Exhaust pipe sizes when tuning

[breitling]

Im a bit confused what to do on my urq.

How much hp and nm can you run trough a 3"/76mm-downpipe, 70mm pipeline with only one silencer in the rear VS 3" all the way with one silencer?

The problem is that 3" exhaust is hard to get over the rear axle without having a lot of vibrations. 70mm is easier..

Will i have a lot of backpressure problems when reaching 600 hp?
Im not sure but i think the sportquattro had 70mm.

Does anyone of you great turbo experienced guys know

[Jamo]

On what car? On the Avant / RS2 the exhaust doesn't go over the axle

Anyhow you want it large up front, by the time it gets to the rear the exhaust has cooled a lot and you can run 70mm over the rear axle but i'd say thats up to 500 bhp for your 600 you want the full 3"

[s2_bo]

If the rear axel and subframe is the same as it is on a coupe then you can get 3 " over it. Its tight but it can be done, there is a few threads about it on here already. I looked in to this too as i thought it was a problem when i had my 3" system made, turned out they got it to fit fine and it doesn't rattle or knock at all.

[breitling]

On what car? On the Avant / RS2 the exhaust doesn't go over the axle

Anyhow you want it large up front, by the time it gets to the rear the exhaust has cooled a lot and you can run 70mm over the rear axle but i'd say thats up to 500 bhp for your 600 you want the full 3"

Thanks
Its for the urquattro.

If the rear axel and subframe is the same as it is on a coupe then you can get 3 " over it. Its tight but it can be done, there is a few threads about it on here already. I looked in to this too as i thought it was a problem when i had my 3" system made, turned out they got it to fit fine and it doesn't rattle or knock at all.

Yes its the same axle. I know it can be done, but i can have a handmade exhaustline that fits like a glove. But thats only 70mm.... he dont want to make a 3"
If its only good for 500 hp i think its too small/tight.

[G60Rallye]

I think its wrong to say that one size will limit the power to a set level. Its more than likely just going to knock a few bhp off what it could do with a larger exhaust.

[Jamo]

As i've said before it's not a limit it's the knock effect of EGT's and back pressure that's the problem, 600 bhp is a lot of gasses to flow at that power ideally you'd be looking at 3.5" downpipe.

A full 3" system would just about cut it so going to 70mm partway is going to have a detrimental effect and with the money being placed on the project not worth the risk IMO.

[breitling]

Hmm...
So the best solution here would be 3,5" downpipe and 3" pipeline..?

[Jamo]

For true 600 bhp and that headroom yes IMO

[AUDIS2avant]

ive done 650 on a 3" stainles system for a few years now and have almost no backpressure, and have a friend with 800 on the same 3" also, but his is shorter then mine.
Would say arr 500 on a 70mm full system, but do a big dp, and push it as long as you can, that would help a lot on things, and with as much straight pipe as possible, the more bends the more backpressure

[breitling]

ive done 650 on a 3" stainles system for a few years now and have almost no backpressure, and have a friend with 800 on the same 3" also, but his is shorter then mine.
Would say arr 500 on a 70mm full system, but do a big dp, and push it as long as you can, that would help a lot on things, and with as much straight pipe as possible, the more bends the more backpressure

800 I already have a 3"downpipe... and if i decide to use the 70mm (only 6 mm less than 3") the only bend will be over the axle and in to the muffler in the rear end.

What about the sound? If the pipes are smaller will there be faster flowspeed? Maybe it will be a more "angry"sound?