[Official] "Do I need a tune with bolt-ons?" thread

[Live4Driving]

What is the leanest AFR that is typically considered safe? I have done some searching on the web and I've seen people talk about the ideal AFR mixture settings with a tune and people warning of leaning out a car but at what point is the AFR considered too lean that it hurts the engine? Anything above 13 or 14.7 or is there another general point that I am missing?

[jwick]

Originally Posted by Live4Driving

What is the leanest AFR that is typically considered safe? I have done some searching on the web and I've seen people talk about the ideal AFR mixture settings with a tune and people warning of leaning out a car but at what point is the AFR considered too lean that it hurts the engine? Anything above 13 or 14.7 or is there another general point that I am missing?

14.7 is idle. I don't recall exactly from my NA tune but I don't think I go leaner than 11.7ish.

[synolimit]

Originally Posted by Live4Driving

What is the leanest AFR that is typically considered safe? I have done some searching on the web and I've seen people talk about the ideal AFR mixture settings with a tune and people warning of leaning out a car but at what point is the AFR considered too lean that it hurts the engine? Anything above 13 or 14.7 or is there another general point that I am missing?

Knock. Leaning a car out to far will eventually knock, same with adding boost and timing. It's all a dance trying to find the perfect combo. You might get away with say 12.8afr but if you're only running 20 degrees of timing then who cares? Your power will suck. I guess most NA tuners shoot for mid 12's on these cars but they also try for good safe timing. I don't know what will get you more hp in the long run but if you go from 12.5 down to 12.3 yet you sneak in another degree of timing then you've done good I'd say. On a turbo car like my old one 1 psi and 1 degree were good for over 10hp. So you add as much as you can till the knock sensor says no.

PS you're correct. High is lean, low is rich. The numbers you see are parts of air (14.7) that equals 1 part fuel (14.7:1). So a lower number means you're taking air away from that 1 part fuel which is richening the ratio.