What is considered to be the best air fuel ratio for a normally aspirated engine under full throttle? I have just installed an AFR meter on my car and it is showing about 12.5 when at WOT. It seems this might be a little lean.

Thanks,

Roger

12.5:1 is actually on the rich side, but safe for an N/A engine. I think it varies from engine to engine, but I think most N/A engines are going to make best power in the 12.5-13.5:1 range. If you have plenty of time to spend on the dyno, you may want to play with the mix a bit to see how leaner mixtures react. I don't think 13:1 would be unsafe in most circumstances. That's about the ratio I'm shooting for on my EFI tuning using an Innovate LM-1 wideband.

Clair

I try to get mine at 12.5 to 13.0. My car runs best right at 12.5. I realy don't want to go above 13 because it will be boardering on being too lean.

Raul

I see a lot of boosted cars go richer, closer to 11:1. I guess they do it for safety. For n/a, I think best power is usually around 12.5-13.0. If you're getting 12.5's now, I think you should just leave it as-is.

Thanks for the replies guys. This AFR measurement is new to me but I like it. I like to play with electronics and the unit I have is a DIY unit called JAW. It uses the Bosch LSU 4.2 sensor. I just wandered what sensor yours use?

Thanks for the info.

Roger