Fun with Hot Cams

I went and ordered a new camshaft for my 650r. It is a HRC copy. Anbody using anything like this with the stock piston? Any advice on the install? Do I need to pull the side cover or can I use the peep hole? It does not have the auto decompression. Also I opened up my airbox and pulled the core out of the stock muffler. I am up to a 182mj and it is a little lean on top still!?? This xr is used for Super Moto and street use mostly and that is why I am after more mid/top end power. Anybody have any idea what kind of power this will produce? Idle quality? Starting? I am not too concerned about the loss of the auto decompression system as I always use the manual one for starting but I wonder if the increased overlap will make it tougher to start. Thanks for the help!

I have not replaced a BRP cam, (yet), but I have with other bikes. If you don't want to pull the rotor cover you can align the cam marks and install the new cam to those marks. You need the factory service manual for this so just follow the instructions.

I would pull the rotor cover, (easy to do), just to be sure. You don't want to make a mistake there.

The factory decompressor is more for kick back while starting. You will be impressed with the bruise it puts on your leg when it happens. :)

I would think you will need a header to really take advantage of this mod. The small diameter factory header is there to boost power at low revs.

Keep us tuned in to your impressions. That will probably be my next project.

I can't comment on the install for the 640R since my bike already had the work done when I bought it. I can tell you that the bike is a 1 or 2 kick deal and puts down 55hp at the back wheel on the dyno. Basics are full HRC engine kit (cam, piston, etc.), perhaps a little head work, Arrow race full system exhaust, opened airbox & UNI filter, 188mj, umm... yeah.

I haven't really gotten to ride it yet (long story) but I did go up and down the street once on cold slicks with no front brake installed (don't ask). It felt like it would pull my arms out as I short shifted to third and the front came up. Oh yeah, she idles well too.



A hot cam is a good cam.

I run a warm cam that Rob Barnum hooked me up with. So far 'its all good'. From what i hear theres plenty of room for advancing things on the BRP. 1-2 kicks and it starts. Changed the sound a little bit. Pulls 15/47 without any problem off road. For SM one could probably get to 15/46, maybe 15/45? Rob is the carb guy for Tumpertalk-but he races BRP's-so ya might want to hit him up for advice. He runs the full blown XR680 with 54 honest rear wheel hp....something to live for :)

what gearing do you motard with?


Well the cam is in and thanks for the replies. The toughest part was adjusting the valves as they seemed a little noisy to me, so I did em again after about 30 minutes of run time and changed the oil too. I can still hear a little bit of clicking, but better a little loose than too tight. The motor picked up some power for sure. This is the cam that Honda probably would have installed in the bike in a perfect world with no enviromental wackos/weenies. (Earth First! We will screw up the other planets later!) I read the "flat as a fart" post awhile ago and agreed with that guy's opinions on the 650 on the street. This cam, along with drilled out airbox, jetting, and no insert in the stock muffler, really brings this motor to life! I would guess I picked up about 5 hp on top an maybe a couple in the mid range. It feels more "revvy" for sure. It may have lost some power down low, but seems smoother off the bottom as well. It wheelies much more readily exiting corners. For Super Moto, on go cart tracks with relatively short straightaways, as an example: Instead of losing 2 or 3 bike lengths to a crf450 it might lose half a bike length now or less. To pass me now a guy has to get a better drive off the corner AND out brake me into the next corner. Before, a 450 could just drive right by me like I was out for a Sunday ride. So I wont claim it is faster than a crf, but with good traction, it is almost as fast and with a lighter rider (I am 225) it might be close. For the street, I have a fmf Q that I hope to try out as well as it is very loud now. If it runs ok with that, it should make for a very fun and rowdy street bike. I am surprised that more people are not running these cams as I see little down side to them. I am a trials rider first and foremost and can appreciate low end power with best of them, but the 650 has so much displacement that a little more overlap on this beast would have little effect on the low end. And might be less abrubt off the bottom. I guess next time I ride Slickrock in Moab I will see. For now I am very happy with the improvement. As for a bigger header, I may try one later, but for now I am pretty happy. Even with stock header it is making alot more power.

Glad to hear of your success with the cam. The performance improvement you describe sound like what I felt when I put on the larger header. I bet the 450 would be in your rear view mirror after you installed that. Notice any difference starting?

Hi Dutch, It starts as easy as ever and I removed the choke plate flapper valve a long time ago! I really could not tell a difference at all. Or with the idle quality. What brand of header are you using? How is the fit? Does it allow you to use the stock muffler if you want? Have you opened your airbox up? MJ? I was using a 182MJ and it was a little lean before the cam change (at sea level). Now I am running a 195 and it is just about right with the new cam. By the way, the cam is from Pro Flow (Hot Cam)and I bought it from Xrs Only. I told them I was going racing and they cut me a deal: $150 including Ca tax and shipping. Most importantly, they had it in stock and shipped it that day. Thanks Guys! It is a new cam, so not rewelded(hardened) so no core and I can reinstall my stock cam if I go insane or somethin...

I'm using the FMF full system. It fit up real easy; the build quality is very good. I'm not sure if the stock muffler will fit this header but I would think so. It is a compromise header in that the pipe diameter is not as large as some - yet is larger, (flows better), and lighter than the stock header. This suites my needs because one weekend "Betty" is flying through the woods and single line trails up here in N Mi. then the next we may be running the Dragon down in Deals Gap. There are better choices of header if you are just running the roads with the BRP.

I have vented the air box cover, (everybody should do this), and I run a 40mm TM flat slide pumper Mikuni.

The main concern I have about running a cam in my bike is the possibility that this modification may make the motor create more heat, I would like to avoid this.

I'm not sure of this and the opposite may be true, but this is something I'll need to know before "Betty" gets a hot cam.

Ok Dutch, I ordered the header today. I went with XRs Only header because of the service I got. I called FMF and asked if their header could be used with the stock muffler and they had no idea! Geez! The guys at xrs only know their s#%t as they should. They probably could tell you if your bike would run hotter or not. I would guess that with more overlap, the cool intake charge would cool the exhaust valves more as it flowed out the exhaust at lower RPMs. And at higher RPMs I dont think it would make much difference and you would be moving faster to for more airflow. But it seems to me it would not heat up as fast at idle. If someone knows about this let us know. I also would think anytime you are making more power...more heat will result.

Yeah - I was thinking that also, about the more power more heat issue, but the correct carb settings and a free flowing exhaust make big power and the bike runs cooler with this setup.

The reason I assumed the FMF header would work with the stock header is that it is the slip on that is sold for the stock header. It would be foolish for them to have a separate muffler for the "system" and a different one for a stock header. It wouldn't be the first time an aftermarket pipe maker did something that didn't make sense to me though.

I'm anxious to hear you impression of the bike with the header, bet you're impressed.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now