afr i know everyone asks but . . . .

[r5_scotty]

my afr`s aint right and i cant correct it. can anyone help???

on idle i got 14 on a 30mph run i got 12.8 at 50 mph i got 12.3.

now at 18psi on boost it drop to 10.4 and stays at that.

yet it starts perfect ,runs perfect.my lambda is on the big jim 20cm from rear of the turbo and is the aem afr so its all good. carb was a fishhead special so should be no issues there. at the moment my mixture screw is right in. and if i turn it out it starts to run very lean ie 10`s on idle.

any help please??

[JP Racing]

That's not too bad for running maybe just a tad rich off boost but not too bad :) don't forget that 10s is rich and 16s would be lean it works the other way to most things :)

[r5_scotty]

That's not too bad for running maybe just a tad rich off boost but not too bad :) don't forget that 10s is rich and 16s would be lean it works the other way to most things :)


my bad . so all is good . maybe a little more boost is needed :D

[JP Racing]

If you are looking for the perfect afr's for a turbo car there are a few different schools of thought on this, but the bottom line is that there is the most potential power available when the flame front speed is the fastest. The textbook answer is supposed to be 12.6:1 for turbocharged engines, but you will find some who say 12.1:1. The problem is that depending on many conditions like octane and intercooler efficiency, the engine may be too knock constrained to be able to run at the AFR for best power, so many people who tune usually go for something more conservative, like 12:1 or richer. Depending on what conditions the car will see (i.e. race track) could also mean that it's a smarter idea to go with a richer mixture to keep temps cooler for longevity.

Personally, for a street car I'd start the tune with a conservative 11.2:1 or so and when everything else was verified as safe, I'd lean it out to 12.1:1, trying to err any deviations above 12.1, as long as there's no knock. I prefer to leave a little safety cushion, even if there might be some power left on the table. Also just a note with the c1j inlet it tends to run lean on the outside cylinders and richer in the middle two :) so keeping it a little rich will be safer :)