General port timing info

[Matto]

Hi guys,

I've searched some info about porting and timing degrees on the forum and I get some info on different threads. But all the informations I get are quite different.

I'm looking for some general port timing info for chainsaws.

In the past years I did a lot of 2stroke motorcycle competition (80 and 125 cc) and did a lot of engine preparation and porting.

When I reed the timings on exhaust and intake on ported chainsaws, I'm surprised how low the values are. For example Ext 142° and Int 111°

On our motorcycle engines we were at about Ext 185° And Int 127° at compression ratios between 1/13,5 - 1/15
Off course these engines are equiped with reed valves and expansion exhaust pipes and were liquid cooled.

Could anyone link me to some threads were I can find some general information or give some general values on chainsaw port timing / compression ratios on air cooled cilinders?

Thanks!

 

[Chris-PA]

I don't have any links right now, but I will try to look for some later. The big difference is the pipe. Because the effect of the pipe is so huge on a 2-stroke, modifying a 2-stroke becomes all about how to make the pipe work better - and most of the books are written from that perspective. Without one it is a whole different ball game.

 

[mgr]

The biggest problem with extreem exhaust and intake durations is heat issues. Air cooled dirt bikes and kart engines have a lot more and bigger cooling fins on the cylinder.