318ti Turbo Conversion info needed!!

[Freedy]

There is alot of tuning that goes into finding the optimum back pressure. If the pipe is too large then the exhaust will not excape as quickly. 3 inch piping may work great on a 3L Supra running 20ish psi, but on an M24 running 8 psi, it will not be near as effective.

Optimum backpressure on a turbo car is no back pressure at all. The pressure difference pre and post turbo is what spools the turbo in the first place, and for this reason it is better to have a very open exhaust after the turbo. Read up on turbos if you dont believe me, but Ive been around them for about 10 years. I know this.

[needle332rur]

less back pressure doesn't mean bigger pipes. a three inch exhaust will not flow as well as a 2.5 in down pipe to a slightly larger mid and even larger end pipe. with this set up the exhaust will pull itself out as is expands. This is mostly used with racecars but if you have a car not completely dependent on boost pressure for power then this will work.

But again if you have a car w/ 7:1 comp and running 30 psi all it is, is a big air pump

[Freedy]

Well, I dunno who the F would make a tapered exhaust for the street, but if it started at 2.5 inches it would still be worse than a full 3 inch exhaust. The backpressure on a full 2.5 inch exhaust is about 2.5 psi. The exhaust backpressure for a full 3 inch exhaust is less than .5 psi. I believe those numbers were from a Turbo Supra exhaust running ~10 psi boost. That means you have to leave about 2 more psi of backpressure pre-turbo in order to create the same boost on both systems. Leaving 2psi more backpressure pre-turbo means your engine is fighting against 2 more psi to get its exhaust out. That means its working harder, and you are not making as much power.