[Jack Gifford]

The wide-band A/F-ratio meter temporarily (?) installed in my '59 GMC (382 c.i. '58 Tri-Power engine) has been extremely useful in tuning for cruise, deceleration, and idle conditions- consistently very close to 14.7 now. But I recently made a point of paying attention to it during full-throttle situations (all four gears, varying speeds). I'm a little bit surprised to see it generally in the high twelves, considering how well it performs. I had thought it would need to be at least down into the elevens to not ping or otherwise misbehave. Anybody have any experience to compare with?

I also included runs on just the center 2-bbl. The full-throttle A/F ratios were amazingly close to what I saw with all three carbs.

[Kenth]

Is the current jetting/calibration far from the original factory jetting?

[Lee]

I've tested LOTS of cars on my chassis dyno. Best power for naturally aspirated motors is almost always right about 12.8:1. Best idle is usually 14.0:1.

[Tom Vaught]

Originally Posted by Lee

I've tested LOTS of cars on my chassis dyno. Best power for naturally aspirated motors is almost always right about 12.8:1. Best idle is usually 14.0:1.

X2. Same experience on engine dynos here: NA non emissions engine like 12.7 or 12.8.

11.5 to 1 is a Boosted Engine Air/Fuel ratio.

Tom V.

[Jack Gifford]

Originally Posted by Lee

... Best power for naturally aspirated motors is almost always right about 12.8:1...

Thanks guys. That makes me more comfortable with what I'm seeing. Hard to believe how closely I guessed on main/power/pump systems! However, trying to tune the idle of this almost-over-cammed street engine by ear was a disaster- letting off the throttle while cruising showed about 11:1 A/F!

[Tom Vaught]

Originally Posted by Jack Gifford

Thanks guys. That makes me more comfortable with what I'm seeing. Hard to believe how closely I guessed on main/power/pump systems! However, trying to tune the idle of this almost-over-cammed street engine by ear was a disaster- letting off the throttle while cruising showed about 11:1 A/F!

Not hard to believe that number Jack. You can get lean spikes on tip-ins if the accelerator pump is not right and you can get rich spikes when you take away the air if the carb is a rich calibration as the air removed portion is instantaneous and the fuel takes time to normalize in the fuel circuits. I do not worry about decel rich spikes. EFI can fix that with a throttle position sensor but carbs are typically too slow for that deal.

Tom V.

[Rugratman]

I would like to jump in here.
I am tuning mine as well. I have 12.5 at 2500 rpm and about 14.7 at idle.

However, deceleration I am up to 16.5. . Is this OK.?

[Jack Gifford]

14.7 at idle, and 16.5 on deceleration are fine.
What is the engine load with the 12.5 at 2,500 rpm? If it's no-load or light load (cruising on level road) I'd want it leaner than that- maybe 13.5 or so.

[Rugratman]

Good point Jack, I am at idle in the driveway now.
Thanks.

I am loving this A/F meter, I should have got one years ago.