I have heard people mentioning having their cars dyno tuned, and having the AF ratios adjusted. I didn't know this was something that you could do easily. How are the computers on these cars set up, and what does it take to re-program them? Are there a lot of shops that can customize the fuel curves, and if so, how much does it cost? I had been under the impression that the only real options were stuff like the powerloader, or similar products which re-flash it. Also...on a side note, does anyone know how to control the AF ratios on new Cadillacs? I figure they might use similar ECUs, since they are both GM. I want to mod my DTS too, so I will need to find a way to adjust it. Thanks a lot for any info

Scott

 

The non-WOT air/fuel ratio will be corrected by the computer no matter what, to 14.7:1 stoicometric ratio.

There are a couple of ways to chagne the WOT air/fuel ratios.

One way is the use a MAF Translator which skews the frequency coming from the MAF with a microcontroller. It sends a higher or lower perceived engine load to the PCM which will increase or decrease the injectors fire rate. But again, remember that at non-wot, the PCM will correct to 14.7:1 no matter what. What you change at non-wot is timing advance because you have modified perceived engine load. You can go further with control using a maf translator, when you use larger than stock injectors. This allows you to indirectly dial in timing advance, while maintaing proper fuel delivery. Settings on MAF Translator are permenant with respect to perceived engine load (and require that you drive a while so the fuel trims will normalize to the new setting), WOT adjustments are instantaneous. Using the MAF requires an OBD-II scan tool and patience to dial it in.

Another option is to use something like the powerloader which is custom programming for your PCM. The drawback is that you have to wait on getting changes made to your code.

Now LS1Edit is on the market, (97-00) (01-02 is in beta form for shop versions). This allows you to make changes to the PCM code yourself without waiting.

for more info on many of these topics see: http://www.vetteguru.com

 

great info kewlbrz, thanks :)

 

kewlbrz sounds like to touched on them all. I think the translator is the easiest to use for custom programs. Is there much to be gained on an un- opened engine with changing the A/F ratios?

 

kewlbrz,
Quick question. I have heard going to larger injectors (30lb) and using a MAF trans can get you more timing and maybe it does. But has anyone actually dyno'd to see if it helps out RWHP or RWT gains? And if so are the dyno sheets available? My understanding is that the most HP from a stock or modified LS1/LS6 comes with between 28-30* max and anymore makes no difference. Since I almost always see 28-30* on a stock LS1, how does this help? I have no clue personally.
I guess my question is - Are folks doing this just because they see more timing on Autotap or a Tech2 or has it been dyno'd to show an actual gain somewhere? Thanks

AJ

 

If your allready getting 28-30 and no KR. Then your in good shape. For many others that is not always the case.

 

Thanks kewlbrz. That is what I thought. I have heard of a lot of people doing this when they already have "good" timing and figured they got talked into something they did not need.

AJ

 

Often times what happens too is that when folks add cold air, maf ends, headers etc, they tip over into the lean domain, and/or aquire knock. In an effort to correct, they use a MAF Translator, but to correct for the lean condition, they loose timing indirectly. Using larger injectors is a way to compensate for the needed fuel, while at the same time increasing timing to where you want it to be by dialing in leaness using the MAFT to compensate for the SVO's. A fairly simple approach to manipulate perceived engine load. Of course PCM tuing would be optimal with something like LS1edit, but that can add complexities for most to deal with.


[Modified by kewlbrz, 9:00 AM 2/26/2002]

 

Since this topic is current...
Within the next week I will be adding TPIs header,Xpipe in place of the cats and a borla exhaust. I already have a blackwing filter. (all on a stock 97') The local tunner shop has as LS1 edit and says I would see big gain by letting him tune the car will the ls1 edit and the dyno. Any coments? would this combination excel with a good tuning?

 

On 3.8 Turbo engines we used to add an adjustable fuel pressure regulator to boost pressure and fuel flow at WOT.

 

Good follow up Steve. Same as increasing injector capacity to compensate for a lean condition. On 99+ C5's it's difficult to do that.

Anth, yes any kind of tuning will unleash hidden power. Remember that modern cars are tuned towards meeting EPA and Fuel Economy Standards as opposed to performance.