Big bore

Hi Steve, don't know much about exhaust system design but I think I'm correct in stating that a big bore exhaust shifts the power band further up the rev range of the engine and, correctly set up, produces more revs and therefore power. Richer carb settings, as you've apparently discovered are required over standard set up. I think their main benefit is for track bikes ie max revs for most of the time, and are possibly not as practical as the standard exhaust dimensions when the bike is used on the road. Of course it depends how you use your bike on the road!

Even the production racers had standard bore pipes and produced plenty of power- I know, I have one. And I also have one Commando tuned for racing which gives as much power as the factory Nortons gave (according to Peter Williams) with probably more torque. A 750, which runs on standard production valves, 32mm Mk1 carbs, and standard pipes (but a PW3 cam, higher compression pistons and TLC head porting). I simply cannot believe the bigger bore pipes give any advantages given the results we had from these two machines, and certainly even less on public roads.

Seems to me the big bore pipe boys are falling into a trap cleverly set for males rather than go for a technical advantage........

I guess Norton came up with the optimum diameter pipes from the start. I've got standard pipes on my Commando, no problems, fast enough and makes the right sound.

Oddly enough, when the SS head was introduced for the Dominators, the smaller bore exhaust pipes were said in the publicity to boost power.