I must say that I read these responses and this type of thread with real interest. I have never understood performance tuning enough to pass valid comment (my original comment was more about function, aesthetics and my impression of "before and after" performance) but would love to know more.
I grew up tinkering with various cars/engines such as BMC A and B series, various Ford (Kent crossflow and Essex V6 mainly) and Triumph straight 6s. I didn't get to VW aircooled until a few years ago. I have rebuilt all of the above engines at some point but any tuning was usually based upon the principle of flowing air through the combustion cycle - hence a raft of Peco/Janspeed/custom exhausts, high lift cams, K&N air filters and re-jetting the carbs "to suit" that sort of thing. I was always of the understanding however that there are trade-offs and opportunities to tune for either torque, a good average across a wide power band, peaky high power in a narrow rev band (never understood the appeal of the Honda S2000 with all it's bang being delivered between 7 and 9000 revs but then I never drove one...) and anywhere in-between. I then got to hear about the "some backpressure is good" argument and at that point I turned to suspension tuning!
I guess what I'm saying/asking is, what is the best question to ask when talking about what exhaust to use? Bearing in mind the giddying array of aircooled VW engine configurations available now shouldn't we be stating what
type of performance we are aiming for?
My understanding of the Vintagespeed (and I recall it being in the literature) is that it does flow a lot more than a standard exhaust (one reason why it's louder) but does have it's performance/design limits compared to merged and balanced headers.
A rolling road, as Sparkywig cites, is king if you want to know what you will achieve but is there a reliable formula that the "bolt on" tuner can refer to? I think it would be good to have a sticky thread with people's configurations (bore, stroke, cam, head/valves, carb/s, exhaust etc) and RR results as a base reference point so that you know where to aim and that way you can get the right blend of practicality, driveability and performance without spending your money several times on the wrong parts.
I'm want to learn more so would love to hear sound, qualified and evidenced views on how to tune our engines. Bring it on!
. Like the side exit exhausts for sure and would be my preference, but reckon the VS may not hang as low and is approx half the price of CSP Python system. Although I prefer German quality. Not got a race engine, just mildly modded 1776 with twin 34 ice Webers.
