Rich? RPMS CRF 277 big bore and rev box Q?

[jr.ink]

Hey Rich what can you tell me about the Big Gun Rev boxes for a CRF250?

I have an 05 CRF250 which is now a RPM's 277 kit. ( I installed it and ground the cases) Valves are in spec and Stock Cam. I was thinking about going with a different ignition to see if I could squeak a little more power out of it for a low cost modification. I have a Carbon Pro Pipe and it is jetted pretty well for MN. I race Vet and Plus 25 A classes.

Big Gun claims up to 4 hp increase with their Rev Box?

What about a stock CRF450 CDI? I am guessing this would be the wrong direction, (Due to rpm's) but I really don't know a whole lot about ignition mapping etc..

Do you have any other cheap modification tips for a 277 big bore? I like riding higher in the rpm range yet love the extra grunt of the big bore out of the corners.

Thanks a lot, and have a GREAT Day!

Jeremie

 

[Rich Rohrich]

Hey Rich what can you tell me about the Big Gun Rev boxes for a CRF250?

I don't know anything about it. Big Gun is a good company but 4 horsepower sure sounds like a lot from an ignition system. I'd need some serious proof before I would believe that claim.

Getting the engine to breath better is generally the best way to take advantage of an increase in bore size. Whether you do that with a cam change, porting, or both, getting more air in and out of the engine is a good place to focus your attention.

One thing is for sure, given how heavy that Rick Petersen piston is you don't want to raise the rev limit in the engine, or where it develops peak HP. If anything you should be looking for ways to lower the rev ceiling, and the peak horsepower rpm. High rpm and heavy pistons are a really bad combination, and that piston is HEAVY.

 

[jr.ink]

Well thanks Rich I appreciate and respect your opinion. I had a 2003 YZF262 that you did and loved it. You know when I purchased the kit from RPM's/Max Power this spring I was not finding any better options for a CRF250. I was afraid of the whole broken skirt issue with using the stock cylinder. Now I see that Athena has a kit. I am wondering how they have gotten around the broken skirt issue? I have to say, I am pretty happy with the RPM's kit. I just wish I had a little more top end power/rev.

Anyway, a cam sounds like a good idea. (cheap and easy, I like it!) Do you have a suggestion on what cam would be best with the RPM's kit I have? Also is it possible to get a lighter piston for my RPM's jug? I was assuming I will have to contact RPM/Max to get my next top end.

PS. I bought the older larger cnc'd cylinder from RPM/Max Power. I got it cheaper than there new version.

Thanks,

Rich!

 

[Rich Rohrich]

I have to say, I am pretty happy with the RPM's kit. I just wish I had a little more top end power/rev.

The fact that it doesn't want to rev is a good thing. Keeping the revs down will keep you from breaking connecting rods. That 277 piston is way too heavy to run at the original redline using the stock connecting rod on the CRF250.

Also is it possible to get a lighter piston for my RPM's jug? I was assuming

I doubt it, but that's a question best answered by them.

 

[RMZRIDER]

i dont see what the point of a rev box is. why would you rev your bike over what is specified. your asking for trouble with a rev box because the manufacturers obviously test to see what the highest-safest for your engine is. i think i have bounced my bike off the rev limiter maybe twice my whole life. maybe thats why i'm not that fast :think:

 

[trial_07]

Sorry for being off topic!

I was wondering Rich what was your job or your studies? Bref where did you get all that knowledge? I am looking to become a mechanical engineer. Any tips for me if I want to specialize in mx bikes development or any other racing machines?

Sorry again for being really off topic! No disrespect meant to the poster.

 

[Rich Rohrich]

Sorry for being off topic!

I was wondering Rich what was your job or your studies? Bref where did you get all that knowledge? .

http://dirtrider.net/forums3/showthread.php?t=40126

 

[trial_07]

I read the whole post. I enjoyed reading your story and I admire the things you did. Thank you! I hope I can contribute to the evolution of dirt bikes one day...