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BlueStreak
03-30-2012, 11:08 AM
This was posted on MSF by Bucker. One of many gearheads over there.

Good info.


I hear tons of talk about fueling this, fueling that, lean me out to make more power! etc. etc. I am here today to demonstrate that leaner mixes generate little to no addition power at the expense of a higher tendency to knock. The ONLY advantage to leaner AFRs I can find are increased headroom for fueling for those who are taxing the DISI fueling system.

I have seen this on my car running as lean as a 13.4:1 gas AFR compared to a 12.2:1 gas AFR that I daily drive. I really started to suspect it meant nothing more recently when I flashed a tune that commanded a 10.8 AFR with all other parts of the tune being the same. I did this because I am running nitrous and I need to be that rich to compensate for the increased O2. What blew my mind what that the tune ran exactly the same as my daily driven tune. The SAME. Logs and VD plots were identical.

I couldn't just say that was a good enough test, though. Other things fell in to line and a member that I am tuning came to me and asked to have me try something: make 2 identical maps, one with an 11.0:1 AFR and one with a 12.0:1. I obliged.

Attached are the logs, and below is the VD plot.

http://i.imgur.com/B7nez.jpg

Don't say it gained 5 peak WHP. It didn't. To confirm that, look at the lower and upper regions of the plot, where the richer run makes "more" power. What this says is that AFRs play a very minute role in power production for us.

fywdyl
03-30-2012, 12:24 PM
Not to discredit his work, but there are too many variables in this. Not sure if the tests were done back to back, but there are no correction factors in the plots. Also, this seems to be based on 2 runs only. I actually tried to do the same thing that he did after reading the post on MSF, and it's basically inconclusive. See below.

http://i923.photobucket.com/albums/ad78/fywdyl/Logs/AFRTest-WithCorrection.jpg

I guess what I'm trying to say is, test it out for yourself first. Maybe different cars react differently. And read through that whole post on MSF because Lex brings up some good points (i.e. better to run richer + more timing, than to run leaner + less timing)

BlueStreak
03-30-2012, 01:11 PM
Thanks, Anson.

We really need "Thanks/Groan" buttons on this forum :D

Fobio
03-30-2012, 01:41 PM
with meth thrown in, it's even harder to pin-point, but not impossible. esp since our meth delivery system is nowhere as precise and consistent than the actually fuel injectors.

VertigoM
04-22-2012, 10:45 AM
I cant seem to find this thread on MSF. Can you post a link? (or is it in the VIP section)

I am planning on leaning out my AFR from 11.4 to 11.7 but if there isnt much benefit then I'll leave it as is (car is still stock).

fywdyl
04-22-2012, 11:59 AM
I cant seem to find this thread on MSF. Can you post a link? (or is it in the VIP section)

I am planning on leaning out my AFR from 11.4 to 11.7 but if there isnt much benefit then I'll leave it as is (car is still stock).

You haz AP & fuel pump?

Best bet is just to try it for yourself. All cars will react differently.

breakfasteatre
04-22-2012, 12:20 PM
my previous car saw some serious power with afrs near the 12s

VertigoM
04-22-2012, 03:56 PM
You haz AP & fuel pump?

Best bet is just to try it for yourself. All cars will react differently.

I have an AP but no fuel pump.

I guess I'll give it a try and see if I can see any difference between 11.4 and 11.7.

Snotrocket
04-22-2012, 04:28 PM
combustion is cleaner 11.8, for me anyway

VertigoM
04-23-2012, 04:36 PM
combustion is cleaner 11.8, for me anyway

Good point, maybe that in itself warrants a leaner AFR. Although I already see a huge reduction in carbon build up on the hatch with 11.4 AFR.

BlueStreak
04-23-2012, 06:12 PM
I recommend aiming for engine safety vs. cleaner combustion. We're not driving econoboxes ;)

Snotrocket
04-23-2012, 08:09 PM
Is 11.8 AFR not safe if that's what your tuned for? Assuming you dont have knock and using proper gas ect? Why not take advantage of the cleaner combustion also ??

BlueStreak
04-23-2012, 08:46 PM
AFRs are only part of the tune and are determined by fuel quality, boost and ignition timing.

It's not quite a set and forget affair.

Snotrocket
04-23-2012, 08:52 PM
Agreed, all im saying is if I can factor it in safely is there an issue there? Or should I just run slightly richer because it's much safer?

Fobio
04-23-2012, 09:21 PM
Agreed, all im saying is if I can factor it in safely is there an issue there? Or should I just run slightly richer because it's much safer?

nothing wrong with a taper to redline to keep things safe, esp when you up other things like boost and timing...

Snotrocket
04-23-2012, 09:22 PM
nothing wrong with a taper to redline to keep things safe, esp when you up other things like boost and timing...

I always do ;)