Porting
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Lukesky36
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Well i only did a piston skirt trim once only because it was not clearing the intake at TDC it does help it breath more on the mid to high rpm but sucks a little power out of the low rpm range it is the easiest mod only way to find out is to take your intake pipe off and check
Cozmik Mezzenger
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FNTPuck
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Be careful skirting pistons just from the cylinder and a loose piston like that video. TDC will depend on base gasket thickness and cylinder casting and can change from motor to motor. By eyeballing and marking TDC as just making the piston crown even with the deck you can easily remove too much of the skirt and have too much duration when assembled, leaving your motor gutless down low.
Proper method is to assemble the top end to the bottom end using the same gasket you will be running, rotate the motor until the piston stops moving up but before it starts moving down (there is some dwell at TDC) and then marking the exposed piston skirt through the intake with a marker. Then you know exactly how much needs to be trimmed. Some motors dont need ANY, and have no overlap into the port while others may need a lot of material removed.
Proper method is to assemble the top end to the bottom end using the same gasket you will be running, rotate the motor until the piston stops moving up but before it starts moving down (there is some dwell at TDC) and then marking the exposed piston skirt through the intake with a marker. Then you know exactly how much needs to be trimmed. Some motors dont need ANY, and have no overlap into the port while others may need a lot of material removed.
HeadSmess
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educate yourself by reading this several times...
http://www.amrca.com/tech/tuners.pdf
buy several cylinders and twice as many pistons (and rings), then get on ebay and order some of these...
https://www.ebay.com.au/itm/USA-Sal...=item3ab8321a5a:g:em8AAOSwa~BYP4JE:rk:27:pf:0
dont waste your time with a dremel. they are useless.
you port the CYLINDER, not the head.
when it comes to changing port heights, trim the piston FIRST, test it out, then port the cylinder to the new timing, with an untrimmed piston.
be careful with the intake port skirt trimming. youre better off making it wider in the port to keep the same timing, but giving more area to get more air in there.
transfer matching, angles of transfers, flow of gases...
porting an engine is down to imagination in visualising the gas flow, being sensible, only making one change at a time, plenty of testing, and experience.
run straight intake and exhaust manifolds to analyse any changes in performance.
then tune the manifold to suit the intake timing, and, if youre that keen, design and fabricate a tuned exhaust to take advantage of the transfer/exhaust timing.
throw all the bling at it you want. none of it fixes the issues with port timing though. that you have to do yourself, and has much better results than silly anodised alloy bits.
yes, expect to destroy five or more cylinders in the learning process.
its an idea to get a cast iron sleeved cylinder so theres no problems with chrome plating no longer running into the ports and protecting their edges... and its hard to destroy a cast iron sleeve when something lets go.
http://www.amrca.com/tech/tuners.pdf
buy several cylinders and twice as many pistons (and rings), then get on ebay and order some of these...
https://www.ebay.com.au/itm/USA-Sal...=item3ab8321a5a:g:em8AAOSwa~BYP4JE:rk:27:pf:0
dont waste your time with a dremel. they are useless.
you port the CYLINDER, not the head.
when it comes to changing port heights, trim the piston FIRST, test it out, then port the cylinder to the new timing, with an untrimmed piston.
be careful with the intake port skirt trimming. youre better off making it wider in the port to keep the same timing, but giving more area to get more air in there.
transfer matching, angles of transfers, flow of gases...
porting an engine is down to imagination in visualising the gas flow, being sensible, only making one change at a time, plenty of testing, and experience.
run straight intake and exhaust manifolds to analyse any changes in performance.
then tune the manifold to suit the intake timing, and, if youre that keen, design and fabricate a tuned exhaust to take advantage of the transfer/exhaust timing.
throw all the bling at it you want. none of it fixes the issues with port timing though. that you have to do yourself, and has much better results than silly anodised alloy bits.
yes, expect to destroy five or more cylinders in the learning process.
its an idea to get a cast iron sleeved cylinder so theres no problems with chrome plating no longer running into the ports and protecting their edges... and its hard to destroy a cast iron sleeve when something lets go.
Links to eBay may include affiliate code. If you click on an eBay link and make a purchase, this forum may earn a small commission.
I disagree with destroying 5 or more cylinders. If the person takes his or her time and does whats mentioned here there should be no problems, also there is nothing wrong with skirting piston, opening intake, exhaust ports & transfers...I get your point as I have see some guys do some pretty strange stuff channeling the cylinders...
Links to eBay may include affiliate code. If you click on an eBay link and make a purchase, this forum may earn a small commission.
HeadSmess
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five cylinders. minimum.
you never played guitar before but get up on stage and prove to be a virtuoso?
you start hacking people open like arigo (look him up) but never studied medicine?
porting a cylinder LOOKS easy. sounds easy. just hacking out stuff right?
no way.
porting is an art, a skill.
reading the head, the piston, the engine sound...is it really better? faster? more powerful? and then... was it rich, lean? was that my latest porting work or jetting that needs a tweak?
despite all the maths and all the research... what actually goes on inside the cylinder when the engine is running is unknown... its ALL imagination that gets us this far!
and experience.
the angles... curves... and repeating them!
its fun to play with water and pipes to get an idea of chaos and fluid dynamics... it isnt always doing what you think it is.
that whole "scavenging loop" of the port angles and people chucking in boost ports is a whole grey area. just cus a CR125 has a boost port doesnt mean a chinese clone of a russian 1950s engine should...
crankcase stuffing, etc... you have to look at it all as a whole, not just optimise one area... and gradual, gradual... so much testing!
imagination (marketing targets exactly that! companies make money off your desires, not necessarily actual effects)
you have to make at least two anchors before you start to fly.... perfection is never attained from then onwards.
and there are the accidents... damn. holed piston.
my favourite is too much width on the exhaust port causing the ring retaining pins to come out
gotta have covered retainers if you widen the exhaust much more... and that means modifying pistons, sourcing alternate rings that cover the retainers and/or alternate pistons...
experience...
you never played guitar before but get up on stage and prove to be a virtuoso?
you start hacking people open like arigo (look him up) but never studied medicine?
porting a cylinder LOOKS easy. sounds easy. just hacking out stuff right?
no way.
porting is an art, a skill.
reading the head, the piston, the engine sound...is it really better? faster? more powerful? and then... was it rich, lean? was that my latest porting work or jetting that needs a tweak?
despite all the maths and all the research... what actually goes on inside the cylinder when the engine is running is unknown... its ALL imagination that gets us this far!
and experience.
the angles... curves... and repeating them!
its fun to play with water and pipes to get an idea of chaos and fluid dynamics... it isnt always doing what you think it is.
that whole "scavenging loop" of the port angles and people chucking in boost ports is a whole grey area. just cus a CR125 has a boost port doesnt mean a chinese clone of a russian 1950s engine should...
crankcase stuffing, etc... you have to look at it all as a whole, not just optimise one area... and gradual, gradual... so much testing!
imagination (marketing targets exactly that! companies make money off your desires, not necessarily actual effects)
you have to make at least two anchors before you start to fly.... perfection is never attained from then onwards.
and there are the accidents... damn. holed piston.
my favourite is too much width on the exhaust port causing the ring retaining pins to come out
gotta have covered retainers if you widen the exhaust much more... and that means modifying pistons, sourcing alternate rings that cover the retainers and/or alternate pistons...experience...
Last edited:
Spare_Parts
Well-Known Member
Come on man, you're going overboard. I haven't destroyed any cylinders, all have been better then stock. Not all where a goid job but not trash either. Nobody is a porting god from the get go. You are making statments as facts that came from nowhere. Stuff Jaguar would say.
Knowledge is key. Search and read. Jennings and Bell are names you should get to know. Both have books that have been post here and all over the web. 2stroke stuffing on you tube has some great info. A rotory tool and burr set is fine. Sanding rolls are great to finish the ports. And if you like you can polish the exhaust port.
Too much width on an exhaust port? 32mm is what I run and 32.9mm is max safe. Don't see a first timer going that far. Has to taper up to 26mm or smaller.
Knowledge is key. Search and read. Jennings and Bell are names you should get to know. Both have books that have been post here and all over the web. 2stroke stuffing on you tube has some great info. A rotory tool and burr set is fine. Sanding rolls are great to finish the ports. And if you like you can polish the exhaust port.
Too much width on an exhaust port? 32mm is what I run and 32.9mm is max safe. Don't see a first timer going that far. Has to taper up to 26mm or smaller.
D
Deleted member 12676
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The more round the top of the exhaust port, the wider the powerband. Always widen a port before messing with its height. This is a bit complex because the three ports (intake, transfers, exhaust) all have their own powerband depending on their height and width. Here's my write-up on porting these chinese engines: http://www.dragonfly75.com/motorbike/timing.html
Street Ryderz
Well-Known Member
Jag have you even seen a current cylinder? Because they currently go against all you suggest as being correct, they have 160+ psi and I've had some over 170 psi right out of the box!The exhaust ports now start at 26mm below the deck that's 154 degrees of duration,transfers have been raised to 30mm from deck that's 125 degrees duration with 13.92 degrees of blow down stock.Now from there what works best is raising the exhaust to get 160 degrees duration and that makes the blow down 17.15 degrees of duration without sacrifice of lost torque.Port width for the exhaust can be 28-32mm safely and should be converted to the equivalent dia so as not to exceed a 23mm dia window and flat across the top yeilds way more power with a pipe than round,round bleeds off the initail pressure slightly ahead of the mass volume witch effects the scavenging and how it aids the pull on transfers.Slightly rounded at the window top helps the rings not catch but the inside roof of port is flat on all performance oriented 2t's.
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