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Discussion Starter · #1 ·
just want to get any feed back on the new 50cc bzm 6 port cyclinder. i am building one for a customer but wont know any performance #'s untill i get-r-done. i just cant believe bzm is calling it a 6 port because they divided up the boost port, i mean they had to because of where the piston pin is located, so why is polini's 40cc 3 port not a 4 port as their boost port is divided also. well someone chime in and give us some info.
 

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Is the port area of the divided port the same as the undivided?If it is the same then there shouldn't be any drastic change.If the port area is larger,then the volume will have changed and would cause a drop in operating rpm,as confirmed by some other people I have spoken to.If this is infact true,then anyone running the larger tracks may actually be at a disadvantage due to the lower peak rpm as compared to the 5 port.

I would think if the volume has increased then you'll need to replace the volume somewhere else,including running larger carbs,but then you will be limited by the reed cage,it will only flow so much,remember small engines are pretty touchy when it comes to altering case volumes,seems they did it just to compensate for the error in the ring gap placement.

I don't have one here so this is purely speculative,but seems logical.


Tom
 

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Discussion Starter · #3 ·
yes i agree with you Tom, i think anyone running this cyclinder MUST run a race crank to get the crankcase pressure up to get some velocity in those huge transfer ports. i think that is one reason why polini on the gp3 cyclinder has the boost port lower than the transfer, to keep the inital velocity in the tranfers up untill the boost port opens. just my 2 cents
 

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grumpy old man
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bulldawg racing said:


I would think if the volume has increased then you'll need to replace the volume somewhere else,including running larger carbs,but then you will be limited by the reed cage,it will only flow so much,remember small engines are pretty touchy when it comes to altering case volumes,seems they did it just to compensate for the error in the ring gap placement.

I don't have one here so this is purely speculative,but seems logical.


Tom

it would seem more logical to move the ring gap rather than design a cylinder (compensate) around it . i see it this way... its much easier from a manufacturing standpoint to to change a location of were a hole is drilled and pin is pressed in on a piston compared to changing cavities, cores ,etc. . they would have to have a shit load of pistons already drilled laying around to justify the cost of that endeavor .

while i can see inside to boost area i will speculate that it was done for the purpose of changing direction of the boost charge . weather they want the two areas to converge at a focused point or the two areas to spread out across the combustion chamber...... either way this should easily be answered simply how the boost port areas look inside .............j
 

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(72) said:
it would seem more logical to move the ring gap rather than design a cylinder (compensate) around it . i see it this way... its much easier from a manufacturing standpoint to to change a location of were a hole is drilled and pin is pressed in on a piston compared to changing cavities, cores ,etc. . they would have to have a shit load of pistons already drilled laying around to justify the cost of that endeavor .

while i can see inside to boost area i will speculate that it was done for the purpose of changing direction of the boost charge . weather they want the two areas to converge at a focused point or the two areas to spread out across the combustion chamber...... either way this should easily be answered simply how the boost port areas look inside .............j
I can see what your saying about the pistons,but If they are ordering in bulk for pricing reasons from an outside company,well there's your parts laying around.

I'm not seeing why you would split the boost charge like that,it would screw with the charge flow around the cylinder,if you think about it,if you split the charge and spread it around in such a small area,it could easily short circuit the flow and cause a decrease in preformance.Seems most of the big motors use one large boost port to avoid that problem and focus the large charge toward the center of the combustion chamber to help with the scavanging process.

just thinking aloud,I'm sure I am totally wrong,I'll see when I get one here in the shop.

Tom
 

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grumpy old man
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bulldawg racing said:
I'm not seeing why you would split the boost charge like that,it would screw with the charge flow around the cylinder,if you think about it,if you split the charge and spread it around in such a small area,it could easily short circuit the flow and cause a decrease in preformance.Seems most of the big motors use one large boost port to avoid that problem and focus the large charge toward the center of the combustion chamber to help with the scavanging process.

Tom
the one large boost port effectly blows accross the cylinders combustion chamber , it (pulse) opens up as soon as it leaves the port and spreads (pressure diference an such). with the curve of the cylinder the two ports could have a focused charge if diveded properly(were the two hit each other )...say around the center of the cylinder/combustion chamber and then spread out creating a point of higher than normal pressure and being wider(starting out) have a wider area moving more gases toward the exaust side ........... thinking aloud myself..................j
 

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grumpy old man
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this is what i was kinda thinking tom......... i know its not accurate and only one dimential , but i hope the pic helps get my thinking across . the angles of the inner (dividing bar) and outer walls of the split port will have an effect on the direction of the charge.....j
 

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