Does retarded WR timing really do anything good?



44 replies to this topic
  • MOmilkman

Posted March 07, 2003 - 04:21 AM

#1

Recently a freind of mine that rides a KTM posted the following message on a local harescramble racing pit board. Im posting his message here to get your guys take on this. He was talking about a WR250F but still his comment still applies to us too.

I will not give his name to protect his identity in case you guys think he is wrong.
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As far as the YZ timing issue I'll set you straight right now The ONLY reason yamaha retarded the exhaust cam is to cut down noise emmisions it DOES NOT make the motor pull harder down low this is a myth. Any one who has spent any time fooling with camshaft timing will tell you that retarding timing increases top-end power and advancing timing has the opposite effect. In the case of the yamahas all it does is decrease power across the board! The reason people feel it has more lowend is they are able to use a greater amount of throttle in slick conditions without spinning the tire (which means the motor is a DOG) this may be of some use on a big bore but my "opinion" is that you can not increase the amount of power coming out of a 250f enough. The more power the better I have ridden several 250f's and have always came away amazed at there ability to pull my lard butt at low RPM's even up steep hills so increasing your bikes power will not have an adverse affect. It only takes about an hour to change it and it requires no parts so it is easy to change it back if you don't like it for some odd reason. I promise it will pull better at all times. I have been trying to convince Darrin to try this for a long time but he is to scared and he thinks his bike may make to much power and for some reason he keeps forgetting that the throttle turns both ways! Just do it. The fact that you are hanging out in a race forum tells me it is the right thing for you. Just don't be dissapointed when I fly by on old Bessie no amount of work will make that thing a KTM!

  • Indy_WR450

Posted March 07, 2003 - 05:49 AM

#2

The new WR450s need a cam swap, but I have heard no complaints on this board with the cam timing mod on WR426/400 where they simply rotate the position of the stock exhaust cam. I think everyone that has done it has not rotated it back. That should tell you something about the performance difference. Hopefully some of the members that have the mod will concur .

  • GPS Dual Sport

Posted March 07, 2003 - 05:50 AM

#3

This is intersting stuff. Where I come from the amount of valve timing overlap (the time both intake and exhaust valves are open at the end of exhaust stroke and beginning of intake) determines where in the RPM range peak power happens. More overlap moves peak power into the higher RPM range.
The WR is timed with less valve overlap than the YZ by one tooth on the cam chain. This moves the WR peak power down the RPM range and is preferred by most normal folks in technical riding conditions.
This tuning trick is possible because of the dual cam on the Yamaha. For the KTM and Honda CRF 450 single cam folks this requires custom cams to adjust valve overlap.
I'm glad your friend is happy with his orange ride. Most of the folks in this forum are happy with the blue ride.

  • Hick

Posted March 07, 2003 - 01:53 PM

#4

The ONLY reason yamaha retarded the exhaust cam is to cut down noise emmisions...



That is the dumbest thing I've ever heard. But that don't mean it ain't true.

Here is my take from personal experience:

Long wheelies are much easier w/ WR timing. :)

And ditto what Zak said, you can definitely feel a power difference upper to mid w/ the YZ timing, but you DO lose some oompf right off the bottom, so where you ride and how you do it should dictate whether you want the YZ midrange zap or the WR lowend punch.

Tell your freind there is no such thing as "free" horsepower (well, maybe higher compression ratio). Changing cam timing moves power around, it doesn't add it, any gearhead worth his dirty fingernails should know that.

  • MOmilkman

Posted March 07, 2003 - 06:33 PM

#5

Excellent post Hick.

I totally agree with you.
I think you are right on the money. Im gonna ride with him tomorrow. I'll throw this info at him and see what BS he will come up with next. :)

  • Dan_Lorenze

Posted March 07, 2003 - 09:27 PM

#6

I've had my WR426 both ways....

Hick, I agree with you.. More throttle control with the WR timing.

  • yamaha.dude

Posted March 07, 2003 - 09:47 PM

#7

If you do the YZ timing mod to a WR, you can get back some of that bottom end lugging ability with the JamesNOW! mod... costs maybe 5 bucks, but takes less time than a cam change...

I went from WR to YZ timing... It adds a whole new dimension to the bike... you can alter the power delivery to a degree with the right timing... add 2 or take away 2 teeth from the back sprocket...

David

  • SPUTTER

Posted March 08, 2003 - 05:11 AM

#8

Or better yet, for a 426, drop in the YZ 450 cam. The power remains linear but much, much more - just about everywhere- and it torques like a John Deere. No noticeable "hit" either. I find myself a gear up on many trails as compared to the stock WR426 cam - for my exhaust set-up the power increase was unexpectedly huge and you have the same throttle control as the WR timing - it feels like 5-10 HP! So, YZ timing is great - with a 450 cam :)

  • Superbike

Posted March 08, 2003 - 05:57 AM

#9

1. A WR 450 has more beans than a KTM 450.
2. YZ cam timing is great, WR timing is great. I may end up with YZ timing.
3. EXC motor and SX motors are completly different, even the crank and bore size are different. Why? To make it better for off road. They also used a 6 speed tranny to help the narroewer power. I looked hard before I went blue again
4. WR timing smooths out the power for better control in tight woods situations. Fact. Yamaha left us the option of full out YZ power with the 5 speed. More power is not always better. KTM uses thatI can haul ass On a 125, I do not think cam timing will hold me back.
5.Why would we want to make it a KTM? If I wanted a KTM I would have bought one. That is a ridiculous statement. Why would I want crappy suspension, that must have almost $700 dumped in it to get the performance of my Yamaha with springs and a revalve? Kinda blows the good hadlebars and Hydraulic clutch out of the "good but catagory.
There are a lot of know it alls in this sport. Some can speak the truth. Most the time people tell you what they want to hear. I see this a lot on here. Not as much on blue as on another (nameless)area
The sad part is I really really wanted a KTM, The suspesion is what held me back. ----Mike

  • KTMKarl

Posted March 09, 2003 - 07:48 AM

#10

I should have known Darrin would go international with this one! Got ya bud! You all need to go back to engineering school. Valve overlap and associated changes thereof does not drastically affect the RPM wherein a motor makes its power it does however have an effect on the amount of peak power and the breadth of the torque curve. In the case of the Yamahas, wr timing does in fact reduce the amount of power available at ALL rpm ranges and throttle openings. Show me a dyno report that shows differently and I'll eat my words! (although begrudgingly). Less valve overlap does has its advantages in some applications, most notably forced indution, however the normally aspirated engines we are speaking of here rely heavily on exhaust scavenging to "fill" the cylinder which is the function of overlap. The exhaust valve being open at the same instant as the intake alows the negative pressure in the exhaust (left over from the last exhaust cycle) to pull in a fresh intake charge. Less overlap, less pull, less power. This said the incresed overlap will make the motor "feel" peakier and conversly trick the rider into perceiving a lack of low end or possibly even the impression that the motor signs off earlier as the sweet spot of the engine is much stronger and noticable within a narrower rpm range however the engine will make more power across the board! The dyno proves this and is much more accurate at determining engine tune than the "long wheelie" method! :D
By the way the Camshaft measurement having the most impact on RPM range is the intake valve centerline (assuming the overlap stays the same) This is where the old game of advancing the cam in your 350 for more low end comes in and retarding for more top end. A tool I have wasted much of my life playing with on racing cars. :)
Also I don't argue that retarding the exhaust was the stupidest thing Yamaha could have done but you guys should be happy that they made it as easy to repair as they did. Of course I can understand where you all would be a little pieved ecspecially if you have ridden a KTM 520 lately. Right MOmilkman! :D

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  • Indy_WR450

Posted March 09, 2003 - 08:47 AM

#11

Well put. Does anyone hear know if there is a significant difference in intake cams between the WR and YZ 450s? I ordered the YZ450 exhaust cam but I am not sure if I should have gotten the intake cam as well.

  • JL

Posted March 09, 2003 - 12:05 PM

#12

What effect will the exhaust have on the power gains ? The reason I ask is due to the sensative nature of some of the places I ride and lack of funds :) I need to stick with my European exhaust with its < 1 inch end pipe, would I see any real gain from the YZ timing our would the restrictive exhaust cause it to run badly by not been able to get the exhaust gases out fast enough? (I need to know before I buy the 03 cam)

  • Indy_WR450

Posted March 09, 2003 - 12:58 PM

#13

JL, I would not bother with the cam mod unless you are going to at minimum use a baha or gyt-r baffle. Avoid a lot of the mods on this board since most are not going to work well with the stock baffle plug in the exhaust.

  • Dan_from_HB

Posted March 09, 2003 - 01:13 PM

#14

With all due respect to KTM riders, I actually ride a '02WR400F full-time. I've spent 2-1/2 years on this very same bike. So, I know its power characteristics quite well. With all theoretical engineering discussion aside, there are some observations I would like to make regarding power differences between WR and YZ cam timing.
1. There seems to be very slight increase in power output in midrange and top end with YZ timing.
2. There seems to be a slightly harder "hit" in the transition to midrange with YZ timing.
3. There seems to be a small power decrease in low end with YZ timing.
4. The power simply seems to have been redistributed in subtle ways. Nothing earth-shattering.
5. This was not verified by a dyno, but I don't ride the bike on a dyno. I ride it on trails with dramatic differences in conditions.
I have selected YZ timing for my bike. I ride mostly enduro-type terrain, but like to test the speed limits on occasion. I ride whoops, sand, rocks, hardpack, roads, singletrack, climb hills, and occasionally break new trails. The YZ power characteristics are perfect, as is the WR gearbox.
A different setup may be ideal for other riders. Depends upon too many factors for anyone to decide except those who are actually riding the bike.
I will say that the mod my buddy made on his WR250F that had the single largest impact on power was the selectable boost ignition from FMF. It's still available from Wolf, I think. Both his bike and mine are still entirely rideable in the tightest conditions you could imagine.
BTW, I've ridden several KTM 520's recently. Pretty good bike, but I'd still buy a WR even if the price was exactly the same.
Dan
PS: MOMilkman, you do what you think is best. Don't let your buddies push you into anything you don't want to do. It's your bike, you gotta live with it, not them.

  • MOmilkman

Posted March 09, 2003 - 06:08 PM

#15

Who's KTMKarl?

Hes acting like he knows me but I dont think we have ever met. ??? Hmmm, thats weird. :) :D

:D

Dan,
Ive always been happy with my bike the way it has ran but recently I have been wanting to explore options that may enhance my current ride. (mostly due to the fact I wont be buying a new bike for a couple years) As far as the timing issue, I wont back down on the fact that my bike felt like it had more bottom hit than a YZ timed bike. BUT, Im not sure if I want to keep it that way any more or not. What Im saying is, Im just thinking about trying it and seeing how it fits my riding style. Plus I am going to add the JamesNow to compliment the YZ timing. Worst that can happen is I dont like it. So I'll just change it back.
I want to do the 03 cam mod and I probably should explore both options before ordering a cam.

Now that being said. Dammit Karl!! Why did you have to come in on my innner-sanctum! :D
This is where I get my info and them pretend like I know what Im am talking about when we all get together and talk shop.! Now my cover is blown! Now Im not gonna have any new news to share with you if you keep coming here... :D

....

hey! How bout that new beasties album!?

  • Dan_from_HB

Posted March 09, 2003 - 06:20 PM

#16

Milkman,
Sounds like we're going to have to get Karl and his orange horse out to a ride with some blue bikes and open up a can of whoopass! Think you and a few other local guys on the blue side can handle it, or do you think a few of us West Coasters have to get involved???
Dan
PS: don't tell Karl. This'll be our little secret!
PPS: I think Karl has a crush on you. Probably just WR envy!

  • Dodger

Posted March 09, 2003 - 06:34 PM

#17

I really like the YZ timing. It's a personal preference for sure, but don't think I'd change back, I like the snappyness.....

Peace

Dodger :) :D

  • JL

Posted March 10, 2003 - 12:46 AM

#18

Indy WR450 - thanks for the answer , I think I'll stick with WR timing and get the 03 WR cam :)

Dan from HB - Exellent reply you are right it's what the bike feels like to the rider that matters , not what the dyno figures say in an artifical enviroment. :D

  • FTD

Posted March 10, 2003 - 02:21 PM

#19

WR vs. YZ timing... I notice that "punch" with the YZ timing. I can launch out of the tight corners much better and it revs out faster. for instance, I have rode a certain trail dozen and dozens of times, after I changed to the YZ timing I came through a creek crossing, it turns right for 100 yards or so and I never before came into that corner that fast. I was amazed!Since my cam adjustment I like the my bike much better. I have no more stalls that I had with the WR timing and we ride alot of tight trails. I do believe pulling the gray wire to change to the YZ CDI mapping does cause me to stall in tight stuff. I decided to put a "gray wire toggle switchon the right radiator gaurd. You can reach it through the vent in the right plastic flare that comes off the tank. Up for desert and down for the mountains!! Works great.

  • Superbike

Posted March 10, 2003 - 02:43 PM

#20

Notice the KTM guys have to compare the 525 to the WR 450? The WR timing on the 450 still has more beans than a 450 EXC. Why does nobody compare the 450 to 450? HP does not always eqaul speed. KTM riders should know that :)----Mike




 
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