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motojason

WR to YZ cam timing. Advantages?

28 posts in this topic

What does changing the exhaust cam timing on a 2005 WR 450 to YZF spec do to the power characteristics of the motor?

Can you get real results by altering the timing only,or do you need a YZF exhaust cam?

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'03 and newer require the YZ cam due to the auto-decompression mechanism.

More power across the band... all good, nothing bad.

It was detuned for emissions.

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i have a 03 wr450 and i changed the timing to yz it runs but it doesnt start when its hot .you have to bumb start it to go do i need to buy a 03 yz ex cam?help

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i have a 03 wr450 and i changed the timing to yz it runs but it doesnt start when its hot .you have to bumb start it to go do i need to buy a 03 yz ex cam?help

:thumbsup::bonk::thumbsup::eek:

'03 and newer require the YZ cam due to the auto-decompression mechanism.

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Pop a beer, sit down, and do a search on this. I bet you could read for about 38 hours straight on this topic alone.

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Pop a beer and do a search? He just had to look 2" above his own post.

I really wish newbies would read the ENTIRE thread before posting.

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Pop a beer, sit down, and do a search on this. I bet you could read for about 38 hours straight on this topic alone.

That's for sure.

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Rich, is the WR REALLY cammed the way it is for emissions??? or is it to smooth the power delivery for easier trail riding? (which has always been my impression)

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Rich, is the WR REALLY cammed the way it is for emissions??? or is it to smooth the power delivery for easier trail riding? (which has always been my impression)

Negative.

Cams tuned for power lower in the rev range / smooth power delivery.

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Then why didn't any of that go away when I installed the YZ cam?

It's a myth that the YZ cam costs you power down low... ask anyone here who's done the mod... there's little noticeable difference off the line (if anything it's better), and a much smoother delivery of MORE power across the entire power band.

I LIVE on the bottom end... I hate shifting under stress, so when I'm approaching a hill or in a sand wash, I tend to run one gear higher than I really should be. Twisting the throttle at any RPM feels like it's going to throw me off the back.

The WR cam comes advanced, meaning that it opens and closes too early.

It opens BEFORE BDC on the power stroke, and closes right at TDC on the exhaust stroke. This creates virtually no overlap, which allows the exhaust pulse to draw fresh fuel/air in at the beginning of the intake stroke.

Also, opening before BDC wastes the last bit of power from the expanding gasses.

The whole thing works as a system. The WR exhaust was plugged up to meet enduro sound requirements. The plugged exhaust causes problems with the stock YZ cam and jetting, so the cam was advanced and the jetting leaned out to lower emissions. Since most people upgrade the exhaust before they touch the cam, the problems with running the stock exhaust and the YZ cam are never apparent.

The throttle stop screw was added to further satisfy enduro requirements. Since the rules say "db measured at 'x' throttle position", reducing overall available throttle means that 'x' is at a lower point, which reduces RPM when tested.

It's the same with the gray wire. A lot of people claim that it's also to smooth bottom end power to make it more friendly on trails. It doesn't. It kills power from the midrange UP by retarding ignition timing by approximately 30 degrees from 6000 rpm on up. Everyone who has put a switch on their gray wire to switch between "WR" and "YZ" has just left it in the "YZ" position.

I would suspect that the same would be true of the exhaust cam if it were a simple matter to switch back and forth.

The WR's weighted flywheel is what smooths power delivery... not the cam.

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'03 and newer require the YZ cam due to the auto-decompression mechanism.

More power across the band... all good, nothing bad.

It was detuned for emissions.

I respectfully disagree with you Rich..

It was not detuned for emissions.............

YZ timing will promote more wheel spin and less throttle control, YZ timing brings its baggage to serious off road situations. I've been there done that with YZ timing, I can't see myself ever going back to YZ timing again.

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WELL SPOKEN!i also reconnected my gray wire, i did;'nt know the specs but i knew the power was off.you seem to be intha know on this subject ,is the intake cams the same in yz & wr?

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Rich,

Great analysis, spoken from experience......

Bruce of Vickery Motorsports of Aurora, CO, (USA Dirt Track Hall of Fame) re-pressed my 03 WR450 cams to his winning oval dirt track specs (trade secret) and now the mid-range torque is way, way up. Perfect for short shifting sand washes and mongo hillclimbs. I asked to port the heads too, but Bruce said the FMF Q (darn CO trail nazis....) could not flow the increased exhaust. Atleast he was honest...saved some bucks and bought the Power Now/JD Kit/ and PowerFilter trifecta instead....

:thumbsup:

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is the intake cams the same in yz & wr?

For '05 and '06, they are the same, part number 5UL-12170-10-00

For '03 and '04, YZ was 5UL-12170-00-00 and WR was 5UM-12170-00-00

For '01 and '02, YZ was 5NL-12170-00-00 and WR was 5PH-12170-00-00

Here's exhaust :

For '05 and '06, YZ is 5UL-12180-10-00 and WR is 5UM-12180-10-00

For '03 and '04, YZ was 5UL-12180-00-00 and WR was 5UM-12180-00-00

For '01 and '02, YZ was 5NL-12180-00-00 and WR was 5PH-12180-00-00

The '05/'06 exhaust cams are about $30 more than the '03/'04.

'01 and '02 lack autodecomp and the only difference is where the timing mark is in relation to the lobes.

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The throttle stop screw was added to further satisfy enduro requirements. Since the rules say "db measured at 'x' throttle position", reducing overall available throttle means that 'x' is at a lower point, which reduces RPM when tested.

:bonk: All of the db tests that I have seen require that the db is measured at "half of the max rpm of the motor"...nothing to do with throttle position.

I'm a fan of the YZ cam. :thumbsup: more power everywhere in the rpms, and I love how it works in the tightest, nastiest, single track that you can throw at me.

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:thumbsup: All of the db tests that I have seen require that the db is measured at "half of the max rpm of the motor"...nothing to do with throttle position.

Hmm... and if full throttle is 2000 rpm lower because of the throttle stop :bonk:

How is RPM measured at an actual field test at an enduro or ranger stop? Do they stick a tach on it or just run the throttle to half? I've heard they just twist to half throtttle.

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I'm a fan of the YZ cam. :thumbsup: more power everywhere in the rpms, and I love how it works in the tightest, nastiest, single track that you can throw at me.

That's where WR timing shines... When throttle position and power delivery are critical.

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WR timing with proper jetting is extremely fast. Poor jetting is much more noticeble with reduced power compared to a poorly jetted using the YZ timed engine. :bonk:

Before you all run off and try YZ timing make sure you have the most of the WR timing. :thumbsup:

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The whole thing works as a system. The WR exhaust was plugged up to meet enduro sound requirements. The plugged exhaust causes problems with the stock YZ cam and jetting, so the cam was advanced and the jetting leaned out to lower emissions. Since most people upgrade the exhaust before they touch the cam, the problems with running the stock exhaust and the YZ cam are never apparent.

Sorry to bring up an old post like this, BUT....

I am running the stock exhaust (baffle out) and am about to install a YZ cam. Should I wait to install the cam until after an exhaust upgrade, or am I ok with the baffle out? :thumbsup:

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I am running the stock exhaust (baffle out) and am about to install a YZ cam. Should I wait to install the cam until after an exhaust upgrade, or am I ok with the baffle out? :thumbsup:

Particularly on the '04 and earlier, I think the stock WR is as free as the YZ when it's unplugged... it's just a boat anchor with a large hole drilled through it :thumbsup:

The unplugged '05 and '06 should be fine... that restrictor makes a BIG difference in area.

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