bar length vrs rpm.

[Cornishman]

Hi Andre Thanks for the elementary phisics lesson. As a qualified engineer with 40 years experience I think I just about understood it. My original question was aimed far above that level. Ever heard of Bernoulli ?  He did a little work with Venturi's.
Anyway I would suggest researching 4 stroking. Wikipedia does a very simple explanation and it will lead you to air and fuel flow through a carburettor. You will then understand why there are two jets on a chainsaw and how mixture varies with airflow. This knowledge is vital for understanding what goes on and might even change your fascination with heat. Please read it.

[Andyshine77]

Hi Andre Thanks for the elementary phisics lesson. As a qualified engineer with 40 years experience I think I just about understood it. My original question was aimed far above that level. Ever heard of Bernoulli ?  He did a little work with Venturi's.
Anyway I would suggest researching 4 stroking. Wikipedia does a very simple explanation and it will lead you to air and fuel flow through a carburettor. You will then understand why there are two jets on a chainsaw and how mixture varies with airflow. This knowledge is vital for understanding what goes on and might even change your fascination with heat. Please read it.

I've done years of research. Do I remember everything? no, but I'm spot on with this subject. I know what the velocity in the venturi does and how it effects pressure. I gave you an elementary answer because you asked an elementary question. The way you worded your previous post, and your defensive attitude, suggests you are no engineer.

Two stroke engines rely on effective scavenging in order to operate correctly. This clears out the combustion exhaust gases from the previous cycle and allows refilling with a clean mix of air and fuel. If scavenging falters, the mixture of unburnable exhaust gas with the new mixture may produce an overall charge that fails to ignite correctly.

That was a quote from Wikipedia. How does it differ from my explanation? They left out the fact heat plays a role, but that's about the only difference. Wikipedia is far from 100% accurate. One very important thing to keep in mind, most of the information on the net about two cycle engines, is based on engines with expansion chambers, which chainsaws don't have. Well unless your running one of EHP's hot saws. ;D   

This book is one of many that will help get you get started.http://www.2strokeengine.net/gordonjennings/twostroketunershandbook.php

[Andyshine77]

 

[Grandedog]

     Howdy,
   The difference in power required to spin a chain under no load between a 16" bar and a 36" is negligible as best. It's the wood that needs to be adjusted to. The safest is to set it on the largest wood you're cutting, and suffer the rich performance in the smaller cuts. For the majority of wood cutters, this will put the most wood in your pile with the least amount degradation to your saw.
Regards
Gregg

[ehp]

I see my work here is done  8)

[dennyb]

I was told that to run a longer bar you need to richen up the saw mixture a bit to give more power under load ?  Just wonder what you guys think ?

Richening the mixture in the carb will give it more bottom end torque which as the bar becomes longer becomes more important than HP in big wood. Richening the mixture in the tank doesn't do anything for power.