ben73

I've had my WB for about a week now and it's already proven to be the most useful gadget I have.
I have been looking here and on other forums at guys WOT WB plots. It seems common to see a lot of cars go pig rich (~11.x:1) initially, then lean out closer to 13:1 when approaching max rpm.
Is this normal, or should I expect a more consistant AFR from say 2000-6000rm at WOT? The plots I am talking about go rich for far too long to be a result of AE only.


Here is an example of what I am talking about, this is NOT mine, it belongs to Scorp, but shows what I am talking about. Ignore the pink line.
Is this normal?

Grumpy

Don't expect anything.
Tune to make the best HP.
What works for one car, might not work on yours.

AE can vary ALOT. Without seeing the AE *flag* you don't know if it's AE or not.

ben73

Thanks Grumpy, but I'm not asking what works best, I'm asking if this is a common characteristic... I logged mine in 2nd gear up to 6000rpm and it made a similar plot. Keep in mind I am currently using a 7747, so PE AFR tables only go to 3200...

I suppose what I want to to know is, do stock engines/tunes show a similar plot, or do they typically show a flatter PE AFR to max rpms?

11sORbust

Not sure about stock apps. Many engine like to go rich at tq peak and lean out at HP peak. Like grumpy said, it just varies. I wouldn't want it dropping into the 11's at all though.

JPrevost

That is pretty normal, like everybody else said . Grumpy, isn't it nice having lockers , AE flag, PE flag, flag this and that 17 times a second!
A lot of stock tunes run really rich to put out the cats, by putting them out (cooling them with unburned fuel) they live a long happy life. Leaning out the AFR on a catted modified car could probably burn through some carpet and/or turn your cat into a molten ball of hazordous waste. I haven't seen this for sure but I can tell you that with a slightly lean AFR from stoich the cat can GLOW, my carpet is proof of that!
Without cats you want to tune a slightly leaner AFR. Depending on the head and type of aspiration the AFR will be between 11 and 14 (14 is for superior chamber designs, 11 for old style turbo engines). The cam tells you where peak torque (peak volumetric efficiency) is going to be and that RPM high load usually requires a richer AFR then the rest of the map.
Running a richer AFR will keep piston temps down because the fuel and oil are the only things that cool the piston.

1bad91Z

iTrader: (1)

My WB AFR graph looks alot different.

Mine started out going from really lean to really rich 1,000 rpms to 6,000 rpms (19:1 - 10.2:1).

Right now, I got it at 15.8:1 - 11.8:1 (which made the motor run ALOT better).

The above is a WOT pass.

Part throttle cruising is still very lean ( between 17:1 and 19:1 ).

So, I'm still in the process of leaning out PE in the areas of (3,200 - 6,000) to get close to 13.0. It seems the more I lean it out up top, the more power it's making.

Also still in the process of adding fuel at part throttle to maintain an acceptable AFR at cruise.

In the next week or so, I'll have my Denso narrow band o2 installed and I'll record a graph from my LM-1 WB.

The Denso o2 is supposed to be the best narrow band, I'll gladly be the guinea pig and let you guys know the results.

JPrevost

On just about every engine the torque peak is below redline (even F1, but not turbo CART) and this is where the engine is "filling" the cylinder with the most air and fuel. Because of this you can get away with a richer AFR and not see any huge differences in horsepower. When you reach your high limits of a motor the torque is low. The motor is "pulling" from horsepower, not torque. So at higher engine speeds the cylinder filling is lower and combustion temps are high so running the lean best torque will give you the best power. It's really hard to explain without showing you pages of research done on AFRs and how they effect an engine, not just power. It's really pretty cool, but for the average joe trial and error are best. Give the engine whatever AFR it likes that is resonable. If the AFR is reporting 14:1 and you're getting killer ET and trap speed than so be it . If it's reporting much leaner than that I'd replace my wideband, fix the exhaust leak, or replace the TechEdge controller with ANYTHING ELSE.
Keep in mind that a wideband isn't an exhaust gas analyzer that costs half a mil from Horiba, it's just a meter that reports trends better than a narrow band.

ben73

Thanks for your opinions everybody. I didn't know it was ok to be richer at the torque peak etc...