Stock Puch Porting questions

does anyone have any maps they want to share? I've got a slew of cylinders that i'd like to start widening/raising or something.. 1hp intake ports are the smallest things ive ever seen.. comparing it to other stock cylinders i should be able to match them.. but i want to go bigger! anyone have any success?

Re: Stock Puch Porting questions

I did a stock high torque cylinder a while ago. widened the intake port and exhaust port a bit. I also trimmed the piston skirt to completely clear the transfers at TDC. This stuff is pretty "safe"

If you plan on raising or lowering the ports, there is a formula to follow in order to keep a well rounded powerband. Jennings has an entire chapter on this. Its a good read.

Re: Stock Puch Porting questions

First off, you NEED to read up on this before you start!

This is what I do and I've never had a problem:

Shorten the piston to where the casting mark is (if you have a low torque piston). Widen the exhaust and intake to 67% of the bore or to be on the safe side a little less (the bore is 38mm so don't go over 25.46mm). Use base gaskets to raise the cylinder until it has the powerband you want it to have. Measure the thickness of the base gaskets you take off and raise the exhaust port that amount. That should give you the results you want without having to do a lot of math.

Good luck,


Re: Stock Puch Porting questions

I forgot to tell you: make sure you lower the intake the same amount that you raise the exhaust.

Re: Stock Puch Porting questions

hmm awesome.. im going to have to get some nice dremel bits, doesnt seem too hard to go mm by mm and see the change!

curious about trimming the skirt, do you cut the pisont so its like a U cut out of it? or do you just shorten it all together?

Re: Stock Puch Porting questions

Jason I have been wanting to do this too. I have a bunch of stock cylinders so If you wanna get together and workshop this email me.

Re: Stock Puch Porting questions

You trim the whole piston skirt on both sides. I'm not sure if its true, but a lot of people say that if you don't it will be out of balance and wear out quicker. Anyway, it doesn't hurt to trim both sides.

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