Exhaust opinions

[euro_urs4]

Hey guys need some opinions on what kind of exhaust to make I'm running a hx40 on the aan motor i'n a urs4 and wondering what's the best size to make for the down pipe and the rest of the piping with the rest of the car with back pressure and all thanks

[nip]

Hey guys need some opinions on what kind of exhaust to make I'm running a hx40 on the aan motor i'n a urs4 and wondering what's the best size to make for the down pipe and the rest of the piping with the rest of the car with back pressure and all thanks

alright, id say 3" downpipe, also 3" all the way

[URSIMPO]

I reckon 3.5" down pipe to 3" for the bottom of the car - otherwise scrapes aplenty!

[DamianURS4]

3 inch minimum - the key is the muffler set up and whether you can live with tinitus!!!!

[UrS4boy]

Hey guys need some opinions on what kind of exhaust to make I'm running a hx40 on the aan motor i'n a urs4 and wondering what's the best size to make for the down pipe and the rest of the piping with the rest of the car with back pressure and all thanks

If you are in the US of A, you should be aware of Stromung and 034. Both are 3" turbo back systems. Stromung is the more refined of the two options and has been designed to eliminate the nasty droning that other options have not. Typically those trying to build their own exhaust systems have great difficulty with droning, typically at highway speed RPMs where the car lives most often. Stromung fixes that.

[Error404]

with a resonator pipe?

Hamish has built the best custom exhaust I've seen, check his SQ thread

[terrybullwon]

I built my own for my S2

It's a 4" down pipe to twin 3" and then it exits each side before the rear wheels also the waste gate tube is separate.

I would not recommend building a 4" down pipe unless you are prepared for the agrovation!

[loxxrider]

3" all the way will be plenty for that.

Base it on your turbo outlet. Of course an infinite diameter exhaust is best for a turbo, but turbo outlet will give you a pretty dang good idea of the size you need to have. Holsluts are typically about 3"

[Error404]

James how much did you have to rape the subframe to fit that 4" DP?

[terrybullwon]

James how much did you have to rape the subframe to fit that 4" DP?

Not as much as you think Alex the hard part is getting it away from the CV boot whilst keeping max ground clearance.

@loxxrider yes my turbo is 3.5" exit hence the large down pipe

[s2_wot]

Exhaust Design

Attached is a file I did a while back to assess my options.

In relation to pipe sizing we refer to a 73-76mm pipe as a 3" whereas from a steel selection point of view it is considered to have a nominal bore of 2.5".
Nominal Bore 3" pipe has an OD of 88.9mm.

PDF attached Amari Pipe and Tube pages 3 & 24 have some useful information.
Excel file attached lets you compare the option of a dual setup to have a greater overall cross section and a better ground clearance. I do intend to do some flow tests on a stardard setup some time in the future. For a urS4/S6 the chart needs to be changes as it's a dual setup all the way back. Wall thicknesses are at 2mm across the board, 1.5mm would be more accurate.

Also worth noting that a dual setup with 4000 sq mm cross sectional area won't flow as good as a single pipe with 4000 sq mm cross sectional area.

I'm purely guessing but a 88.9mm downpipe and 76mm cat back looks like a pretty free flowing exhaust.

[terrybullwon]

Hang on.....

76mm is 3"

So where's 88mm come from?

[s2_wot]

Pipe & Tube is sold on the internal bore so to standardise outside diameters pipe & tube has a notional "nominal bore".

[diesel des]

Normal bsp 3 inch pipe is about 90mm od. But its real heavy wall. 1.6mm wall stainless dairy bends and pipe is way better, leaving a 73mm id on 3 inch pipe so not true 3 inch.

[diesel des]

Shane, your thinking of bsp (british standard pipe) sizes which is always id measurements. Exhaust tube in Europe is sold and referred to by its od. So 3 inch is 76mm od, usually 73mm id.