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Old 11-11-2007, 03:47 PM   #1
jwlowtheman
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Default air fuel ratio

is there an optimal area for air fuel for a tune? I have a diablo custom tune and it shows air fuel at 14.75, that seems a little rich but I am at 3K feet of elevation, any ideas?
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Old 11-11-2007, 04:03 PM   #2
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u mean 14.75 a/f at cruising speed or idle right? i believe the predator is maxed out at 14.75 is why u are seeing that. i could be wrong. mine is showing bout 11.8 to 12.5 on wot.
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Old 11-11-2007, 05:03 PM   #3
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Originally Posted by jwlowtheman View Post
is there an optimal area for air fuel for a tune? I have a diablo custom tune and it shows air fuel at 14.75, that seems a little rich but I am at 3K feet of elevation, any ideas?
Amigo, allow me to share a little voice of advise...

EACH car is different, some cars run great with A/F at 13.3 while others prefer A/F at 12.7 or whatever. There is no magic number, that it why custom tuning is best...NOT handheld device tuning.

Now, running at 14.75 is lean NOT rich. The higher the A/F numbers, then leaner the mixture...the lower the A/F numbers, the richer the mixture will be.

I hope this helps.

Thanks,
Carlos
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Old 11-11-2007, 06:10 PM   #4
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Quote:
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is there an optimal area for air fuel for a tune? I have a diablo custom tune and it shows air fuel at 14.75, that seems a little rich but I am at 3K feet of elevation, any ideas?
The 14.75 is your a/f ratio in cruise mode. All cars are tuned at about that figure. What you want to know is what is your A/f at wot. I initially went the Predator route with my Z and their default setting is around 12.2-1. If I remember right they do it in two stages, 0-4000 rpm's and 4000-7000 rpms. You can lean it out a bit more if you choose but only in those 2 ranges. A dyno tune can raise and lower it through out the entire rpm range at any point. The same goes for timing. I can tell you I then went with a custom dyno tune and it picked up about 8 horsepower. That may or may not be worth it to you. The Predator is a pretty good value I think as it does logging and diagnostics as well. Hope this helps!
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Old 11-12-2007, 10:12 AM   #5
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14.68:1 is not rich nor lean. It is the perfect burn for gasoline and is the stoichiometric value GM sets all Z06s to in Closed Loop, which is the case of the Z06 is any throttle position below 48% at most rpms. A higher rpm, the throttle position is 25% to active open loop.

14.68 lbs of air for every 1 lb. of fuel is the chemically correct burn. Lean would be considered 14.8 or above, fuel enrichment would be considered any value below 14.68 or 14.5 and below.

11.5:1 is the open loop (fuel enrichment) value used by GM on the Z06 at full tilt (6,000 rpm), which most tuners consider very rich for a normally aspirated car.

Since gasoline needs 14.68 parts air to completely burn all the fuel in the cylinder, then running 11.5:1 sends all the excess fuel out into the atmosphere. Very Un-Green.

When I tune the Z06, we set the air fuel ratios leaner than the stock enrichment code, closer to 12.5:1. That is still fat, but much better for overall power.

Ethanol based fuels have a completely different stoichiometric value. For instance, E10 is 14:1, and E85 9.8:1. All of the newer cars adapter to the E10 fuel without any programming, but E85 needs the newer E38 ECM with the E80 table and MAF table to adapt to this Bio-Fuel.Click the image to open in full size.

It takes 3 gallons of E85 to trip the ECM as a refill event. This refill event causes the ECM to look at the short term fuel trims to see if they are in a new "learn" state. If so, the assumption is that a percentage of ethanol is in the tank, and the ECM adjusts to the fuel up to 90% ethanol.

The LS3 E38 ECM already has this table built into it, which means that GM is getting ready to get EPA approval for certain cars running Bio-Fuel. I do NOT recommend trying to run the LS3 and soon ZR1 in bio-fuel mode, since GM has not yet approved these cars to run the fuel, but it is coming soon.

My educated guess is that the LS9 will be a Flex Fuel car. It will have the LS3 style ECM onboard for sure, since the MAF tables go to 1822.12 g/sec vs. the current 512 g/sec airflow allowed in the E38 used by the Z06. So why is it necessary to supply code 3.5 times higher than the Z06 tables?

The Hz goes up to 15,850 Hz on the newer Hitachi Probe MAF sensor, so forced induction freaks, just wait. That kind of airflow table will support over 2000 HP!

Back to air fuel ratio. Your diablo thing is just providing you with the closed loop values, and they are at the perfect burn.

Jim Hall

Last edited by Halltech; 11-12-2007 at 10:15 AM.
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Old 11-12-2007, 10:12 AM
 
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