I have seen a few different things here about AFR for boost. I was under the impression that 11.5:1 was best, then I see a few guys making a decent amount more power around 12:1. What seems to be the consensus for best AFR under boost? I won't be running any more than 8-10 psi.

 

I would think 11.8 would be the target area.

 

the gauge is never going to read steady, but for me at 8 #'s boost my afr is low to mid 11.0's to a quick bump to 12-12.1 but stays in the 11's. hope it helps.

 

a/f is in the equation of timing, psi, knock, and EGT's. 11's is generally a safe area that gives good EGT's and aids in knock elimination. Moving into the 12's may run you a little hotter, might even cause the pcm to go into knock retard mode and could make you pull a little timing out. It's something you'll have to play with if you're trying to get that last bit of hp out. If you can run 12.2 a/f w/ full timing, keep good EGT's, and no timing retard then you're ok. You might sacrifice a little power to be in the mid 11's, but you'll be safer. I myself target 11.2.

 

will egt's get to a harmful level under boost if you were at 14.7:1? (only theoretically, i dont want to test this theory)

 

So it sounds like 11.5:1 is probably about right for a good balance of performance and safety. Thanks guys

 

for me it depends on how hard i am pushing it. if i am not right at the raged edge i shoot for 11.5-12.0 but if i am really pushing it i shoot for 11.5 max. last time i blew out a head gasket i was in the 12.0 range and i was running 20psi and a 100shot. i always wonder if i had kept it in the lower 11's if it wouldn't have poped.

 

Agreed. I dont like to see above 11.8 on my FI cars and ideally I feel safer with 11.5 or a tad lower. No sense in pushing safety just for an extra 20rwhp