Air/Fuel ratios?
Thread Starter
Drifting
Joined: Mar 2011
Posts: 1,886
Likes: 9
Air/Fuel ratios?
What A/F ratios should I be shooting for? I have a Qjet equipped 74 smallblock, and an A/F ratio gauge from Jeg's plumbed in, so I can drive the car and see the A/F ratios in real time.
Idle?
Part throttle and cruise?
Heavy throttle?
Wide open throttle?
Idle?
Part throttle and cruise?
Heavy throttle?
Wide open throttle?
Intermediate
Joined: Dec 2011
Posts: 26
Likes: 0
From: Newport News VA
Here are some guidelines. The readings must be at steady state and not transient conditions. Also a carb may not hit ideal AF ratios at all conditions but will provide more of a straight line best fit from idle to WTO. 14.7 is the ideal number for emissions. 12.8 is usually a generous amount of fuel for WTO acceleration. Leaning out to 15.2 at cruise should be OK, but can cause overheating.
Please have someone else monitor the engine rpms, load and AFR, I tried once to do logging and driving at the same time...not a very good idea.
I'd be interested to know what your readings/results turn out to be.
Idle? - 14.2
Part throttle and cruise? - 14.71
Heavy throttle? - 13.8
Wide open throttle? - 12.8
Please have someone else monitor the engine rpms, load and AFR, I tried once to do logging and driving at the same time...not a very good idea.
I'd be interested to know what your readings/results turn out to be.
Idle? - 14.2
Part throttle and cruise? - 14.71
Heavy throttle? - 13.8
Wide open throttle? - 12.8
Race Director
Joined: Sep 1999
Posts: 11,361
Likes: 383
From: Plano TX
Stock camshaft? It should idle fine in the 14.0-14.7 range. Cruise you can go 14.5-15.0. WOT you want to see around 12.5.
If it has some cam in it you may need to run it a bit richer at low rpm and idle.
If it has some cam in it you may need to run it a bit richer at low rpm and idle.
But here is a general guide:
