Porting a non powervalved engine

[pyromaniac]

I have bough maybe the most sold 250cc off-road engine ever made.

It hits very hard in the upper mid but doesnt rev much and the low response pretty good actually. It have a very short usable powerband and i would like more overrev and a little earlier pull so im thiking of the mo-better porting but what can i expect from a non powervavle engine compared to one with?

 

[Studboy]

A narrower powerband than that of a powervalved engine.

 

[motometal]

My old '74 TM125 was ported and had decent top end, but low end and mid was so weak you couldn't let the clutch out in 1st gear without revving the crap out of it. We take for granted the advantages of powervalves in modern engines...

 

[jaguar]

That TM 125 was ported for top end power only, obviously.
I once got a back seat ride on an old (70 something) Husky 125 that was so strong that we easily climbed hills and pulled wheelies. But I doubt that it could rev out very far. Not that it needed to.
Ideal is all the ports (and pipe length) to change as the revs change. Now just the exhaust port changes and lets too much blowby making the design a bit inefficient.

 

[pyromaniac]

Well can i expect a big change from a porting job on this type of engine?

 

[jaguar]

yes, big change