YZ/WR cam timing and in between

jmics19067 · Jan 18, 2005

what I am working with;
2004 WR 450,yz cam,throttle stop,GYT silencer with GYT 96 decibel end cap.
what I notice& what I want;
As the usual feel /mindset the WR cam just doesn't pull very well, the YZ cam pulls very nice but a little beyond what I need ,also believe the 96 decibel endcap is holding it back a bit at the upper revs. The bike is a do it all play bike for my novice(?) skills. have been riding for about 20 years not fast by any standard but ready to try and ride anything,MX,Hare scrambles,Enduros,Dual Sports,trail riding , and the most important ,racing to the beer meister when the day is done.

I was wondering if it is feasible take a yz cam apart and repress the gear on say 5 degrees advanced? Trying to get camshaft timing and exhaust configuration more in tune with each other and hoping that the 5 degrees won't mess with auto decompresion at cranking /kicking speeds.

Before I try has anyone ever tried this succesfully?
Are Hotcams available for a low/midrange boost compared to the yz?Also would advancing the intake cam a couple of degrees be beneficial to my ideal by lessening valve overlap?

thanks

BSWIFT · Jan 18, 2005

You might consider using the YZ flywheel with the WR cams. It would give you quicker reving without the overall YZ grunt. I like the YZ450 power but really need some flywheel weight but have just never done the mod. I'm installing an autoclutch and hope to solve my stalling issues(heavy on the back brake).

ironworker · Jan 19, 2005

I believe you can also do the Grey Wire mod and automatically change your WR Cam timing to YZ timing by simply unplugging the grey wire.

jmics19067 · Jan 19, 2005

hmm interesting approach,but I am not sure if it will satisfy what I am looking for. Although the WR cam timing will rev out it just doesn't have the pull I am looking for.If I had my druthers I would prefer an engine like a klx/drz 400 type of power.Something in me just thinks I would rather stretch out the throttle cables on the rare occasion I open it up,then to ride a massively corked up, ill timed, racing engine at 1/2 throttle.I love how the YZ feels but realistically it is more than I can handle properly and trying to get that 12000 rpm 100 decibel monster more human
Working at a Yamaha dealer kind of limits my choices on bike purchases,besides the fact that I think the WR has a much better chassis/feel for me. Thats the reason why I am thinking of screwing around with the cam timing, to try and get its compromises more in tune with me.

I have the WR camshaft I can sacrifice, so dropping it off at a machine shop with the possibility of it coming back junk not really bothering me.Maybe I will retard that one and see if I can start the bike afterwards. Just hoping someone has tried this before and looking for experienced views/ideas

thanks

PS yes on the grey wire mod thanks and sorry

ironworker · Jan 19, 2005

I hope you find what your looking for, it doesnt hurt to try the gray wire mod anyway.
The gray wire changes the WR "mapping" to YZ specs by advancing the ignition timing curve. You can do this by removing the seat and gas tank. On the right side front of the motorcycle there's a black box (CDI unit). Follow the wires down to the junction connection and cut/unplug the gray wire. Be sure and use electrical tape to cover any exposed wires.

This improvement makes the WR450 behave more like the YZ450 power wise. If you want pure YZF like power you'll need to change the exhaust cam. Rotating the cam to YZ specs.

If it dosent help so be it but I did it to mine and it made a world of difference.

Good Luck

Rich Rohrich · Jan 19, 2005

It's important to keep in mind that the intake cam timing (specifically intake close and it's balance with compression ratio) has a far greater influence on the "personality" of an engine than the exhaust timing does. Small changes in the exhaust cam centerline have little or no effect on the engine. The only reason the WR has that bizarre exhaust cam timing in the first place is to eliminate some of the pumping losses associated with the super restrictive stock exhaust setup. They had to make a nearly 23 degree crank angle change to accomplish it. Like I said small changes in exhaust timing don't mean JACK. ;)

All they are doing with the stock WR timing is starting the blowdown portion of the cycle super early (which kills torque) to work around the exhaust restriction. The smoother power people think they have with a WR is just a lack of torque. :) The restriction and the shortened overlap tends to limit some of the TDC pump through that comes with high rpm engines but it's a bandaid fix that works better when removed. Yamaha knew people would remove the exhaust restriction which is why they made it so easy to convert the bike to the proper timing.

Eliminating that compromise is the first step towards a more useful power spread. You can do it with a an OEM YZF cam or one of the good billet aftermarket cams like Hot Cams. Depending on the type of power you are looking for you can add an aftermarket intake cam and fill in the midrange and upper rpm power spread as well.

My advice would be to put in a YZF exhaust cam and leave it alone. You won't find powerband nirvana diddling with exhaust timing. A Hot Cams intake has an adjustable cam sprocket standard and tuning the intake close timing will give you far better results in trying to reach your performance goals.

jmics19067 · Jan 19, 2005

Rich Rohrich said:
It's important to keep in mind that the intake cam timing (specifically intake close and it's balance with compression ratio) has a far greater influence on the "personality" of an engine than the exhaust timing does. ......... Like I said small changes in exhaust timing don't mean JACK. ;)...... A Hot Cams intake has an adjustable cam sprocket standard and tuning the intake close timing will give you far better results in trying to reach your performance goals.

Thats the direction of my question, I know it seems sacreligious and strange buying a WR converting to YZ specs and then detuning it :coocoo:

Thanks

Jaybird · Jan 19, 2005

Hotcams has a nice little camshaft installation kit for $130. Dial indicator, base, studs, and degree wheel. Makes life easier if you don't have the required toolmakers toys.

jmics19067 · Jan 20, 2005

Yes it looks like I am having to do some scrimping so I can get some new things to play with,(adj,intake cam). The ins. setup kit sounds pretty sweet, I do have a dial indicator, but the degree wheel I will need, and the mounting setup sounds a lot easier then having to figure out/fabricate one.

Thanks.

Rich Rohrich · Jan 20, 2005

The early Hot Cams install kit didn't come with a mount for the flywheel, but it's really easy to make one that will work with a K&N style flywheel puller. If you guys want to see an example I'll post some some pictures of the one I made tonight.

Here's some not so detailed pics :

http://dirtrider.net/teamdrn/showph...02a48468cd1be3f35b24dcd8a43586/sort/1/cat/500
http://dirtrider.net/teamdrn/showph...02a48468cd1be3f35b24dcd8a43586/sort/1/cat/500

jmics19067 · Jan 20, 2005

If a picture is worth a thousand words send me a thousand pictures , That should get me enough info to be dangerous :bang:

Ok here is where I am really going to get thinking on this project; or should I say ask questions

When I get the intake cam and I want to advance it a few degrees(lessen overlap,weaken top end and promote bottom if I have my direction right) I might run into a problem of too much dynamic compresion. So I shim up the jug with a thicker base gasket, that in my mind is going to advance both cams again(I am thinking in my head extremely small amounts that probably will be not worth mentioning but something I am going to make sure isn't)

I have replaced many parts in my life but never have blueprinted an engine. Does Eric Gorr's new book dive into these situations?

SFO · Jan 20, 2005

What might be, and what is, are two very different things.
Most certainly there will be mechanical constraints to your desires before theoretical considerations come into play.
A single scribe line on the cam/sprocket interface is worth nearly a degree of LCA. (in my humble experience)
Bumping the intakes into the piston could be an issue.
Quick degreeing is really fun to learn.
Keep records.

Jaybird · Jan 24, 2005

The Hotcams kit still does not supply a degree wheel holder.

Weld a 10mmx1.25 nut on each end of a 1/2"x 3" piece of black steel pipe and you have your degree wheel holder.

jmics19067 · Jan 24, 2005

http://www.mcmaster.com/

page 3001

dang so close too bad it was a 1.5 pitch I guess I can butcher a smaller NCF(?) size running a tap thru it probably a lot truer than me trying to weld straight.

Rich Rohrich · Jan 24, 2005

I didn't get home till fairly late last night but I'll post up some pics tonight of my fairly simple setup.

jmics19067 · Jan 24, 2005

anytime at your convenience would be greatly appreciated

YZ/WR cam timing and in between

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YZ/WR cam timing and in between

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