Hi all,

I've been looking at getting a CSP Python exhaust system for my 1641cc 1970 beetle.
These exhausts come in 4 different sizes - 38mm, 42mm, 45mm and 48mm.

My question is - is there any simple rule of thumb that matches certain sized exhausts with specific engine capacities? Or is it just pot luck?

sorry mate i can't answer your question but i have been wondering the same. I'm looking for a 71 1600 twin port where are you shopping?

Capacity, cam, headwork, expected rev range all play a part in selecting an exhaust system.

Unless you're going to upgrade your 1641 to something bigger, then the 38mm would be the go. Of course I'm assuming you're not planning on revving it to 9K.

there are some calculations you can look up on the interweb for exhaust system design.
basically depending on the engine size will dictate the diameter of the exhaust primaries, which is probably what CSP are referring too.
I do have the calcs somwhere in a notepad but without looking at it I'd say for a 1600 the 38m will be fine. Thats 38/25.4= 1.5inches primary diameter and this is good upto just over 2L engines but does depend on valve sizing and other factors like volumetric efficiency.
So if you don't want to do the research then go with the 38mm and should be fine.

Stock is 1 3/8" or 35mm

I have a 1916 and my exhaust tapers on the primaries from 35 to 38

In one of the lastest hot vw mags there is a great chart for sizing the exhaust to your engine.

VW trends did some articles ages back

read here
http://www.vwtrendsweb.com/tech/0109vwt_volkswagen_exhaust_test/index.html 

and here
http://www.vwtrendsweb.com/tech/0109vwt_volkswagen_exhaust_test_2/index.html 

Those are pretty good article you have linked to Bizzare. Thanks.

Yogie