Randy, my take on the above is that the route you choose to increase T/A becomes dependent on the geometrey of the piston and ring. In that at some point when widening the port the arc of the circumfrence of the piston covered by the increased port width will allow too much ring expansion into the port. Generally this IME becomes more critical the larger the diameter of the piston since the arc becomes larger and less of the ring is supported by the piston groove and the jug wall. T/A is just a number important to performance but still just a number when considering the mechanics of the engine. In my case I use a Excel spread sheet that solve simultanious equations to get some idea of where I am at prior to determining which was to go. Was created by an old MX racer that is on CR (1manband) I'll e-mail you a copy. You basically do a bunch of measurements, plug them into the spreadsheet and it does the calcs for you. You can then modify the numbers you plugged in one at a time until you get what you want.
No thanks......I'd rather not confuse motorcycle tech with saw building. Too many people do that very thing. There are zero similarities between porting a motorcycle, and porting a chainsaw. I've ported close to 800 saw engines........and have the timing numbers right where I want them in most cases. I hope that didn't sound like I was bragging, or being a smart azz. That's not my intention. I've studied too many dead ends already.....and prefer not to travel another.
Program not designed for motorcycles, designed for doing T/A specifically without regard to use. No problem I understand where you are at. OH and on the original question once you have the rotational timing set, and want to increase T/A from there the only way you have left to go is a wider port, do you not agree.
T/A doesn't cross over from a piped engine to a can muffler though. There is no one size fits all program. Bar length, type of work, fuel, etc all play a role in selecting timing numbers. I can't see any program that is designed for doing T/A specifically without regard to use......
I agree with that, T/A is a standard formula that can be adapted for all kinds of things including draining the pond on your back 40, or calculating the run-off time in a certain geography. The 'can be adapted' is the part that seldom is done the same way. Jennings originally used it and since then others have taken issue with even his adaptation.
You should have seen the intake. It could have swallowed a golf ball. Had the biggest WG out there too, opened up and smooth out. Have pic of back of carb but not intake.
Randy, this is motorcycle stuff but I'd like an opinion about a port shape, the logic of which has escaped me for quite some time. It has to do with the transfer ports. They were trapazoidal with the base (wider section) facing the cylinder head, and about 1/3 taller than they were at their widest point. The engine had two transfer ports one each side. They were very deep at their lowest point and only 1-2mm deep at their top edge. Almost as if they were an OP design but the jug was CP. Never could figure out what CZ was after with that particular arrangement. Got any ideas at all, because I am at a loss.
I ported 2 460 cylinders this morning when I couldn't sleep. One D shape with no machine work and finger ports and then a brand new mahle with the chamber and base cut without finger ports. Wonder which one will run better?
I'm willing to wait to find out!! Are you gonna use them both on your saw? Or are these for someone else's saws?
These are both mine. One will likely be sold as soon as I decide which one I like better. I'm going to test the new mahle first since I had the base gasket back on and the piston with the rings to the intake. I have to switch the piston around and delete the base gasket for the other jug. If the rain slacks up enough today I may get some run time on this one and a compression reading if I can find my adapter hose
