Off topic (cr250) Porting gurus, take a look!

[latheboy]

This is a cylinder I took off a CR250. Unknown history other than it currently doesnt seem real fast. I see a cleanup type port job, by someone unknown. The all the ports seem to be stock size and height. The intake area is hogged out a little. But in the transfer ports, there is two large hunks of expoy or something making thetransfer tunnels smaller. The transfer windows are not affected. Why would someone do this? What will the motor act like if I remove the epoxy? This bike will be flattracked and ice raced at WOT most all the time..... below is a phone photo of what i am talking about.
http://i460.photobucket.com/albums/qq330/latheboy/20110528192305.jpg

[All250R]

There really isn't enough information here to give a quality answer. There are so many variables that go into making an engine run poorly or well. That is an odd modification though in my estimation. I'm not sure how that would make it run better, but for higher rpm applications, I can't imagine it helping in many scenarios.

[jcs003]

i know nothing when it comes to porting. but one thing i can say is the volume of air entering the cylinder is measurable at different engine speeds and modifying the port chambers changes this. my thought is that whoever did this was changing the volume of air/fuel into that specific area to change the performance of the engine. but, logically speaking; restriction and turbulence in flow is counter productive.

[latheboy]

Thanks for all your input. I will probably be removing the epoxy. As mentioned, I just can't think of a good reason why someone would do this, unless they ported into the water jacket. Overall the porting doesnt look aggressive tho. Maybe it will be clear why the porter didnt engrave the cylinder and take credit for their work........

[machwon]

It's probably an Eric Gorr recommendation or perhaps he ported the cylinder.

[latheboy]

Do you know what the theory this?

[stever250r]

Quick Search brought up a few discussions...

http://www.thumpertalk.com/forum/archive/index.php/t-921007.html

http://www.network54.com/Forum/186548/thread/1047292584/Eric+Gorr+porting

[jcs003]

all250r(jason) is a very knowledgeable guy and if he is stumped on this one then there are only a couple of other guys on this site that can help. neil in particular, will have something to contribute; as he is a top notch porter/engine builder.

[number5]

I had an interesting cylinder one time that had alot of work put into it. It was that sleeve in a trx cylinder. Some one had made caps for the triple exhaust ports for the outside and welded them on. It looked very good.

[latheboy]

It sounds like Gorr would use the epoxy to get the transfer ports "aimed" at one another. It helps to smooth out the low end power. I dont even know if this a Gorr cylinder....

At any rate, it didnt have a very hard powerband hit and the top end seemed a little flat. Almost as if the main was lean, but it was actually on the rich side all winter.

[woodsracer144]

I'd wait for RustyATV or neil to chime in cause i know rusty has a epoxy mod that a buddy of his does that he doesnt really tell people about.

[C-LEIGH RACING]

If filling that area of the transfer would make for any performance gain, then it would have been something Honda would have already done while the cylinder was being cast.

When you reduce the size of a transfer, it will cause the speed of the flow to go up + reduce the amount going through it because of its smaller size.

I would guess who ever did that mod, was trying to change the angle that the flow entered into the cylinder bore & by reducing the amount going up through it, would cause more flow to go through the main transfer. It would add just a little to crankcase stuffing which would cause the flow pressure to be higher.

More you speed up the flow, more it is for higher rpm output range.
Make that flow lazy but a greater amount & bump the compression up high & it would be good for bottom end to midrange output.

More attention to port opening times & compression is more important that any odd mod in a transfer.
Neil