383

Im running a 12:1 cammed C6Z with LG exhaust. Im currently at PE= 1.145 with a stoich of 14.1 (12.1) across the board.
Should I be running richer up top for safety/cooling? Im not concerned about every ounce of power or MPG's just reliability

tblu92

The only way to know for sure what your ACTUAL WOT AFR is --is by checking it with a wideband 02----On a completely stock engine the commanded PE will match the actual AFR--
However with major mods just because you "ask" for a 12.1 AFR it does not necessarily mean that's what you'll end up with--Especially with LT's and a mid to large cam with lots of overlap--- Actual WOT fuel needs to be verified using a wideband
Doing lots of data logging and correcting to the VE table will bring your commanded closer to the actual-But even that is not needed
Best is to realize that you may have to command like a 11.8 PE in order to get an actual 12.1--- and vice versa--- this is the most used method still very accurate
Back your your original question--- Assuming you are using a wideband --dedicated race cars seem to make the most HP with an AFR somewhat leaner---Like 12.7 to 12.9
A weekend racer D/D maybe 12.5 to 12.6
D/D more like 12.3-12.4
Depends a lot on how much timing you are running as well-- Some like running a richer AFR and more timing---some like running a leaner AFR and less timing
Old school reasoning dictates that the lean route makes more HP and the richer route makes more TQ---
My guess a track with log straights shoot for more HP and a track with many tight turns shoot for more TQ

383

yes I verified all my fueling with a wideband. wouldn't it be safe to say that rather than raping PE to get correct fueling with cam overlap you should tune the injector timing?

mowton

What's explained above is not "raping" the PE, rather it is tuning with the PE. The procedure is to get your fueling (MAF, VE ) dialed in pretty close to +/- 2% error with steady state data collection either on the dyno (safest and fastest) or the street (be careful). Your target is always your commanded Lambda/AFR. Once you have that done then you tune with different values for PE to give the motor/setup what it wants. Normally you will go a bit lean up to max cylinder pressure/Torque and then richen a few points out the door for safety/cooling as you call it.

Raping the PE would be if you would just disregard the MAF/VE values and set PE values to bring the Lambda/AFR in. You would see values like 1.5 which you know is ridiculous.

As far as the cam timing, one would hope that you actually performed that task during your idle tuning phase to preclude "false lean" readings and/or "stinky" idle. I have seen two sides to the argument whether this procedure helps just the idle/light load cruise or high power scenario's as well....but doing it for the idle will put that discussion to bed.

At the end of the day, you tuning strategy and procedures is developed to produce a well integrated tune from key-on to red line. That is what we teach and mentor here.

Ed M

383

I'm within about 2% and my pe always seemed to match command. I thought once you got ve and maf transfer lines up pe would be good too I wasn't aware you needed to "tune" pe. Mine is good. I was just wondering what some track rats do for fueling. The pig rich stock tune made me question my 12.1. Thanks for the responses

tblu92

The only time you ever need to change the injector flow rate is if you change injector size
messing with injector timing is just asking for trouble--GM engineers have spent years on getting these tables spot on--so no need to mess with them---Only change you will ever need to make is if you install LARRGER injectors then you must raise the IFR table to match the new size Messing with injector timing is a bad idea !!

383

I meant the eoi. I moved the whole table a bit and cleaned up my idle.

mowton

What are your cam specs. If you have a decent overlap, then you would modify the EOIT. Idle running lean (actually false lean as you are sending raw fuel out the pipes) and idle "stink" are indications that this modification will help.

The overlap causes a "short cicuiting" of fuel as the intake and exhaust valves are open at the same time. You want to move the EOIT so the injection ocurrs after the exhaust valve closes.

You will move the values in the direction they go as temperatures increase. You log the idle Lambda/afr before an adjustment and note it. make a small change, maybe 5%. Reflash and let things stabilize and log the idle lambda/afr again. If it has become richer, then you are moving in the right direction. Continue until there is no improvement and go back to that previous value. You will have to retune your idle airflow of course but small price to pay for better idle and performance.

Ed M

383

Yup that's exactly what I did. 232 242 118. cammotion endurance lobes. Do you think I should go fatter than 12.1 for the track?

mowton

That cam only has 1 degree of overlap, shouldnt have been too bad.

No, I wouldn't think you would need to fatter than that. I did not see are we talking 1/4 mile or road race? could be more in the area of 12.7/12.9 for 1/4 mile, maybe 12.4/12.6 for road course to cover the long duration, high heat, high load runs (torque).

The values I am stating are what you would read at the WB, not necessarily what you are commanding.......

Ed M

383

I was surprised how much smoother the idle got when I adjusted it being a mild cam. I'm guessing wilder cams would see bigger improvements but it was worth it for me. The cost was only some of my spare time. I do mostly hpde and autox