I been asking lots of question to the guys that make header systems and here is the low down as I understand it.
I am not saying this is 100% accurate but my take on the info I have gleaned from several reputable bike and car tuners plus info I found on the Net,
No Arguments will be entered into by me
a
2 inch system is more suited to forced induction and highly modified R3 motors and on a non internal modified motor will only give benefit at high RPM where most of us do not go or otherwise not spend a lot time there, so yeah a Carpenter exhaust system is great if you are running Hi comp Hi reving cam profiles in eg carpenter 240 kit worked engines or are running a SuperCharger, in other words it is designed to work at higher revs or move large amounts of exhaust to work at its best, it will still work on a std engine but not as efficiently as a slightly smaller OD header (something about loosing velocity in the larger OD)
a
1 3/4 system will suit a stock engine and give benefits to it offering good scavenging and good all round performance but if you then wish to go to hi comp pistons and cams that work in a lower rev range eg Ponters bike with his Neville lush worked engine and Reband exhaust it will then be working at it designed level
a
1 5/8 system again will suit a Std engine and also some slight mods but not a lot more unless it is a 3 into 1 system with a decent size choke, then it has more potential for a modded engine
Again I am not looking to start an argument just stating the fact that I have found to help someone trying to decide which size/type exhaust to buy for their bike
