copmagnet80cc
New Member
I'm ordering a new jug for my 66cc 2 stroke motor..I'm wondering how much I need to port on the intake, exhaust and tranfer ports...I've heard a few measurments to go by but just want ideas from all yall..thanks
How much to port?
- Thread starter copmagnet80cc
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rogergendron1
New Member
Well if you dont know how to use a deg wheel and do not know how to measure port timing then i sugest measuring down from the deck hight . A larger measurement from deck to exhaust roof wil net a lower power band and high static comp but a shorter measurement from deck to exhaist roof will net a higher rpm and lower static comp powerband
anyway if you want a high rpm midrange to high end power band bike and just want to hash it out beginer style and know its going to work then widen the exhaust port 1mm each side and rais the exhaust port roof 1mm do not lower it any then lower the intake port 1mm and widen it as far as you can and trim the piston skirt to clear the port at top dead center then add transfer port and exhaust port ramps to further alter the timing . . . Dont worry about cutting the piston i have taken a whole 1/4 in off the entire skort on the intake side and a added large ramps on the dome and it ran like a beast at high rpms . Then deck ur head way way down or buy a puch or fred head and raise the comp and a sbp exhaust is simple and effective tpo
anyway if you want a high rpm midrange to high end power band bike and just want to hash it out beginer style and know its going to work then widen the exhaust port 1mm each side and rais the exhaust port roof 1mm do not lower it any then lower the intake port 1mm and widen it as far as you can and trim the piston skirt to clear the port at top dead center then add transfer port and exhaust port ramps to further alter the timing . . . Dont worry about cutting the piston i have taken a whole 1/4 in off the entire skort on the intake side and a added large ramps on the dome and it ran like a beast at high rpms . Then deck ur head way way down or buy a puch or fred head and raise the comp and a sbp exhaust is simple and effective tpo
rogergendron1
New Member
So widen bolth ports about 1mm each side . Lower the intake 1mm and raise the exhaust 1mm, trim the skirt of the piston to clear the intake port at top dead center then mark the dome of the piston and add ramps for the transfers and wxhaust port jist file 1mm ramps down the edge. . . This allong with a high comp head and an x chamber will give u a powerfull bike that will be reliable reguardless of what carb and intake you ise
Get a 50c protractor from the news agent, I don't do any port timing changes without one.
Then you need to give an idea what sort of power curve you want, and what sort of exhaust you will be using.
The jugs can vary a surprising amount with port timing, I like to know what I'm starting with before I change anything, Blow down time will be one of the major factors as to where you will get best power.
Transfer duration is where to start, and it is often better to lift the barrel with gasket and or spacer to get desired transfer time than it is ramping the piston or playing with transfer roofs.
Then lift the exhaust port to get the desired blowdown.
and trim piston to get intake time.
I widen the inlet a little, but it is good to keep the velocity up in the inlet port, so no need to over do it, but port match the inlet manifold.
I widen the exhaust considerably, and center it, so take a lot more from one side than I do the other, exhaust roof determines power charicteristics also and a flat wide roof will give a harder hit, more rounded will make the motor quieter.
Give the exhaust a good polish, port match manifold.
I match the cases to the transfer ports, I widen the base of the transfer ports giving a good taper to the port to increase velocity, I cut as much as I can from the lip and casting dags around transfer openings, And I get right up into the exhaust port side of the transfers and dig as much as I can out to redirect the flow.
Then use a piece of plastic hose and cigarette smoke to test the direction of flow.
Examples of port timings I have used would be.
Exh. for Low down 150 dur. For top rpm 168 dur?
Trans. I stick to around 120 slightly more for revs slightly less for grunt.
Inlet I stick to 120 deg for low down and 130 for more revs.
A big difference can be had! and even with my 'conservative' figures.
If your not after top speed, getting the port timing correct to my lower figures will give a very torquey and enjoyable ride with max revs in the 8000 area.
Then you need to give an idea what sort of power curve you want, and what sort of exhaust you will be using.
The jugs can vary a surprising amount with port timing, I like to know what I'm starting with before I change anything, Blow down time will be one of the major factors as to where you will get best power.
Transfer duration is where to start, and it is often better to lift the barrel with gasket and or spacer to get desired transfer time than it is ramping the piston or playing with transfer roofs.
Then lift the exhaust port to get the desired blowdown.
and trim piston to get intake time.
I widen the inlet a little, but it is good to keep the velocity up in the inlet port, so no need to over do it, but port match the inlet manifold.
I widen the exhaust considerably, and center it, so take a lot more from one side than I do the other, exhaust roof determines power charicteristics also and a flat wide roof will give a harder hit, more rounded will make the motor quieter.
Give the exhaust a good polish, port match manifold.
I match the cases to the transfer ports, I widen the base of the transfer ports giving a good taper to the port to increase velocity, I cut as much as I can from the lip and casting dags around transfer openings, And I get right up into the exhaust port side of the transfers and dig as much as I can out to redirect the flow.
Then use a piece of plastic hose and cigarette smoke to test the direction of flow.
Examples of port timings I have used would be.
Exh. for Low down 150 dur. For top rpm 168 dur?
Trans. I stick to around 120 slightly more for revs slightly less for grunt.
Inlet I stick to 120 deg for low down and 130 for more revs.
A big difference can be had! and even with my 'conservative' figures.
If your not after top speed, getting the port timing correct to my lower figures will give a very torquey and enjoyable ride with max revs in the 8000 area.
copmagnet80cc
New Member
Thanks! I've shaved down my stock angle cylinder head a little bit..I've already cleared the piston on the intake side already, and I've ramped my piston but not sure if it was done properly..thanks again though man!
Sorry but throw you angle fire head.
Unless you have no other choice due to space restrictions or you live somewhere really cold, the angle fire head struggles to cool these motors once improved, and does not preform as well as a center fire head.
Check and correct your squish, but after you get a different head.
Honestly, a well set up motor with high compression and an angle fire head will run hot.
Unless you have no other choice due to space restrictions or you live somewhere really cold, the angle fire head struggles to cool these motors once improved, and does not preform as well as a center fire head.
Check and correct your squish, but after you get a different head.
Honestly, a well set up motor with high compression and an angle fire head will run hot.
copmagnet80cc
New Member
Ive also heard some things about using J B weld to correct the transfer ports??
nsanecopilot
New Member
I know this is an older thread, but i just ported my top end "beginner style" with great results. After first opening up the intake manifold and chamber flange, I felt confident in going further. I cut the piston skirt down and smoothed the ports. The transfer ports were harder as i had to use a round file with patience and care. This engine has a nice upper midrange and is a little smoother. And a snappy throttle response
.