BannedCR500Riders.com

OK so here is the story. I am currently building a cr500 engine for oval ice racing and i want to know if i'm on the right track.My objective is to build a mostly mid to top powerband.

so here is what i have come up with right now with all the info i gathered over the net.

Porting : raise exaust port 4mm and boost port 1mm... ( any suggestions on anything more agressive than that??)

Head: Machine the head for a .9mm squish.
machine the combustion chamber for a less deap combustion chamber.

I don't really know what compression ratio i should run for a top end motor......(????)

Intake: PWK39 soon to be 41.5....... stock reed cage.

Exaust: PC pipe and exaust......( also have fmf gnarly)

Ignition: CR250 2001 stator , cdi, cr500 coil......

Gaz: depending on the compression ratio......( i wanted to make my own racegas mix with either toluene and xylene but i can't find it anywhere here in quebec canada...)



by the way this is an AF.....

"86" the bridge......

I agree w/ 808, ditch the bridge, raise the port to about 200* (probably like 5-6mm, but degree it anyway) run like 150*int on teh transfers and upper boost port. open the shit out of the side boost ports and if you're brave enough drill some aditional transfers.
you want low compression unless you are running alky. you are on the right track w/ the head.
I wouldn't do a PC, you should go custom, or even modify an existing pipe. PC pipes have strong mid and suck everywhere else. you can have a fmf gnarly modified to be much better, or even find yourself an old fatty or signature from FMF, they are some kickass pipes.
the fact remains, no matter what you do to a 500, it will never rev like a 250, so don't expect it to.

I don't really want to make it rev like a 250.....
I just want to extract the most HP i can out of it. With the knowledge and ressources i have....

The jug that was on the bike when i bought it has some work on it. I don't know if the exaust port was raised or anything but the intake and exaust bridge is alot larger than my stock cylinder. I did some tests with both Procircuit and fmf gnarly.

I thought because of this it would work better with de PC. I didn't want to have porting for high end power with a low end pipe.

PC: no low end ..... no middle......top was a little better.......The only significant thing i noticed was that the bike went faster lol

Gnarly: good low end.......MONSTER middle.....poor top end

I never thaugh a pipe would make all that diffrence but i think the jug was probably set up for torque.

I'm gonna take it appart and take mesurments...compare it to my stocker...

bvmbvm

39pwk and 95 250 ignition really woke mine up.

if the exhaust was already widened, then you can't remove the bridge.

my 86 jug is almost 79mm wide at the exhaust port and bridgeless

dannygraves wrote:if the exhaust was already widened, then you can't remove the bridge.

If the bridge is "relieved" and the ring dosent touch it ..... What difference does it make if the clearence is 0.001", or infinity.

If it dont touch.. it dont touch.

ya, um, my exhaust port is almost the width of the piston, almost touches the transfers and the releived bridge does get touched by the rings, so I cannot remove that bridge. If I remember correctly it was either 78 or 80mm was what the math came out to for the maximum width for a bridgeless setup and mine was well into the 80mm range, like 85 or 87, can't really remember.

widening the stock shape of the exhaust and removing the bridge is a bad idea if you ask me. now if you were to rework the exhaust to an eliptical shape then remove the bridge, that would be cool. when i ported my '98, i took the top of the exhaust to almost the diameter of the bore, darn near 89mm, no way in hell am i removing the bridge because it eases the rings back into position so they dont snag the roof of the port, the piston and rings would certainly suffer a very fast death if i removed it. becarefull and understand what your doing before you go hacking and grinding

dannygraves wrote:you should go custom, or even modify an existing pipe.

You have any experience with modified pipes you would like to share?

I have alway wanted to shorten a pipe, but havent had the chance yet

CR480R wrote:

dannygraves wrote:you should go custom, or even modify an existing pipe.

You have any experience with modified pipes you would like to share?

I have alway wanted to shorten a pipe, but havent had the chance yet

I've got one that dewayne did, but haven't had a chance to try it. DeWayne swears by it. I was gonna try it out on the gen-1 last time at dumont, but mfdb wanted to see how the improvements on his 450 went and asked me not to touch my bike from the previous ride. I'll be running it next time in the sand, maybe at pismo, if not definitly when the season starts back up at dumont.

I think i will go with those porting specs danny.....but idont want to ditch de bridge.

Does anybody have any spec pictures or any information on midified pipes?? do i go longer or shorter???
I know a guy who builds his own costum pipes for his snowmobile.... he could help me out but i just want to have a little more info.

I definatly want to have a run on the dyno with this baby once i'm done. I'm still waiting for my PC silencer and pwk39 i ordered from ebay and still don't know what compression ratio i'm gonna run....????

thanks alot guys for the infos.....

you want to shorten the head pipe to get more revs. I believe dewayne shortened my gnarly by over half an inch at the head pipe, then modified the cone area and opened up some othr parts. give him a call if you want to know more about it, his number is in the approved vendor section.

if you keep the bridge, like I did, then widen the crap out of the exhaust port and even narrow down the bridge. I had a thread on some of the porting I did on the gen-1 here somewhere.

i'll be seeing a gnarly moded by dewayne soon too, i'll see whats up, apparently hes balooning the chamber and removing the clearence dents

thats what he did on mine

is there any chance of having plans or spec for a modified gnarly??
I don't want to ship my pipe all the way to the us when i can get it done here.......