best AFR for Power??

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360duster

360duster

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Hi Guys, thinking about a dyno session to find a little here and there.....at the moment i run 12.5 AFR and 35° BTDC Ignition timing at full throttle (Holley Sniper).

to the guys who did some more engine testing, what AFR produced the best Power numbers for you?

I think i´m around 500 hp (car runs 10.70 @ 120mph), testing time at the track is very limited so i wasn´t able to check such things "live".

Engine combo: 408SB, 10:1 compression, Procomp CNC´d cylinder heads, comp hydraulic roller 250/250° 108 LSA, .620" Lift, Victor intake with 1" open spacer and Sniper EFI, Hedman 1 7/8" headers with a mini bullet.

Thanks!

Michael
 
On my 440 10.9:1 engine I been running my AFR at 12.3-12.4 for the last 2 years. Car is very consistent and doesn't seem to change nearly as much as my competitors when the weather changes from good spring/fall air to crappy summer air.
 
Not sure if this helps you at all, since I'm on e85, but my car runs about the same between 0.77-0.82 lambda. Outside that range and it is loosing power (for my engine).
 
My af gauge is a great tuning instrument, but what my plugs are saying is what I make my ultimate decision off of..
A chassis dyno would be great but it would likely just be perfect for the weather that day... I've lost a half a second at the track because of bad air..
Ultimately you're going to have to do more test in tune and watch the weather as well to get down to the last 16th of a horsepower... For that day and that air..
 
j par said:
Is that e85 talk?..
Click to expand...
I use lambda on my AFR gauge, because it normalizes the air fuel ratio by taking into account the stoichiometric coefficients of the combustion reaction. You can use AFR if you like...I just like lambda because its what I'm used to. Here is a chart I stole from somewhere online that helps to show the lambda and AFR scale (the highlighting was not from me).
lambda-afr-chart-jpg.jpg
 
Last edited:
j par said:
My af gauge is a great tuning instrument, but what my plugs are saying is what I make my ultimate decision off of..
A chassis dyno would be great but it would likely just be perfect for the weather that day... I've lost a half a second at the track because of bad air..
Ultimately you're going to have to do more test in tune and watch the weather as well to get down to the last 16th of a horsepower... For that day and that air..
Click to expand...
I used to tune by MPH and plugs at the drag strip, but e85 burns so clean that the plugs look brand new after a run (or multiple runs for that matter). This is why I had to get a wideband AFR gauge. Its pretty much required to safely tune e85.
 
Not sure on where you have the sensor mounted. Mines on the left side 3” exhaust pipe about a foot from the collector flange. Get good readings but tried using it on a collector for at the strip and couldn’t get accurate readings (showed way lean) likely because I drilled and welded the bung too close to the end I guess. So I just use MPH for getting the jetting right at the track. The ratio number (if sensor was mounted correctly) would be whatever it would be. MPH would be the better number obviously.
 
flyfish said:
I use lambda on my AFR gauge, because it normalizes the air fuel ratio by taking into account the stoichiometric coefficients of the combustion reaction. You can use AFR if you like...I just like lambda because its what I'm used to. Here is a chart I stole from somewhere online that helps to show the lambda and AFR scale (the highlighting was not from me).
View attachment 1715811302
Click to expand...

Thanks for posting that chart. It's an important reminder that AFR's don't necessarily mean anything without knowing what fuel the engine is running. If one person says their car runs it's best mph at 12.0, without knowing the fuel type, what does that tell you? Even 10% EtOH makes a difference.
 
NA motors usually peak around 12.8 to 13.0. It depends on RPM, Load, Octane etc. A dyno session is around 500.00 usually and "they/dyno #s" will tell you what AFR work on your setup. Look at my recent engine dyno results with AFR's listed per 100 rpm increments. 91 octane, 180 deg engine temp, 34 deg timing, 10.2 to 1 compression.
 
good information, i change between regular gas and E10 from time to time...... So i think i´ll make the trip to the dyno, we´ll see what happens. When the best tune is established, then i´ll stay with the same fuel.

Thanks@all!

Michael
 
mopowers said:
Thanks for posting that chart. It's an important reminder that AFR's don't necessarily mean anything without knowing what fuel the engine is running. If one person says their car runs it's best mph at 12.0, without knowing the fuel type, what does that tell you? Even 10% EtOH makes a difference.
Click to expand...
Yep, for our lovely CA gas I had to change the AFR gauge reference from 14.7 to 14.1.
 
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