How to lightly port stock PA II cylinder?

I have to take the jug off anyway, to clean out some carbon. I might as well do a little bit of porting while I'm there. What's a good place to start?

I will only under stand if you say things like "widen exhaust port 1mm each side" or raise transfers 1mm. If you say increase exhaust duration to 170 I will have no idea what you're talking about. :)

Re: How to lightly port stock PA II cylinder?

Maybe start by matching everything ? Case and Exhaust

Re: How to lightly port stock PA II cylinder?

I will actually be getting to this tonight. I scored another hobbit yesterday and am starting to finish up going over everything. As long as everything is functioning properly, and it seems too, I will start porting tonight after we get done playing music.

Like Rick said, case and exhaust. I know the hobbit has huge transfers and can't remember if the jug matches them. At least I can raise the exhaust to match the proma I had sitting around. I'll chime in later if we don't smoke too much.

Re: How to lightly port stock PA II cylinder?

Do case/exhaust ports really not line up? Or are you referring to "blueprinting" per jennings.

Also "raise the exhaust to match the proma" makes no sense. Are you talking about matching the port outlet diameter to the ID of the exhaust header?

Re: How to lightly port stock PA II cylinder?

I'm with Jo on this...

can you explain as tho' we are 3yr olds please. MATCHING mean...cover the mope in gas, then light a couple of matches and toss them on it....'cause thats what i wanna do right now with mine.

Re: How to lightly port stock PA II cylinder?

yea, my bad. My pipe is right next to the computer. It's the first thing I see when I come in to break from wrenching.

Anyway, yea, it doesn't make sense, especially with a circuit. Raising the exhaust would decrease the distance from TDC to the exhaust port and thus advance the exhaust port timing, lengthening the port duration, and decreasing the compression ratio giving it more rev's for a pipe that can't support them and robbing it of bottom end.

for simples like me: don't make da exhaust hole bigger front to back, instead widen them, but don't go more than 62% of the bore. So if you have a bore of 38.6 mm, (that's about 49cc), you COULD widen it to about 23 mm, so long as the exhaust and every other f@$ing variable can support that. Also the rings, make sure you don't fuck with how the rings sit. Everything you do matters though and is a compromise, the shape, length, height, and texture of the port. Keep shape on the ports. Just start mild, and go bigger if you are feeling it.

I'll try to port pics. No promises though, it's the civil war game tonight.

Re: How to lightly port stock PA II cylinder?

Ummm yea... I spoke too soon. It's been a few months since I've been inside the top end.

There's no need to port anything. The transfers are huge on the case and could be matched only slightly on the jug. The exhaust port is 21mm, so is the circuit.

I just got all of the carbon out of there and cleaned up a bit. I cheated and threw a top end off my other hobbit before it was kitted. I got the hobbit with 93 miles on the odometer, so the rings, piston, and cylinder are gorgeous. sweet.

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