rpm and porting

[booger1286]

Just been readin up on some porting and was wondering what kind of rpms do you guys generally gain from porting a cylinder, In the cut and out?
Also how do you guys use a tach to tune after porting? I usually just go by ear but i would like to be more precise.

 

[Andyshine77]

Just been readin up on some porting and was wondering what kind of rpms do you guys generally gain from porting a cylinder, In the cut and out?
Also how do you guys use a tach to tune after porting? I usually just go by ear but i would like to be more precise.

Each engine is different, and it all depends on what you're going to use the saw for. I use a tach more or less as a reference, not as a strict guideline to a specific rpm, unless I've predetermined a good working rpm through testing and experience. With a stock saw you can tune to the max recommended rpm and the saw will run fine, but there is often more to be had. I try and keep a normal ported work saw tuned within about 1,000/1,500 rpm of the factory max rpm, even if it's getting plenty of fuel at a much higher rpm. All of this changes when you're simply going to cut a few cookies as fast as you can.:msp_smile:

If you want to keep rpm's down when porting, keep your exhaust and transfer timing numbers stock, add a little intake duration, and don't go crazy wide with your ports. Honestly if you're just blocking firewood, a simple muffler mod can do wonders. opcorn:

We all start somewhere, it's best to take baby steps first, than to try and run a marathon on your first day walking.:msp_smile: