pmhellings

I have an '03 running FM's Voodoo II ( yeah, I know). I have FM's Crossflow radiator and their stage II fan kit. Intercooler. I'm currently running 8 psi and my Wideband shows about 11-11.5 at full boost. Car runs fine no overheating or detonation.

Recently on a club event, the driver of the car behind me commented on how rich I was running in boost. Some black smoke he said. At 11-11.5 I can see how that could be.

QUESTION IS: is the purpose of fueling at boost to provide fuel to be burned? Or to act as a cooling agent? Some of each?

At 8 psi I'm considering tuning the Voodoo box to try to get closer to a 12 AFR. Would I lose the cooling properties of the extra fuel? Or is it what I should aim for.

I'm aware of the virtues of Megasquirt. I'm just not ready to give up my stock ECU. Trying to get the most efficiency out of what I have, while keeping the engine safe.

Paul

patsmx5

iTrader: (16)

Extra fuel cools the charge a bit. It also helps prevent localized lean spots in the fuel/air mixture by putting extra fuel in. It also slows down the flame front, which shifts peak pressure to the right of TDC, which lowers peak pressure in the cylinder. This will allow you to add timing to the engine to shift the curve back to the left (closer to TDC). Generally on a knock limited engine, rich allows more timing, and makes more power than running lean and running less timing, and is "safer" too.

pmhellings

Thanks Patsmx5. A little technical, but answered the question.

Paul

Girz0r

iTrader: (1)

You could also inspect your plugs to observe if its bad and/or inadvertently upgrade your ignition to light up that rich mix more efficiently

codrus

Personally I don't think I'd mess with the Voodoo to try to lean it out. You've got a 10:1 compression ratio motor with stock rods, and a piggyback fueling system that lacks a lot of safety measures. Running 11:1 *is* your safety measure.

I run something like 12.5:1 at 8 psi on my car, but I've got a built motor, 9:1 compression, a full ECU that knows about the turbo and the knock sensor, and I run 95 octane in it.

--Ian

TNTUBA

iTrader: (1)

I personally don't think running 11:1 on a 8 PSI motor is a "safety margin" and unless your oil change schedule is on the aggressive side....might actually be a detriment to it's longevity. If your motor is detonating due to spark timing or compression being too high...throwing fuel at it isn't the answer.

sixshooter

iTrader: (12)

12 or 12.5 would be better, but as stated above, since it is a Link you have less fine control. If you decide to remove a little fuel, compare your timing to others with similar compression to ensure you aren't playing with fire.

pmhellings

This is the OP. There is no detonation and the motor is running fine. To re-state, I wondered about how much of the fuel was for, well, FUEL, and how much was for the cooling effects. As stated, I'm running about 11-11.5 AFR. I'm considering dialing the AFR back to about 12 to minimize over-rich condition. I agree with TNTuba with respect to excessive fueling requiring more aggressive oil changes (currently 3,000 miles. Synthetic)

My fuel management is via a voodoo box and I'm running -4* static spark retard. I appreciate the thoughts of those more experienced than I am.
Paul

patsmx5

iTrader: (16)

Yes if you had a standalone, you could run it leaner possibly. But with what you have, I'd leave it alone. 10: comp with no timing control running boost with piggy backs is not ideal, leaning it out could be dangerous.

Joe Perez

iTrader: (8)

I hate to be a wet blanket, but I honestly don't think you're going to find a definitive answer here.

This forum is host to a tremendous amount of solid practical experience built on empirical research and real-world application, but this question exceeds that which can be expected of even the most experienced engine tuner. I would suggest that you seek out a forum frequented by members of the SAE (society of automotive engineers) and its many university-level affiliates. These will be the people most likely to be able to provide a satisfactory answer supported by reputable data.