2004 wr450 camshaft questions Grayracer?

[jsantapau]

2004 wr 450     I do not like the power with the stock cam,   the yz camshaft is too powerful for my limited riding capabilties and estart issues.  I am assuming the only cams available are stock  yz  and hotcams  which I tend to read as yz timing  with the auto decompresion set up for estart.

 

the question I ponder is if I buy the hotcam and a high compression piston  and then  space the jug up to lower the compresion back dow to say 10  or 11 to 1 .  hopefully advancing the cams a smidgeon buy pulling the timing chain tighter.  I am a very strong class b fleet mechanic  but i do not build race engines the tools and work should not be a problem the lack of knowledge and direction is.  my mind is telling me that lowering the compresion should soften the hit, advancing the exhaust  bleeds off combustion pressure to soften the hit  and then tryng to retard the intake cam  lessening(?) the overlap should tame the feel of the engine  to a lower rpm freindly zone..

 

barage of question time  is my thinking mechanically correct?    at what point  can I lower the compresion, at what point  does the intake cam  being retarded  at closing time  does it wreak havoc with the combstion stroke starting.  everybody wants to build a more powerfull bike so it is kind of hard to find info to mellow one out. Is there a custom  cam grinder that  could possibly grind down the cams by  my verbal wants that you would trust?

 

Thank you in advance

[grayracer513]

Well, you're off a bit in several places.  It sounds more like you should bump the compression with the stock cam to pick up some more low/mid power.  Add an aftermarket ignition to monkey with timing.  Either that, or the Hot Cams exhaust and an aftermarket black box.

 

The raise the compression, then space the cylinder routine is like two steps forward and then two steps back; a self cancelling waste of time and money.  Besides, the YZ timing wouldn't like the 10:1 thing very much.

 

Your understanding of the valve event timing in a four-stroke is a bit weak, too.  The intake valve does not close during the power stroke at all, but rather at around 120 degrees BTDC during the compression stroke, so retarding the intake weakens the intake signal through the port, and the overall compression.  Retarding the intake will kill power faster than just about anything, but if you move the cam one tooth, that's 22.5 crankshaft degrees, and the bike would not only be weaker, it would run like crap.  Worse with the YZ/Hot Cams exhaust than with the WR, most probably.

[jsantapau]

yeah sorry about my brain farts   i should  of said compression stroke. when the intake  valve is closing  please let me straightem myself out  and try again.

 

I would like a more in between power  than than either wr  or yz .  so  by trying to space the cylinder up to the limitations  of lowering the compression of a high compression piston I can hopefully advance the yz exhaust cam a couple of degrees..  it will not be  the 22 degrees  or whatever a tooth would be  it would be 40 links of chain trying to span 10 1/8th of length compared to 40links of chain to 10 inch length of crank center to cam center.(not truthfull of the measurements just hypothetical)   similar in concept to using a thicker base gasket on a 2stroke to raise port hieght.  using thicker base gaskets and or spacer to advance cam timing.  unfortunately that would bring the intake cam timing forward also  so by either pressing the gear on and off or by using an adjustable cam sprocket(I believe hot cams had an adjustable intake cam)

and hopefully getting the couple of degrees of correction or maybe a skoche of retarding to get a more desirable result.    Mind you it is a 2004 relatively low hours  but abused ie: upside down running  and drowned in water abuse.  and the only time the engine was opened  was to try the yz cam  and to pour the water out of it.  I am looking at a rebuild soon  so buying a piston and  valve train parts  are probably going to be in the works anyway,  just  kinda blueprinting in a backwards way(?).  like setting up my valve lash on the looser side of allowable then tighter to lessen timing and lift.

 

what would be more important to consider on the intake cam   valve overlap timing  or  the intake valve being open upon the compression stroke?  I am still under the guessing that on the intake cam the stock Yamaha cam is prbably the mildest . if I have too much overlap  by advanced  intake cam there is a exhaust dilution  and blow back torwards the carb scenerio    too retarded of cam timing there will be still a blow back torwrds the carb  from the compression stroke .

 

am I kinda making myself clear?  sorry if I am pondering a position that is difficult too understand   I don't care if I have a week yzf engine in fact I kinda want that I just want a more powerful engine than the wr

Edited October 24, 2015 by jsantapau

[dg400sm]

keep us posted on the results please. i have a yz426 that i would like to mellow out too

[SteveThe Snakes]

I think your going in the wrong direction with lowering compression it will just take away from low end. Finding a knowledgable tuner to advance the cam sprocket on a Hot cam is what you might want to do.

[jsantapau]

keep us posted on the results please. i have a yz426 that i would like to mellow out too

 

 

I think your going in the wrong direction with lowering compression it will just take away from low end. Finding a knowledgable tuner to advance the cam sprocket on a Hot cam is what you might want to do.

dg 400 If I am not mistaken the 426  was a manual decompresion bike    if you advance the yz exhaust  cam 1 tooth  you would have the wr engine   if you  tried  the wr timing and found it way to anemic   you could use  those two test runs to make a very rough comparison . following stevethe's suggestion  and take it to a reputable machine shop and have them press off and on the gear  say 1/8th  of a tooth advanced.

by the way  my old wr 400 I loved with the yz timing . I don't know if it was a slighlty smaller engine  or a slightly younger in better shape person riding it at the time  but I liked the yz400 power a lot better than i like the yz450  and I do not care for either in wr tune  please understand it was not a test of 4 different bikes  only  2 wr's  the 400 with yz camshaft timing  and the 450  with an actual yz cam 

 

I like your suggestion stevethe but the auto decompression and electric start I still haven't quite wrapped my head around   I do know that my bike does not like the yz cam with estart  starts fine kicking  but why the hell would I carry around a battery and starter if I am not going to use them    I have read on these forums about the decompression pin having different lengths  I have also heard that grinding down  the longer pin down to an appropiate hieght would be a no no.  but I am wondering if hotcams  would  actually assemble a cam a couple of degrees off to suit my wants.  might have to pay a pretty penny  to have somone in R&D to pull some parts of the assembley line and custom press it   but I guess the question would be free to ask them on the phone   thank you for the idea    

[dg400sm]

as a side note when it comes to taming bikes. i own a yz426 and a wr450 2003. from memory the yz exhaust is 45mm and the wr450 exhaust is 39mm, this plays a big part in how aggressive the the motor is. check your WR does not have a YZ exhaust

[jsantapau]

as a side note when it comes to taming bikes. i own a yz426 and a wr450 2003. from memory the yz exhaust is 45mm and the wr450 exhaust is 39mm, this plays a big part in how aggressive the the motor is. check your WR does not have a YZ exhaust

it is the stock exhaust with the billet insert    tried the gytr exhaust  but I really didn't notice the power as much as the noise difference  so it came off quick  maybe I will try the stepped header with the stock muffler

 

any how I didn't realize that there was a company called webcams  that sells ajustable cam sprockets..http://www.webcamshafts.com/index_blank.html?pages/vehicle_search.html      I think I am just  going to start with yz specs and slowly advance the ex timing to find what I was looking for.  then figure out  what i have to do  if estart problems creep up

 

thank you all for your help