Something very interesting

4 replies to this topic
  • xr650Lroostnya

Posted January 01, 2004 - 05:49 PM


The uncorked XR650R has significantly more total power in terms of torque than the stock race ready CRF450R, but they have very similar power to weight ratios and that's very important, especially on tighter courses.

An uncorked XR650R produces close to 42 lb/ft of torque at 5,500 RPM and close to 48 rear wheel HP at 6,500 RPM. The CRF450 comes stock as a full fledged race bike and produces about 29.5 lb/ft of torque at 6,500 RPM and 40 rear wheel HP at 8,000 RPM. The CRF450 has a much broader powerband that's very linear and it will keep pulling where the XR650R falls off in the RPM range, so naturally it will feel faster to some people. Gearing also plays a big role in all of this.

A modified CRF450R that includes a special cam grind that's installed to the correct degree with higher performance valve springs, retainers, guides, porting, 12:5.1 piston, power now valve, Doma exhaust and running Nutec Special 5 fuel produces about 34.7 lb/ft of torque 7,200 RPM and about 53.4 rear wheel HP at 9,200 RPM.

Now if you modify the XR650R with a 680 kit, cam, piston, header & exhaust, you can boost the torque to about 50 lb/ft at 6,000 RPM and raise the rear wheel HP to 64 at 7,500 RPM.

If you take the total torque of the bikes and divide it by the weight of the bikes, you'll get a better idea of the power to weight ratios.

CRF450R @ 29.5 / 225 = 0.1311 lb/ft torque per lb of bike weight.
CRF450R modified @ 34.7 / 225 = 0.1542 ft/lbs torque per lb of bike weight.
XR650R @ 42 / 277 = 0.1515 lb/ft torque per lb of bike weight.
XR650R modified @ 50 / 277 = 0.1805 lb/ft torque per lb of bike weight.

You can clearly see that an uncorked XR650R engine still makes more raw torque than a stock CRF450R and it's very closely matched to a modified CRF450R in terms of total engine torque, but an uncorked XR650R makes its power with more reliability, with less effort, thus less with maintenance. When you modify the XR650R with the 680 kit and other goodies, then the choice becomes very clear, especially on courses where weight isn't an issue. No matter how you slice it, the CRF450R is a very attractive bike and extremely competitive due to its lighter weight, but the XR650R is still very competitive when the weight of the bike isn't as much of a factor.

Gary, Resident BRP Einstien

I found this on thought it was very interesting.

  • TimBrp

Posted January 02, 2004 - 05:01 AM


Guess there's no replacement for displacement...

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  • irondude

Posted January 02, 2004 - 09:19 PM


For sure the BRP is better in high speed stiuations, and the 450 is better in tighter stuff-any way ya slice it...its sort of apples and oranges comparing the 450 motocrosser and the 650 Baja blaster....

I would love to read a comparison of the KTM 525, Husaberg fe650, XR650R, XL650L, KX500, KTM 620, KTM 660 Rallye, KLX 650, BMW650gs, ATK 700, Vertemati 570. That would be interesting reading...
Best Motard: Husaberg
Best Ride to Work: BMW
Best Ride to School: KLX650
Best Hare and Hound: KX500
Best Baja: BRP
Best if ya can only have one: :)
well we all know the answer to that!

  • motometal

Posted January 04, 2004 - 06:23 AM


the 450 is not known for being all that great as a tight woods bike. My friend has several bikes, and he actually preferrs his cr250 to his 450 for woods. on the 450, it's a bit heavier and the power is very abrupt. It also doesn't like to be lugged-the chain "clacks".

  • irondude

Posted January 04, 2004 - 07:01 PM


yeah-for sure the 450 needs some flywheeel weights, tank, stator work, dampner, sprocket change, and maybe the BD wide ratio tranny to do the woods right. Better yet just wait 9 months and get the new 450X. For the tightest woods the KDX200, EXC300, YZ250F, Gas Gas 300, and of course CRF250X are the way to go...unles of course you have a '72 DKW 175 in the garage!

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