4mm stroker 250r

[machwon]

Here is a run from a trx250R with a +4mm hot rods stroker crank. The cylinder was an 87 bored .060 over which makes it 272 cc's. Other details were boyseen rad valve, FTZ pipe, 40.5mm keihin carb 58 pilot, DGH middle, 185 main, cool head.

[criminalpoet]

Respectable numbers for a pretty much stock bore bike!

[machwon]

Thanks, I thought it would do a little better than this, but its still really good. We got it upto 52.7 hp last week, hopefully I can find some more!

[headache]

what type of porting does the motor have? Was it ported for the stroker crank? if not then your definetly not getting the full potential out of that motor.

[machwon]

The motor has what I consider a full top end port job and it was cut specifically for the 4mm lr stroke. There's not much more to do other than make it a full out drag port. I would be interested to see any info you have on a stock cylinder motor pulling mid or high 50's without using alky or oxygenated fuel.

[criminalpoet]

I have an 89 stock long rod motor with the stock cylinder still on it, 1 Dir Racing built it and it pulled 52hp with 32ftlbs of torque with their MX/Dune porting. I have recently sent it back to them for their pre-pusher design and this time around I am adding a timing advance plate. Im told to expect 60hp with somewhere around 35-38ftlbs of torque. They also offer a custom inhouse pipe for their pre-pusher engine design which is supposed to increase the power by another 15-20%.

Im not sure if they offer their pre-pusher design to the public or not though, ive been a customer of theirs for over 10 years now. But those guys have been building race bikes for over 30 years and theres always little trick here and there to add hp. You should see how they modify their pistons too, its pretty wild. Attention to detail, thats why I like them, and with an inhouse flow bench and inhouse dyno they are able to check for things and do the type of testing on your motor before sending it out that most other shops cannot do.

No matter what though those are very respectable numbers! Most builders/shops out there are not getting their customers over 50hp on a stock cylinder.

[machwon]

Criminalpoet, are those rear wheel dyno numbers or from the countershaft? Do they have a website with there info? I would be interested in seeing any of the stuff they have.

Not that I'm doubting what you say, but I don't think I've seen but one or two dyno runs that just hit 60, and I'm pretty sure they had it on alky. You are right about hitting 50 hp as well. There's not many who get that high either. I got my hands on a 38mm alky carb, so I'm going to hopefully try it soon.

[08 GPX 177 ATC]

I would like to get my 250R atc dynoed.

[Buttermilk]

http://www.exriders.com/vbb/showthre...hreadid=349083

The link is to my own 250R with a +4mm crank. It's taken me about one and a half years to get it to where it's at now.

Regards,

Rog

[machwon]

Buttermilk, those are awesome numbers for a stock cylinder. Keep up the good work!