Turbo exhaust considerations.
Turbo Mini Forums

I know that some people are using 2" exhausts, and some are using 2,5" exhausts. We all know that gas velocity are important, maybe even more so when a biggish turbo are being used. But, then again a big turbo will probably need a bigger drain when big boost is used.

This is theory, can someone with some practical experience please shed a light on this?

no expert on this, but when I used to have my r5 gt turbo i went down the route of fitting a large bore exhaust system and it considerably reduced the back pressure on the turbo.

I managed to lose 4 psi just by reducing the back pressure the exhaust was creating!

I have also heard in the past although i am unsure of how much truth is in it mind, is that fitting too larger bore system can cause problems with the seals within the turbo. I didn't see this with the exhaust i had on my r5, nor have i known anyone else with this problem with numerous other turbocharged cars.

BIG is best!!!

Vegard, your Mrs left her glasses case at my house!

Jon.

hey dan a turbo expert at a turbo reconditioners told me that to if the exhaust has not got enough backpressure that it will leak oil past the seals but ive since come to the conclusion that this isnt the case.imo

didnt jimster just have a big long tube at avonpark?

no longer a series, but still 1.3 turbo.

back pressure is bad, full stop.

to many people confise it with gas velocity.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

im sure i read that the best possible exhaust for a turbo is no exhaust

back pressure is good if you have a 2 stroke!

on a related note how powerful is the gas coming out of your exhaust? mine will move stones on my drive on tickover!?!

Think jim was just using some left over tube from something. Did the business though.

I have a PlayMini single box exhaust I plan to use on my car, anyone have any comments on this? Any good? Too big/small?
I have a maniflow downpipe to mate with this, have got a bit of tube that will sleeve over both so no problem there.

ive got a 2" minimine exhaust which is the same as the play mini, dont think it has any flow restrictions,as on idle the gases coming out are powerful enough to move stones on my drive

All my investigations has led me to think the following,

THe gas velocity is important in the engine side of the exhaust system. Optimum tuning of the primaries here will gain extra response from the turbo, but i suspect that due to there very short length and back pressure, that nothing can be done to help scavenge the cylinder. After the turbo the least back pressure the better. There are no benfits in trying to tune this area for gas velocity etc. This is due to exhaust tuning only working in normally aspirated engines by tuning pulses in the pipe to give a low blowdown pressure. So i figure that you cant go to big in terms of less back pressure. However its certainly going to give you diminishing returns and at some point any form of silencer box you run is going to have a much bigger effect. I cant see how running no exhaust would cause an oil leak as inside the turbine housing is always going to see posotive pressure with the engine running, if it didn't it would never spin the turbine.

2 stroke exhausts are a totally different kettle of fish. They are tuned to suck out a little fuel into the exhaust manifold whilst the cylider is inducting(the low pressure also helps scavange exhaust gas). The exhaust is made from two cones that reflect the exhaust gas pressure pulses back up the pipe. before the exhaust port closes high pressure arrives back up the pipe and pushes the fuel air in the top of the exhaust manifold to enter the cylinder. More fuel / air = more power.

For road use i'd go for a good single box setup.