Chainsaw Repair

With the Poulan 46 you usually have to make a carb insulator block that attaches to the cylinder with set screws

First I have removed the metal piece or heat shield in the exhaust and then widened the exhaust port to eliminate the step.

That's about what I had planned. The only issue I see is that the top step will still be there. I assume this is not ideal for it will create eddies. Is there a way to smooth the step without actually removing it entirely causing timing changes? Maybe just a bevel. Or adding material in that little crevice even? I didn't plan on touching the intake unless it makes sense to do some sort of balancing...

Like 660 said you should look for mods that give torque but not RPM.

Does widening ports actually increase torque or is it only RPM really?
8,000 rpm isn't too far off cutting-saw peak performance is it. Don't many saws peak power at around 9,000 rpm? For planes is it that they want lower rpm simply because a super high speed prob is less efficient than a larger more consistent speed one with more load/force output?

In regards to the intake... this probably will show my ignorance, but do some saws use one way valves and others don't? As far as I can tell there is nothing stopping flow back out the intake of the cylinder through the carb. No valve that is. But I've heard of some of that physics stuff that describe why most of the fuel air doesn't blow back out...

To answer your question about the step in the exhaust port.   Yes I did taper mine, but I did not raise the port.   That will drop compression, lose torque, and raise rpm,   

The point of widening the ports is to increase flow through the engine.   If the exhaust flows out better then it will also allow the incoming fuel air mixture to increase.

  In reality I think anytime you make any changes to these engines that helps to increase the HP rating there is also going to be a small increase in RPM.   

"But if you are used to Husqvarna 346 and 357XP's, you get the impression that the Homelite is not running full throttle.

I don't really know how the Poulan and the Homelite compared in the cut?"

Yeah, for the short test I did do with the Poulan before ripping it apart, it felt a lot more sluggish than the Husqvarna XP models. Kind of like you said: not feeling wide open when it actually was. Not sure what this means in terms of airplane engine performance or how it will change if I do any porting or muffler mods, but we'll see!

first thing is, this is an insomiac reponse, so tread lightly.

sounds like the torque curve of the motor needs to come down in rpm, and the powerband needs to narrow up.

similar to this idea: http://www.epi-eng.com/aircraft_engine_products/ls_crate_engines.htm

maybe a smaller venturi carb, or better yet a smaller carb plus less intake port x-sectional area/duration may help?

compare the airplane optimal torque curve from the first link to page 19 of the second link here: http://www.vintagesnow.com/SledU_Folder/delivery_ratio-1.pdf

epoxy will be your friend.  don't know if rc folks do any of this?


regards
-joe


edit:  would help if i could spell and actually include the links