Porting

Tha rider

New Member
Joined
Dec 7, 2020
Messages
13
Help me out guys I removed the casting lips in each port I know how wide I should go but how high can I raise the exaust before it’s way to much
 


Akutey

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Joined
Dec 10, 2018
Messages
557
How and where do you ride? In the city? Flat open prairies?

60%-70% of bore width for port width maximum. Wide ports don't always mean wide band and can kill low end.

Hard to say their are no fast rules for height, need proper measurements to figure out proper port timing in relation to transfers for the blowdown.

Measure the exhaust and transfers from the top of the port and then the deck height. (Piston at TDC to cylinder deck) Or better yet port map it.
 

Tha rider

New Member
Joined
Dec 7, 2020
Messages
13
How and where do you ride? In the city? Flat open prairies?

60%-70% of bore width for port width maximum. Wide ports don't always mean wide band and can kill low end.

Hard to say their are no fast rules for height, need proper measurements to figure out proper port timing in relation to transfers for the blowdown.

Measure the exhaust and transfers from the top of the port and then the deck height. (Piston at TDC to cylinder deck) Or better yet port map it.
Yeah only thing I would have to measure is a tape measure I was gonna eye ball the whole thing just figure out how much I can go it’s a cdh 40mm stroke pk80
 

Tha rider

New Member
Joined
Dec 7, 2020
Messages
13
Yeah only thing I would have to measure is a tape measure I was gonna eye ball the whole thing just figure out how much I can go it’s a cdh 40mm stroke pk80
And also I live in Louisiana it’s very flat and I ride from country to town on it but looking to get more than 40 mph out of it I only have a head Reed and windowed piston wanted to do some porting cause it’s not fast enough after the upgrades I did
 

Akutey

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Joined
Dec 10, 2018
Messages
557
And also I live in Louisiana it’s very flat and I ride from country to town on it but looking to get more than 40 mph out of it I only have a head Reed and windowed piston wanted to do some porting cause it’s not fast enough after the upgrades I did

Well then you probably still want low end but good mid and high end. Still very doable with reeds. Nearly all modern bikes run reeds still. (Big topic)
Easiest is to fix your intake situation, carb dialed in and maybe switch to a 40T.

Reeds boost low and mid range. They tend to limit top power.
OZ Reed can be good if it's the 4 petal one with the wedge shape like the one in the picture.
Problem is most windowed pistons come with wrong timing. Too much or wrong place can be worse on performance.
You only need 140-160 degrees. Most can be done via notching the piston skirt. Too much with a fistfull of throttle will case blubbering and dying.

Tape measure is fine just don't use the end as 0 use any other and have the metal end clear the cylinder so its flat when measuring. I just ussally use the 1 foot mark. Sense whre talking about intake, measure the intake from the bottom of the port to the top. Guess the deck height, should be no more then say a dime at tdc. If it lower, theirs geometry issues, if their's more it's ok. Stamp marking on the conrod helps alot too. PK80 should have a FM80 stamp.
 

Tha rider

New Member
Joined
Dec 7, 2020
Messages
13
Well then you probably still want low end but good mid and high end. Still very doable with reeds. Nearly all modern bikes run reeds still. (Big topic)
Easiest is to fix your intake situation, carb dialed in and maybe switch to a 40T.

Reeds boost low and mid range. They tend to limit top power.
OZ Reed can be good if it's the 4 petal one with the wedge shape like the one in the picture.
Problem is most windowed pistons come with wrong timing. Too much or wrong place can be worse on performance.
You only need 140-160 degrees. Most can be done via notching the piston skirt. Too much with a fistfull of throttle will case blubbering and dying.

Tape measure is fine just don't use the end as 0 use any other and have the metal end clear the cylinder so its flat when measuring. I just ussally use the 1 foot mark. Sense whre talking about intake, measure the intake from the bottom of the port to the top. Guess the deck height, should be no more then say a dime at tdc. If it lower, theirs geometry issues, if their's more it's ok. Stamp marking on the conrod helps alot too. PK80 should have a FM80 stamp.
Thanks for the info and I’m at a 36 tooth sprocket and love it thinking about dropping to a 32 tooth for that bit more speed idc about being legal cause cops aren’t around here to much and don’t really bother you so trying to hit 55 and idc about low end I want it all up top I’ll pedal it out if I have to
 
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