Back pressure exhaust and engine temp

[RH1300S]

Something my simple mind can't get on terms with.

If an expansion chamber design works on a 2-stroke, why are 4-strokes different?

[flynfrog]

because the a 4 stroke has an intake valve where a 2 stroke has a piston port


i think it could be made to work but the losses do to poor cam timming would out weight it

[DaveKillens]

This may offer some explanation.
http://web.tampabay.rr.com/redroby/3liter/exhaust.html

[mep]

Nice artice dave.

This explains why the F1 cars start to smel after
unburned fuel if they run slowly or at low revs.

Can someone explain (or give a link) the
effect of changing the exaust pipe diameter.