A/F Ratio
 

question for ALL. Seems most of the time when looking at dyno sheets for boats A/F ratio's are 12.1-12.5. when doesn't anyone like 13.5-14 ,,, just trying to understand

lean is mean,,but in a boat it will melt down.

Well for NA engines, around 12.8 will give the best dyno numbers.

Like he said. While 14.7 is stoch, best power can be anywhere from 11.7:1 to 12.8:1 depending on the motor.

Now, don't confuse widebands O2 readings on dyno sheets for what the dyno computes as AFR. I have seen them very as much as two points.

WOW!!!!!!!!!!!!!! I thought I had some bad ones in the past.... LOL thats something else

That stainless steel top hung in there!

i have a few that look a lot like that one!

Engine's are run at WOT on the dyno.

Therefore, all data you see is measured at WOT...including A/F ratio's.

Not on everyone's dyno. ;-) I make pulls at different throttle positions to verify that the tune up is right. I have seen a few different carbs come in with tuneups that have caused motors to melt down at cruise. They were right at WOT but 19:1 at partial.

Yes, I agree. When we tuned my S/C mustang did about 6 or 8 pulls tweaking at low rpms working towards wot. Then another 3 or 4 at wfo tweaking that. Almost 40 k on that setup. So unbelivably reliable, only 6 psi and as I recall kept the A/F just below 12:1. Traded extra power for reliability.

We are running NA engines at 13.3 -13.5 AFR at 6500-6800 RPM with about a 9.3 to 1 CR. We have never had any signs of detonation. Even at the 13.3-13.5 range the plugs are still mostly black. In my experience, a 12.5 to 12.8 AFR for a low compression NA marine engines is over safe and makes the transom black and wastes fuel.

Yea, probably agree with that. But my mustang is 10 to 1 and we can only get 91 octane up here. The only time I once in a while will get a little pinging is in 5th gear low rpm on the back side of the power curve and you get into it. Don't know about the canned tune that whipple does on the 500 efi kit but that's what I plan on running