just a question about what diameter piping everyone is using for their turbo manifolds.... wouldn't 1.75" be the closest in size to a b series exhaust port if it was squished a bit in the middle? i imagine most people use 2" i am going to make my own and wanted to use 1.75" but it is impossible to find mandrel bends this size anywhere. what advantages or disadvantages has anyone encountered with the size pipe they are using? any input is appreciated.

 

On my D I used 1 1/2 steel pipe weld els.

 

These bends from mcmaster work perfect, 1.5 is actually bigger than the exhaust ports even if you squesh them down. 1.75 and 2.0 is way to big.

 

....besides pipe doesn't come in 3/4 sizes. It goes 1 1/4, 1 1/2, 2, 2 1/4 2 1/2, 3 and so forth. 1/5 is your best hope.

 

hah, well not everyone buys plumbing pipe from mcmaster We have a local guy who sells 1.75

 

the thickness of the weld els are also a definately advantage over buying basic 18gauge mandrel bent small piping (which is not recommended).

 

i'm going to assume the mcmaster 1.5" is the id and not the od. some measurements:
circumference of my exhaust port is 132.814mm
circumference of 1.75" circle is 139.644mm
circumference of 1.6875" circle is 134.657mm (bingo!)
circumference of 1.625" circle is 129.669mm
circumference of 1.5" circle is 119.695mm
i have some 1.75" od 304ss pipe but no bends, only straight. from my measurements, something with 1-11/16" id would work the best as it is closest to the port size but nobody makes that. wouldn't 1.5" restrict exhaust flow i little bit?