A 4stroke has valves and does not rely on exhaust scavenging for power band or tuning like on a 2stroke. RPM range of a 4stroke is based mostly on the cam profile (primarily the valve overlap, duration, and LSA). Although some backpressure does move the TQ peak lower in the RPM range, its not actually making more TQ - its just making the same or less TQ earlier on.They call those poo-poo mufflers for a reason.
If you're using a 2-stroke exhaust on a 4-stroke, bear in mind there are half as many exhaust pulses, so the tuning effect will be off by half. A 2-stroke exhaust meant to work at 5,000 rpm won't "come on the pipe" til you hit 10,000 on a 4-stroke. I don't think any of these little engines will do that kind of rpm more than once.
crazydan has had his race motor up to 9,800 rpm I think he said or atleast 9k. Zenoahs and goped motors can do 11, 12k.They call those poo-poo mufflers for a reason.
til you hit 10,000 on a 4-stroke. I don't think any of these little engines will do that kind of rpm more than once.