Air/fuel ratio question
Thread Starter
Instructor
Joined: Nov 2007
Posts: 178
Likes: 0
Air/fuel ratio question
Just had the car tuned and the tuner stated the a/f was around 12.0 to 12.1:1
I've read a couple places that 12.8 is pretty optimal.
Was wondering what other people thought about this.
Is it worth getting the car re-tuned to achieve this?
I've read a couple places that 12.8 is pretty optimal.
Was wondering what other people thought about this.
Is it worth getting the car re-tuned to achieve this?
Thread Starter
Instructor
Joined: Nov 2007
Posts: 178
Likes: 0
Sorry everyone. My car is an 07 C6 manual. If the 12.5 is the case, would I see any type of significant gains by getting it tuned to 12.5 or 12.8?
Melting Slicks
Joined: May 2004
Posts: 3,017
Likes: 2
What kind of dyno? If it is an inertia type, your car will run a bit leaner on the street. It could be the tuner went with a good bit of spark advance and kept you on the rich side to avoid spark knock. Unless you are looking to eek out the last bit of HP, then it is fine where it is. I would rather be a little fat than too lean...
Racer
Joined: Jul 2007
Posts: 264
Likes: 0
From: Southern New Mexico
mine is set somewhere around 11.5 and seems fine and strong as hell. ls2 see profile for details. 6000ft elevation though. The set it in phoenix for best guess at my altitude. (the 11.5 was in phoenix).
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Racer
Joined: May 2008
Posts: 463
Likes: 4
From: Park City, UT
I'm sure SpinMonster will jump in if he sees this, as I've learned much of what I know from him.
Is your AFR is ~ 12.5 is decent when in Power Enrichment mode (@ WOT), but for around town driving you should be shooting for 14.7.
If I recall correctly, AFR is tuned primarily through the MAF and the power enrichment tables.
Good Luck!
Is your AFR is ~ 12.5 is decent when in Power Enrichment mode (@ WOT), but for around town driving you should be shooting for 14.7.
If I recall correctly, AFR is tuned primarily through the MAF and the power enrichment tables.
Good Luck!
Thread Starter
Instructor
Joined: Nov 2007
Posts: 178
Likes: 0
What kind of dyno? If it is an inertia type, your car will run a bit leaner on the street. It could be the tuner went with a good bit of spark advance and kept you on the rich side to avoid spark knock. Unless you are looking to eek out the last bit of HP, then it is fine where it is. I would rather be a little fat than too lean...
Melting Slicks
Joined: May 2004
Posts: 3,017
Likes: 2
No, it is how they optimize the tune. Each motor can be a little different, and the amount of carbon on the pistons, fuel quality can influence how a tune comes out. What were your before and after numbers? Can you post up the dyno sheet? If you are not satisfied, I would air my concerns with the tuner.
Burning Brakes
Joined: Aug 2008
Posts: 802
Likes: 6
From: Oro Valley AZ
10% ethanol brings your stoich down to about 14.1:1 At .87 lambda at WOT gives you about 12.3:1, so, you may be slightly rich. If your tuner used HPTuners to tune your car, get a copy of his last scan and post it. I'm sure a number of people will give you an honest critique.
Safety Car
Joined: May 2006
Posts: 4,016
Likes: 93
From: St. Louis, MO
Tech Contributor
Your car should be tuned to run around 0.85 lambda at wide open throttle... and that's for pure gasoline and E10. For a wideband programmed to display stoich as 14.7, it should read 12.5 at WOT. This is the best AFR I've found for any LS2/LS3/LS7 car.
Thread Starter
Instructor
Joined: Nov 2007
Posts: 178
Likes: 0
Thanks for the information. I spoke to the tuner again today and he said there were a couple areas that hit 12.3, but mostly kept it around 12.1 or so. He recommended I leave it there as I am not bringing the car in to the shop all the time to have the spark plugs checked and things like that. It makes sense I guess.
After I got the headers/axle-back put on, the car made 383/381. Was kinda hoping for close to 390. This car isnt a daily driver so I was kinda hoping for a little more aggressive tuning. You think I would be safe in asking the tuner to be a little more aggressive with the tuning as long as I am running 93?
Thanks.
Le Mans Master
Joined: Aug 2002
Posts: 8,472
Likes: 38
From: Houston TX
St. Jude Donor '11
Every car is a little different. A good idea is to dial it in to 12.5:1 across the RPM band. Then drop the PE to command 12:1 and compare the dyno pulls. Where you lost power or didnt gain power, change the PE to 13:1. If you made more power for an RPM range leave it at 12:1. If you didn't gain or lost power in the areas you leaned it out on, revert back to 12.5:1.
This is assuming the tuner is using the MAF table to tune and not hacking up the PE table.
This is assuming the tuner is using the MAF table to tune and not hacking up the PE table.
Drifting
Joined: Oct 2006
Posts: 1,569
Likes: 4
From: Phoenix AZ
St. Jude Donor '09-'10-'11
A/F ratio
As stated above, each application is different and there is no magic formula as a 'one size fits all'. The Dyno is your best friend for working this out based on all factors concerned--i.e. D/A, fuel composition, engine mods, use of car, etc.
Advanced
Joined: Feb 2008
Posts: 66
Likes: 1
Mostly cathedral ported heads run well at 12.5:1.
With LS3 heads I have had varied results. Generally 12.7 is a good number to shoot (if w/b is accurate) Richer then this it loses a bit leaner then this hurts it too. I can feel if a car is too lean just by the way it pulls up top.
Having said that I had a combo that made very good power at 12.5:1 and consistent repeatable power. Over time I found if I pulled timing out and ran the engine leaner at 13.1:1 .9 lambda it picked up a hidden 20 hp which surprised me a lot speed splits improved 130-160 km/h by 3 tenths, and ran 3 mph faster at the track.
I have tried the same technique with the new motor same L92 heads.
It hates being lean won't make power, this one has much more overlap less dyn. compression and loves fuel and spark, it runs 31-32 deg timing and 12.75:1 afr and is a freak at these settings (my main jet is on the money and dizzy set right lol)
Old motor had 23 deg lead so go figure. Moral of the story all motors are similiar but never the same, Generally I tune to 12.5-12.7 and find MBT but if I play for a while and experiment I find more.
With LS3 heads I have had varied results. Generally 12.7 is a good number to shoot (if w/b is accurate) Richer then this it loses a bit leaner then this hurts it too. I can feel if a car is too lean just by the way it pulls up top.
Having said that I had a combo that made very good power at 12.5:1 and consistent repeatable power. Over time I found if I pulled timing out and ran the engine leaner at 13.1:1 .9 lambda it picked up a hidden 20 hp which surprised me a lot speed splits improved 130-160 km/h by 3 tenths, and ran 3 mph faster at the track.
I have tried the same technique with the new motor same L92 heads.
It hates being lean won't make power, this one has much more overlap less dyn. compression and loves fuel and spark, it runs 31-32 deg timing and 12.75:1 afr and is a freak at these settings (my main jet is on the money and dizzy set right lol)
Old motor had 23 deg lead so go figure. Moral of the story all motors are similiar but never the same, Generally I tune to 12.5-12.7 and find MBT but if I play for a while and experiment I find more.
Drifting
Joined: Oct 2005
Posts: 1,549
Likes: 1
From: Roanoke Virginia
Thanks for the information. I spoke to the tuner again today and he said there were a couple areas that hit 12.3, but mostly kept it around 12.1 or so. He recommended I leave it there as I am not bringing the car in to the shop all the time to have the spark plugs checked and things like that. It makes sense I guess.
After I got the headers/axle-back put on, the car made 383/381. Was kinda hoping for close to 390. This car isnt a daily driver so I was kinda hoping for a little more aggressive tuning. You think I would be safe in asking the tuner to be a little more aggressive with the tuning as long as I am running 93?
Thanks.
After I got the headers/axle-back put on, the car made 383/381. Was kinda hoping for close to 390. This car isnt a daily driver so I was kinda hoping for a little more aggressive tuning. You think I would be safe in asking the tuner to be a little more aggressive with the tuning as long as I am running 93?
Thanks.