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MegaSquirt Carb to EFI Conversion: One Step at a Time
Part3: MPFI Conversion
From TBI to Multi-Port EFI, with Ignition Control...
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 driveability, 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
MegaManual 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 say 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 MegaManual
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. There are books available now that provide
at least 'some' information on the topic, or (shameless plug here)
Matt and I (Jerry) recently wrote a book titled 'Performance Fuel Injection Systems'
that is now available. We went through alot of effort to cover this topic
in great detail, but from a practical perspective. (Click this link if
you'd like to check out/purchase our book.) Lastly you can
always take
it to a pro.
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
Tuning Tools
MultiPort Fuel Injection (TBI) EFI Hardware
You can order this MPFI System here:
Holley 81504001 Stealth Ram Satin Finish Multi-Point Fuel Injection Power Pack Kit - 30 PPH
So you want our tuning map?
This time around we haven't posted a new tuning map, we could, but it likely
wouldn't be any more helpful than the map from the end of article part2.
The ignition table didn't change any, the fuel did but no matter what we give
you you're going to have to dial the fuel in for your vehicle anyways, this map
will get you started and very close to where you need to be if your motor is
similar to ours.
DIY's 1977 Nova Project
Fuel/Ignition Control (Article Part2) .MSQ File (right click
and choose Save As, remember where you save it, then when connected to your ECU
you'll be able to 'FILE>OPEN' this file)
Note, this was built on a Small Block 350 Chevy motor from a 76 Monte Carlo
(swapped into this Nova). Edlebrock Performer Intake. GM TBI from a
350 Chevy (65lb injectors). GM HEI8 Small Cap Distributor installed as per
the above article. MS2 ECU Configured as per the above article. Headers into 3" Exhaust and Flowmasters.
Stock heads and cam. This was built, and should only be used on, a
MegaSquirt-II with firmware 2.888.
I DO NOT recommend you drop this file on your car and go any more than I
would with the base map. Each individual tuner, whether that's you or a
professional, is responsible for making sure the EMS is properly tuned before
driving!
Want to learn more about EFI Systems and
specifically more on how to tune the fuel and ignition on your
MegaSquirted Monster? Matt Cramer (lead tech here) and Jerry
Hoffmann (founder/owner) wrote a book on it!
Check it out on Amazon.com!
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BONUS: What about the Holley 900cfm TBI?
In our testing, on our weak motor, the Holley 900cfm TBI did
not make more power, but instead made less (yes this surpised me too).
I suspect this TBI just doesn't flow quite as well at the lower CFM's
demanded by this motor, on a built/bigger motor that needed the additional
capacity I expect we'd see the Holley 900 do much better than the GM TBI
with it's somewhat limited flow rating. We didn't do enough testing on
enough configurations to be sure, but I don't think we'd find the Holley a
loser in circumstances where it's flow capability was needed more.
What's coming in future articles?
- More Ignition Control Options -- You don't have to do what we did here
though if you're running a Chevy, this is easy and hence what we recommended.
We'll show you some other options though as well that will work on a
Chevy or any number of other engines.
- Turbos. Yes, two of them.
Links to all Articles in this Series:
Carb-To-EFI Conversion: One Step at a Time - 1977 Chevy
Nova with SBC 350
Carb-To-EFI Part1: GM TBI Fuel Only
Carb-To-EFI
Part2: Adding Ignition Control (HEI8)
Carb-To-EFI
Part3: Converting to MultiPort Fuel Injection (MPFI)
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