Milling intake 'port' in piston

I had an idea last night, and thought I would pass it by you all before I destroyed something experimenting.

I was thinking that if one were to mill out a half-circle shaped opening at top the base of the piston with the same diameter as your fuel intake, it would allow for more time for the engine to draw fuel into the crank case.

See attached picture for further explanation of what I'm thinking.

1225288695_piston.png

Re: Milling intake 'port' in piston

Yeah Moby's have that that on their piston but it's rectangle shaped..

I beleive if you do the intake side you should do the exhaust side to keep the piston balanced.

Re: Milling intake 'port' in piston

yeah its extending your intake duration by cutting your piston skirt.

Re: Milling intake 'port' in piston

no, mobys don't have that.

Its called piston skirt cutting, it will allow for a longer piston port open intake time. just do the math first so you don't take off too much.

example: my 70cc athena sachs kit has an asymetrical piston, the intake side is about 2mm shorter than the exhaust.

Re: Milling intake 'port' in piston

Actually, it just occurred to me that with this modification, although you are extending the duration of the actual in-flow of fuel, it could also (if done too much) create a situation where both the transfer ports and the intake port are open simultaneously for a brief period of time during the power stroke and could create a small burst of positive pressure in the intake manifold (a bad thing)... I suppose one just must be careful not to over do it... unless I could rig a reed valve into my stock build ;)

Re: Milling intake 'port' in piston

Be VERY careful. If you do not have a reed valve motor, this will change your intake timing. This is not necessarily a change for the better.

http://edj.net/2stroke/jennings/ Download the zip file, read that book first.

Re: Milling intake 'port' in piston

Hmmm my moby has the square hole in both sides of the piston.. I removed the lower part of the skirt to let even more fuel in..

Re: Milling intake 'port' in piston

mars!~

i did this on my a55 piston, and ive done it on my PUCH pistons with positive results.

dont take too much off.

and dont touch the exhaust side.

~SABAT!

Re: Milling intake 'port' in piston

Yea it works. It improved my top speed and hurt my low end a bit. Go easy on it.

Re: Milling intake 'port' in piston

Moped Game Sally Struthers /

i did this to a metra kit piston. it destroyed my low end, but i went too big. the port was about the size of half a quarter. i got that piston close to running again with a tricked out 3 shoe clutch...just need a day away from the lady to tune.

Re: Milling intake 'port' in piston

Moped Game Sally Struthers /

oh, hai mike!

Re: Milling intake 'port' in piston

On the negative side you will have less primary case compression because the piston will close the intake port later. Cutting the piston in that way will tilt the balance to provide more RPM but as others have said, be conservative

Re: Milling intake 'port' in piston

Though it has a skirt on the bottom it still has the cutout on the piston for more fuel

Re: Milling intake 'port' in piston

lets say 1/4 of a quarter is a safe mod.

any bigger is gonna affect your low end negatively.

maybe...

experiment experiment experiment.

ive got a few spare pistons kicking around mendon if you want one.

~SABAT!

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