puch porting question

This is my first time posting to mopedarmy, so here it goes. My only bike has a 1 hp cylinder on an e50 engine. I have an extra cylinder so I figured I would give porting a shot. I've been reading on puchforum.net quite a lot and I've seen a port map of a 50cc airsal cylinder. The mopedwiki said that it is best to model a ported cylinder after a fast cylinder so I'm giving it a go.

So far, I've ported most of my cylinder after the airsal fast 50cc kit.

The intake is 10mm by 10 mm and I want it to be 10mm by 27mm, but the stock intake is 5mm higher than my soon to be ported intake. My question is, will it ruin my cylinder to make the intake as large as the airsal and move the enlarge the port to be 15mm by 27mm? Will it mess up the ideal port time area?

My piston is cut to 49mm which is the same as the airsal, so will that make the timing ok?

The picture shows the airsal port map with my intake in place over the airsal intake.

Airsal port map from puchforum.net

Will it work? If I ruin the cylinder, I have another, but I hate to mess up if I can help it.



Re: puch porting question

Yea! First try pic worked!

Re: puch porting question

Bump please? Somebody has to know.

Re: puch porting question

First, let me say I know very little about 2-stroke engines.

Second, I was hoping someone would replay because I am interested in a similar modification.

Finally, I will give my opinions based on what I have come to understand so far...

The location and size of the ports are in effect the "camshaft" of the engine. Reworking the intake port as you propose is like installing a cam with more lift and opening the intake valve earlier TDC and closing it later after TDC. If you put a degree wheel on the flywheel you could actually measure timings. Perhaps overlap as well.

Anyway, if opening the intake port is the way you go, I don't see why you need to make it the full 15 by 27. Why not make the shape more like an inverted "T"? With just the portion of the original window peeking above the airsal window.

Has anyone ever discussed ports in terms of crank degrees?

Re: puch porting question

Jason Jason Bobason /

Read A. Graham Bell's book on two stoke performance tuning. It will tell you everything you want to know (and then some).

Re: puch porting question

It will work ....did that cylinder have that case hardened plug in it... make the intake wider under the old one so your new intake port would have a little square notch in the top of it...that will keep intake signal stronger and not be so boggy...the width of the intake is what ever the cylinder can hold ...1/8 of cylinder surface is good for sealing...you might want to start mearuring ports in degrees instead of measuring down from top of cylinder...thats covered in the book written by the real guru...hope you have good results

Re: puch porting question

So, all you're doing is enlarging the inlet with 10 by 5 upwards? Or did I misread that?

Unless you want to mount a carb which is too big for the current inlet, I don't know why you would want to enlarge the inlet? You'll only notice performance differences when you start messing with the inlet timing, for which you have to enlarge it the other way, to the back.

Also, if you're gonna do it, make sure your pistonrings won't go into the inlet! If so, you can say goodbye to your cylinder...

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