first of all, let me just say that I only know the basics of the stock ECU. My car is currently carb'd and N/A, but I am building a procharged 396 small block for my next engine (whenever this one goes...*** please, no time soon). The main reason I went carb'd and may have to stay that way was $$$. I was just reading another post and a guy said he was going to use his stock ECU with an FMU and hopefully achieve the same results as a DFI setup. Will the stock ECU work with say 700+hp and 15+lbs of boost? If I can use a stock ECU, then I am going to have to seriously reconsider. Also, what would the limits of cam duration be if I were to use it?

 

how come I can't say G.O.D.??? that is pretty dumb...don't even get me started

 

Seperation of church and state....

Could be the Mods are Buddist??

But serious, read thru the DIY PROM part for gettin' up to speed, because a stock ECU can be used. Heck Grand Nationals can control upto 15 PSI with factory gear.

You will need to learn how to program a PROM and read/understand the ECM's data.

You can use either the SD setup or MAF, but the MAF will have intake air draw limitation.

If you have a rumpity-rumpity cam, the SD system will have problems idling (maybe).

 

If you have a big cam then you are actually better off with SD because of reversion issues.

With a boosted setup you'll just need to switch over to the 749 ECM (Syclone/Typhoon ECM). It can handle high power levels ... and if you toast an ECM then you can buy a new one for $50. Plus, they are available locally and you won't have too much down time.

Tim

 

Besides a dead stock motor (maybe one with only small bolt-ons) with a supercharger, you need to go to aftermarket DFI or something equivalent.

The typical NA computer (GM, Ford, MB, whatever) cannot handle the demands a boosted motor makes on control systems. You can't really run a computer without a boost sensor (MAP for 2+ Bar manifold pressure or better) when there is no provision to add one on. Ok, the GN and Typhoon motors came turbo'd from the factory, but obviously not tuned so great - a good chip can unlock 50+ hp with pump gas, so that is just a band-aid too.

What you need is an aftermarket system that allows infinite tuning of timing, injector pulsewidth, injector resistance (in ohms), and of course a provision for a MAP sensor that reads positive pressure precisely.

I don't want to be a wise-asz, but why the hell would you spend $10k plus for hardware (engine and parts) and use 10+ year old software (stock GM computer with a FMU) when if you upgrade to the newest software (DFI), you could be ahead of everybody? Oh yeah, it may cost you $1k-$2k for DFI, but it will probably add 50-100hp easy. There are a lot of shops out there that can set up DFI and tune it for you - just ask/look around.

 

No you don't.

Agreed.

Not true. GM tunes things very conservatively and doesn't allow as much boost as the motor can handle. THAT is why you can see higher levels of power with a chip change. It has nothing to do with the computer or software that is being run. That is kind of obvious since the computer DOES handle the extra 50hp with the new chip.

The GM computer does all of that except for the injector resistance.

Why?
1) The computer can be found at any parts store for a fairly good price. If you blow your DFI then you are fu(ked. You have to wait for a new one. How much does that cost? If your stock ECM goes south then you can go to your local parts store and pick one up.
2) GM has dumped tons of money into ECMs. These things were designed to go 100,000+ miles! Was DFI designed in the same manner? The Syclone and Typhoon ECMs are tried and true. They handle boosted motors easily and do it with reliability.
3) GM computers have some extra stuff that really helps out driveability. Highway Mode saves major gas, PID routines control sensors like the IAC that manipulate the metered air to help idle, special spark routines that constantly change the spark at idle to give a nice smooth idle, etc. These things are nice.

Now there is a statement I wouldn't have expected from you Paul. easily add 50-100hp with DFI? Are you kidding me? How the heck do you see that? A properly tuned chip on a 749 would not be 50-100hp less than DFI.

Here are what I think are the best reasons to go to DFI:
1) Big low impedence injectors. GM ECMs only handle the high impedence injectors but most of the really big injectors are low impedence. You can't run those with a stock ECM. However, with that said. You can run 50lb injectors with a stock ECM. That is about the limit though. Furthermore, a sequential system will allow for a better idle with really fat injectors because you only have to fire the injector once as compared to twice with a batch motor.
2) BIG boost. Need a 3-bar map and you're not running a GN? Good luck ... you're probably better off with DFI. The GN crowd has a hacked mask that will allow for a 3-bar map. I haven't heard about one for the 749's $58 yet. Maybe there is one but I don't know about it.
3) Wide band O2 at WOT. For me this is the biggest reason. The amount of time saved because of the Wide Band O2 at WOT is very significant and it provides a very safe tuning. There are people out there who have integrated a DIY-WB signal in with stock ECM programming. But, it's not widely available and probably will not be for awhile. So, DFI is the way to go on this one.
4) User Friendly. DFI, in my opinion, is much more user friendly. With PROMs you gotta program a chip and then possibly have some special adapters here and there. DFI is much easier to use.

So - as you can see - I am not in any way against DFI. I love DFI. I just want to let people know that it is not the only route. The GM 749 ECM can handle A LOT for a lot less money. But, you have to be more 'computer oriented' and willing to put in the extra time to figure things out.

What I think would be the coolest would be to have an adapter that adapts your stock harness to the DFI and an adapter that adapts your stock harness to the GM 749. Run DFI and then if by chance your DFI goes south then just plug-in the 749 until you get your new DFI. This assumes you have the money for DFI. But, it would be cool. Would also be cool to do some side by side comparisons of horsepower and driveability. Why do I have the feeling that I will be doing this one day?

Tim

 

 

Tim,

I have never seen any chip burned for a heavily modified TPI motor ever be tuned exactly correct - let alone a forced induction car. There are too many parameters you have to change in order to get the tuning exactly correct, which the GM CPU just can't handle - it doesn't have the capacity to.

If you set everything as perfectly as you can with a stock GM computer, you may see 650hp on a supercharged 406, but if you go DFI and really get everything perfect - injector pulsewidth, timing on each cylinder, wide band O2 sensor... You may see 700 to 750hp then. The magic is in the tuning, and its a lot harder to do with forced induction than a NA motor - that is why a lot of people (those without the experience) take their cars when assembled to a shop that specializes in DFI tuning to earn their money for the service.

This is not a flame against you, but just to let people know out there that the parts and tuning matter equally as much - I have seen too many 500hp motors make 300hp because they were mismatched and were tuned by a blind monkey.

The computer is only as good as the software that can be run on it, that is the most important thing to remember. DOS VS Win NT is a big difference (GM OEM=DOS, DFI=Win NT).

 

Originally posted by SATURN5

I had no idea. Sweeeeeeeeet.

That was one of my biggest complaints. The need for 15+ PSI. Definitely need a 3-bar MAP. 'pick up from the SyTy guys'? I feel like a newbie saying where do I get one of these but ... where do I get one of these? I'm fairly familiar with the DIY field yet I haven't heard about this (or about the P/H for 7 bucks).

Others ARE doing more than this. I know of one person running a DIY-WB in place of the normal O2 sensor and it is used ALL the time. Obviously, code changes were necessary - but it IS being done.



Amen.

Tim

 

Originally posted by paul_huryk

I have never seen a DFI setup with a tune that is exactly correct - let alone for a forced induction setup

You're preaching to the choir Paul. I've been preaching this longer than I can remember. That's the reason for the DIY-PROM forum.

I'd like to modify this and say that the tuning is only as good as the tuner. DFI isn't as great as you think it is. I would really like to know what you think DFI has above the $58 code? I've admitted to Wide Band, Low Impedence Injectors, Sequential Injection, and Usability. But, what else are you talking about? You said "There are too many parameters you have to change in order to get the tuning exactly correct, which the GM CPU just can't handle - it doesn't have the capacity to." What doesn't it have the capacity to do in addition to what I mentioned? You did mention individual spark timing for each cylinder. What DFI are you talking about? As far as I know FAST and Accel don't have this. I believe that MOTEC is the only one and this is like $4K or so.

Tim

 

As far as swapping the drivers...

http://www.syty.net/phpBB2/viewtopic...hold+injectors


The 3 Bar chip with extras (called the Ultimate) for $390, and no as far as I know its a closely guarded secret, but once I get the time I'm going to get into the code and see about working out the changes.

http://www.arautosports.com/

Read up on the StTy.net site for more info. But for someone looking into an alternative, really not hard to modify the ECM with new drivers, the hard parts going to be figuring out the code changes, but I'll figure it out sooner or later.

 

The biggest problem with GM ecm's is the injector drivers. Otherwise, the ecm is actually quite comprable and in some ways more sophisticated then most aftermarket setups. What nobody has mentioned here yet is that GM goes to a lot of trouble to make these things do everything well, and then tunes them for max economy, emissions and durablility. Performance is easier and cheaper to add other ways if the factory sees the need.

My debate with this is simple. If I knew it would work this is a no brainer. I'd go with a factory ecm, the extra hassle of scanning, burning a prom and rescanning is nothing, it will just take a little extra time to get things where I want them. The issue is, will it work? To be blunt, I'm mounting twin turbos and haven't found anyone that has this working well on a serious boosted small block. I've discussed an assortement of ideas with some of the locals that do a lot of ecm tinkering (tim, I'm not sure why but somehow you've managed to get somewhat excluded till now), and some others (probably the most notable, Bruce P.- Grumpy) and the answers I've gotten ranged from "I doubt it" to "it won't work, just go aftermarket" (Grumpy).

I realize that I'm trying to do something that not a lot of people (that care to talk about it) have experience with, so I don't know that I'll get a real answer till someone like saturn5 gets his setup going. Now the way I see it I'll need to get into this thing about $4-500 to even get a good indication if it's going to work (ECM, repinning 'stuff', proms/burner/software/assorted related 'stuff', cable and scanning software...), which is more then half way to a Holley Commander 950 (which supposedly will plug right in and work with a 3 bar map) or Haltech (which I've got a lot of experience with on my brother's car running both a 2 and 3 bar...).

 

Plenty of people have run the 749 on a non-749 equipped car. Some have even run $58 code in a 730. I think the main problem here is that you want to talk with one of these people and they aren't here on this board for you to talk to ... cept for Saturn5 and YenkoZ28. Check out this thread on the DIY-PROM forum...

https://www.thirdgen.org/techbb2/sho...hreadid=117111

Tim

 

Answer: I already have many of the parts that are on this motor or I have laying around and seriously doubt I will have $10k in this engine. All I need is crank, pistons, and the Supercharger pretty much and I will have everything I need. Again, knowing only basics, I did now that driveability was better with them, and It seems I would have much less invested. If I go injected I am going to have to spend another $2k on injectors, manifold, fuel rails, TB...etc. I just want to make sure it is worth it.

 

I'm curious, If I run a blower and consistently the A/F on the dyno is ideal in the mid 12:1 range on the boost throughout the range (using an FMU) and the timing is as high as I would care to run (on the edge of detonation) then how will a chip help me? I have seen a few guys try removing FMU's on our Dyno for a chip (both ford and chevy) and end up switching back before they leave because there was no negligable gain. (the exception was the guy that NEEDED bigger injectors and HE WAS helped by the chip a bunch when he was now able to change injectors). the chips gave the same A/F as the FMU so I figured thats why there was no gain.

 

Dragstrip performance wise... none. WOT A/F is just that, doesn't make a difference how you get it.

The real advantage is twofold. first, most don't take the time to tune them right and just run somewhere between way rich and somewhat lean. Second, driving it around at part throttle will add to the tuning issues, and almost noone has them optimized for that use...

 

I agree if a car has a perfect A/F under WOT or "power" conditions, and cant drive around then hell yeah a chip is definitely needed.