Air Fuel Ratio or Timing for Peak Power

[WeathermanShawn]

I know this is a fundamental tuning question that has been throughly discussed over the years.

Does anybody have any sound research results that definitively proves that adjusting Air Fuel Ratio (AFR) to an ideal figure gives better results than adjusting timing, or is it vice versa? Some of the literature from Greg Banish and Innovate Motorsports seem to insinuate that finding the 'fastest flame speed' for gasoline (~.9 lambda), then finding the correct cylinder pressure through timing adjustments is the route.

I have not been to the dyno in about a year, so I have spent the last week doing some street runs using various combination of AFR and Timing. I have logged runs using AFR's from 12.2-13.1 and timing adjustments of +3-4 degrees at WOT. While the mixture near 12.5-12.7 did seem to reduce knock, the technical literature seems to discredit the cooling effect of richer mixtures and suggests that you are simply burning less oxygen..hence you may get less knock but you will have less power.

Any thoughts?

[eficalibrator]

Some of the literature from Greg Banish and Innovate Motorsports seem to insinuate that finding the 'fastest flame speed' for gasoline (~.9 lambda), then finding the correct cylinder pressure through timing adjustments is the route.

While the mixture near 12.5-12.7 did seem to reduce knock, the technical literature seems to discredit the cooling effect of richer mixtures and suggests that you are simply burning less oxygen..hence you may get less knock but you will have less power.
Although peak power (versus lambda changes ONLY) is usually around 0.9 lambda, I have typically found that a little bit of enrichment buys you more knock safety margin and cooling. This allows you to run closer to MBT, even if you're further from LBT (lean best torque, the ratio). Typically, closer to MBT timing-wise (mechanical efficiency) wins versus trying to eek the last bit of chemical power (thermal efficiency) out of the combustion event. It also leaves you with a bit more safety margin for that occasional tank of bad gas. I run most N/A applications around lambda=0.87 and just dial torque with timing after I have consistent control of fueling across all airflows.

[WeathermanShawn]

Thanks Greg.

I was leaning that way, but just needed some reassurance I was on the right track. I did not know if that was a rule applicable for all NA engines, or if higher NA compression setups had differing 'rules'.

I think you answered my question, so thanks. If you or anyone else have further insights let me know. But, for now I will shoot for ~.87 Lambda.
:cheers:

[Chevy366]

Just for reference { Lambda :14.7 x .87 = 12.789
EQ : 14.7 / 1.15 = 12.782 }
Not for you but anyone else who stumbles across this thread .

[jetblast]

i'm not sure what the intentions are for weatherman, but in the world of drag racing, at least at the strip/street level, there is a slightly different approach. many people who habitually tune at the track have reported better trap speed results by sloping the fuel curve from rbt to lbt and also sloping the timing curve in a similar fashion, perhaps 2 degrees of spread between the the rbt and lbt regions. as fuel mixture lean out they slow down, i believe. employing this method has given me the best result at the track, all with good quality fuel. if any of this info is incorrect please feel free to clarify.

[redhardsupra]

what do you mean by 'sloping the fuel curve?'

[WeathermanShawn]

Marcin I will let Jetblast speak for himself. I think I get what he means. (richer toward TQ, leaned out higher Rpm's?)

Believe me I have tried all sorts of fuel iterations this last 3 months (street) using the infamous EFILive VSS/per second change in mph. I have chose 3rd gear in my setup just to keep speeds somewhat sane.

So far I have just had more luck locking in a solid 12.55-12.75 AFR from 4000-6400 Rpm's. It just did not make much a difference in my case. In 3rd gear I go from 3000-5000 Rpm's in ~4-5 seconds..so how long do you ever hit a sloping AFR long enough to do much. In first or second gear far less time is spent at any Rpm of course.

Maybe there is something superior to just just keeping a locked AFR. JetBlast not disregarding your experiences, just telling you some results of some logging I have done recently. I have kinda gone the same route with timing at WOT. Per SSpdDmon's suggestions of locking WOT spark.

Thanks for all the suggestions. So far, my conclusions have only worked on my setup. It may differ on yours. As always, I advise you find a track. I am lucky to have some closed off country roads I can use from time to time.:grin:

[jetblast]

fuellcurve.png[/IMG]one gear is just too narrow to do any kind of successful tuning for the track. here is an example of two fuel curves with different ve maps respectively.

[WeathermanShawn]

http://img9.imageshack.us/gal.php?g=fuellcurve.pngfuellcurve.png[/IMG]one gear is just too narrow to do any kind of successful tuning for the track. here is an example of two fuel curves with different ve maps respectively.

I agree. I am somewhat limited in my WOT tuning at this time. I'll get back to the dyno or track (next year) soon. I just picked 3rd to avoid traction issues in 1st and 2nd, and 4th to avoid going 125 mph.

[jetblast]

the picture on the left is the curve i relied on when tuning for n/a for a long time. the second one is also n/a but it is used for the spray and is what i'm currently working on. by the way, those graphs are actual curves representing wot from 1st to 4th at the track.

[jetblast]

i'm relatively new to tuning efi engines and so my application may not be adequate for other set-ups. the track is pretty safe to tune, if something goes wrong there should not be any trees to worry about . i have tuned on the highway, but it gets too nerve wrecking,just too many variables to deal with.:grin:

[WeathermanShawn]

Your right, the track is the place. I use a flat access road on private property..but I agree anything can happen.

I understand your point. Once our 5800' foot track reopens next year, I'll get a chance to do it right.