Ive got a 6psi Powerdyne and i recently dynoed 359 rwhp and held 11.4-11.5:1 until 5k where it tapered to 12.5:1 at 5500rpm. What is the ideal air to fuel ratio and how much extra power do you think i can pick up.

 

Ideally, it would be 12/1 the whole way. Power gain would be <10 hp.

 

I ran mine at 11.8:1 up to about 5 PSI, above that or above 4500 it was set to 11:1 to 11.2:1. Not breaking stuff was top priority for me.

 

well the reason i ask is that i thought you made more power as well as it being better for the engine to be somewhat leaner around 12.5:1

the car doesnt get that great of gas mileage, probably around 17 avg and the exhaust tips are black from unburnt fuel.

 

12.5:1 might make slightly more power, but it doesn't give you much room for error. I've heard of some of the Mustang guys making the best power leaner than that, but unless you dyno, you don't really know for sure, and even then, it can be off by a bit. You're not in boost most of the time anyway, so if your mileage is sucky, look at the O2 sensors and see if they are doing their job.

 

Good point. To add to that also keep in mind that your actual "moving air/fuel ratio" is likely to be leaner than your "dyno air/fuel ratio" due to less load on the engine on the street and more moving air. You're better off to stay at 12.0:1 or slightly richer just to be safe IMO, as your ratio on the street may go to more like 12.3:1 if you're hitting 12.0:1 on the dyno. Also, WOT tuning hits targeted values for the most part, and colder and/or less humid air than what you were tuning with on the dyno can also cause your A/F to go leaner than what you tuned for. Stay safe, unless you have lots of money to play with. In fact, I would leave the 11.5 part alone or take it to no more than 12.0, and I'd richen the 12.5 part up a little ...get the whole thing around 12.0 IMO.

 

Most of 'em like ~12.3-12.5:1 and that is safe. However, you need to be careful about your tuning conditions relative to your driving conditions. If you test in bad air and it's in the range I suggest, it will be too lean in good air. Also, a hot engine is going to need a richer mixture to help keep the heatr down.

Rich