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Discussion Starter · #1 ·
i picked up a blown 2004 pro x ves motor for 50 bucks from a friend, i am turning it into a race motor for one of my grass drag sleds. i have all the new pistons and everything to rebuild it. the cylinders are currently being honed. and i have some high comp heads on order.

now heres my questions-

--first off i want to do a little light porting to the cylinders, i have never done this before (i have all the rotary tools for the job) so if someone who has knowlege of two stroke performance porting, could you give me a little background on how to port and what my main objectives are? and please dont tell me to send it to a profesional cause i want to start doing this myself. i have two set of spare cylenders from the friend just in case.

--and the second question is about the exhaust valves? is there and kind of mods to do to them? can you do anything to them to make more power or torque? ive heard of putting stiffer or softer springs in them, what does that do?



thanks for the help guys,
nick
 

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Honestly, I'd look into another place for tech info like this. Give "The Crankshop" a call. They're in Vermont and Im sure they'd help you out. Also try HCS ( a lot of guys on there that modify these motors ). I know theres a few people on here that know a little, but a race shop is your best bet.
 

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Discussion Starter · #3 ·
yah ill give hcs a try too
 

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stiffer or softer springs would determine when the valves themselves would open up at
 

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fox440 said:
i picked up a blown 2004 pro x ves motor for 50 bucks from a friend, i am turning it into a race motor for one of my grass drag sleds. i have all the new pistons and everything to rebuild it. the cylinders are currently being honed. and i have some high comp heads on order.

now heres my questions-

--first off i want to do a little light porting to the cylinders, i have never done this before (i have all the rotary tools for the job) so if someone who has knowlege of two stroke performance porting, could you give me a little background on how to port and what my main objectives are? and please dont tell me to send it to a profesional cause i want to start doing this myself. i have two set of spare cylenders from the friend just in case.

--and the second question is about the exhaust valves? is there and kind of mods to do to them? can you do anything to them to make more power or torque? ive heard of putting stiffer or softer springs in them, what does that do?



thanks for the help guys,
nick
for the exhaust valve as you lift the roof of the exhaust port you might need to lift the vavle by adding gaskets or cutting the bottom of the valve. as you change springs you change the opening rate of the valve opening, that changes the power curve of the engine. test and tune on that to dial it in.

on the porting itself as you widen ports take a look at the shape of the port in the wall. the shape and angles as the ports come into the cylinder you want to keep the same, just moving up or over.

in all honesty talk to race logic.com for a template, for 80 dollars they send you an exhaust port template so you get all 3 cylinders the same, or 2 cylinders for the kids sleds, ha!. you dont need to raise the intake ports much more than a mm or two max.

race you can take the exhaust port to 70% or little bigger of bore, or as you change triple exhaust port shapes you can add lots of flow without making huge ports to be ring eaters.

my 1000 triple is based off 700 cylinders, i wish i could send you the drawings of the porting, but thats secret stuff for my engine.

the big thing is getting some pipes to get your rpms up to the 9000+ area. talk to jaws and see if they can get you some prostock race pipes for that engine. there not cheap but if hp is your goal then thats the way to go. also getting some real high comp heads where you need some 116 octane fuel will really make some more hp.
 

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Discussion Starter · #7 ·
okay thanks for the help, ill check into that template.
 

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you have to be honest with what you want. if you want just a hot trail or pure race. that will determine everything. for hot trail i would widen the exhaust port by 1mm on each side and move the roof up 1 mm, then maybe widen the triple exhuast ports some, but on the outside looking in you can really remove alot of the bridge between the triple ports and the main port,

on the transfers i would see if you can widen them at all, raise them about a mm,on the bottom of the cylinder and top of case the rear boost port can really be widened up, like a 1/16" on all 3 sides. sharpen bridges in the side transfers.

for the ring gap line you want to keep 4-5 mm wide in that area, between the front and rear main transfers, the ones on the side, you can get as little as .100" there,
 

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Just curious, does porting require rejetting or anything
 

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when i did a minor clean up on my first 800 xcr jetting stayed the same, but the nice thing was that with a nice setup the sled was making 165+ hp in "stock" trim and got the same milage or better than a lot of friends that had 600 and 700 cc machines.
 

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Discussion Starter · #11 ·
madcow said:
you have to be honest with what you want. if you want just a hot trail or pure race. that will determine everything. for hot trail i would widen the exhaust port by 1mm on each side and move the roof up 1 mm, then maybe widen the triple exhuast ports some, but on the outside looking in you can really remove alot of the bridge between the triple ports and the main port,

on the transfers i would see if you can widen them at all, raise them about a mm,on the bottom of the cylinder and top of case the rear boost port can really be widened up, like a 1/16" on all 3 sides. sharpen bridges in the side transfers.

for the ring gap line you want to keep 4-5 mm wide in that area, between the front and rear main transfers, the ones on the side, you can get as little as .100" there,
it sounds like your talking about a tripple cylinder engine? would this be the same for the polaris 600 twin ves that i have? but yah i just plan to do a hot trail porting as you stated, if this porting you are explaining is for my twin 600 could you go into more detail please if you could? [;)]

thanks,
nick
 

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its for all engines, everything for portings is mostly rule of thumb plus years of experience. i am learning both,

you need to keep the angle of the port side walls the same as they are now so air enters the cylinder the same, but you are just adding a little width to each port and hieght to each port, heck if all you did was open up the rear boost port on the case and bottom of the cylinder, knife edge the bridges in the side transfers and dechamfer the port windows. that little bit of work should be more hp gain than any aftermarket single pipe.

polaris already engineered the port shapes and stuff all you need to do is raise the roof on them and widen them out slightly.
 

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Discussion Starter · #13 ·
okay thanks for the help [thumb] one question tho, where is the rear boost port located?
 

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its the big port on the back of the cylinder. then to each side you have the rear main ports then the front main transfer ports then the exhaust triple ports then the main exhaust port.
 

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Discussion Starter · #15 ·
madcow said:
its the big port on the back of the cylinder. then to each side you have the rear main ports then the front main transfer ports then the exhaust triple ports then the main exhaust port.
okay thanks, you have been a load of help. ill start doing this as soon as i get the engine torn apart
 

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Discussion Starter · #16 ·
now is there anything i can do to the exhaust valves to get more power?
 

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Discussion Starter · #17 ·
springs? bellows?
 

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make sure the bellows are in good shape, the ves system doesnt make peak hp, it helps create low end power, by changing when the valve opens you change the shape of the power curve, if you have it open sooner you can loose some low speed hp. if you have it open to late you can loose upper midrange hp. i would leave it as is.
 

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Discussion Starter · #19 ·
madcow said:
make sure the bellows are in good shape, the ves system doesnt make peak hp, it helps create low end power, by changing when the valve opens you change the shape of the power curve, if you have it open sooner you can loose some low speed hp. if you have it open to late you can loose upper midrange hp. i would leave it as is.
okay makes sense, thanks
 
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