Thread: NA air fuel ratios

I am running rich at about 11.6:1 @ WOT. I still made decent power.
I will lean it out closer to 13:1 and I know I will make gains.

N/A engine with anything higher than 9.5:1 CR I see no reason to run any higher than 12.7 - 12.9:1. Not even more power is made.

Now for a all motor car I thought a 14.7 afr is optimal. Does this change the higher the compression ratio is? How much is the optimum ratio affected as the compression rises?

14.7 is stoich and is optimal for idle and low cruising speeds. You can even lean it more to 15.5:1 for better fuel economy. But for WOT on a SR20 N/A engine is way lean, in fact, if you are bold enough to try it, you will find the car very slow. Richen it to 13.5:1 and it will be better, but richen it a bit more to 12.9:1 and you will feel the difference. SR20s like fuel and a fuel pressure of no less than 52psi. Go test it on the dyno, at least you will tell me 12.9 and 13.5:1 made the same power.

I aim for 13.0:1

I like 12.8:1 for N/A WOT (for best power) but sensors aren't perfect and a dyno is best for final tuning.
Leaner obviously for the lesser loads.

Ben ive found with my VE, between 12.8-13.1 on my innovate wideband is perfect.

On the dyno sensor this is between 13.1-13.4

Dropping the dyno range into the 12.5 area made the car loose power and torque. This is with me running up to 7degree peak timing figure. Engine is 13:4-1 with N1 pistons and 16ve cams - so dynamic compression is quite high. The difference from 12.5-131 was 8-10wheel kw varying in different points (indicating my timing tuning was a little out and compesnationg for various engine efficiencies at different rpm) however it was literrally lifting the graph completly.

I think i could run to a flat 13.5:1 and around 28-maybe29 degree with N1 and probably near 30 degree with E85.

Yah when I said you'll want to use the dyno for fine tuning, I meant you'll want to use it to see where best power is. Not that you'll want to use the dyno wideband. The wideband sensors at the dyno tend to read all over the place.
I recommend a dedicated wideband in your exhaust for sure.