Straight pipes??
1st Gear
Joined: Jan 2005
Posts: 46
From:
RE: Straight pipes??
despite popular belief you don't need back pressure after a turbo. the less backpressure the better. think about it......backpressure is resisting the spool up of the turbo.
the reason that a smaller diameter exhaust is recommended is not to add "necessary" back pressure.......it is to increase exhaust gas velocity in the pipes. however this only works up to a certain amout of flow.....once this maximum flow capacity is reached, the pipes then become restrictive. so you have to size your exhaust based on where you want your power.
smaller pipes = higher velocities = moves torque lower the RPM scale
larger pipes = lower velocities, but higher capacity = moves torque up the power band and allows for more potential power.
this is why i always shake my head when guys with hondas put a 3" exhaust on tiny engine. they think more flow means more power........but they lose all their low-end grunt which is where you almost always want to be when driving a street car.
the reason that a smaller diameter exhaust is recommended is not to add "necessary" back pressure.......it is to increase exhaust gas velocity in the pipes. however this only works up to a certain amout of flow.....once this maximum flow capacity is reached, the pipes then become restrictive. so you have to size your exhaust based on where you want your power.
smaller pipes = higher velocities = moves torque lower the RPM scale
larger pipes = lower velocities, but higher capacity = moves torque up the power band and allows for more potential power.
this is why i always shake my head when guys with hondas put a 3" exhaust on tiny engine. they think more flow means more power........but they lose all their low-end grunt which is where you almost always want to be when driving a street car.
1st Gear
Joined: Jan 2005
Posts: 46
From:
RE: Straight pipes??
ORIGINAL: audiboy1618
I dont know **** do i? You want some small back pressure after the turbo unless you are running gt35 or bigger. But what do i know?
I dont know **** do i? You want some small back pressure after the turbo unless you are running gt35 or bigger. But what do i know?
i didn't say that you didn't know ****...........but any book i've ever read on turbocharging states less backpressure = better. do what you want......to each their own.
4th Gear
Joined: Dec 2004
Posts: 4,540
From:
RE: Straight pipes??
ORIGINAL: MmmBoost
despite popular belief you don't need back pressure after a turbo. the less backpressure the better. think about it......backpressure is resisting the spool up of the turbo.
the reason that a smaller diameter exhaust is recommended is not to add "necessary" back pressure.......it is to increase exhaust gas velocity in the pipes. however this only works up to a certain amout of flow.....once this maximum flow capacity is reached, the pipes then become restrictive. so you have to size your exhaust based on where you want your power.
smaller pipes = higher velocities = moves torque lower the RPM scale
larger pipes = lower velocities, but higher capacity = moves torque up the power band and allows for more potential power.
this is why i always shake my head when guys with hondas put a 3" exhaust on tiny engine. they think more flow means more power........but they lose all their low-end grunt which is where you almost always want to be when driving a street car.
despite popular belief you don't need back pressure after a turbo. the less backpressure the better. think about it......backpressure is resisting the spool up of the turbo.
the reason that a smaller diameter exhaust is recommended is not to add "necessary" back pressure.......it is to increase exhaust gas velocity in the pipes. however this only works up to a certain amout of flow.....once this maximum flow capacity is reached, the pipes then become restrictive. so you have to size your exhaust based on where you want your power.
smaller pipes = higher velocities = moves torque lower the RPM scale
larger pipes = lower velocities, but higher capacity = moves torque up the power band and allows for more potential power.
this is why i always shake my head when guys with hondas put a 3" exhaust on tiny engine. they think more flow means more power........but they lose all their low-end grunt which is where you almost always want to be when driving a street car.
GOD DAMN, if I didn't know better, I'd say you learnd that from me. Good job. I didn't thing anyone else really go that consept. One part you left out is that you need the pipe to scavang the exhaust from the head/ turbo, So having it just wide open actualy will decrease the efficantcy of the engine do to the extra exhaust left in the combustion chamber.
1st Gear
Joined: Jan 2005
Posts: 46
From:
RE: Straight pipes??
haha. yeah. apparently i don't know what i'm talking about though. too bad i wasted all that money on those fluid mechanics and thermodynamics classes i took in school.........and those books on turbocharging.
too bad i haven't learnt anything by building a custom turbo setup for my 1.9L engine in my '69 Beetle that is intercooled and fuel injected.
.......just thought i'd throw that in there. thought maybe some of you might appreciate it. (it was not quite finished at this stage)
oh and maybe some of you were wondering why i have a 2-1/2 exhaust and why i have a 1-5/8...............its because i have the exhaust from the wastegate going out its own pipe so it won't cause turbulence in the exhaust gas flow coming out of the turbo. Turbulence = reduced flow = more backpressure = slower spool up
too bad i haven't learnt anything by building a custom turbo setup for my 1.9L engine in my '69 Beetle that is intercooled and fuel injected.
.......just thought i'd throw that in there. thought maybe some of you might appreciate it. (it was not quite finished at this stage)
oh and maybe some of you were wondering why i have a 2-1/2 exhaust and why i have a 1-5/8...............its because i have the exhaust from the wastegate going out its own pipe so it won't cause turbulence in the exhaust gas flow coming out of the turbo. Turbulence = reduced flow = more backpressure = slower spool up
