18 replies to this topic

[Tobias Press]

hi. i intend to fabricate my own manifold for my turbo build. what is the best sized pipe i should ise for my exhaust manifold? i intend to fabricate a 3'' down pipe as well. thanks

[MRA]

hi. i intend to fabricate my own manifold for my turbo build. what is the best sized pipe i should ise for my exhaust manifold? i intend to fabricate a 3'' down pipe as well. thanks

 

That depends on what engine you have and what you want out of it and how you will drive it !  but there are general sizes, tell us more about your engine and what you want out of it ?

[Tobias Press]

ok so its a 1293 and its gonna have 18cc dished pistons with 24 cc chambers, phase 2 cam etc. its going in my clubman and will be used on the track as well as on the B roads ;) going to be running a gt17 turbo but not sure about what boost i could run atn

[Steve220]

3" is WAY too big. 2.5" (although still a bit on the big side) will be better and will allow a better mandrel bend under the car from the down pipe and will be good for over 200bhp applications.

Edited by Steve220, 18 March 2017 - 05:40 AM.

[Tobias Press]

ah great thanks Steve220. so i should use 2'' or 2.5" for both the manifold and the downpipe?

[Steve220]

You mean from the ports to the turbo? You need small as possible to aid gas velocity to spin the turbo best.

[Turbo Phil]

Basically you want a big differential pressure across the turbine, so high pressure upstream and low pressure downstream. This will provide the most energy to drive the turbine.
Unlike a NA engine, you can't really go to big on the downpipe/exhaust. 2.5" will be sufficient here, you may see gains going bigger if running the most extreme power but it will be almost impossible to get past the subframe/pot joint.
As for the manifold, somewhere around 28mm ID will get you in the ballpark for most applications. This is will keep gas speeds/pressure high to drive the turbine without being to restrictive.

Phil.

Edited by Turbo Phil, 18 March 2017 - 08:27 AM.

[mini13]

space is the issue with the down pipe, no way you'll get 3" down ther 2.5 is a strugle

[Tobias Press]

brilliant. thanks for the info.

[MRA]

space is the issue with the down pipe, no way you'll get 3" down ther 2.5 is a strugle

 

A 3" round pipe is not possible but if you modify the shape you can get the same flow along the pipe, but this needs to be done in a such a way that doesn't then just increase the internal restriction, is it worth it ?  I think it is, as it allows the turbo to spin up quicker but also allows lower losses at higher RPM

[Turbo Phil]

There will be a point where going bigger on the downpipe becomes pointless though. If you're running a turbine the size of a 5p I doubt going from 2.5 to 3" would be of any benefit at all.
If the turbine can't support high RPM it won't matter as much.

Phil.

Edited by Turbo Phil, 18 March 2017 - 06:05 PM.

[Tobias Press]

ok so just to clarify a 1.5" or 2" manifold would be suitible. as for the down pipe 2.5" may be just about ok? please correct me if im wrong

[Turbo Phil]

Even if you could manage to make one and fit it in, which would be almost impossible in a Mini, a 2" manifold would be terrible.
Like I said in my original post, somewhere around 28-30mm ID will get the job done.

Phil.

[Tobias Press]

ok. i do have a turbo box so i do have more space than normal.

[Turbo Phil]

Think of the size of the ports in the cylinder head, now think of the size of a 2" pipe. Do you think this will work as a manifold ?
If your answer is yes, then I can't help you .....

Phil.