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well i got my exhaust on yesterday, and now im boosting about 2psi more than before. i was running 7psi, and now with my crush-bent 3" its at about 9. is this because of extra backpressure not allowing the gasses to escape fast enough? im running the ssauto external WG with an integrated dumptube. its not creep, because i get the extra pressure right when i normally hit full boost and it just stays there until redline. any insight on this?
 

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Tibs said:
more exhaust going out now so the turbo can spin more?
Not having any exhaust piping wouldnt change how much exhaust comes out of the engine. But if ur boostin and runnin all header ur turbo will probably spool up faster so i dunno if that has anything to do with it or not.
 

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i am thinking you're right in your first post... the WG is only 35mm right?

i am thinking that since there is more backpressure it lets more air pas the WG and into the turbine.
 

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There's less backpressure, so the turbo will spin faster. Think of it as pressure drops...

For example's sake, say the air being pumped out through the exhaust exits at a pressure of 50psi. Then, say, it takes 25psi to spin the turbo at 50,000rpm, and 50psi to spin it at 100,000rpm. Then, say, the backpressure of the exhaust is 10psi...

50psi (from the engine) = ((25psi)/50,000)*x (rpm of the turbo) + 10psi (ex. back pressure)

so, with this theoretical setup, our turbo would spin at:

x = (50 - 10)*(50,000/25)
x = 80,000rpm

If that backpressure would be reduced to, say, 5psi:

x = (50 - 5)*(50,000/25)
x = 90,000rpm

Now, if we would look at a compressor map for our turbo, it might say that at 50,000rpm, it produces 5psi of boost, and at 100,000rpm it would produce 10psi.

so, that would leave our first setup with:

x (boost pressure) = (5/50,000)*(80,000)
x = 8 psi

and our second setup:

x (boost pressure) = (5/50,000)*(90,000)
x = 9 psi

So, by cutting the backpressure in half, we'd up our boost pressure by 1psi in this theoretical setup.

HOWEVER: this is not a realistic example. Yes, the effects will be the same, but to a different magnitude. We all know a compressor map isn't linear, and the effects of manifold design, exhaust temps, etc, all play a role. Pressures and air velocity will also change as the exhaust cools...

What it does illustrate, though, is that there will be a gain by a lower backpressure exhaust system because the engine will only pump a given amount of air and at a given pressure. Remove some of the restriction of the exhaust, and that leaves more energy to be used to spin the turbo. Spin the turbo faster, and it'll produce more boost (to a point), as well as spool faster.

~hope this helps.
 

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Looking back, I may have read the original post wrong...but still a decent lesson nonetheless... I was thinking he went from a smaller diameter exhaust to a larger one...

As far as I know, the wastegate bleeds off the exhaust side...meaning as the pressure on the compressor side builds, it opens a valve on the exhaust side to slow down the turbo. Air can only be pushed through a hole so fast... So, if the hole is too small, not enough air mass can move through it at the speed you want it to go.

On a boosted application, too small a wastegate will not let enough air escape in the amount of time you need it to, which would be instantaneously. So, the pressure builds up between the exhaust ports and the turbo, which, if you read my previous post, will provide more pressure to spin the turbo.
 

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MBC? i dunno their wierd like that...
oooor since the dump tube is intergrated the tube actually causes a vacume towards the wastegate valve, n/m that not right actually that will make you boost less.. hmm idunno, but wats wrong with 9psi rock it man :TU:
 
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