which YZ exhaust cams work in POST(!) 2012 WR450F

Cool, well I will give it a shot later on in the summer (06 YZ exhaust cam) and if the cost is not outrageous, I might dyno before and after and post my findings here.  I would love to port the head, but that's probably not in the cards for awhile.

I think you will get more performance out of a different intake cam and a stock exhaust cam.

I use a stock exhaust cam for off the bottom power. But I don't think it would change much with a YZ exhaust cam. My understanding is it's pretty much just moved the lobe centers a bit.

Edited by stevethe

When you have the timing chain off you can rotate the stock exhaust cam backwards to see where the pin touches the bucket.  Around 2 teeth before TDC.  If you stick a YZ cam in there shimmed properly the pin will touch closer to TDC.  I'd try to grind the pin till it touches the bucket at the same place the stock cam did.  I don't think where the valve opens is as important as where it closes.

Edited by chewbaccauncircumcised

 

Is there anything to be gained by retarding the exhaust cam one tooth on the 07+ WR450F?

 

Can I simply install a 06-09 YZ450F exhaust cam (understanding that they're not all the same, would go with the 06 based purely on what I've read on here) with the decomp pin ground and polished approximately 1mm and still expect the electric start to work?

 

1) Not really.  It will have some of the same effect as retarding the cams on the earlier (pre-'03) bikes did, but not as much because the exhaust cams on the later bikes, from '06 and up, were no longer the same grind retimed as they were up until '05.  The lobe profiles were the same on both bikes before that, so it was a matter of just timing the cam the same as the YZ had it.  That doesn't work anymore, and, obviously, it introduces the complication of dealing with re-timing the AD.

 

2) That's been covered.  You can make it work, but it's tricky.

When you have the timing chain off you can rotate the stock exhaust cam backwards to see where the pin touches the bucket.  Around 2 teeth before TDC.  If you stick a YZ cam in there shimmed properly the pin will touch closer to TDC.  I'd try to grind the pin till it touches the bucket at the same place the stock cam did.  I don't think where the valve opens is as important as where it closes.

 

With the timing chain off, you can make the pin touch the bucket with the crank in any position you can name.  There's no point in it whatsoever.

With the timing chain off, you can make the pin touch the bucket with the crank in any position you can name.  There's no point in it whatsoever.

I think he meant w/o chain he could hold down the cam with one hand and gently rotate it

until the decomp pin gets stuck at the exhaust valve's bucket.

If he does that when the exhaust lobe is pointing at something between "front wheel" and "skyward"

he'd be at the very position where the decomp would have closed the valve.

 

When he then compares the position of the 9 'o clock punch mark of the WR cam decomp pin touching the valve

with the position of the 9 'o clock mark of the to be adapted YZ cam when the pin touches the valve,

he can find out if he still has to file/dremel away more.

 

Personally I'll not do that with the cam in the head. :naughty:

- Too risky to drop particles into then engine,

- rather tricky to press down the cam by one hand, while the other hand tries to feel the "pin touching" point

  and - w/o the slightest movment - one has to check the position of the punch mark.

 

I'll do that cam comparison outside the engine, when I'm filing down my YZ cam's pin.

Of course, I'll start a thread about Rowdy's Cam Timing Comparison Tool here on TT. ;)

Edited by WRF-Rowdy

Ahh yeah, maybe TDC wasn't the right word to use.  I think you know what I'm saying.  You could put the cap back on the cam to hold it in place.  It will stop when the pin hits the bucket.  The pin won't retract unless you push the weight mechanism thing.  Yeah, I wouldn't actually do any grinding with the cam in the head.

Edited by chu

I miss that guy.

 

He livened up the place.

 

I'm still around...

FYI, the 2012+ heads are different beasts compared to the pre 2012 heads.   Much larger port volume than previously. With these heads you can have too much of a good thing.  Too much overlap, too much duration or too much lift may cause issues like flow reversal.  I don't know for sure, I haven't tested 2006 cams.

 

FWIW, no cam is going to make a difference until you open up the exhaust.  Both the cam(s) and the exhaust are restrictions on the 2012+ engines. 

 

I have an 08 exhaust cam in my 2012 WR.  I could not be happier with it.  I've ridden it back to back with an identical 2012 WR450F (gearing, exhaust, engine tuning, etc.) and its a night and day difference.  Much wider powerband, way less engine braking, much more bottom end, much smoother bottom end.  The difference is really noticeable in any difficult trail condition, but especially when climbing hills.  Its way easier to ride, way more controllable.  The decrease in engine braking is really noticable and appreciated too.

 

Other combinations may be better than what I have done.  I don't know.  But I would never go back to stock.

 

Hope this helps.  

 

PS: I have no idea about the decompression pin.   I removed my starter.   WRs kick a lot easier with a YZ exhaust cam.  WRs don't eStart with YZ exhaust cams because eStart spins slower than kickstart and the YZ decompression pin lets off too much compression.   If you installed a stronger starter and/or battery, you may not need to grind the YZ decomp pin.  I dunno.

Edited by MidlifeCrisisGuy

FYI, the 2012+ heads are different beasts compared to the pre 2012 heads.   Much larger port volume than previously. With these heads you can have too much of a good thing.  Too much overlap, too much duration or too much lift may cause issues like flow reversal.  I don't know for sure, I haven't tested 2006 cams.

 

FWIW, no cam is going to make a difference until you open up the exhaust.  Both the cam(s) and the exhaust are restrictions on the 2012+ engines. 

 

I have an 08 exhaust cam in my 2012 WR.  I could not be happier with it.  I've ridden it back to back with an identical 2012 WR450F (gearing, exhaust, engine tuning, etc.) and its a night and day difference.  Much wider powerband, way less engine braking, much more bottom end, much smoother bottom end.  The difference is really noticeable in any difficult trail condition, but especially when climbing hills.  Its way easier to ride, way more controllable.  The decrease in engine braking is really noticable and appreciated too.

 

Other combinations may be better than what I have done.  I don't know.  But I would never go back to stock.

 

Hope this helps.  

 

PS: I have no idea about the decompression pin.   I removed my starter.   WRs kick a lot easier with a YZ exhaust cam.  WRs don't eStart with YZ exhaust cams because eStart spins slower than kickstart and the YZ decompression pin lets off too much compression.   If you installed a stronger starter and/or battery, you may not need to grind the YZ decomp pin.  I dunno.

It's a Bummer you didn't Dyno your bike to show everyone how much power you really gained. At least Rowdy did.

It's a Bummer you didn't Dyno your bike to show everyone how much power you really gained. At least Rowdy did.

 

Good for him. 

 

I rode my bike back to back with a stock WR450F.  I don't care if I didn't gain any HP.  Its an all round better bike with the exhaust cam in it.   A stock WR450F has more than enough HP for trail bike, remember ?  The exhaust cam just makes it that much better.

Good for him. 

 

I rode my bike back to back with a stock WR450F.  I don't care if I didn't gain any HP.  Its an all round better bike with the exhaust cam in it.   A stock WR450F has more than enough HP for trail bike, remember ?  The exhaust cam just makes it that much better.

Well more than enough of 42 RWHP is never enough for some of us.

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