I've done a search and looked in the stickies but could not find what I was looking for.

I'm trying to find out a few things.

1). What was the stock A/F ratio?

2). If that was leaned to 14.5 to 1, how much affect (if any) would this have on dyno testing air lids? This was on a catback only car BTW.

I'm in a debate with someone who insists airlids are only good for 1-4 rwhp on stock cars. I showed him the GMHTP article where lids gained anywhere from 5-11 rwhp. But he claims the fact that the A/F ratio was leaned to 14.5 to 1 caused those numbers to be higher and thus he discredits that whole article.

Is he right? Would that really more then double the HP output of a lid? I am not a tuning expert so I want to ask someone who is.

Thanks in advance for any input.

Heres a link to the article if anyone needs more info on this particular test. Just click on the word "here" and it takes you right to the article.

http://www.motorsporttech.com/fbody_air_intake01.asp

 

Just a little FYI, on GM PCMs and probably most others, it will really not run much leaner than stock. The only way that the PCM will run the engine too lean, is if the injectors cannot physically support the engine. The MAF sensor directly measures the incoming air and transmits that data back to the PCM. The PCM then looks up the frequency from the MAF in its lookup table and matches it to an incoming air volume. The incoming air value is then used for the fueling tables. Most stock GM calibrations run extrememly rich down low and lean out toward the top. Most calibrations stay under 12.7:1 in Wide Open Throttle or Power Enrichement modes. I have taken and purposly adjusted the fuel pressure down on a 1997 LT1 to try to eliminate this. That lasted for all of 30 seconds, as soon as I went back to closed loop and part throttle, the Long Term Fuel trim increased the fuel back to the engine via longer pulsewidth to the injectors and the wideband dropped back to 12.2:1 or so. You are not going to lean out an engine short of massive airflow increases or very restricted fuel delivery.

 

The California PCM calibrations for every car built since 1988 has been 14.7:1 a/f ratio. It is also refered to a stoichiometric (sp? Stoy-kee-Oh-metric)

 

If they leaned it to 14.5 they would have lost HP due to the PCm pulling timimg(knock retard)

 

Thanks guys. I didn't think it would have made any major impact but I wanted to be sure. A little knowledge is always a good thing

 

dynoing a car, I hope to god you don't sit it at 14.5:1 AFR... and actually I saw a guy dyno a car that lean, and he had his friend tuning his car saying 'yeh man you are dead on, your not going to get much more power out of it'

(this was a ls6 head and custom cam car 02ws6)they dyno the car the first time with the laptop on the mobile dyno, the laptop about jumps off of the dyno b/c of KR.

i then b****** at the guy saying he needs to add fuel and he added 10% and left the timing alone, gained 20HP......

so this 14.5 AFR is crap; WOT dyno tuning a car with airlids the stock AFR will go to a 12.1 or so up high, and around a 12.6 i think it is WOT but not in the high rpms

call bullcrap on him. or just let him keep thinking that and leave him alone.

 

Thats true, at PART THROTTLE. The second you cross the TPS for PE threshold and pass the time delay, you are down to low 12:1s.

Not trying to threadjack, but here is my conclusions drawn from custom tuning my work van. The same principles can be applied to any GM ECM/PCM though. They all have crazy high TPS settings for PE/WOT mode and a LONG PE delay. This is what I use for my mostly stock 1993 G20 TBI 350, pulling 5,600 lbs with 3.08 gears and 29" tall tires. (5,000 mile Goodwrench HD L05, Edelbrock 3704 TBI performer intake, Doug Thorley DTE 316 Y3 Tri-Y header kit, high flow cat, Flowmaster 40 series delta flow 3" single in/ dual 2 1/2" out, 1,800 rpm converter in the 4L60E (4,600 RPM WOT upshifts).

Stock GM PE table



Slightly Leaned out



Changed the TPS% value for Power Enrichement/Wide Open Throttle mode from the values on the left to the ones on the right.



Here is the difference the limited changes that I did made. Drove it to Kennedale on the modified chip, ran it, then came back and ran it on the stock calibration. Notice the 60' with the modified chip, it was ripping tire off the line with the "HOT" tune.

Stock Chip (I am car 881)



Custom Chip (Raised shift from 3,800 to 4,600, 10% more line pressure in WOT mode, eliminated PE delay, leaned PE air/fuel ratio to 12.9:1, VE learn on the fuel tables.



The end result was even though my 60' was .10 seconds slower, I still went from an 11.64 to an 11.41 and picked up 1/2 MPH with the custom calibration.

I probably could have gotten more by messing with the timing advance curve and amount. It is a 5,600 lbs work truck that frequently pulls a 5,000 lbs trailer, so I didn't. The changes that I did make however really help this thing pull much harder.





http://www.youtube.com/watch?v=UEeZ5ruugWA