Is there any way to machine ports (like the 70cc puch kstar) into a cylinder that didn't have them to begin with? It seems as though there must be some way. I'm trying to pull a little more speed out of a highly ported stock cylinder. I can easily cut holes in my piston, but what about the grooves in the cylinder? Can this be done with a dremel if I create a jig so I don't cut too far in any direction?
Thanks,
Eric
I saw a post where a guy did something similar on an 80 metra which he had reedvalve-ized. I believe he used his intake port as a starting point and just raised a strip of it as a boost port.
I'm no expert but the intake on the K-star is much farther down the the bore of the cylinder which means that the holes in the piston never see the intake. you can cut the piston to match your ported transfers and the skirt so that it clears the intake at TDC.
Just measure well. I would love to see it done.
Make them even with the transfer ports and stop before the intake track. Use a marker on the piston skirt through the intake track at BDC so as not to cut your windows to far down.
I would start small and make them bigger and bigger until you are satisfied. They will have a strange effect on scavenging so you may actually see a boost in your bottom end torque to a point and then it may F it up. One cool perk is that your piston will be cooler because of the flow through it and the wrist pin.
Basically I would try and emulate the shape of the K-star ports as best as you can. I would cut straight down with a thin carbide dremel bit and then up to make a V shape so the ends are square, then work them to produce the arc shape. If that makes any sense to you.
You can also round the piston crown where it meets all your ports for better flow.
Good luck. Makes me want to buy a new piston and try it out on my old cylinder.
wait a way to increase low end on a k-star? any rules to piston cutting (skirt/dome) that i should know aboot?
You should be careful with cutting boost-ports. They may look simple, but the theory behind them is complex.
They work by directing a charge of fresh fuel over the top of the piston, to the top of the cylinder after the exhaust port opens and just before the transfers open. This way they force the remaining exhaustgasses out.
They need to be timed and directed well. Take a look at a cylinder with boostports. The ) shape is used to create a sort of venturi effect. The piston comes down, compressing the fuel into the port and then when the port opens it shoots it out, aimed at the top of the cylinder. Aim too low and you will blow fuel out of the exhaustport (Not a big problem, just a waste of fuel), aim too high and you will foul plugs like crazy.
And take care to mark the piston position in BDC through your intake, so your boostwindows will not show. If the windows show through the intake, your bike will run like crap.
^ and what he said!
Read Gordon Jennings book and you will get an idea of whats going on. I would start shallow, foul some plugs and work my way deeper and deeper until it seems to be in a sweet spot. Also I would leave the timing the same as the transfers but thats just me. Working slow will be the key. I would say that if you just cut them fully open to begin with you have a 50/50 chance of screwing it up, maybe a little more. The scavenging works via a big loop and as schijnheilig pointed out you could potentially aim the things incorrectly, also you will be introducing a new proprietary force into the equation. This in tern could interfere with the scavenging loop causing turbulence and pockets to be formed. Without sophisticated computer modeling its a crap shoot as to what will happen to flow in the cylinder.
What we can say is this: you will be slowing velocity and decreasing resistance (historically this means less torque and more rpm's), It is likely you will be aiding in scavenging at some point in the rpm band and hurting it in another (hopefully aiding it down low and your extra flow will make up for it up top)
Again read Gordon Jennings book and it will help. Also I wouldn't do this to a good cylinder you are afraid to ruin!
Rob the K-star already has these ports.
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