I have an 88 with stock ECU. I'm in the process of completing my new engine/trans combo and I need advice on what to do for a fuel management system.

These are the basis of my mods; 396ci, 10:1 comp, MiniRam intake (ported to 1206), Brodix Track 1 heads, 521/556 (w/1.6RR) 224/236 112LSA hydrolic roller camshaft, 30# injectors, 58mm TB, Hooker 1 3/4 headers, Richmond 6spd, Dana 44 w/4.10, etc ...

What should I do? Stick with the stock ECU and mass air, with a custom burnt chip?

 

You'll have to have some tuning. Were it me, I'd convert to the '730 based speed density ecm and start with the ANHT code and modify from there. The ANHT code was a great start for my 408. After adjusting the injector constant, the fuel tables were fairly close. I had to add a bit of fuel toward the top, but that was really about it.

 

I agree... The 85-89 MAF (even modded) is fairly restrictive, though I've seen them support a 500 hp motor. If you are going to stay with a OEM type control system get the 90+ speed density computer. I run Accel DFI on my 90; I've used it for a long time and it's one of the older systems (6.32) piggybacked in with one of Mac McKenzie's harnesses (Fasttrack Performance). But, if I were going to do one now I'd look at the new Gen VII DFI or the FAST SEFI8LO system, or the Electromotive Tec2 or new Tec3. All of these offer much more sophistication over my old DFI and they have iterative functions that will actually take your specs and build a base fuel map and ignition map that is actually very close... You just need to fine tune from there. They also all come with a wide-band O2 option and full sequential capabilities; both of which give you superior control over the parameters.
-Jeb Burnett

 

All this can be yours for a small fee... enough to buy another C4!!! :(

 

Has anyone has any sucess with tuning a stock MAF system? What vehicles have the 730 ECU and what else do I need? What is involved in doing the conversion? How much?

 

Mojo...It's not 'THAT' much... :D But you know the old adage; "Speed costs money, how fast you wanna go?" You can get a wideband batch fire from either Accel or FAST for around $1500.00... 396Roadster, someone else on here can fill you in on what it will take to convert over to a OEM speed density set-up; but I would think you'll need the ECM (obviously) and either a complete harness, or some sort of piggyback to splice into the stock harness. The only "real" operating difference between the two is that the speed density system uses a MAP (manifold air pressure) sensor instead of a MAF for metering the air. I will tell you one good thing about the MAF systems though, they will compensate pretty well for up to a 15% change +/- in air flow where you have to reprogram a speed density for anything over about 5%.
-Jeb Burnett

 

Add a few hundred to the $1500 if you need an adapter or harness with the wideband and FAST system. Figure somewhere in the $1700 to $2000 range to get a complete bank to bank system. The tech support from the dealer also gets figured into the selling price. If you get a cheap price - don't count on a lot of support from the dealer.

Jeb - Did you run the DFI in Alpha Numeric or speed density with the 396 and big cam ?

 

This is true... A piggyback harness would add a few hundred to the cost; but it's worth it!! Slo I run it in "SD" but I don't have it idle in closed loop because the big cam doesn't want to be that lean down low. It tends to pop and fart and surge if it runs at stoich at idle... I set the closed loop parameters to come on at 1200 and it idles at 900-1000... It's pretty fat at idle but it's very smooth for as big of a cam as it has.
-Jeb Burnett

 

I converted to a GM '730 based SD system for around $500... Including power programmer, Tunercat and software!

 

I have a very similar setup - except more CID, compression, cam, injectors. If you're going to use the stock ECM, to get full potential out of the engine you'll definitely require a custom chip. It will take more than a mail order chip. We're talking about recording real time engine data, burning chips and repeating this cycle many times until you've dialed in the combination. Of course you'll need to do just that with any ECM.

I did manage to successfully run the stock 88 ECM, a very custom chip and a fully modified MAF. That combo was good for about 530hp at the crank. I have now switched to DFI with S/D because the MAF is a substantial restriction when you're up over 500hp. It also makes tuning difficult because the max MAF airflow (as read by the ECM) is pegged at a relatively low rpm. I haven't had a chance to dyno the new combination, but on paper it definitely increases the max HP potential.

IMHO, after having experience with both ECMs, I'd go for the DFI S/D or '730 setup. :cheers:

 

396 Roadster,

I just converted mine from a Holley ECU to a GM speed density. I'll admit I had my eye on an Accell Gen-VII, but I really wanted to keep everything on the cheap. Recent marriage has somewhat changed my judgement regarding such matters.....

There's a lot of info on the GMECM website from DIYEFI. Following the hyperlinks from that site, I was able to get all the info I needed to get started. However, I find it easier to ask people questions from this forum. Just a personal preference...

Anyway, the conversion isn't too difficult if you've been experienced with some basic automotive wiring - and soldering to put a socket in the computer's MEMCAL (this allows easy EPROM changes.)

As far as what used a '730, it's listed on the GMECM website. But, you needn't limit yourslef to the '730. There was an "under-hood" unit which was electrically (and programatically) identical to the '730, called the 1227727. The difference is in the connectors on the ECU. This is what I'm using, since there isn't much room in the passenger compartment of a C3 for ECU placement (but the fenders can hide a small cruise ship).

The '727 was used on 90-91 Corvettes w/TPI. It was also used on just about anything with a 2.8L V6 made from 87 up (until GM went to SFI in about 95). This would include the Baretta and the Corsica - and there were A LOT of these cars.

I ended up using a '727 from a Baretta.

General cost I'm up to now is:
'727 ECU - $45 (local junkyard)
Two complete wiring harnesses - $40 (local junkyard)
Pocket Programmer - $150
EPROM Eraser - ~$40
10 27c259 EPROM's - $15 with shipping on EBAY!
Tuner Cat - ~$100 w/ECU definition file
Datamaster - ~$100
Parts to build my own interface cable, and MEMCAL mod -~ $30, Radio Shack and Digi-Key

So, I'm up around $500. NOTE: This doesn't include odds and ends like solder, electrical tape, new wire loom, etc. But, these things are inexpensive - and you may have some on hand.

I look at it like this. I haven't spent all that much money. And, if anything goes wrong, replacements are cheap and easy to find.

I'd be happy to answer any questions you have. There isn't much instructional information on building your own wiring harness that I could find. But, you have the option of learning from my mistakes....


Peter

 

I've got a real similar cam to 396's going into a 383. The idle quality with the GM ecm is the only thing that has me a little worried. I can see 1000 to 1100 rpm to smooth things out.

Jeb, I've done the same thing with my Buicks. I'm going to try making the 727 ecm work with the Corvette.

If it doesn't work than I'm going to go to a 6.32 DFI box.

 

The '727 will work fine with some tuning.

 

Does removing the GM ECM (and installing an aftermarket FAST, etc.) cause problems anywhere else in the car? As in, does the digital dash, etc. still function? I've thought about buying an 80's C4 to play with since they're so cheap, but I don't know if you can rip the stock engine electronics out of them without "upsetting the applecart".