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LEMMON1

WRF 04 exhaust cam -> 426F

5 posts in this topic

so i always hear bout the 03 450F exhaust cam or the hot cams cam goin into the 426s, but is there any reason to believe that hte 04 wrf exhaust cam wont work?

reason is i found one cheap, and if needed the intake cam as well...any thoughts?

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The intake cams are the same in '03-'05 YZF and WR450 models. The exhaust cams are one of the major differences in the two engines, and the WR has 6-8 hp less than a YZ450. If you use a WR cam, figure your bike to drop at least 5 hp as a result.

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The exhaust cams are one of the major differences in the two engines, and the WR has 6-8 hp less than a YZ450. .

I think you're thinking bone stock, corked up WR. Pulling the cork out of the WR's ass helps a bunch. Motousa.com tested an '08 WR on the dyno and it made 42 hp. The '09 YZ made 48hp and change. I think the dyno they use underrates the engines because ever other magazine dyno I've seen a stock '08/'09 YZ is about 50hp and change and a stock WR is about 44-45.

When its all said and done its still a 2-3 hp diff between an uncorked WR and a YZf. The biggest differences that I felt between the two engines ('07 uncorked/piped WR vs. '08 piped YZ) was the YZ pulled harder off the bottom (cam/ignition), revved faster (flywheel weight & combination of the other two), and was in general a snappier, higher strung engine.

A YZ with a WR exhaust cam is most likely going to lose some snap off the bottom and some power at peak. It'll be mellower and more tractable.

If you want to retain the YZ character, the '03 YZ cam is the way to go.

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Inertia dynos are somewhat imprecise, and are better used comparatively than as measuring tools. Nevertheless, the numbers I've seen posted from reputable sources for '06/8 models run from 49-52 for the YZ450, and 42-45 for the WR. Given that, I'd say a delta of 6-8 is reasonable. Note that I said the cam by itself would cost 5.

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