HeadSmess
Well-Known Member
- Local time
- 11:34 PM
- Joined
- May 17, 2010
- Messages
- 3,048
a kx 125 has virtually all of the cylinder wall turned into holes for ports...different timings, different intakes, and a lot of pre-production design followed by lots of testing... these things are never going to perform the same way. EVER.
on that note, a good tuned pipe makes all the difference. i never bought any pipe as i make them myself, but all the talk on here says the banana pipes are pretty lousy. apparently adding a few inches (up to 8 or more?) to the header does wonders, as they seem "designed" for about 12k or more rpm... i say "designed" cus they arent! no, i cant point you to a decent pipe but there have been links to a few that look like the real deal on here... compare the basic outline of whats on the kx to whats available and with some experience, you can see the similarities. you want something that resembles the ktm50 type pipe, but even longer for the lower rpm... pipe design is complicated but they all follow the same pattern, so to speak. angles affect the strength of the powerband, length affects the RPM it comes in at, and length then changes the angles... confusing! the banana pipe is just designed so its easy to make, no more.
trimming the piston skirt does help, but if you remove too much, you need a new piston. start by just removing 1-2mm at a time, you really still need a few mm left exposed when pistons at TDC. i usually scribe a line while its at TDC and trim to within 2mm of it. remember to chamfer the trimmed edge slightly, a curved notch (use half round file) is better than flat. overdo it and you lose all the low rpm power.
fiddling with the length of intake manifold also helps, try to do those mods with no exhaust pipe at all... or set it up with a over sized header into a large auto type silencer, so you dont get any effects from the exhaust pipe.
the parts are cheap, so there is no harm in experimenting, but when doing port work, start with the least work possible until you know what works for you... make one change at a time so you know whats doing what, be prepared to push home occasionally... i gave up on porting too much as my custom built pipes were always based on standard port timings... too much work to redesign a pipe and make it each time!
dental drills off ebay are way better for porting than a dremel...you can get right into the transfers etc and remove all the casting flash.they are also cheap
you do need a source of compressed air, about 30psi, to run them... a full kit on ebay is still cheaper than a dremel.
ramping the top of the piston helps in making decisions on port changes before hacking into the cylinder itself, but the ramps in the piston affect combustion characteristics as well, so dont use a ramped piston instead of changing the cylinder if happy with the results.
get a degree wheel if you want to do porting...
here we go again...
reading material. read it a few times...
http://www.amrca.com/tech/tuners.pdf
on that note, a good tuned pipe makes all the difference. i never bought any pipe as i make them myself, but all the talk on here says the banana pipes are pretty lousy. apparently adding a few inches (up to 8 or more?) to the header does wonders, as they seem "designed" for about 12k or more rpm... i say "designed" cus they arent! no, i cant point you to a decent pipe but there have been links to a few that look like the real deal on here... compare the basic outline of whats on the kx to whats available and with some experience, you can see the similarities. you want something that resembles the ktm50 type pipe, but even longer for the lower rpm... pipe design is complicated but they all follow the same pattern, so to speak. angles affect the strength of the powerband, length affects the RPM it comes in at, and length then changes the angles... confusing! the banana pipe is just designed so its easy to make, no more.
trimming the piston skirt does help, but if you remove too much, you need a new piston. start by just removing 1-2mm at a time, you really still need a few mm left exposed when pistons at TDC. i usually scribe a line while its at TDC and trim to within 2mm of it. remember to chamfer the trimmed edge slightly, a curved notch (use half round file) is better than flat. overdo it and you lose all the low rpm power.
fiddling with the length of intake manifold also helps, try to do those mods with no exhaust pipe at all... or set it up with a over sized header into a large auto type silencer, so you dont get any effects from the exhaust pipe.
the parts are cheap, so there is no harm in experimenting, but when doing port work, start with the least work possible until you know what works for you... make one change at a time so you know whats doing what, be prepared to push home occasionally... i gave up on porting too much as my custom built pipes were always based on standard port timings... too much work to redesign a pipe and make it each time!
dental drills off ebay are way better for porting than a dremel...you can get right into the transfers etc and remove all the casting flash.they are also cheap
you do need a source of compressed air, about 30psi, to run them... a full kit on ebay is still cheaper than a dremel.ramping the top of the piston helps in making decisions on port changes before hacking into the cylinder itself, but the ramps in the piston affect combustion characteristics as well, so dont use a ramped piston instead of changing the cylinder if happy with the results.
get a degree wheel if you want to do porting...
here we go again...
reading material. read it a few times...
http://www.amrca.com/tech/tuners.pdf
