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Old 10-04-2001, 12:34 PM   #1
SubaruStu
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Default Foolish random mod thought of the week

Bear with me here....now if the idea behind a turbo-back exhaust
is to reduce or eliminate back pressure to help the turbo spool
up and run efficiency, what about forcing air through the exhaust
some point after the turbo, which would create "negative"
back pressure in the exhaust. It appears that this should help
both the turbo and scavenging exhaust.

Ideas? comments?
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Old 10-04-2001, 01:23 PM   #2
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you mean like an exhaust leak?

I think I see what your saying, but you would need some pretty high pressure air coming in to offset the exhaust pulses..I doubt you would gane much..hook a vaccume up to your tail pipe, turn it on and see what happens.....

I AM SO KIDDING HERE GUYS....:monkey:
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Old 10-04-2001, 01:39 PM   #3
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Actually, I've heard or people putting check valves in their exhaust manifolds so that when a pulse is moving down the tube and the valve closes behind it, it'll suck air in from outside to relieve the vacuum behind the pulse (kinda like putting your finger at one opening of a straw to hold the fluid in, but then sticking a pin in the straw to release the vacuum)

This is on an old, American, NA, V8 engine though. The positive (or negative) side effect is the extra oxygen will burn some or the unburned fuel, raising exhaust temps, and allowing the cat to work more efficently.

If you try it, make sure it's after all the O2 sensors.
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Old 10-04-2001, 02:50 PM   #4
MY99 2.5GT
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Sounds like there would be an enormous heat problem. Even detination of unspent fuel if you went with the above idea. Otherwise it sounds like it would work well.

You could use one of these


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Old 10-04-2001, 06:53 PM   #5
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yeah, that's why i put "negative" in parentheses. High temps are good for the cat, but really bad for the turbo.

Is the O2 sensor before or after the turbo?
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Old 10-04-2001, 09:30 PM   #6
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It's called secondary air injection. Most cars use it, for emission purposes. Some use check vales, and some use pumps. Electric, or belt driven. Forceing air into the exhaust will only raise back pressure. More exhaust volumn in the same space equals greater pressures.
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Old 10-06-2001, 11:47 AM   #7
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Quote:
Originally posted by LVSUBARU
It's called secondary air injection. Most cars use it, for emission purposes. Some use check vales, and some use pumps. Electric, or belt driven. Forceing air into the exhaust will only raise back pressure. More exhaust volumn in the same space equals greater pressures.
But I was thinking along the lines of closer to the end of the exhaust, not right up front like emissions controls. If it could be done, then it "should" actually draw exhaust gas through the
pipe (like how a paint gun/airbrush draws paint fron the cup). I
think also that it would cool the exhaust at the end, meaning a
quieter exhaust, without sacrificing flow.
????
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Old 10-07-2001, 02:57 AM   #8
LVSUBARU
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A paint gun uses a venturi effect like a carberator, right? And like the paint gun, the paint in the cup doesn't make the paint come out any faster. I don't think that turbos use the exhaust gas's velocity so much as the expansion of the gases in the pipe.
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