What makes a turbo belch flame on decel?

[CamB]

http://www.gtpro.com/dyno843.mpg

And does it hurt the car?

It doesn't happen stock - so what mod does it?

Thanks

Cam

[Jdub]

I dunno but if they ever put that in a can I'm buying two!!!!

Actually I think the car dumps unspent fuel into the hot exhaust and, voila, the emissions police have a heart attack!

Great movie.

Jw

[Bill Verburg]

Fuel that is not burned in the combustion chamber. On overrun the air to the cc is cut off but fuel often is not, cis and carbs are particularly bad in this respect, the raw fuel is dumped into the exhaust pipe where it mixes with whatever air there is(on turbo cars the wastegate often dumps bypassed air here also) and is ignited by the hot metal of the pipe.
You can achieve the same effect if you can manually retard the ignition somehow, you will then get a large bang and several feet of flame(from straight pipes anyhow) don't know what it might do the muffler but I suspect it wouldn't be pretty.

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Bill Verburg
My Home Page My Pelican Gallery page My Porsche Owners Gallery Page

[makaio]

That would be sweet for tailgaters!

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Matt Chamblin
78 911 SC

[rattlsnak]

For the newer turbos, all stock wastegate pipes have a flame arrestor built into them. For the older ones, the wastegate exhaust usually goes into the muffler. With an exhaust kit put on, most wastegate pipe dump straight out to the air via a 3-4 inch pipe. The unburned fuel also hits the red hot turbo causing ignition on the other side through the less restrictive aftermarket muffler. A stock turbo will shoot flames out, but a modified one will will shoot out flames like a blowtorch, as you see on the video!

[Colby]

I don't know how they do it, but I recall a V8 hotrodder saying that the way he did it was to somehow install a spark plug into the tailpipe and run the car rich....turn on the plug and you will have a steady stream of fire from the tailpipe.

Colby

[Bill Verburg]

That would do it also. Old cars and mcs had manual spark advance controls in the cockpit or on the handlebars. It is also often seen at NASCAR races.

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Bill Verburg
My Home Page My Pelican Gallery page My Porsche Owners Gallery Page

[Doug Zielke]

A cam with a lot of overlap will cause the flame-throwing as well. Lots of unburned fuel out the pipe when the motor is running at less than peak volumetric efficiency.

If you've ever noticed a mist of raw fuel spraying out of the open velocity stacks of a race engine...this is called reversion, and this too is related to rpms at which the cams are causing interfering pressure waves in the intake tract.

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'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
The Blue Bomber's Website