of it, cleaned it off/out and cut it where I had it marked.  Deburred it good and then reinstalled the two pieces.

I drilled holes in the framerail for the mounting straps (yes you should use both straps, I only have one on in the picture below).  Then I bolted the fuel pump in place, attached a low pressure inlet line to a AN-6 inlet fitting, (could have used a 3/8″ barb fitting but this just felt cleaner), and built a stainless AN -6 line for the outlet (high pressure) side to attach it back to the factory fuel hardline.  The last step was to wire the ground connection for the fuel pump to a local chassis bolt and the power connection for the fuel pump to the ‘FP’ terminal on the MegaSquirt Relay Board under the hood.  I chased the fuel line up to the engine compartment with this wire, covered it with the smallest split loom I had, and zip tied it all up neatly.

Note– the fuel pump location here is a bit on the high side.  I tried and killed a different manufacturer’s pump in this location, the Walbro has held up fine although I would recommend mounting it lower as it’s close to the top of the fuel tank in this install.  There just isn’t a great location in front of the fuel tank and clear of the exhaust that I can see.  But now that I’ve looked harder, behind the fuel tank attached to the bottom of the trunk area is lower and would get a better gravity feed of fuel and will be where I mount the new pump.  (We’re using this car to test all sorts of bits, next up, the SX Performance line of pumps)

Next I installed a small ‘pre pump’ fuel filter just at the outlet of the tank.  (Yes this is important.)  Note this fuel pickup had a ‘sock’ strainer inside the tank, but it was old and worn and I didn’t want to trust the life of my fuel pump (and potentially my engine) to it.  A 60-100 micron stainless filter just outside the tank and before the pump will do a fine job.

Then I installed a second ‘after pump’ 40 Micron fuel filter on the fuel feed line at a factory break in the hard line where there was a worn out rubber line that needed to be replaced anyways (as it wasn’t designed for EFI pressure), just under the passenger side door.   The fuel filter had -8 AN male fittings on either side, I used a pair -8 to 3/8″ barb fittings from a local hardware store plumbing dept. to adapt this to 3/8″ barb and clamped it on the line with worm clamps.

Note this fuel filter is very small and not really intended for long term use without servicing.  Something along the lines of the SX Performance filters we’re now carrying would be much better suited to this job.  The SX Performance 10 micron paper filter anywhere after the pump and before the injectors (before the TBI) will do the trick.

Completing the Fuel System

Now for the fuel return.  This car being a 1977 has a very tempting vent tube coming back up from the fuel tank to a charcoal canister under the hood.  Resist temptation and don’t repurpose this as a return line.   On our test car there is an obstruction that does not allow adequate flow in this line and it does not make a suitable return line.  Besides that, it’s venting your fuel tank, and that’s a good thing.

Instead, you’re going to want to add a return line to your fuel tank.  Sounds like a pain, but at least in our case it really wasn’t that bad.  You’ll want to disconnect the fuel lines and drop the fuel tank.  Check out your tank and how much space you have to add a new return line, it doesn’t take much.  Remove the locking collar and pull the line assembly out of the tank.  (Make sure to clean up the top of the tank first to keep junk from dropping in.)

Now, you can either get a steel fitting and weld in a nipple, carefully making sure the entire apparatus/lines are fuel free first.  Or you can do what we did and simply drill a hole and thread in a barb elbow.  I ran up to the hardware store and grabbed a 90 degree barbed to pipe thread elbow fitting and a couple pipe nuts.  Found where I could center it so that I would still be able to spin the nuts when it was in place.  Center punched that spot, drilled it out, and threaded the elbow in place using a bit of gasket maker to seal it up (just a tiny bit).  Make sure to point the barbed nipple in the direction you want your fuel return to come from taking into account obstructions when the tank is remounts (probably safe to follow the other lines), leave room for a clamp on the hose, and make sure you can get the locking ring back on to seal your tank back up.  Reassemble the tank, attach your lines including your new return line, clamp it down, and hang your tank back on your car.  Don’t forget to hookup your fuel level sender wiring!

Here’s a progression of images that tells the story pretty well.  Like any of the pics in this article, you can click on any of them for a closer look.

Note I did not use the rubber washer in those images, instead I used a bit of silicone gasket maker on the threads/nuts, just a touch.

Back under the hood to finish the fuel system up–   For the fuel feed I used stainless braided 3/8″ fuel line and slipped one end on the factory hardline and the other on the feed hardline on the back of the TBI.  Standard worm gear clamps hold it all in place preventing leaks.

What about a Fuel Regulator?

When using a factory GM TBI system the regulator is built right into the TBI unit itself.  It’s almost too easy ;).

Checking the Fuel System for leaks

At this point, everything is in place that is needed to fire the engine up.  The fuel is plumbed.  The intake system is wired in and throttle linkage has been fabricated.  It’s time to check for fuel leaks.  Have a properly rated (for fuel/chemical fires) fire extinguisher nearby for this just in case, better safe than sorry.  I key’d the power on to the ECU and could hear the fuel pump prime for 2 seconds and then shut off.  Got out and looked in all of the obvious places for leaks, this includes everywhere I’ve made a fuel connection (hose, filter, pump, TBI, etc).  Look under the car for wet spots that weren’t there before.  Smell for fuel.  I didn’t see anything obvious so next you can either jumper the fuel pump relay on, or what may be easier than that is to just have someone turn the key on/off several times letting it the pump prime for 2 seconds each time while you check for leaks everywhere.  I used the second method an in my case I did find a leak where the rubber hose I was using for a return line slipped onto the TBI hardline.  I didn’t have it clamped down tight enough, I corrected that and then all was well.   After the car is fired up I’ll check for leaks again.

Preparing for the First Start

Use the MSExtra MS2 Manual to configure your MegaSquirt ECU for your engine.  This will include setting the ‘constants’ which are parameters that set the MegaSquirt up for the size engine you are running the EMS on and the size and number of injectors are you using as well as the type (low or high impedance).  It’s important that you use the manual to configure your MegaSquirt, just follow it through reading each section and setting one setting at a time.  It really doesn’t take that long.  Here are a list of links for the most common setups:

MS2 Extra Manual – This is the latest ‘greatest’ firmware on the newest hardware.  Full featured code still under heavy development to add even more features and improve the current featureset.

In most cases it’s wise to configure your ECU while connected to it and with it powered up.  The reason for this is this will allow you to start with the base settings that are in the ECU as it ships to you, instead of a completely blank slate, and it will make your job of configuration simpler.  So power up your car, connect to the ECU with the tuning software, and configure the settings in the configuration sections of the manual for your hardware/firmware.  You can also do this using a stimulator to connect to your ECU is you prefer not to sit in the car while you configure the ECU.

What did we use?  On this 77 Nova we have been running the MS2 Standard Firmware.  It runs the car beautifully, though I may move over to MS2E for the closed loop idle speed control.  The base MS2 code controls the idle motor just fine warming the engine up with the valve open and closing it down as the engine warms up, but not in a closed loop fashion allowing me to target a specific idle speed.  MS2E will target a specific idle speed once warm keeping your idle right where you want it.

Final ‘Sanity Check’

Connect to your MegaSquirt ECU with the tuning software.

  • Make sure the IAT and CLT readings look fairly accurate given the ambient temperatures.  Keep in mind heat soak from glaring sun if the car is exposed to the sun.  If a sensor is completely disconnected it will typically read -40*F.
  • Make sure the throttle opens and closes with your application of the pedal.  Go ahead and calibrate the TPS sensor from the TOOLS menu if needed.  This is simple, no tools required.  With the power on and engine off it will just take a reading while off throttle (while off the throttle you click a button on your PC), and then take a reading at full throttle (while at full throttle you click a button on your PC).  And then you close the tuning software, power the car off and back on, open the tuning software, and the calibration is complete!  It should now go from 0-100% as you apply the throttle.  If you can’t see the throttle readings on one of the front gauges you can select ‘Realtime Display’ from the Tuning menu at the top of the screen.
  • Make sure your Engine MAP reading is reasonable.  Sea Level is 100kpa so if you’re near sea level 99-101 kpa would be normal, above sea level will be less than this.  For instance in Atlanta,GA elevation ~1000ft above sea level 95-97 kpa is pretty normal.  In Wendover, Utah (Bonneville, elevation 4227ft) ~84 kpa is normal.  This reading depends on your elevation and air density.
  • If you find a problem with a sensor reading you should find the source of the problem, the EMS will need the sensors reading properly in order to properly run your engine…

Time to Fire it Up!

If you’re running a fuel only TBI setup fairly similar to what I’ve outlined in this article and it’s wired up right, you’ve got fuel pressure and the ignition system is still functioning properly (independently of the EMS at this point), then firing the car up should not be a problem at all.  Just as a test I tried firing this 77 Nova up with the ECU completely misconfigured, I just left the base map on it which is setup for a multiport EFI (8 injector) 408 small block.  On my small block 350 with only 2 injectors, the motor fired right up and started idling.  A bit rough but it idled.  I shut it down and quickly configured the MegaSquirt for this engine.  Care to watch the entire process?

Tuning your EMS

Without getting into a ton of detail in this article, yes your EMS will need to be tuned now.  The MSExtra MS2 Manual goes into pretty good detail on this.  There are several books on the topic if you’d like to tune it yourself.  Go to Amazon and search for ‘EFI Tuning’ for example.  Or you can take it to a pro. 

On the Dyno

I put the car on our in-shop dyno and dialed it in.  Compared to the factory Quadrajet and cast-iron intake this car makes much more torque and upper-end horsepower now than it did, but I now need to tell you a bit more of the story as I don’t have a comparable dyno plot from the Quadrajet/stock intake.  Before I converted to EFI I tested a couple different intake manifolds and tried a brand new Holley 600 carb as well.  Not suprisingly I found the best combination for this mild 350 was the Edlebrock Performer manifold and Holley 600 carb, where it made 186.9whp peak and 295ft/lbs of tq at 2300rpm.  The best I was able to do with this GM TBI, which is a 480cfm 2-barrel by the way, was 184.3whp at peak and 311ft/lbs of tq at 2300rpm.  A slight decrease in the top end horsepower, and a decent increase (16 ft/lbs) in low end grunt.

Test5 was the best we did with any Carb/Intake combo.  That’s the dotted lines.

Test 9 was the GM TBI, that’s the solid lines.  You can see this does great up until about 4000rpms on this mild 350.  It then falls off a bit due to lack of airflow, then pulls back ahead at higher RPMs as the AFR (air/flow ratio) with the carb got too rich up here killing power, and we kept the AFR in check with the EFI system.  If the carb had been leaned out a bit up top chances are it would have made a bit more power up top than this small TBI did.  A bigger TBI though would take that advantage away.

If you want a simple install using a TBI like this but want a higher flow TBI, there are modified hi-flow GM TBI’s available in the aftermarket (ebay is a good place to look), and Holley has a 900CFM 4-barrel TBI that works just great with MegaSquirt, you can often find them used on Ebay or Craigslist.  The airflow is the problem, 480cfm just isn’t enough, 900cfm, that would be nice on this motor and give room for a few mods.  And unlike a carb you’re not going to have a problem if you go a bit larger than you need, you’ll just have room to grow.

Either way, I’m only out what, $75 on this TBI even after the rebuild even if I decide to upgrade to a bigger unit, or go MPFI (which is what I’m thinking).

Another Dyno Chart you should see for future comparisons

In the middle of this project I had the opportunity to get a new dyno, a much bigger dyno that can handle about 3x the horsepower of the dyno I had been using.  I had to jump on it.  It’s the same brand (DynaPack) but it’s a 2WD 4000 good for 1100-1200whp.  What this means to this test is the dyno graphs I’ve got from the old dyno will not directly compare to this new dyno as it will read differently, they all do.  This machine reads a good bit lower than my old machine did, about 14% on this car it seems.  I wanted to show a graph of the results from the old dyno, compared to the results as taken on the new dyno for comparison.  Keep in mind that the car is in the exact same configuration, I’ve changed nothing at all, not the tune, not any hardware.  The only difference between these two plots is the dyno used to take them and the day they were taken on.  On future tests in future articles, the new dyno plot here is what we’ll be comparing to as I’ll be continuing to test on this new machine.

You can disregard the funky torque reading right at the beginning of the pulls, that’s the torque converter causing that.  It’s not there on the new dyno pull as I started it at a lower RPM and that funkiness is off the chart to the left.  You can see though that at peak WHP it’s a 22.5whp difference in the readings from the old dyno to the new.  Same car configuration and tuning, just different dyno, different day.  My old dyno apparently read a bit higher than a typical DynaPack, and this new one is going to be a bit of a heartbreaker.  That’s OK though.

Just keep in mind in future articles related to this car, you’ll be comparing to the lower numbers here to see how we’ve improved from the initial TBI fuel only setup– I wish I had this dyno around when I had the carb setup on it so I could keep all the comparisons consistent, but that’s just how it goes.

Impressions

The car just flat out runs better than it ever has.  Fires up on the coldest of GA mornings (mid-high 20’s water temp) with the first turn of the key and warms itself up beautifully just like a new car would.  Idles itself up when cold and down when warm.  I had a steady idle at 360rpm once, but I tuned it back up to a bit more reasonable speed as I don’t trust it to always be happy idling at that speed under different loads.  It’s making within 2-3hp peak of what the best 4-barrel carb I tested did (Holley 600) and this is with a 480cfm 2barrel TBI.  In every way the car runs better than ever, but under highway cruise conditions the TBI sitting on the carb manifold doesn’t distribute the air/fuel mixture evenly enough to lean out the mixture too much on this car so I’m running it a bit richer than I’d like, not that different than the carb.  As the air/fuel mixture isn’t as even as I’d like to see I can’t lean it out when cruising where it needs to be to get the mileage, so I’m not seeing a big improvement in gas mileage.  Only the slightest bit better than the Quadrajet on the stock manifold.  Multiport should go far to correct this, and I should also mention my heads are a pretty nasty casting with the ports being pretty horribly mismatched to the intake, many of them about 10% blocked due to the poor casting.  I left them this way for consistency in testing, but I know it’s playing a role with fuel puddling and falling out of the airstream.  MPFI will certainly help but if this nasty casting is playing a large role that will still get in the way some.  After I convert to MPFI and test I’ll be dropping new heads on.  Until then I want to leave this factor in place for consistency.

As far as enjoyability and driveability– it’s vastly improved.  That’s great for one of the least expensive routes to EFI, and one that can be easily adapted to MPFI if you’d like to later, in fact, that sounds like a good idea for another article.  Taking what we’ve got here, a good thing, and showing how, in baby steps, we can make it better.

Part 2: Ignition Control

Objective of this Article

This article will walk you through the process of installing a MegaSquirt EFI system on a classic carb’d vehicle attempting to go the least expensive route possible using junkyard parts and DIY ingenuity.  We’ll be using an MegaSquirt-II v3.57 ECU.  This is Part 2 of the process, in Part 1 we completed the initial Fuel Injection Conversion, converting the car over to an EFI ‘fuel only’ setup leaving control of the ignition in the hands of the old school distributor initially.  This is easy to do for the first-time EFIer and takes much of the intimidation out of the process.  Now with that foundation laid the ignition control will be pretty simple to add as well so here in Part II we’re going to take control of the ignition with the MegaSquirt-II as well.

We chose a 1977 Chevy Nova with a 350 small block as our subject, but the principles laid out here can be used just the same on a big block Chevy, or a Ford or Dodge small or big block engine, inline engine, a foreign motor…  a motor is a motor is a motor.  You may not be able to use the same exact distributor we snagged as we took one from a computer controlled smallblock Chevy that was actually originally used with the same TBI system that we grafted onto this car.  But if your motor was ever used with a computer controlled ignition you can likely snag those bits and follow our lead to do something similar.  Or there are always other options, such as modifying your stock distributor to lock down the mechanical ignition advance (vacuum and centrifugal) and then using it with computer control.  Or fitting a crank trigger wheel to your engine and either using your distributor to spread the spark around, or converting to a coil pack ignition system.  We’ll cover what we did on our car in detail, but then we’ll also cover your other options.

Note that though this is one example of a Carb-to-EFI conversion using a MegaSquirt-II this system can be used on just about any vehicle, using TBI or Multi-Port injection, even Central Port injection if you so choose.  We’ve kept the focus on these first two articles on converting to EFI as affordably as possible, in stages allowing the first time EFI to take on EFI in steps that will help take much of the mysticism out of the process.  We’ll be doing further articles including converting to Multi-Port EFI soon which will involve more cost, and provide more performance.  Stay tuned.

As always, we highly recommend you dig into the MSExtra Manuals in addition to these articles.  It’s a big read, but it’s a valuable resource that our guides are meant to supplement and not replace.

Stock GM TBI Era Distributor

Digging up the Distributor and Coil

I headed back down to the local pull-a-part looking for Chevy/GMC vans again as this seems to be the most prevalent source of GM TBI era bits for Chevy V8’s.  Look for VIN ‘K’ vehicles for SBC 350 motors, though for the ignition parts the 305 bits would have been just fine I imagine.  I found a distributor, coil, and all pigtails with a foot or so of wiring attached.  Paid my $31 for them and was on my way.  On the way back to the shop I stopped and picked up a new cap and rotor for them.  That was $29, about as much as I paid for the dizzy and coil ;).  So I was $60 in.  Not bad.

By the way-  make sure your dizzy has the HEI module inside of it, I saw a few with this missing.  And check for broken clips on the pigtails, there’s always another van you can snag them from if you need it.  You can probably find the same pigtails in the 6cyl vans in a pinch.

Distributor rebuilder Pierre Payant contributed a couple of tips about common problems to check for on used HEI distributors:

First concern: the distributor uses a plastic base to secure the cap. The ears on that base are very-often cracked or broken… These distributors are nearly impossible to fix inexpensively, so checking the cap-mounting ears is very important. Junkyarders should remove the cap and check for damage before they pull and purchase. Also, using caution whenever reinstalling the cap is of paramount importance… this is old, heat-cycled plastic and those tabs are easy to break. It doesn’t take a lot of fastener torque to secure a distributor cap, so don’t go crazy.

The other thing to check is the factory ignition coil used with this setup. These are notorious for voltage leakage from the coil’s windings through the case to the laminated surround plate, which will cause intermittent misfires under load that can drive a person to drink trying to diagnose. The problem is easily seen, though, by inspecting the coil itself. If the plastic coil case has what appear to be “hard-water” stains (dry white or grey marks) near the laminated surround, it shouldn’t be used as the coil has been grounding itself and will continue to do so. The problem with this leakage is that it seems to only happen under a load, making it nearly impossible to diagnose in the shop. High-performance aftermarket coils seem less susceptible to this problem while GM and parts-store replacements seem to eventually fail in the same manner… though these E-coils rarely outright die.

I thought you might want to insert this information in your ignition article to avoid heartbreak or frustration among the frugal Chevy guys duplicating your setup.

Thanks, Pierre!

Checking out what I’d found

All appears to be in good shape.  The distributor has an 8-pin HEI module inside of it.  Two of the eight pins go straight to the VR sensor inside the distributor.  Then there is a 2 pin connector and a 4 pin connector on the outside of the distributor, both mushroom shaped.  You did get the pigtails for these right?

Installing the Distributor  (don’t pull the old one out yet!)

You install your distributor pretty much the same way you would any other time.  There’s one notable exception– you get to choose which distributor terminal is #1 now.  To reduce the chance of confusion, and because your plug wires are probable already laid out for it, I’d choose the distributor terminal that’s in the same position #1 has always been in.  Here’s a step-by-step though….

  1. First get your #1 cylinder at TDC on the compression stroke.  The easiest trick to do this is to pull the spark plug out of the hole, cover the plug hole with your finger tip (not in the hole, over the hole sealing it) and have someone ‘just bump’ the ignition until it pops your finger off the plug hole with a burst of air.  You’re close to TDC now.  Look at your damper timing markings and use a socket on the crank pulley bolt to line it up just right at TDC.
  2. Pull your old distributor out.  If you waiting until now to pull it out your life will be easier as the slot in the top of the oil pump shaft will be lined up just right to drop in the new distributor.  If not then you’re going to have a bit of fun with a long screwdriver or pry bar lining that thing up before the next step.  Don’t drop the screwdriver.
  3. Determine which way you want the electrical connectors on the HEI8 distributor to point out.  I pointed mine directly out towards the passenger fender.
  4. Insert the new HEI8 distributor with the electrical connectors pointed where you want them, and the rotor pointed just a few degrees COUNTER-clockwise of the #1 plug position.  As you sink it into place it should seat all the way down and the rotor will rotate a few degrees back clockwise now leaving it pointing at or near the #1 terminal (or where that terminal will be when you install the cap).
  5. Snug the distributor into place, you don’t have to crank it down yet, you’ll set base timing a bit later and will need to twist it a bit.

Mount the Coil

Find a suitable place and mount the coil.  Many aftermarket intake manifold have holes drilled/tapped in the factory location for this coil right next to the distributor.  If your throttle bracket isn’t in the way then this is the perfect place to mount the coil.  If it is in the way, or you need to put it somewhere else for another reason, then find a good spot and mount it up.  I’m more into function than form myself and just mounted it to the firewall right next to the distributor.  Keep in mind the wiring length you’ve gotten from the junkyard for the Coil-to-Module wiring (which you could extend if you wanted to really).  Also note that the coil bracket needs to be grounded.  Bolting it to the engine is perfect, in my case it’s working fine bolted to the firewall with that as a chassis ground.

How do I wire it up?

Pretty straightforward setup here — Note I’m only showing the ignition related wiring attached to the relay board here.  If you were previously running a fuel only setup similar to what we detailed earlier then you had a wire run from the TACH terminal on your old distributor to the TACH terminal on the relay board.   You’d remove that (and it’s shielded wire that was connected to a ground on the relay board).  Then you’d wire the new setup in as shown above.

  1. COIL 12V POWER: It’s pretty simple to use the stock 12v wire that used to connect to the factory distributor.

  2. COIL to MODULE WIRING:  This is two wires (C and + in the diagram above) with factory connector on each end.  Just plug  the coil into the HEI Module, that’s it.

  3. COIL to ECU WIRING:

    1. G (Ground): Wire to TPS Ret on the Relay Board

    2. B (5V): Wire to VREF on the Relay Board

    3. R (Signal from Reluctor/Module to ECU):  Wire to TACH on the Relay Board

    4. E (Signal from ECU to HEI Module to fire the coil):  Wire to S5 on the Relay Board (S5 goes back to pin36 on MegaSquirt)

One note:  You might notice in the MSExtra MS2 Manual, the recommendation to wire the B wire (5V) through a relay that makes this 5v signal hot when the engine is running, but not when it is cranking.  Let me explain why– this 5v signal tells the HEI module to allow the ECU to control the timing.  When the ECU is NOT getting a 5v signal it goes back to base timing (whatever you set with a timing light here in a few minutes).  The stock ECU does NOT send 5v when cranking so that the engine cranks at base timing.  Wiring this as per the manual creates the same type of behavior.  My wiring recommendation above goes about this differently, but works well nonetheless.  The difference is the computer is controlling timing during cranking.  This shouldn’t cause a problem as long as the computer is configured properly, and in my tests I’ve had no negative effects at all.

Ignition Timing Connector- The factory wiring you snagged had a single wire disconnect on the B wire (wired to VREF on the Relay Board).  This is there to allow you to set base timing as controlled by the module.  Go ahead and disconnect this leaving this circuit open for now.  This will allow the car to be started at module base timing, you can then set the base timing with a light (with the old dizzy twist) and then you’ll connect this connector back up, giving the computer control.

Reconfiguring your MegaSquirt for HEI8 Ignition Control

First off, don’t let this part scare you off.  We’ll do it for you for a few bucks if you don’t want to do it.  But the configuration the MegaSquirt-II ECU’s ship in, while suitable for some ignition systems and for fuel-only control like in the first article in this series, needs to be reconfigured (or modded internally) to control your HEI ignition.  Thankfully we’ve been able to make this incredibly simple, particularly if you’re using a MS2 v3.57 ECU purchased since the release of this article.  We’ve updated the ECUs themselves and released a ‘mod-kit’ that makes converting these units for HEI use as simple as it possible can be.

First, you’ll need to order the MK-HEI Mod-Kit from our website.  This included some header pins you won’t need, but more importantly it includes to jumper wires, one of which has a resistor in the middle of it.  In text steps, this is what you do on a v3.0 or v3.57 board:

  1. Remove the TachSelect to OptoIn jumper, and the XG1-XG2 jumper.  You won’t need them anymore while running HEI ignition.
  2. The Red (resistor) wire runs from the #3 pin (OptoIn) to the 5v Pin near the MS2 Daughterboard.
  3. The Green (no resistor) wire runs from the TachSelect pin (middle of JP1)  over to the XG1 pin.
  4. That’s it.  But for the more visually inclined learners, how about a video?

Don’t turn the key yet! (not even part of the way)

Before you power anything up, you need to reconfigure your MegaSquirt-II for your new ignition system.  You can do this in the car, with your laptop connected to the MS-II.  But before you do anything, disconnect the connectors on the coil and distributor that you just installed.  This is to make sure that nothing (HEI module or coil) is damaged while you are configuring these settings in the event that something is improperly configured when you first power up or anything while you’re messing with the settings.  Then once you’ve confirmed the settings are correct you’ll plug everything back up.

You can access these settings on the Ignition Setup>Base Ignition Settings screen.  Make sure you BURN TO ECU any changed settings.  You’ll also need to power cycle the ECU for these settings to take effect if you need to change them (any settings in red require this).  Here are the settings you’ll be changing and/or confirming:

  • Ignition Input Capture: Falling Edge  (Assuming you used our MK-HEI modkit which inverts the input signal.  If you did your own thing this setting could be different)
  • Cranking Trigger: Trigger Rise
  • Coil Charging Scheme: Standard Coil Charge
  • Spark Output: Going High (Inverted)

Once you’ve configured these settings and Burned them to the ECU, you can power off the car (at the key) and plug the coil/module connectors back in.

Most of these settings match the default settings in the base map, one is different, and you should always verify.  The wrong settings here can damage your HEI module, your coil, or just cause really erratic ignition timing.  That’s why I had you unplug the connectors to your coil/module until you made sure the settings were correct for the HEI ignition system you are using.  Note that if you’re following this article but using a different ignition system, you can still follow the general guidelines of this article, but the configuration of the ECU hardware and software settings may need to be different for whatever ignition system you are using.  Feel free to contact us and we’ll help you sort it out.

MegaSquirt Ignition Control EFI Conversion Installation Help

Starting the car for the first time

Up in the wiring section I suggesting leaving the Ignition Timing Connector disconnected after you wired everything up.  This will allow you to crank the engine up at module commanded timing without the ECU controlling timing yet.  Ignition timing will be at a fixed number of degrees and will not move at all as there is no advance mechanism in this distributor, that’s why you will need the ECU.  But for now, the Ignition Timing Connector is disconnected.

Start the engine.  It should start fairly easily.  The timing won’t be spot on, and you may have to adjust the distributor a bit to advance the timing a little if you had it turned too far retarded to run well, but it should fire up.  Our car fired up on the first try, and there’s nothing magic about it being our car.  Not all setups will be this easy to get fired up, but this HEI8 distributor is one of the easiest.

So what if it doesn’t start?  (Troubleshooting)

If you’re doing a similar install to this (GM HEI8 dizzy), you’ve got good parts, and you’ve got things wired up as above it’s going to start.  If for some reason it doesn’t, first things first– make sure the MegaSquirt EMS is getting a TACH/RPM signal in the tuning software.  Your engine will never start if the ECU isn’t seeing the engine turn over as it won’t fire the injectors or the spark plugs until it sees RPM (even though right now the ECU isn’t controlling the spark because you’ve disconnected the Ignition Timing Connector, it is still controlling the fuel).  If you’re getting a steady TACH/RPM signal in the tuning software (should be 200-300rpm when cranking), then check over your wiring comparing it to the diagrams above.  Make sure you’ve wired everything up properly.  Now check it again, it’s easy to overlook mistake when you’re checking your own work, most of us tend to scan over details assuming we did things right rather than really look close.  If the wiring is right, check and see if you have spark at the plugs.  You probably know a trick to do this, screwdriver in a spark plug boot works well.  Then placing the shaft of the screwdriver close to something that’s grounded such as a valve cover or almost anything metal that’s under the hood.  Keep your hands away and turn the key looking for a spark to jump from the screwdriver shaft to the grounded metal.  If you don’t have spark, check for power to the coil, and recheck your wiring.  You might have a faulty HEI module or even VR sensor in the distributor.  Remember, at this point the ECU is not in the picture at all because that Ignition Timing Connector is disconnected.  If you have power to the Coil and the HEI module (which gets power through the Coil), and the engine spins, it’s going to spark.  Get this working and get the engine running on module based timing before you continue.

Setting the timing  (step 1)

This is pretty straightforward, with the Ignition Timing Connector disconnected (B-VREF wire) use a timing light to set the base timing by loosening the distributor and twisting it to set the timing and then tightening it back down.  I like to set this to 10deg BTDC.  Anywhere from 0-10 BTDC should be fine.  If you have a timing light without advance capability, 0 is probably easier.  If you light lets you dial in 10 degrees then that works well.  I’d let that make the decision.  This isn’t the most critical timing adjustment, the next one is what matters.

Setting the timing (step 2)

Now that your base timing is set with the module controlling timing at a static figure, plug the Ignition Timing Connector base together to allow the ECU to control timing and it’s time to truly set your ECU controlled ‘base timing’.  This is what ensures that the timing that the ECU is commanding is actually what you’re seeing at the crankshaft, so it’s very important.

Open the MegaSquirt Tuning Software and look at the Ignition Advance gauge.  Start the engine and let it warm up.  You want to make sure the your ‘commanded’ ignition advance, that is, the advance the ECU is sending, and that your monitoring on that gauge in the tuning software, is at a fairly stable number.  The simplest way to do this is to open the ignition table and set all of the cells in the area the engine is idling at to a single number, such at 10*BTDC.  This way you won’t have to worry about the engine drifting about from cell to cell when you’re setting the timing in a moment.

So now to set the timing, from the tuning software open ‘Ignition Setup > Base Ignition Settings’.  With a timing light on the engine, you’ll be adjusting the ‘Trigger Offset’ setting on this page to make it the commanded timing (10*BTDC if you flattened the table out like I mentioned a moment ago).  Each time you make a change to the Trigger Offset you’ll need to click ‘Burn to ECU’ to save the change.  Feel free to play with it a bit- adjust the Trigger Offset up 2-4 degrees and see what happens at the timing light.    Adjust it back down 2-4 degrees and see what changes at the light.  When you’re finished, the goal is to have adjusted the Trigger Offset so that what the timing light reads at the engine matches what the computer is commanding.

IF YOU JUST ZONED OUT THEN READ THIS LINE:  OK, I know that’s a lot of directions.  Let me repeat the last line in that paragraph as it’s all that really matters:  When you’re finished, the goal is to have adjusted the Trigger Offset so that what the timing light reads at the engine matches what the computer is commanding.

Once that is done, the base timing is set.  If it’s still not clear, no worries — I’ll cover it in the video below.

Look Mom, my Laptop is controlling my Ignition Timing!

My mom always told me not to play with fire.  I didn’t listen very well.  I remember when I discovered you could even light the asphalt road in front of our house on fire with a propane torch if you help it on there long enough (small flame, goes out really fast).  I think I was about 13.  Anyways, now you get to play with computer controlled fire.  As you saw above when setting your timing adjusting the Trigger Offset effected the ignition timing as seen by a timing light.  You might have even detected a small change in idle speed when doing this.  Now open up the tuning software and save a copy of your current Tune File (Project>Save Tune in TunerStudio).  Now with the engine running open up your ignition table in the tuning software (Basic Tables>Spark Advance Table in TunerStudio).  You will see the dot near the bottom left of the map where the engine is idling.  You can increase or decrease the ignition timing here and see that increase or decrease of timing with the light, and hear/see what that increase or decrease in timing does to engine idle speed.  For instance, if you’re idling at 15 degrees, go ahead and grab (multi-select – see video below for more info) all of the cells around where the engine is idling, hit the (-) button at the top right of the screen, and subtract 10 degrees from those cells in the table.  You should immediately hear the engine idle down.  Now with thos same cells selected, hit the (+) button at the top right of the screen, and add 10 degrees those cells in the table and it will idle back up to about where it was before.  Go ahead and add another 10 degrees there if you want to and it should idle up futher.  You can confirm all of this with a timing light too if you want.  When you’re finished, subtract the 10 to get back down to where it was when you started.  If you goof it up or loose track of what changes you made, you can always go up to Project>Load Tune and load the file you saved at the beginning of this section before we started mucking around with this.  That’s why we saved it.

Part 3: MPFI Conversion

Objective of this Article

This article will focus on the process of converting our 1977 Chevy Nova test vehicle from the very functional and affordable GM TBI fuel injection hardware to a much more modern multi-port fuel injection (MPFI) design utilizing a Holley Stealth Ram MPFI Intake and the same MegaSquirt-II EFI system we’d previously installed in Part 1 and Part 2 of this Carb-To-EFI conversion series of articles.  If you haven’t already viewed those articles and the videos that are a part of each then they’re a good place to start particularly if you’re new to EFI and looking to convert a carb’d vehicle to EFI, whether it’s a SBC or not.  The first article covers taking control of the fuel system and the second covers taking control of the ignition for a fully computer controlled engine.  The goal of the first two articles was to get you up and going on a setup using as many junkyard available parts as possible, keeping the total bill as low as we could and showing just what can be done, what gains could be made not only in power but also in mileage and in drivability, which is where the biggest gain was in the TBI setup over the previously tested carb configurations.  But we didn’t want to stop there, we wanted to continue on in an attempt to show you just how good it could be.  With the conversion to multi-port fuel injection we should see a bigger improvement in fuel economy, along with more power potential.  It should also be as just about as well mannered as any new vehicle on the road, definitely a far cry from a typical 60’s or 70’s era carb’d motor.  So here’s what we did, and what we found…

We chose a 1977 Chevy Nova with a 350 small block as our subject, but with the proper intake the principles laid out here can be used just the same on a big block Chevy, or a Ford or Dodge small or big block engine, inline engine, a foreign motor…  a motor is a motor is a motor.  The SBC has the benefit of a large aftermarket making off the shelf aftermarket MPFI intake systems readily available, but truth be told we could have gone back to the junkyard to find a modern MPFI intake system that would have fit our motor with minimal modification (a couple bolt holes on the intake manifold need to be modified to fit the early Chevy heads).  So yes, you can do this cheaper than we did it, your driveability and economy results should remain much the same if you do, though ultimate power potential is likely to be higher on the aftermarket unit we chose, and we have some plans for this car when we’re finished with these articles so we went ahead and went for the higher dollar induction setup.  We will likely continue on in this series of articles, in fact very soon we have plans to add forced induction to this beater of a motor to see just what we can get out of a 70’s smog era 2-bolt 350.

As always, we highly recommend you dig into the MSExtra.com in addition to these articles.  It’s a big read, but it’s a valuable resource that our guides are meant to supplement and not replace.

What we did:  Holley Stealth Ram MPFI

Ordering ‘The Big Kit’

So no digging at the junkyard this time, we ordered up Holley part#81504001.  This is a direct bolt on Stealth Ram MPFI setup.  Two piece intake with lower manifold and upper plenum.  Comes with the fuel rails regulator which directly attaches to the rails for easy mounting.  This kit came with 30lb-hr injectors which is more than enough for our extremely mild 350 Chevy at this stage.  It will give us a bit of room to grow and we can always swap in bigger injectors when we’re ready.  FYI They do offer the kit with several different injector size options though.  It also came with an LT1 style 58mm throttle body complete with TPS sensor and Stepper Motor Idle Valve (IAC)

Now, as this is Holley’s ‘big kit’ it also comes with some items we didn’t really need, and depending on where you are in your EFI adventures you may or may not.  For one, the fuel pump.  We already had this in place from our previous EFI conversion and since we used an MPFI capable pump with our TBI conversion it was already ready for MPFI action now.  It also came with IAT and CLT sensors which we would be reusing from the TBI conversion.  Lastly, it came with a GM 3-bar MAP sensor, which though we could use with the MegaSquirt EFI system, there’s really no need to as the MegaSquirt has it’s own internal MAP sensor that does the job just fine and simplifies things a bit.

So what didn’t come in the kit?

  • K&N Air Filter     p/n RC-5050 which —  with little effort slips right on the inlet of the throttle body and clamps down.
  • Spectre Alternator Bracket     p/n 47293 — needed because this intake moves the mounting point forward from where the stock intake bolted.
  • Lokar TPI Throttle Bracket     p/n TCB-40TP2
  • Lokar TPI Throttle cable      p/n TC-1000TP
  • Lokar TPI + TH-350 Kickdown cable     p/n KD-2350TP

We could probably have gotten away with junkyard TPI cables and bracket, so to save a few bucks you can likely go that route.  But the Lokar cables are sexy, move incredibly smoothly, and didn’t cost that much.

Installing the Stealth Ram MPFI Setup

This is basically a bolt on affair.  First we removed the GM TBI setup we had on the vehicle and the wiring that was run to this we simply stuck out of the way for now.  We managed to reuse the coolant temperature sensor and IAT sensor wiring.  The IAC wiring needed to be extended, and of course the injector wiring had to be redone from scratch.  The TPS on the Stealth Ram also needed its own connector.

The manifold drops into place with very little drama. It’s a two piece design, much like a classic tunnel ram.  In fact, the lower section is closely related to a Weiand Hi-Ram.  The upper section is a boxy plenum with several pipe thread ports.  We used the two small ports on the back for the MAP sensor and fuel pressure regulator, used one of the large ports on the back for the brake booster, and plugged the other port.  We installed the IAT sensor in the port on the underside of the plenum.  We were able to reuse our small cap HEI distributor; a cap-in-coil distributor would not have worked with the upper intake.  The Stealth Ram kit included a TPI type throttle body with ports for PCV on the throttle, so you don’t need to use the ports on the plenum for your PCV valve.  The package even included a built in fuel pressure regulator on the fuel rails.

The one area where this package is not a straight bolt on, as we noted before, is the alternator bracket. The stock bracket mounted to a hole next to the thermostat housing.  The Stealth Ram moves this hole forward about an inch.  We solved this using a Spectre bracket that bolts to one of the main manifold bolts.  It’s also nice and shiny ;).

We used a Lokar kit for the throttle cable bracket, transmission kickdown, and throttle cable. These need a bit of trimming to fit, being universal cables.  The throttle cable fit our accelerator pedal after removing the clevis, while the transmission kickdown cable is a direct fit but took some finesse to install because of the headers.

How do I wire it up?

We ended up making a new harness that used the temperature sensor and ignition wiring of the old harness, combined with new wiring for the IAC, TPS, and injectors.

Pretty straightforward setup here– it’s much the same as the setup used for Part 2, where we converted to computer controlled HEI ignition.The only major difference is that there are now eight injectors instead of two.  Even the IAC valve wires up with the same connector and pinout.

Starting the car for the first time

If all you have changed is the induction system and your ignition system and timing are unchanged, then chances are the car will fire right up, or at least try to, off of your current map.  You may find that the idle is rich or lean, so be ready to adjust the tables for this quickly.  You’ll also need to adjust your warmup enrichments, and your afterstart enrichments, for the new induction system.  Generally speaking your new MPFI setup should need LESS fuel for both Warmup Enrichments and for Afterstart.  This is because the fuel enters the cylinders better atomized, as it has not had to travel the length of the intake runner mixed with the air like it did with the TBI.  Less of it will stick to the walls and puddle, and more will enter the combustion chamber, allowing you to start and warmup the car on less fuel than before.

Tuning your EMS

Now you’re ready to retune the Fuel/VE table on your EMS.  The timing should not have changed any, though if you’d like to be cautious you could pull a few degrees while retuning the fuel in case you run it a bit lean at some point, this will help make things a bit more forgiving.  Then you’d put the timing back in when the fuel is right.  The easiest way to do this is to pull approximately 4-5 degrees from the entire table at once, then add it back when you’re done.  As we’ve mentioned in previous articles the MS2 Manual on MSExtra.com covers some tuning basics.  There are several books that go into more detail although to be quite honest, ignition tuning has always been somewhat of a closely guarded secret (by professional tuners, who tend to write the books) than fuel tuning and as such there is much less specific information out there about it currently targeted towards the average DIYer, part of this is for good reason as to fully tune every cell in your ignition table properly you really need access to a steady state load bearing dyno. 

Back on the Dyno

This time on the dyno, I left the ignition timing right where it was after part2 of this series, and I retuned fuel for the new MPFI setup.  This motor definitely had a little more in it that was being restricted by both the earlier carb and the recent TBI setup.  Part of this is surely due to to the manifold design.

So we basically picked up about 12whp peak, and made more power everywhere after peak as well.  We lost a tiny bit of torque down low (5-6 ft-lbs), but when you’re in the loud pedal, how much time do you spend under 2600rpms anyways?

Impressions

The TBI ran the car good, but this MPFI setup has the car running even better.  I can run the engine leaner, cleaner, at cruise getting better fuel economy (1-2 mpg is all we could eek out over the TBI setup, but it ran much smoother when leaned out to get this).  Other than that my impressions haven’t changed much.  Basically everything I said before about the TBI, but things just ran that little bit better now, and on a little less fuel.  As I said before the drivability is amazing for a classic car like this.  Properly tuned you can reach in the window, turn the key, and it’ll pop right off, doesn’t matter how cold it is.  It’ll idle up and warm itself up just like a much newer OEM car.  You can hop right in without wasting any time and drive off.  Car runs great.  We’re making more power than it’s ever made.  There’s just no negative.  Stayed tuned though, this series isn’t over, there’s more to come.  It’s time to make this motor put out some better numbers in a bigger way.

Parts Used in this Article

This is not a complete list of every little bit part you’ll need, but rather what we offer as well as the major TBI components

Engine Management System

Fuel System

  • Walbro GSL392 255lph Inline Fuel Pump
  • Walbro 400-939 Fuel Pump Install Kit
  • Fuel Filters (Pre Pump and Post Pump)

Tuning Tools

Throttle Body Injection (TBI) EFI Hardware

  • Junkyard TBI unit from 1992 GMC 2500 Van with 350 Motor
    • Included injectors, several inches of all attached wiring, and fuel hard lines
  • TBI Adapter Plate, Summit Racing Part# TRD-2210