Pro Circuit/Thumper 270 X with '05 R Head - Ride report

Two problems that I wanted to address on my 2004 250X, are the problems with the cylinder skirt, and the valves. I had always planned to make the bike a 270 the first time I had it apart. I have installed the Thumper 280 kits in my friends YZFs, and have been impressed with the results. The Thumper 270 uses a ductile wet liner, and a Wiseco piston. Their new liner is 8mm wider at the skirt than the stock cylinder, and it is matched up with an 81mm Wiseco piston which also has a wider skirt, both of which provide added strength and stability to the piston and cylinder. I took the time to weigh the pistons for comparison: Stock CRF 78mm = .308 lb, JE 78mm = .352 lb, Wiseco 81mm = .340 lb. The forged 81mm piston is comparitively light for its added size. When I read that Honda had improved the ports on the '05 CRF, for better low-mid acceleration, I figured it would make an ideal mod for my X. Especially if you have the intake valve problem and have to do your valves and seats anyway. At a little over $200 (Service Honda) for a brand new head with better ports, it is a bargin. When the head arrived it was better than I had hoped, the new intake port has a lot less volume than my X head (keeps up the velocity), and a much straighter shot at the intake valves. When I pulled the head from my X, it revealed that I was coming down with the disease, my right intake was starting to recede. I have some history with the company that PC gets their Ti valves from, and they are good stuff! So I took my new head out to Pro Circuit, and let them install new seats (to compliment the Ti valves) and blend and match the ports to the new seats. They also worked the exhaust port a little to help the flow. Beautiful work! I screwed everything back together with Pro Circuit valve springs, and installed my X cam. The X had been sitting since a Colorado ride in early August, but when I hit the button, it lit in about 3 revolutions, awesum! Boy does this thing sound bad ass. Went out yesterday to an area that is unfriendly to small 4 strokes. Steep, technical, deep sand. 6 buddies on 250 2 strokes, 1 YZ 450, all moaning that I brought my X, and left my YZ 250 at home. I would have to take the girls trails instead of ride with them. I honestly can't believe that 20cc increase in displacement can make such an increadible difference in the power and personality of this engine. It literally BARKS off the bottom, and pulls HARD through the mid, to a decent top end run out. I suspect the acceleration gain is due to the increase in displacement further enhancing the velocity thru the R intake port, and Pro Circuits head work. If you are looking for some balls out of your X, this is it! The thing climbs the technical hills far better/easier than my previous attemps on it, or my 250 YZFs, with power to spare. Three of my die hard 2 stroke buddies that rode it, all were amazed at how much power it had. Frankly, I am too! So back to the cabin to install the '05 CRF 250 R camshaft. It took about 30 minutes to install the cam. I had the X cam set up at .005"/.008", the R cam was looser at .006/.010, but close enough to not bother shimming. Again the engine started at the first hit of the button. It sounded slightly softer off the bottom, but still picked up revs "like pulling the trigger on a gun". With the R cam, the engine pulls off the bottom pretty much like the stock X did, pretty good, and then builds in a linear rush to the top end (Now I know why you guys like your CRF Rs so much) man this thing is FAST! Acceleration wheelies are NO problem. This set up would be a hoot in more open terrain, and it still has very respectible bottom end. After sleeping on it, I'm going back to the X cam. I really like that powerful bark off the bottom, and the quicker acceleration. With the R cam it takes a little longer to build, but pulls like a mutha' through the mid top. I should also mention that there is a lot less mechanical noise from the engine. If I can beg some dyno time this week, I'll run both cams and post the results.....Man, I'm pumped, this thing is way better than I expected, I'm ready to go ridin' now....Tecate, with my YZF buddies. I would tell 'em it is still stock, but the bark would give it away! I'll post the technical (jets, needles, etc.) details later....

Lot's of good info, thanks for the post :cry:

The Thumper 270 kit sounds like a good fix. Pardon my asking, but how much was the kit and where did you get it?

Also, keep us posted on how the PC Valves work ... if they ever need any adjusting.

Great post Tuner!! :cry: I have been thinking of a big bore once I wear out my top end and piston. What material is ThumperRacing using for thier cyl liners? I know they used Iron liners with the DRZ and it was not dependable.

Great post!!!!

What header do you recommend with a CCC modded X with an R cam upgrade, the R header OR the stock header?

Thumper switched suppliers, and materials, for their new CRF liners. They are using ductile now. Contact Gary for the details....

I would go with either the Dr. D exhaust system (I use and works great) or the FMF Powerbomb header and Q muffler.


Sorry, I didn't mean to ignore you're question. I just don't's pretty subjective.

Did you rejet when you switched cams?

I jetted for what I thought might work with the "R" cam and pipe, at 5000ft, before I left home, knowing I was gonna' switch cams. Which worked really well for the "X" cam as well, using the R pipe. Although it felt a tad richer on top with the X cam, it worked well under WOT load on a couple of long, steep, deep, climbs. It felt perfect across the board with the R cam, but I never got back to the same test hills. It really doesn't matter how I jetted, because everybody on this forum lives at different altitude, relative humidity, temperature, different exhausts, gasoline, riding style, etc. I can only tell you what worked on this ported (in effect), 270cc engine, Sunday. I want to see it on the dyno before I post. I'm pretty happy with where it was, and my buddies thought it felt perfect.

Sorry for not posting this with the original post. I hope I'm not breaking rules? I have recieved a few PM's asking for the price of the Thumper 270 kit. It sells for $510 and includes, 81mm piston, rings, pin, clips, head and base gaskets, ductile wet liner, installation in your cylinder, and a jet kit (Jets vary). You can contact Gary at Thumper Racing 800-259-5186

Tuner, Check your PM's when you have a chance! Thx Marklb

Update: I have over 20 hard hours (actual engine use, not time out riding - Big differentiation) on this engine set up now, and to say I am pleased would be understating it by quit a bit. The bike was for sale before doing the engine modifications, and now I think it is one of the best, and most versatile, motorcycles I have ever owned (67 by last count, and some were very good). As for the engine, everybody that rides it comes back with a smile on their face, and are shocked at how much power it has. The Pro Circuit valves and seats have not moved at all since the initial ride, I am running .006 intake, and .008 exhaust. Solid as a rock! It has not used any oil since the initial break in. I have gone richer on the needle than I would have thought initially. I am running (4000ft./70 degrees) : 45 pilot, F/S 2 turns out, 55 leak, 165 main, DVR needle in the 4th clip. That is with a full OEM, CR 250F exhaust. Running at 6000ft/up with the stock muffler (baffle in), and CRF head pipe, I am running 3rd clip, 42 pilot, 160 main. The DVR needle is 2 diameter sizes richer than stock. What impresses me most is the depth of power, and the hard acceleration from first pop, clear through the extended rpm range, with excellent roll on power out of tight, up hill corners, and switchbacks, or carrying a higher gear through up hill rocks. I am a serial clutch abuser (all those 125's) and the clutch has been bullet proof with the Pro Circuit springs. I am making things now that I only made with 400/450 4 strokes, or my YZ 250 before, and my buddys are letting me ride with them again, and constantly wanting to ride it. I'm getting a lot of time on different bikes these days! For my preference, the 20mm clamps really solved the front end push, and vague steering. It now steers like I think it should, any line, any time. The engine comes on hard and controllably, making steering with the back wheel, and lofting the front wheel very predictable. It accelerates, has great throttle response, and a wide predictable powerband........I'm happy! Last add: I rode with a guy in Moab that had 2900 miles on his stock X, with no valve issues......

Gary's sending me a kit 270 for my '05 250R. At 6'400' I can't wait toreport gains. I'll start a new thread after install this weekend. Tuner's right ..... if you have any questions, call Gary. He's a great guy, he really knows his game, and he'll educate you.

For 04 head work, Steve @ Revolution Performance. They did some great machining on my buddies X

If I can beg some dyno time this week, I'll run both cams and post the results.....

Any progress on the dyno?

Everybody is to the max developing the new bikes, and gettin' ready for the race season. I haven't pushed it because i've been busy as well..........I'll try to get it on after the holidays......our riding conditions have been awesum, so I've been riding every chance I get.

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