[wileecoyote]

Now that there's some exhausts coming out for the 335 I was wondering whether there should or shouldn't be an X-pipe?

My understanding of X-pipes was for NA cars to assist with scavenging. Pressure waves (exhaust pulse) comes out of exhaust valves and out the exhaust pipe. The wave hits end of pipe and a return wave goes back up the pipe and if timed right (pipe length\diameter,) scavenges or pulls the next exhaust pulse out of the cylinder. I thought an X-pipe assisted with this by crossing\mixing the waves up and down the pipes to assist with scavenging.

However, this is a turbo car, so the pressure wave can't make it back to the cylinders because there's a turbo there, so I would think scavenging doesn't really work. I thought the pressure wave has to get back to the cylinder\exhaust valve area to pull the next exhaust charge out of the cylinder. The turbo wisdom I'd heard with my other car was no exhaust pipe is better, the least resistance the better.

So am I way off here? Is there another reason for a X-pipe or am I wrong as to its function? My thought would be the seperate pipes would work better because there's less overall restriction?

[Ryan.M]

Check out this link- http://www.e90post.com/forums/showth...=X-pipe+H-pipe

[wileecoyote]

I did see that post, but it is dealing with NA motors and none of it goes into turbos at all, does that change the equation any? I would think with a turbo you get less pulses as the turbine takes those pulses and then spits out a smoothed out or blended exhaust for lack of a better term. Do you still need an X-pipe in that case?

[HyperM3]

I started that thread with the same intentions as you. Unfortunately it took a turn to NA cars but it was with the entire idea centering on the turbo 335. I dotn know how it changed subjects.

[wileecoyote]

Seems like there's a number of S4 owners on here, maybe they'd have some input as that is a twin turbo platform which is pretty well evolved. Maybe they have some experience one way or the other.

I'd really like to hear from some of the exhaust manufacturers as to their thoughts like Vishnu and AA for instance since they are fairly active here.

[hotrod2448]

Maybe try some of the Supra forums. I know most of them go to big singles but, I'm sure some of them still have twin turbo setups.

[eriks]

Originally Posted by wileecoyote

Seems like there's a number of S4 owners on here, maybe they'd have some input as that is a twin turbo platform which is pretty well evolved. Maybe they have some experience one way or the other.

I'd really like to hear from some of the exhaust manufacturers as to their thoughts like Vishnu and AA for instance since they are fairly active here.

There's no such thing as an x-pipe in the S4 world. I had a Milltek SuperDual exhaust that had two pipes, one for each cylinder bank, and they never intersected. Amazing sound, btw.

From my understanding, the 'x' connection is there to pull exhaust pulses from the other side (same thing as was mentioned in the beginning of this thread). In a turbo charged car, you want to get the exhaust gases out of there as quickly as possible with minimal changes in direction. With an x-pipe, you're forcing the flow of the two pipes to intersect and basically push past each other on the way out. It's a bottle neck.

I think of it as a fan (exhaust turbine) that's pushing the air out. It's a smooth flow that doesn't like to be interrupted. The x-pipe interrupts the flow. BMW must have their reasons for putting it in there but I seriously doubt it was to improve performance.

My $.02

[HyperM3]

Originally Posted by eriks

BMW must have their reasons for putting it in there but I seriously doubt it was to improve performance.

More than likely it was to quiet things down. Theres already enough performance restrictions with the crimped and flattened parts.

[wileecoyote]

Alright, that's what I was thinking along those lines too, no x-pipe, thanks for your input guys.