Dennis Cahoon
Addicted to ArboristSite
That's right!.....a domed pop-up.......makes a BadA$$ Racesaw......Work saw, a waste of time!
Here is a 2 stroke piston, what say you on flow across the piston with this.
That's right!.....a domed pop-up.......makes a BadA$$ Racesaw......Work saw, a waste of time!
The piston in my old Clinton saws looks similar to that. I've heard those being called a "wave separator" style piston.
The Clinton piston is ramped more towards the exhaust ports and has a shelf on the intake side.
Pretty much all of Stihl's pro-grade models in the 70's used domed pistons at one point or another with the exception
I believe being the 090. But they did a lot of playing around with combustion chamber shapes and sizes on the 090.
Yep, I haven't heard of any dynos available for saws. The tach is something everybody can have access to.
<iframe width="420" height="315" src="http://www.youtube.com/embed/zwdMSCJULgU" frameborder="0" allowfullscreen></iframe>
That comes out to a little short of 20hp, folks.
......but why is it a waste of time?
I already told you in post #6.........IMO......"You can get all the compression you need in a work saw without using a pop-up piston."
So Andy, what's your thoughts/experiences?
A popup can be worked beyond your typical lathe spin. Sometimes the gains can out weight the negs. For me a reworked popup piston with top ring pin shifted for a wider port and one ring on a windowed piston (not that I care for windows) produces more than I can get from a kit piston. Very few have the means to access a popup let alone further machining methods. For sure you see some lowers over worked to the point you could see they would struggle with velocity.
......but why is it a waste of time?
I already told you in post #6.........IMO......"You can get all the compression you need in a work saw without using a pop-up piston."
Right! LOL, sorry. I'm listening. Setting up today to be able to cut squish bands. Figured I'd give it a try.
Got some more done for the 390, don't even know yet I'f I'll have to cut the squish band or not.
Pay no attention to those stray holes! LOL, I assumed the bolt pattern was square, well it wasn't, LOL.
......that's the trouble with dnyo's!......people Bull$hit you about how much hp they're making to sell their products.......064 with 20hp.....Hahahahahahaha!
sorry...don' have a direct link to this, it's a file i have saved on my hard drive very long time ago. but it should be available by a search.
national committee for aeronautics
technical note #674
title research paper: scavenging a piston ported two stroke cylinder
""......an improvement in scavenging efficiency of approximately 3% was realized by substituting a round top piston for a flat top piston.(good info on intake and exhaust port angles in that paper).
using some on-line engine simulation calculators, i found that by plugging #'s in for a small displacement engine bore, stroke, rpm that an increase of 0.1 ft/lbs. of torque could be gained by raising compression.
hope it helps.
Enter your email address to join: