23Racer

I was on another forum discussing the interesting phenomenom of rotaries blowing flame out their tailpipes on overrun and shift lifts. I was watching my car during its last race weekend and noticed that the flame coming out of the tailpipe wasn't the happy yellow ***** that it used to be. Now the flame is steady and looks more like a gigantic propane torch and kinda blue and angry. I can tidy it up by leaning out the bins that provide fuel in those areas, but what is the flame colour telling me?

Is the car to rich? Is the timing too retarded, I have always felt that the car is a bit soft at 22 degrees advance and that I could add a few degrees. It is just so different to what I normally see coming out of rotaries and is more like an F1 car or if you ever watched Top Gear, it looks like what Jeremy Clarkson's Audi was blowing out at Mugello. The car runs great in every other way so I know I am close on tune.

Ideas?

Eric

diabolical1

iTrader: (3)

well, i'll take a crack at it and say it's probably simply a matter of how much fuel is being spit out the exhaust to ignite in the atmosphere. from what i remember from chemistry, blue flames are hotter than the yellowish/orangish stuff we're much more used to seeing. if i recall correctly, they are leaner.

23Racer

Yeah, that's what I am thinking as well. I was talking to a guy who used to race and tune a PP and he said that the flame that's blue is leaner than yellow. The fact that it comes out in a stream instead of a flame ball is that the exhaust flow is higher and carrying more velocity.

In other words, all is good and very close to where the engine wants it to be.

I am happy now, LOL.

Eric

peejay

When I had a short primary exhaust, I was told on several occasions that it would jet a foot or two of blue flame when I'd do an ignition-cut flat shift, no matter what port I was running.

With the long primary exhaust, no fire and it doesn't pop or bang or do anything untoward.

j9fd3s

iTrader: (3)

no fire comes out of mine

if i went to a more track orientated tune it would though, i'd put a larger idle jet in it, and this would need a higher idle rpm = fireballs. basically the reason is so the carb delivers fuel, and thus premix at zero throttle

peejay

That is the funny thing... I have my car tuned to dump mass amounts of fuel at high RPM/off throttle for cooling purposes. I think my 20kpa bins are around 50% VE...

j9fd3s

iTrader: (3)

maybe you need a little more air?

there was this one time, i had forgotten to zero the TPS on the 3 rotor, so it wasn't doing zero throttle fuel cut, and in normal driving it was just getting bad mileage, but giving it 1-2psi of boost and then letting off = 20 foot fireballs.

we left for sevenstock at night, so i could clearly see fire in the rear view mirror.

the climax, was the one guy who was tailgating, i pulled the ebrake, hit the gas, let off, and ten watched his headlights dip and disappear!

you don't expect the car in front to shoot fire at you!

peejay

My '80, when fully OE, could cause a report and fireball so reliably I could do it at will. Full throttle, let off... two... one... *BAM*. Great way to get rid of tailgaters. Timed to occur under an overpass, it was also a great way to clear out flocks of roosting birds

I think a good chunk of the "fireball" concept comes from airflow in the exhaust. If you have exhaust leaks, you get pops and bangs and fire. The SA's emissions system functioned by throwing all the fuel in the world at the engine and then an air pump added air to burn it all in the exhaust manifold...

23Racer

This past weekend, I ran the car at TMP again. Really long sustained fire out the exhaust. Cleaned up all the soot in the tailpipe and made the car ready to rock and roll. It was making really big power and drifting on to the front straight like a Trans Am car. I love the tune I have in it now and how much power its making. The huge flames are a really nice touch, but I think I burned out my Air/Fuel sensor last weekend as it only reads 14.7 now.

Should take it to a chassis dyno, but the butt dyno thinks its making a good 210+ rwhp.

Eric