Recommendations for sort exhaust pipe diameter

[merbesfield]

Wanting to build my own homemade sport exhaust for my 66 2.0. What is the recommended dia. pipe. I know stock is about 2" what about a larger dim. say 2.5". How do you think that would affect sound and performance?

[merbesfield]

Come on people, 122 views and no comments?

[Paragon]

My go to guy on this was George Narbel at European Racing Headers. My guess is that he would have suggested 2.5". Maybe some of the engine building gurus can chime in here.

[merbesfield]

My go to guy on this was George Narbel at European Racing Headers. My guess is that he would have suggested 2.5". Maybe some of the engine building gurus can chime in here.

Thanks Jason.

[Bullethead]

It's not as simple as just adding bigger headers. Pipe diameter and length affects the exhaust pulse, a positive pressure wave which should collapse
as it reaches the outlet... the returning negative pressure wave if timed properly scavenges more exhaust from the valve port, greatly effecting performance. Backpressure. Bigger tubing isn't necessarily better and valve diameter, port shape & size, intake length & dia. at inlet and manifold
are all part of the equation. You could immerse yourself in the engineering, or have a good engine specialist provide guidance.
I'd bet every combination for Porsche engines has been recorded.

I bought a kit of pipes and bends to build a set of headers for an M88 BMW motor. Figuring out how the snakes fit together was like Chinese algebra. Good luck!

[merbesfield]

It's not as simple as just adding bigger headers. Pipe diameter and length affects the exhaust pulse, a positive pressure wave which should collapse
as it reaches the outlet... the returning negative pressure wave if timed properly scavenges more exhaust from the valve port, greatly effecting performance. Backpressure. Bigger tubing isn't necessarily better and valve diameter, port shape & size, intake length & dia. at inlet and manifold
are all part of the equation. You could immerse yourself in the engineering, or have a good engine specialist provide guidance.
I'd bet every combination for Porsche engines has been recorded.

I bought a kit of pipes and bends to build a set of headers for an M88 BMW motor. Figuring out how the snakes fit together was like Chinese algebra. Good luck!

All true, but all I am doing is low buck old school hacking of existing muffler with slight mods for the fun and sound. 2" or 2.5" is the question.

[Bullethead]

All true, but all I am doing is low buck old school hacking of existing muffler with slight mods for the fun and sound. 2" or 2.5" is the question.

Sorry, should have understood you were cutting just the muffler... go 2.5"! (still might need carb tweaking)

[MoparBoy72]

Looks like 2" is noted on the old article:

http://forums.pelicanparts.com/porsc...t-muffler.html

[merbesfield]

Yea orig was 2" but 2.5" would look a little cooler, , just didn't want to screw anything up with too fat of a pipe.