After riding today i decided that the port job i did last weekend wasent cutting it so off came the cyl again and i added the boost port and below are pics of how i made my boost port map,i used a carbide dremel bit then cleaned it up with a sanding stone,i also didnt use a gasket on the cyl just some yamabond to bump the compression up a lil.
tommrrow im porting the carb the reed cage, tapering my needle and lighting the flywheel.
For anyone that missed my port pics before i added them in,that port job alone with out the boost port provided a killer low mid range.
first pic with the blue tape is how i mapped out my boost port i then traced out the port with a sharpie,2nd pic is after i removed the tape and the sharpie remains where i cut out.
last pic is where i removed the box with the sqiggly lines and put my 42F sig on it .
that looks like a 47cc barrell [ did you know that?] my 49cc barrell has 4 fins covering the transfere exterior case, as you can see in pic yours has only 3 fins over. check on this.
IMO I wouldn't even waste your time with adding a boost port unless you want to end up with a cracked cylinder, just ask Bryan and Lil'John. Plust they don't do $hit for performance, just look at my vid of my bike with a stock head and piston turning 13,350 rpms. It takes a special combination of things to make a boost port work correctly and most people don't understand that. You can make a stock cylinder scream and still be reliable if you know what to do.
IMO I wouldn't even waste your time with adding a boost port unless you want to end up with a cracked cylinder, just ask Bryan and Lil'John. Plust they don't do $hit for performance, just look at my vid of my bike with a stock head and piston turning 13,350 rpms. It takes a special combination of things to make a boost port work correctly and most people don't understand that. You can make a stock cylinder scream and still be reliable if you know what to do.
the problem with most boost vain cylinder ports are they are cut too deep, this will result in the premature cracking of the bores wall, if the depth is kept to no more than 2mm there is not a problem with any cracking. if you do know what you are doing with the machineing / cutting of cylinders to add these boost ports at the secret size and length there is no chance of a non boost ported cylinder / piston comparing, i do have single boost barrells reving in excess of 14,560 rpms and still have the needed torque / horsepower. would you like to see 17,000 rpms and a real screamer.
just cut mine on my buds milling machine...glad i filled the fins with epoxy since i started to bust through. trying to get that 55 degree roof angle is rough, didnt have a end mill that would cut that angle so tried to finish it with a dremmel bit.. boost port length is 26mm with angle ending at 30mm (transfer ports are 30mm). did anybody angle the roof of their transfers, i notice mine basically just stops with no chamfer (basically a 90 degree angle). the sides of the transfers look good, just wondering if the roof is supposed to be a right angle?
This is a very interesting article as I have been experimenting with porting of 49cc barrels with various & sometimes suprising results. But there is one puzzle I have that I ahvn't seen mentioned.
On the 49cc barrels, there is a vertical slot above the ehaust port. This slot depth, width & length varies from bike to bike. for example a luck 7 49cc barrel has a different size slot to a standard 49cc barrel.
Can anyone tell me what purpose this slot serves?
after the piston closes the exhaust port, the compression stroke starts & this slot reduces the compression duration.
Just out of interest the 47cc(40cc) version of this engine doesn't have this slot.
If I were to fill it, would it degrade the performance or increase it?
That slot is a compression relief to help ease starting. It does rob some performance but it would be impossible to fill it in completely as the piston rings would have to ride on it.
did you fill it with carbon or was it the carbon deposited by combusion?
I widened & raised the exhaust port on a barrel I experiment on & the result was huge top end poer but weak low & midrange. If i could fill that slot it should in theory compensate for that.
has anyone got any reccomendations of a filler material that i could use? I heard that "pyro putty" & liquid metal" could be used.
did you fill it with carbon or was it the carbon deposited by combusion?
I widened & raised the exhaust port on a barrel I experiment on & the result was huge top end poer but weak low & midrange. If i could fill that slot it should in theory compensate for that.
has anyone got any reccomendations of a filler material that i could use? I heard that "pyro putty" & liquid metal" could be used.
Next time only raise the exhaust port in the center and taper down to the sides so that the top of the exhaust port looks like an eye. That shape will give you good top end but will not sacrifice too much low end.
looks good dude but how would i go about widening mine when the boost port is in the center? do i just tape off inside the cylinder and gets to dremeling?
i dont know i runiend my first stock head trying to do it with a dremal but i seen dremal makes a mini drillpress now, im gonna get one soon i did the ones tonight on a drill press with a 8mm carbite tree bit its a stock 40mm head but i might have removed to much material off the piston its so thin im worried about it
just got to take her for a ride and holy #### it has some great top end doesnt idle real well but after the point were it use to fluter out it now pulls like mad not sure about the rpm but i would guess i gained alot it has way more pull than my ddm44 billet kit, top end, gona try it out in my cag soon with a 2 shoe and some lower gears 6-74 the only problem im having other than the idle most likely caused by the air leak in the carb,only problem is that its running lean with a 72 jet my 44 onlys needs a 68
but how would i go about widening mine when the boost port is in the center? do i just tape off inside the cylinder and gets to dremeling?
