AFR Questions
Originally Posted by Zemo
I believe it refers to "parts"....11 parts air to 1 part fuel is 11:1. the higher the number on the left, the more air, the leaner. 14.7:1 is, I think, gasoline's "ideal" number. any leaner than that could be dangerous. better to err on the side of safety...although, I am no tuner.
14.7 is the ideal mix for gasoline. it is a good cruising afr, ie, all the time you are less than 1 psi.
12.5 would be a starting point for a NA car.
11.5 is a popular point to start for FA cars.
the point to remember, a half point or even one point off perfect is not going to make one horsepower difference. On the other hand a point above minimum will screw your motor.
If that is the case, might as well be a little on the safe side. IOW 11.5 and 11.1 will not show a difference in HP. But 12.7 at 25 PSI might just add to the recycle bin.
The bang for the buck is in the timing. Unless you have a knock control ON and set correctly leave timing to a tuner with a dyno.
12.5 would be a starting point for a NA car.
11.5 is a popular point to start for FA cars.
the point to remember, a half point or even one point off perfect is not going to make one horsepower difference. On the other hand a point above minimum will screw your motor.
If that is the case, might as well be a little on the safe side. IOW 11.5 and 11.1 will not show a difference in HP. But 12.7 at 25 PSI might just add to the recycle bin.
The bang for the buck is in the timing. Unless you have a knock control ON and set correctly leave timing to a tuner with a dyno.
Originally Posted by housedj
stock evo AFR's have been between 10.5-9.6. very rich from the factory to keep people from blowing motors. the ideal AFR for an evo is 11.5:1 on unleaded fuel. if u run any kind of leaded race fuel, you can get away with 12:1-12.5:1.
for example, there was a guy in AZ who had his car tuned @ Dyno-Comp but his AFR was 12.5:1 (waay to lean for a turbo car on 91 octane pump gas). he went over to Mynes & they richened the AFR to 11.5:1 & he gained 30WHP!!!!!!!!!!!!!! he also no longer has detonation...
for example, there was a guy in AZ who had his car tuned @ Dyno-Comp but his AFR was 12.5:1 (waay to lean for a turbo car on 91 octane pump gas). he went over to Mynes & they richened the AFR to 11.5:1 & he gained 30WHP!!!!!!!!!!!!!! he also no longer has detonation...
Depends on relative octane, boost, timing, EGT.
On 93 the best is an 11.5 tune on 20.5psi. When you start getting to 11.7's on 93, you start to hold timing. 11.2 is conservative and what some tuners program wild customers cars for due to liability.
Originally Posted by 05 EVO RS
you are right BUT that 14.7:1 is for NA ONLY 12.5:1 is boost applications so i'd say 12.2:1 to be on the safe side
WHAT!??!?! 12:5:1 and 12.2:1 on pump gas? Are you mad?!??!
Please don't post wrong info like this, because some people will actually think it's right and blow their motors sky high.
14.7:1 is stoic and is what you should be seeing at cruising. On boost, with pump gas, you should be in the low to mid 11's.
In reality, AFR is only part of the equation of tuning, you can knock enough to blow your motor even if your AFR # is nice and safe. You have to monitor AFR, knock voltage, timing, etc.
Last edited by razorlab; Dec 20, 2005 at 09:47 AM.
