The OEM YZ and WR cams have nearly identical decompression operating specs. Here's how they break down;
duration @.010" lift 124 degrees
open @ .010" 30 degrees ABDC
close @.010" 26 degrees BTDC
center of lift 84 degrees BTDC
duration @.010" lift 143 degrees (the difference from the YZ is from the early WR cam pin having a flatter profile)
open @ .010" 3 degrees BBDC
close @.010" 40 degrees BTDC
center of lift 110 degrees BTDC
duration @.010" lift 79 degrees
open @ .010" 28degrees ABDC
close @.010" 73 degrees BTDC
center of lift 111 degrees BTDC
As you can see, the YZ and WR decompressor have the same pin height and duration. The difference between the YZ and WR is from the WR cam being advanced about 13 degrees (closing the exhaust valve 13 degrees earlier than the YZ cam). This would actually increase cranking compression on the WR when compared to the YZ. You will also notice that the YFZ cam has a decomp pin that shorter by 1.5mm. This effectively reduces the lift and duration of the of the YFZ decompressor but more inportantly, it closes the exhaust valve 33 degrees earlier than the WR cam.
The YFZ has less compression and a considerably larger battery than the WR and don't have a problem spinning over with the exhaust valve closing this much earlier.
Early Hot Cams had some quality control issues and variation on the decomp pin that was th source of e-starting problems. They also have some issues with application listings on some of their products.
OEM YZ cams will work without issue in the WR, but OEM YFZ cams will not. As far as aftermarket cams go, if it is listed for the YZ, it should work ok in the WR but the best thing to do is check your cam installation with a degree wheel and dial indicator.
The '03 and later WR cams use a different base circle diameter from the '98-'02 cams and require different shimming if using the later cams in earlier bikes. The timing marks are located differently between early and late and make direct swaps difficult. The difference of 1 tooth equals 22.5 crankshaft degrees. Although this would put the WR cam in YZ territory as far as cam timing, it delays the closing of the exhaust valve until 18 degrees BTDC and wouldn't leave much compression left and may make for hard starting. On the other hand, the YFZ cam with the shorter decomp pin should work with the timing retarded 1 tooth (even on the WR). The decomp pin closing would occur @ 52 BTDC, only 12 degrees earlier than the stock WR cam.
On WR's from '03 to '06, the cams were the same lift and durtion as the YZ, the only difference was the exhaust being advanced about 13 degrees. Beginning in '07, the WR had intake and exhaust cams that were completely unique to the WR. The '07 WR cams have about 1mm less lift and make very good low end power in the WR.
In another post on the YZ450 side I did some checking of a bunch of cams I have in my shop to answer some questions about year-to-year changes. Here's a summary;
Ok, here's the scoop on YZ450 cam profiles. ALL '03-'09 YZ450's have the SAME lift and duration (as far as I can tell with a degree wheel and dial indicator) and appear to be a symmetric profile.
I checked the lift, duration, lobe center, and decomp pin stats for the following cams;
5TA-00 intake ('03-'05 YZ and WR)
5TA-10 intake ('06 YZ/WR, '06-'09 YFZ)
5TA-10 exhaust ('06 YZ)
2S2-00 intake and exhaust ('08-'09 YZ)
5TJ-10 exhaust ('03-'05 WR)
5TG-00 exhaust ('04-'05 YFZ)
4023-1IN Hot Cams
402-1E Hot Cams
I will be checking a set of '07 YZ cams, GYT cams, and a set of '07 WR cams in the near future.
All of the OEM cams listed above had a lift of 8.61mm intake and 8.43mm exhaust and all had a duration of 244 degrees intake/exhaust @.050" lift. The only difference that I found was with the 'lobe centerline'.
The '06 YZ cams had an LCA of 106.5 degrees intake and 104 degrees exhaust (for a lobe seperation angle of 105.25 degrees)
The '08-'09 YZ cams had an LCA of 102.5 degrees intake and 99.5 degrees exhaust (for a lobe seperation angle of 101 degrees)
The '03-'05 YZ intake had an LCA of 109 degrees.
The WR and YFZ exhaust had an LCA of 126.5 and 127.5 degres, respectively and an LSA of 117.75 and 118.25 respectively.
For a good explanation of what these numbers mean, go to Web Camshafts site [color=#0f72da]http://www.webcamshafts.com/[/color] and click on the menu in the left side titled "Degreeing in Your Cam".
Edited by 2grimjim, January 23, 2012 - 04:33 PM.