I spent a ton of time reading WR/YZ cam threads from all over the web last night. This thread is a compilation of what I learned and hopefully we can update it with new information as we go along.
PLEASE do not turn this thread into a debate on whether or not a camshaft should be updated. This thread is about camshaft information.
This thread is SPECIFICALLY about camshafts for 2012+ WR450Fs. As you will see, they are a different beast from previous WRs. Please don't discuss putting a cam in a different bike in this thread, unless it has some application to the 2012+ WRs.
This thread ignores aftermarket camshafts, for a number of reasons. i) I couldn't find any concrete lift, duration, etc. information on them. ii) When I did find lift numbers, it was in excess of the YZ lift, which I, rightly or wrongly, didn't think would work well with the 2012+ head and iii) I could not find anyone that had put an aftermarket cam into a 2012+ bike.
Here is what I learned.
1) The 2012+ WR450 head is a different beast from previous heads. Previous heads had a port geometry that was maximized for velocity. The 2012 WR ports are huge, sort of maximized for volume. I don't know why this was done, but it was.
The change in head geometry is discussed in detail by two guys on the YFZ (ie the Yamaha quad) forum. The first guy's user name is mixxer. He apparent is a head porting expert. The second guy's user name is mbirt. I'm not sure he owns a quad, but he is a grad student who works on WR450F engines because his college uses them in SAE Forumula cars.
2) Prior to 2007, all (?) of the WR and YZ cams had the same duration and lift. The only thing that changed between the various years and models was how far apart and where the lobes were placed, ie lobe separation.
Thus in those years people speak of doing the "YZ mod" on WRs, which was to retard the exhaust cam by 1 tooth, thus making the lobe separation on the WR similar to the YZ model.
3) I compiled the following chart of WR and YZ cam part numbers and specifications.
This table is obviously incomplete, but its a start. It also only contains Yamaha OEM cams. It doesn't contain YFZ cams either, mostly because those cams are tuned to a much different powerband to suit a heavier and much different vehicle, ie a quad. However, you might be interested to know that some of the newer YFZ engines use the same intake cam as the WR450Fs.
Its extremely confusing compiling this information because its leaked out in dribs and drabs all over the place and people propagate information with errors in it as they go. It took a lot to get this to where it is.
4) There are 2 major changes in the WR450 engine lineage as far as cams and heads go.
i) In 2007 WRs stopped using YZ based cams and got their own WR specific cams. All post 2007 cams have lower lift than the previous WR and YZ cams.
The uptake on this is that even if you swapped a pre 2007 WR cam into a post 2007 WR engine and the cam had the same duration and lobe separation, you would *probably* see a performance gain from the increased lift alone.
ii) In 2012 the head on the WR450F went from a velocity maximized design to a volume maximized design.
5) A 2012+ WR450F owner has *many, many* choices when it comes to making cam changes.
i) retard the stock exhaust cam 1 tooth. There is evidence that this works on all WR450F engines up to and including the 2011. Here is a graph that illustrates the improvement (cam plus exhaust) on a 2011. Remember that the 2011 uses the velocity style head and the low lift WR cams.
The poster, our friend Mixxer. He says this:
The "YZ timing" test features the exhaust cam retarded 22.5 crank degrees (1 cam sprocket tooth), the "grey wire mod", a modified exhaust, and needle clip changes to maintain 13.5:1 afr. After retiming the cam, cranking compression was only 10 psi, down from 50. We took a risk and carefully ground 1mm from the decompression pin. It worked and restored cranking compression to 50 psi--starts at least as well as it did with WR timing. The exhaust used was a Venom TRX450R headpipe (1.625 OD into 1.875 OD) and a Ron Woods TRX450R megaphone/muffler . The tuned length comes out close to 30" and is to thank for the torque peak at 6500rpm.
No, I cannot quantify how much was gained from the exhaust modifications vs. the cam timing, but I know lots of full exhaust system comparison tests exist. With a 67 deg. BBDC EVO and only 20 degrees of overlap, spending big bucks on an exhaust system for a stock WR seems pointless. The same goes for retiming the cam without fixing the exhaust. The two changes are very much complimentary and should be approached holistically.
Some of the gain is due to the grey wire mod, but most of that should only come into play above 8500 RPM.
Remember that this gain is from better exhaust breathing alone. No changes were made to the intake system. I can't help but think that this engine is going to run cooler too. The energy that is now being converted to power with the exhaust system change was previously kept in the combustion chamber, mostly as a recycled EGR sort of thing.
The really interesting thing to note about this mod is that the retarded exhaust cam engine is making more torque and power at 4,000 RPM than the stock engine was. So much for the myth that "YZ timing", at least on the exhaust side of things leads to peaky power.
I haven't found evidence that its been tested on the 2012+ WRs, but being that it is an exhaust based gain, I have no reason to see why it wouldn't yield a similar sort of gain. In fact, I suspect it might yield more gain as the 2012+s were subjected to even more stringent emissions. I suspect that the low lift and restrictive exhaust aspects on the 2007 and especially on the 2012+ WR450Fs is as much about using in cylinder EGR as it is about maximizing the powerband for enduro use.
Furthermore, one of the things some WR450F owners would like to see is less engine braking. Retarding the exhaust cam release more energy from the cylinder and would likely reduce engine braking significantly.
ii) Replace the 2012+ cam(s) with pre 2007 WR450F cam(s).
As explained above, the pre 2007 WR cams have higher lift than the post 2007 cams. However, being WR cams, they still have conservative, broad WR timing, at least more conservative than the YZ cams of the same era. Doing this would be like going half way to YZ cams.
One also has the option to mix and match solutions, ie run pre 2007 WR cams and retard the exhaust cam by one tooth. One doesn't have to do both cams either. One could do just the intake or just the exhaust.
However, the thing about using the higher lift WR cams with the 2012+ WR engine is that, apparently (from mixxer's discussion) the intake port is susceptible to flow reversal. And, apparently, the higher the valve lift is, the slower the charge velocity and the worst this problem can *hypothetically get*.
However, others argue that Yamaha kept the lift low on the WR cams because the exhaust cam closed early (in cylinder EGR ?) and the intake cam needed to as well to keep those products in the cylinder. (I'm half paraphrasing and half espousing here !)
iii) Replace the 2012+ cam(s) with 2003 to 2009 YZ cam(s).
There are many, many factors to consider here.
- one could do just and intake cam or an exhaust cam.
- different cam years have different characteristics.
- how will the YZ cams, which were designed for velocity ported heads, work with the 2012+ volume ported head ?
I have not been able to find any evidence of people putting YZ cams in their 2012+ WR450F, save for Jed Haines, so this is essentially new territory.
There is lots of information about people putting YZ cams into pre 2012 engines, but I am not sure how applicable that would be. Specifically, is intake flow reversal going to be an issue.
So there is where we stand as far as information that I could find about putting Yamaha OEM cams into a 2012+ WR450F. I welcome other people to contribute data and information, subject to the posting request at the top of this post.
Caveat: I know just about nothing about camshafts.
I found an interesting pattern when I was reading posts last night. Many times on paper the pundits stated that camshaft xxx wasn't going to work that well. And yet when the bike owner tried it, he was generally happy. There were very few reports of people saying that a cam made their bike worse.
All of this totally ignores the compression release pin. That can be added to the discussion as we go forward.
I hope this thread helps someone.
Edited by MidlifeCrisisGuy, August 23, 2014 - 09:31 AM.