This is a post I put up at .com a little while back and didn't get responses one, I figured I'd try my luck here: Thanks!
-Shivadart

I would HIGHLY suggest you get a system you can program. IIRC Bob used a GM computer. I also bought a kit that is GM computer based. The only way to program those is take out the chip, put it in a programmer, make a change, reinstall it, and see what the change did. Big hassle, and you don't see your changes in real time. You can buy ROMulators so you can change variables in real time but that is just another layer of complexity....

If your worried about the electrical assembly side of things, there are people that offer assembled/tested kits as well for a nominal fee.

I was thinking about that but then figured that you can get the assembled ECM for about $300, you can get everything you need(including extra items) un-assembled for about $240. I was thinking I might buy a pre-assembled ECM so that the most important part is done right and then assemble the rest of the items(such as relay board, if I get that wrong I do know how to wire them individually). Guess getting the ECM put together raises the cost a lot, but since it is sort of the heart of the FI system I'm thinking it might be worth it and it's still be cheaper than getting one of the FI that cost around $1400. Other opinions?

I don't want to give the wrong impression here because from what I understand the MS is a very good set-up. But, I'm wondering why some consider it cheaper and less of a hassle than what I used. A GM ECM is typically about $25 in the junk yard and for another $25 I can carry a spare in my trunk. And, you don't have to build it. The thing that I've always liked about the GM set-up is the MAF sensors ability to self tune. The flexibility of this was demonstrated to me when I went to a turbo with the same ECM and chip that I used without the turbo. I only had to change the MAF and the injectors for the turbo. I'm not at all convinced that I could have done any better with a programable ECM without a dyno at my disposal. And, I didn't need a lap top to tune it. Being able to tune it might be kind of cool, but since I'm not much into programing, for me anyway, that would be quite a hassle.
I would agree that if you are going to do serious racing, and are going for every ounce of power, that a programmable ECM is desirable. But, I'm not convinced that for street performance that it is really any more practical.
Pierre, what does "IIRC Bob used a GM computer" mean?
Bob D

IIRC = If I Recall Correctly

I am not familiar with MAF systems. The Howell setup I got is MAP based with an o2 sensor, GM# 1227747 computer. After about the 5th or 6th "Custom Tuned" chip from them, I gave up. The car gets poor gas mileage (15 or less, the 1920 did better!) and the rich code keeps getting set. Most of the time the idle isn't steady, and the fuel decel cutoff is way too sharp (RPM drops significantly then slowly rises when I break for a stopsign)

Unless the MAF setup is significantly better at self tuning then the MAP, my opinion is you should go with a MS unless you are prepared to burn countless chips.

Hmm, makes me wonder how hard it would be to convert my system to MAF based and use the same computer you did. I wonder if the harness connecters are the same for your computer as mine.

Oh, I think I see the source of confusion. The MAF set-up is considered "self calibrating" while speed density set-ups are not. I covered that in the EFI article:

"The 1982 through 1985 3.8L batch fired engines also used a Mass Air Flow (MAF) sensor as opposed to the Manifold Air Pressure (MAP) sensor that is used with the later and much more common Speed Density systems. The MAF sensor makes this setup very flexible for adaptation to engines with different volumetric efficiencies. This is because the sensor actually measures the mass of the air entering the engine. The ECM (computer) then uses this information, along with information from the other sensors, to determine how much fuel the engine needs at any given instant. The effect, then, is that this setup is self-tuning, at least for a limited range of engine variables. With a speed density system the ECM uses the Manifold Air Pressure (MAP) sensor (which measures manifold vacuum), an air temperature sensor, the engine speed (RPM), and the known volumetric efficiency of the engine that is stored in the ECM memory to calculate the amount of air entering the engine. Change the engine volumetric efficiency with the Speed Density system and the whole equation is thrown out of whack, unless of course you have access to the ECM's internal memory. This is why all of the aftermarket systems, which are speed density systems, require a laptop computer to tune for individual applications"

Another really nice feature of the MAF set-up is that it will automatically compensate for the ageing of other components and doesn't need constant re-tuning to keep things optimized.
Bob D

Although my slant version of TBI has not coughed to life ...my other TBI projects have gone very well. I use the GM truck PCM, sensors etc. My slant version will use the 4.3l Astro/s10 setup.

The speed density TBI setups are pretty good at self tuning. My 1973 work truck weighs 8800lbs loaded and has a 350 chev with TBI on a Performer intake(Turbo City adapter), headers . Flowmasters and 3" exhaust. The cam is a split duration 262/272 adv. EGR delete, exhaust crossover blocked, cold air intake. We pull a 12000lb trailer with it. It operates from sea level to 13000 ft in temps from -30 to 100f. It easily makes 50% more torque than stock and the mileage has increased 35% over the carbed version. It always starts and idles nicely. When I make a modification I always "kill the puter" to let it relearn its maps. It takes about a week for it to get totally worked out.

It has a one-burn chip and some fuel pressure tuning. The biggest deal was to get it timed right at 0 degrees.

I find the TBI setups I have like a ton of cam ,,,at least 262 duration to prevent low speed detonation. You must increase fuel pressure at least 2# to prevent lean codes. ......biggest EFI tuning tip for any setup,,,,NO vacuum leaks

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Yeah....Im the one who destroyed this rare, vintage automobile.....

So basically the computer can learn the VE tables without programming? Any Idea how far out of whack it can get before the computer can't correct for the changes?

Just curious...

I have programmed MS & custom FI before, but usually there is not a whole lot of wiggle room in the factory stuff (so I have been told/led to believe)?

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There is PLENTY of wiggle in GM (OBD1 stuff at least). Check out www.diy-efi.org and the gm-ecm pages. People have done lots of reprogramming with GM computers.

Sandy,
What do you mean by "one burn chip"?
Bob D

Thanks for all the feedback! There is something I am wondering about FI, I know that it provides better part throttle performance, but actually performs as well at WOT as a carberautor. I'm just wondering if the throttle body puts outs as much power as a one-barrel or greater? I.E. by converting to a 3.8 liter GM throttle body would I expect one-barrel WOT performance or greater?

The 3.8L throttle body is meant for multipoint fuel injection, so right away you gain the advantage of a dry manifold, better fuel distribution.

As to the amount of air that particular throttle body will flow, I'm pretty sure it will be higher then a 1920. If not, there are readily availible 500 and 600cfm throttle bodies from GM TBI cars like the one I'm using (pix here: http://www.slantsix.org/forum/viewtopic ... 12&start=0 ) that you can just take the injector stack off of and use for mpfi purposes.

Carbs are usually a bit rich at WOT to avoid going lean and detonation. It depends on the system, but I believe for the GM stuff that when TPS is at max (wot) then it goes into open loop temporarily, disregarding the o2 sensor. So as long as the main fuel setting is appropriate, you won't be going lean either.