I am having a new fuel pump and McLeod Street twin put in and I wanted the shop to do a before and after dyno run. He did the before and said my AFR was steady at 13.7:1 but the car still managed to put down ~340RWHP on a Mustang dyno. So now after he gets the stuff installed he is going to tune it back to the 12.5-12.8 range. How much power do you think I will gain from that?

 

Why would you want to make it richer?! 13.0-13.2 is good and safe, stock af in PE mode is 11.7, which is waaay to rich.
If you're safe at 13.7, stick with it.
BTW, you will LOSE horsepower if you make it richer!!

 

that's true! my car made best power at 13.6:1 AFR!!

 

Probably not much but I would feel alot safer at 12.0:1 or 12.5:1 vs where you are now. A few extra hp isn't worth the risk of toasting a piston if you get a bad tank of gas or something.

 

I am hoping I will gain some more power because he also said that the car was pinging from being so lean. When he tuned it a year ago he had to pull out so much timing to get it to run without knocking at 12.8:1 that it actually lost power from when he had it set at 12.5:1 with the timing put back in.

Plus I would definitely feel safer running in the 12.x:1 range when I put the bottle on the car.

 

I actually lost power going from 11.0-11.5 A/F to 12.0-13.0 A/F. My car likes to be rich I guess. Anything can happen.

 

12.5 is good for a blower car, but generally too lean for an NA car. But a major reason to tune is to find out what works best. You may gain power, lose power, or it may make no difference. In general ~13-13.4:1 works best for an NA LT1.

Rich Krause

 

mine when it was stock was hitting 11.1 or 11.2 at wot in pe mode. but when i got it programed to 13.0 there was a ig increase in power. what you need to do is go get your car put on a wide band o2 dyno and they can tell you where you make the most power (A/F ratio wise)

13.7 is to lean for my taste

 

also remember that when you tune on the dyno you will get less air than if you are moving. if you tune to 12.7 on the rollers you may be at 13.0 on the street.

 

Sometimes its not all power... its smoothness.. maybe the car runs smoother with a bit more fuel...

I like to tune for 13.0:1 for NA and 12.3:1 for forced induction...

The thing is that 13.6 as happened with latinspace... its the result of measuring though the exhaust and not the headers... so it was nice at 13.6