Just curious what everyone is running for AFR at WOT......
11.9-12.1 regardless of what some "are" running,lol, 12 is safe
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16:1.... I just like the number. It can be divided by 16, 8, 4 and 2. That makes it pretty special, plus its square root is 4.
Yeah. 16:1 for teh win.
-Chris-
-Sweetness-
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Slowly but surely may some day win this race...
thanks Ge_forcez22. i appreciate it. right now i running 12.5 but have been hearing people saying they running 10.5:1 but to me that sounds a little too rich.
There is no perfect air fuel ratio to aim for. You want to run as close as you can to 14.7:1 with zero knock and EGT's within reason. Running richer than 14.7:1 (to an extent) will lower cylinder temps and EGT's and help prevent knock. The only way to find the best a/f ratio for your motor is to dyno tune fuel and spark for peak power while monitering EGT's and knock.
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addendum to the previous poster...
The 1st sentence is perfectly correct.
The second sentence is somewhat incorrect. Fuel an air do not stay mixed very well under higher pressures. In order to make sure every possible molecule of fuel that could get burned, compared to the quantity of air in the chamber, does get burned, it is generally necessary to run more than the perfect amount of fuel.
How much more fuel depends on the particular engine. Beyond that, most people add even more fuel to keep temperatures down since extra fuel with nothing to react with actually works as a fire extinquisher.
Fully understanding that ^^^^^ 1st, it is generally thought that the majority of NA engines will make best power between 13 and 13.5 A/F and still survive well. Most forced inducted engines do better in the 12:1 range since the pressures and temps are higher.
But a theoretically perfect engine would make the best power and survive well closer to 14.7:1.
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Turbo car tuners need to provide a way to power the turbo. Fuel has more mass than exhaust gases and can transfer heat better. Unburnt fuel from a richer AFR can help carry combustion heat to the turbine. It's one more piece of the puzzle to consider.
My AFR's tend to be between 12.0 and 12.5 with turbo cars. The engine decides what it wants, I just have to be smart enough to listen.
-->Slow
wish i knew myself on my car
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slow joe, i would think a leaner mixture is better to spool that turbo. after all leaner is more EGT and therefore = more heat.
this is the first time i have heard of this theory
farmerz24
Though I hate to bring a post this old back from the dead; I was wondering now that we have many more turboed ecotec Js, what AFR is producing the best for "YOUR" car?
Darryn
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I'm supercharged and my afrs under wot range from 11:1 to 11:6
11:6? do you mean 11.6:1?
im NA and run a nice 12.8 to 12.9:1... right where i need to be.
1997 Cavalier Z24 - 15.647 @ 88.02 MPH
yea im sorry 11.1 to 11.6 afrs lol.
SweetnessGT wrote:16:1.... I just like the number. It can be divided by 16, 8, 4 and 2. That makes it pretty special, plus its square root is 4.
Yeah. 16:1 for teh win.
-Chris-
i just watched a turbo 3cyl geo dyno and it was running a 16:1 afr, put down 63 to the wheels
pvc was used for piping aswell
i dont think it liked that afr really, it was bucking like a wild horse on a few runs
Im running 12.7-12.9 on a N/A ecotec.
i'm running 11.7-12 with M45 s/c
as a reference, this is from a doc i found on the web ... probably for N/A cars but you get the idea
9.0:1 BLACK SMOKE (NO POWER)
11.5:1 RICH BEST TORQUE @ WOT
12.2:1 SAFE BEST POWER @ WOT
13.3:1 LEAN BEST TORQUE @ WOT
14.6:1 STOCHIMETRIC AFR ( CHEMICALLY CORRECT )
15.5:1 LEAN CRUISE
16.5:1 BEST FUEL ECONOMY
18.0:1 CARBURETED LEAN LIMIT
22.0:1 EFI LEAN LIMIT
14.82 @ 97 mph
Everyone keep in mind that 14.7:1 is not the best AFR for an engine.
14.7:1 is simply the ideal mixture chemically for the catalyst to do its job. Its simply a step towards perfect combustion. To be quite honest, perfect combustion does not make alot of power. We find ways of adding power by changing variables and moving them further away from chemically perfect which can result in better efficiency and more power.
Perfect combustion is not efficient. At least not in "modern" day engines. Especially four-strokes
To Slowolej, You are forgetting an important factor in turbo design. A turbine is NOT driven by pressure. A turbine is driven by heat. Heat in exhaust gases drops dramatically when you richen the mixture for two reasons,
1. There is less stress on the ignition system to ignite the mixture because fuel conducts electricity better than compressed air. Thats why on an ignition drive circuit on a scope you can see whether AFR's in particular cylinders are problem areas by looking at the spark line. This results in a richer mixture that will not completely burn and instead is forced out with exhaust gasses where it is comparatively cooler than its surrounding gas and works to reduce EGT.
2. Secondly, and this is part of number one, but an incomplete burn will not generate as much heat and will also serve to wash the cylinder walls and result in gasoline buildup around the ringlands usually resulting in another rich combustion event in the next cycle.
There is a reason intake valves can be set with tighter guide tolerances and one of them is because they are constantly bathed in fuel which serves as the only internal coolant of the combustion chamber. Otherwise the face of the valve is exposed to even more heat than the exhaust valve. the exhaust stroke is when the exhaust valve receives the most heat.
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Fuel mixtures are also leaned out to improve mileage. Thats why newer cars are going to be attempting to run even leaner mixtures in the future. The problem with lean is high heat. The engine itself would run fine lean if it wouldnt kill itself in the process. Obviously you would loose power with lean mixtures but thats why its called lean cruise. You dont need but 10-20 hp to drive down the road at 45 - 60mph. So theoretically, the less fuel the better. And thats what they are aiming for (variable displacement engines come to mind? DOnt need all 8 cyl to pull the thing down the road...)
BUT lean isnt good for power. Thats why even on stock cars they run a mixture close to 12 to 1 under power enrichment to build more power. Running rich with hydrocarbons flying out of the tailpipe. Havent you ever been to a drag race? Stand behind some of those cars and feel your eyes water!!
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The problem with lean is high heat.
wrong. EGTs drop when you go leaner than stoich.
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Many people think that the leaner you go, the higher the EGT gets. This is also incorrect. Peak EGT occurs at stoichiometry- about 15 to 1 for our purposes. If you go richer than 15 to 1, EGT will drop and if you go leaner than 15 to 1 EGT will ALSO drop.
thread containing this quote:
AFR/EGT tuning questions? GOOD READ
the best way to get a motor to perform better is to maximize the efficiency of the motor (not talking about fuel efficiency per say). if you can make a motor run more efficiently, you can gain lots of different advantages depending on how you want it to run. tuning the motor for maximum power, maximum fuel efficiency, or minimum emissions does not always give the same results or take the same process to get there.
for example, the manufacturers are more concerned (generally) about fuel efficiency and emissions for government regulations. having an 8 cylinder motor shut 4 of its 8 cylinders down when cruising at a steady highway speed with no acceleration happening has more to do with improving the efficiency of the motor in turns of output power to input power than anything else.
making a car run leaner, as PJ said, will actually bring heat down, same with bringing it richer (the fuel will then act as a coolant in this case). the manufacturers aim for 14.7:1 because, from what i remember, this is where the cat is most effective at scrubbing harmful emissions from the exhaust stream. this how ever is not where maximum power is, which is why when the motor enters PE, your not still aiming for stoich.
its always been about efficiency... unfortunately the internal combustion engine is not very efficient on its own, hence the invention of different motors (rotary), displacement on demand, forced induction, etc. the more efficient you can make a motor, the better performance and/or fuel efficiency and emissions can be.
1997 Cavalier Z24 - 15.647 @ 88.02 MPH
whitegoose wrote:the manufacturers aim for 14.7:1 because, from what i remember, this is where the cat is most effective at scrubbing harmful emissions from the exhaust stream. this how ever is not where maximum power is, which is why when the motor enters PE, your not still aiming for stoich.
14.7:1 is stoichiometric... an almost completely balanced reaction with little to no remnants. Anything other than stoich will have something left over.
and this is only theoretical, in the real world nothing is truly stoichiometric.
True ^. At 14.7 the car releases the least amount of hydrocarbons, CO, and NOx .(Collectively). Individually the numbers will differ based on the gas in question. Hydrocarbons are least durring lean, CO the least durring stoich, and NOx the least at colder cylinder tempatures.
The world of car making revolves around emission standards.
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