A/F ratio tuning question
Is it best to tune the a/f ratio the same across the entire rpm range, for example I am at 11.7:1 across the board or is it best to go leaner at the bottom then richer as you go up or visa versa?

in vacuum, you want to be as close to stoich as possible (14.7). generally, you have to run a littl richer than taht at idle, like high 13s, and in many cases you can lean it out to mid 15s in some areas. the leaner the better for vacuum, you just lean it out until it starts running shitty, then add a little back in. Under boost is totally different. what you want to do is have a fuel curve that gets richer as you boost more. start out at around 14-14.7 at 0 pressure, then subtract a little for every pound of boost. It varies by car, and how you tune, but i like to run about 13 at 2-4 psi, 12 at 4-8psi, 11 from 8-10, and high 10s above that. thats pretty conservative, but it works well for me. pat

The Mustang is N/A mind you, but what patman is saying is putting you in the right direction. I have a lot of overlap, so my idle likes to be lean so I have an idle in the mid 15s to high 14s (varies because of the map trying to make since of that big cam's vacuum changes). Under vacuum when cruising it is in the high 14s and under load at part throttle it is in the high 13s. At, WOT it is in the upper 12s until just right at top end where it is tickling the 13s. Now this is just from very little tuning, but it seems to be working great so far.

If it helps, my Lightning has been tuned to be at between 12.5-12.1 at WOT and boost.

Excellent post patman.

^^^^Yes, I agree.

Thanks for the help, I need to finish tuning mine. I just had a rough tune and didnt get to finish because the police pulled me over, lol.

haha yeah i finally found a good spot to do pulls where theres never any cops, but i used to worry about that all the time.

by across the board i hope you mean only in boost, that would be ungodly rich in vacuum. yeah that setup looks fine to me

Looks safe to me.

Timing is where your power is going to be at.. do you have control of this? I keep my AFR at 11:5:1 at its leanest point. I give a little extra fuel before and on the rpms that peak tq is made just to be safe. I don't see much extra power going leaner... but running a lil more on the rich side allows me to use more ignition timing which does yield a significant power gain (even 1 degree). Monitoring knock during this process is a must.

Yea, It is a good idea to mention timing. I don't think Tim can control his, but that is where the power will be more so than A/F. Andy, your A/F is nice and safe (rich), what kind of timing are you running if you don't mind my asking?

Depends... with Alky injection I run pretty aggressive..It peaks around 22*. On pump I have a "snow" map that peaks at 14-16* and another map that peaks around 17-19*. The big changes are in the low to mid range.. I can run ALOT more timing with the alky or race gas than I can with pump. I'll be refining my tune as soon as all my new parts in... I'll post all the goods up when this goes down. Time for a standalone, Tim! ;)