First off there are very specific times when one is better then the other.

First off when your going to do anything to increase the fuel demand of the engine, you'll have to figure out how to satisfy that. If you want to double the HP of your engine, then you should think about doubling the size of the injectors. The GM code is set up for long term drivibility, and using the Bl limits to keep things happy. Trouble is as you get to 1.0 msec and less at idle you can start to have metering problems. Lowering the FP, and higher idle speed can help. Up until this point being oversized is no problem, and is actually easy to tune.

However, if you have use the .5#/HP BSFC formula for injector sizing, then your really either wanting too go with a aftermarket ecm, or spend lots of time fine tuning a gm ecm. When your right at the edge of the limits of the injector, your waking a slippery slope anyway. What an aftermarket ecm does is dumb down the system to make life easier on you.

If your at the 1.0 msec PW for idle, then life tends to get rough, because saturated injectors just operate so fast. So then the only next option is Peak and Hold injectors. They can operate well, down to like .5 msec PWs at idle. BUT, often can get a little erratic at those openings, or not be real linear.

Then comes price.
The aftermarkets are always more expensive then a GM. With a GM you can easily afford to carry a spare. The aftermarkets when they break can be real expensive to fix, and take several weeks.

WOT
One continually repeated claim is that with a aftermarket WOT is easier to set. Nope, you have to do exactly the same amount of testing to find best AFR at WOT reguardless of what ecm, you're using. What is easier (somewhat) is that WOT can be more divourced so it's easy to think about. The power in EFI is knowledge, not the software, or interface. You have to figure out how your system works. The aftermarket try and keep it simple as possible, but in simplity comes problems. So far I haven't seen a lean cruise mode aftermarket ecm. Or highway spark.

What amazes me is how folks will compare a MAF oem system to an aftermarket and proclaim the aftermarket better. Well to date I haven't seen an aftermarket MAF ecm, so that kind sheds a new light on things.

Up unitl you run out of injector PW at idle there is no advantage in running an aftermarket. Even then different injector drivers can be installed in some oem ecms, and raise the limit to when you need an aftermarket ecm.

One neat trick some of the aftermarkets do is actually batch fire the injectors. So that they have the same operating times as a SEFI unit. What some clever person needs to do is take the output of a say a 730 and use a flip flop to two new drivers, and you'd have the same thing, and about never need to go aftermarket. Heck use two big Power MOSFETs, and you could run Peak and Hold injectors, and have a swell time.
Course that would lead to nulling out lots of the code, and you could have exactly the code, and parameters you want.

I base the above on having actually studied the Accel, Motec, Electromotive, Haltech, and some obscure systems software/ editing material.
The injector sizing info., I've actually done on my own cars, and many test miles on calibrating and testin them.

 

Very good points Bruce. As I see it, there are 4 main reasons to convert to an aftermarket ECM. I believe you hit on one of them. However, I wanted to bring up the others.

1) Already mentioned by you: The need to run bigger injectors. There are 2 parts to this. The first is the need for low impedence injectors which the stock ECM can't handle. This is kind of a moot point because you can get high impedence injectors in fairly large sizes. However, even when installing these big lb/hr high impedence injectors the BPW may be too low at idle for out batch systems (which must fire TWICE every crank revolution in comparison to SEFI systems that only fire once every crank revolution). Aftermarket ECMs not only offer the ability to run low impedence injectors but also offer SEFI which will effectively DOUBLE your idle BPWs.
2)Wide Band O2s. A couple of the aftermarket ECMs (SpeedPro and the new Accel unit) have a wide band O2 option that is used specifically for tuning your AFR (especially at WOT). For an all out 'performance nut' this can be a very nice feature. Although a lot of tuners are looking for driveability ... most of us F-Body freaks got into PROM burning for performance reasons. So, in a way, our view is a little twisted toward performance. With an ECM that comes outfitted with a WBO2 you no longer have to go to a dyno OR buy a wide band. Tuning WOT with a Wide Band is tons easier than 'guessing', 'feeling', and also in many cases - 'experience'. Granted, a car needs what it needs and you have to give it what it wants. But, a WBO2 has to be one of the best tools for insight into what your car wants. Eventually, the DIY-WBO2 will come to the rescue once it is in a format that is tried and true AND easy to figure out.
3) 2-3Bar MAP sensors. When installing a supercharger or turbocharger on an F-Body you have NO choice except to convert to a SyTy ECM (*if* you want to do it right). SyTy ECMs aren't plentiful in the wrecking yards (even though they were used in other applications). Aftermarket ECMs make this easy.
4) The ability to tune without worrying about PROMs, Erasers, Programmers, etc. Just plug your laptop up to the computer. OOOP - there it is.

I am by no means suggesting that aftermarket ECMs are better. I just wanted to raise other points to what you have mentioned. Personally, I love everything that the 730 gives me (especially all the driveability stuff like IAC learn routines, DFCO, more control of knock, etc.). LOL - now if I could just get a 2-bar compatibly $8D along with the DIY-WB I would be set! I am not worried about point #1 because I am running 30lb injectors with BPWs in the 1.9ms range which means that I could convert to 50lb injectors and probably be AOK. I am not worried about point #4 because I LIKE taking the extra time for tuning because it gives me more time to think.

Tim

------------------
TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

Tim, I plan to play with the Assembly Language of the 7730 to address the 2 bar MAP problem. As you know, it is possible to "fudge it", but I want the correct solution.

I just need some "free time" (vacation is just around the corner) to dive into the code and come up with a good 2 bar MAP bin that retains all the resolution of the 1 bar MAP but handles 200 kpa instead of 100 kpa.

While I am at it, I also plan on extending all the rpm ranges to a higher limit.

This won't solve all the problems with the 7730, but it will address that one issue. Of course, the next problem will be that we will need a new TunerCat Definition File unique to this BIN as there is no way the stock 8D will work.