The Polini and Gila kit magnum and maxi bikes I have can low 60s mph easy with big pipe, higher rpm setup but I set them up to go slower 55-60 mph basically all were built/setup 11-12 or longer years ago,
I also had a mild rpm build small port metra 80, 19mm PHBG maxi that did 57mph that ran great for several years before I sold the bike,
All engines have original stock asbestos clutches (some with springs/mods done to them) pretty much (well I’ve changed a few), stock bells and gears inside and of course all engines have maintenance done to them,
Power Down Low and a Low RPM cap/limit you can still have a reasonably fast but very reliable bike, just 5-7 miles slower with around 1,500-2,000 less rpm increases the life dramatically on a puch engine and no extra expensive parts needed like HPI, straight cut gears, super clutches, special clutch bells, pull starts etc.
When I feel like having a speed run I’ll take the estoril/low rpm pipes off and put on a Motomatic, MLM pipe or other big pipe on (needle crank engines only), do a bit of tuning and go for a speed run:
But when I do go for a fast 10 mi run It feels like something wants to blow/is ready to blow, though it don’t,