When tunning on a dyno for best power... what AFR to shoot for?

I've had better results in NA with 13:1 than 12.5:1.

Once thing is to be considered and it is that the dyno AFR will not be the street afr so you always have to run richer on the dyno... but... what afr is best for maximum power?

 

Thats what I went for, 13:1 Stick to what your experience tells you is my suggestion. As for what makes the most power, I dont believe all cars will ever tell the same story, especially when gasoline, buildup, VE and yada yada is going to be so different. If you know the weight of the dyno wheel being lighter than your car (they are 3k pounds often), then shoot for a little richer, some people also remove some timing for the street compared to thier dyno tune (2º or so tops should do it, maybe 1º, I made no changes but also didn't have lots of time for timing ).

 

I usually do timing on the street... but the AFR on the dyno...

That was one of the other things why I tune richer.. it is the dyno wheel... I just didn't know what people shoot for when on a dyno...

I had my car on 12.8:1 which was rather lean for what I wanted...

I will tune it this time for 12.0:1 or even 11.7:1

 

You need to experiment. But as your last post suggests, the AF ratio that produces max hp isn't necessarily the best one. Just one example: if you tune on a warm, humid day for max hp, your car may be lean enough on a cool, dry day to cause engine damage. Similar story with changes in altitude and barometric pressure. Another example: gasolines may vary markedly in density (specific gravity). If you tune for max power with fuel of high sg and switch to fuel with a low sg, it may also be lean enough to cause damage.

Based on the above, for an LT1 I recommend ~13:1 or a little richer for an NA car and ~12.5:1 or a little richer for a SC car. But you still need to keep in mind the conditions under which the tuning was done vs. the conditions you are likely to encounter on the road. If you are tuning on a day with a high density altitude (thin), go a bit richer. If it's a good day (low density altitude) you can go a little leaner.

Rich Krause