Epoxy in the rear transfer ports

[sidecase]

I found an old article in a Dirt Bike Magazine article by Eric Gorr were he was using epoxy in the rear transfer ports of a cr 250 to change the power band for low to mid power. Has anyone ever done this on their own? I gathered from the article that the epoxy changes the direction of flow of the rear transfers to improve loop scavenging efficency. In stock form the rear transfers are aimed at the exhaust port pushing the burnt gases out faster. With the expoxy in place, the flow was aimed more towards the rear of the cylinder (near the intake). What effect does this mod have on top end power? Do you lose all top end, a little top end, or no top end?
I also have been reading the forums here for a while and see that a lot of people get their cylinder base turned down to get more bottom end power. Is this a necessary mod to increase bottom to mid power or can you acheive a bottom to mid power increase with porting alone? Once you have the base of the cylinder turned down there is no turning back if you don't like the the shift of power to the bottom end. I have a 2001 CR500 and have been contemplating some porting work and I am just trying to get a feel of which direction I should head to increase performance. I primarily ride the eastern PA woods with lots of hill climbs, muddy and rocky trails with roots. My final question is how much could I have shaved off the head to increase the compression without having to run race gas? I run super 93 in the bike right now. I am trying to learn as much as I can because once the cylinder is ported, there is no going back to the stock power band characteristics without buying a new cylinder. Thanks

 

[Faded]

More than likely Eric can do the Mo Betta porting package, which will increase the power everywhere, enhancing the stock powerband. On the '98 CR250 we sent him for the Mo Betta he did epoxy the transfers. There was a big gain in bottom end compared to stock. It didn't get broke in all the way, otherwise I'd be able to comment on how the top end felt.

Why you want to port a CR500 is beyond me though, my only CR500 experience involved a '99 CR500 WFO in 2nd :scream: and a chain link fence...the result was a dislocated shoulder. Since then I tend to shy away from 500s.

 

[marcusgunby]

If you shave the cylinder you can stack a few base gaskets to put it back to std.As well, you can fit epoxy and if its not right you can remove it.It depends on how far out the std porting is-if std its totally aimed at top end it may need both mods(like maybe a 2001 CR250)the Cr500 i guess is capable of alot more power as they are tuned to enable most rider to live for more than a week;)

 

[sidecase]

Thanks Guys

 

[EricGorr]

Right now I picture the editor of Dirt Bike, Ron Lawson, choking on his coffee reading my name associated with his magazine, yeah I'm his number 1 cub reporter :eek:

Actually it was Dirt Rider where you read that article. I was a contributing editor and founded the Ask Dr. Dirt column and worked there from 1988-98

Time to put all those old copies of magazines in the garage sale and just click on DRN from now on.

 

[flynbryan]

:thumb: I remeber you doing those articles as well Eric. I have to say that MUCH of my current knowledge came from reading your articles(as well as others) in Dirt Rider Magazine when I first got into the sport. And Eric is right sidecase, There is a vast plethora of educated gentlemen(and ladies :eek: ) and chances are you can find SOMEONE here who has had the same scenario on a topic as yourself. And if not ask Eric:) Thanks again for the time/sponsorship you put into this forum Eric. :worship: As a matter of fact my uncle is sending you a cylinder here shortly. You made a good impression on him a few yrs. back and has sworn by you to me ever since. Keep up the good work. :thumb:

 

[steve.emma]

what sort of epoxy do you use though? and do you ever have problems with the epoxy not sticking to the port surface and falling into the cylinder? how does it handle the heat and fuel in the ports?

 

[Faded]

Originally posted by steve.emma
what sort of epoxy do you use though

Check it.

 

[shifting]

I own a 98 cr250 that Eric Gorr got a hold of. He gave it the Mo-betta port job. The bottom end is unreal. But the best thing is how much midrange and topend I have. I can pull anyhill in 3rd where as before I had to down shift. It does have the epoxy in the ports. The 98 cr Faded refered to is this one.