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tool

changing intake cam timing

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ive been thinking about altering the intake cam timing. is it possible to change the stock intake cam 1 tooth? or would i have to get a hotcam with an adjustable sprocket?

lets say i did end up getting the hotcam, would i advance or retard to get more bottom end?

thanks for the help

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On the 03's the intake cams are identical between the YZ450 and WR450. It's the exhaust cam that is different. I'm not 100% sure but I belive this holds true for the 400 & 426 as well. Any one else out there got input on the 02 and older bikes?

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here what im wondering... see, ive changed the exhaust cam to wr timing which helped bottom end. i cant see why i couldnt do the same for the intake cam, is it not adjustable? if a hotcam intake is adjustable, and you can adjust the stock exh cam timing... then why not the intake?

what would happen if i did change it :thumbsup:

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Changing to WR timing gave you less valve overlap, which is more efficient at idle and low RPM's. YZ retarded exhaust cam timing improves higher RPM efficiency while increasing natural exhaust gas recirculation which lowers peak combustion temperature while improving it's knock resistance and increases hydrocarbon emissions. WR timing increases NOx emissions...

I believe the intake cam timing is already optimized for the engine's design, considering combustion limits in a 12.5:1 compression engine. You may consider getting a hotter intake cam but you would get more for le$$ with a thorough head porting and cleaning (smoothing) and manifold matching job. You can do most of this yourself if you're handy with rotary tool on fully dissasembled head...

By the way Tool, when changing to WR timing, did you experience any pinging or a need for a change in jetting?

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Kev, Thanks for backing me up :thumbsup:. Do you know if the profiles are the same and the cams are just indexed differently between the YZ and WR? Or is it a whole different cam profile between the two?

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there is a noise that wasnt there before, coming from the left side of the engine. :thumbsup: the jetting was a little off both before and after, but not much change. it might have helped my plug fouling issue a bit cuz i think the yz timing was running too cool.

it runs stronger at idle through the mid, but its still got so much top end. i dont even use the top end.

im gonna try a torque pipe, but is there any other way to make this engine really torque? :devil: i would be willing to trade some top for some bottom. i was hoping i could just swap the cam

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My 426 is YZ timed, and I just fitted a stepped GYT-R header pipe and YZ muffler. It make massive torque down low.

These figures are for the 426.

Inlet cam lobe centre 110

Exhaust Cam lobe centre (WR) 119.5

Exhaust Cam lobe centre (YZ) 101.5

It's my personal opinion, and that of the local cylinder head guru and of my mechanics (who had heaps of experience with the 5 valve heads)that 105 centre on the inlet would be ideal with the Exhaust cam in YZ spec. If you want more power in 'chug chug' mode, add another base gasket or two.

Make sure you check piston to valve clearance if you plan to alter from the standard YZ or WR cam timing specs.

Hamish

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The Power Now Valve improves response and low end torque by increasing intake air velocity from idle to half throttle. The FMF Power Bomb SX is quieter and also tuned for low to mid grunt with impressive roll-on power improvement. Port, manifold and carb smoothing and matching helped too as did NGK 's CR9EIX iridium plug and 1/3 aviation gas.

By the way, is the(...TZZZZZK!...)noise present during acceleration at mid RPM's in top gears, and is a power surge felt when noise disappears?... or do you mean a mechanical noise?

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By the way, is the(...TZZZZZK!...)noise present during acceleration at mid RPM's in top gears, and is a power surge felt when noise disappears?... or do you mean a mechanical noise?

i doubt its mechanical, cuz something would have to be really loose to make that noise. but it does only happen at about mid throttle. no power surge though. could be some type of detonation or ping? what would i do about that?

as for cam timing, i recall reading an article on how you can advance a CRF's cam by 5 degrees, and that results in an increase in bottom to mid. but to do that, you would be advancing both sets of valves :thumbsup:

i would think that a DOHC engine would be ideal to configure cam timing to exactly my liking, since i can isolate the intake and exhaust.

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i would think that a DOHC engine would be ideal to configure cam timing to exactly my liking, since i can isolate the intake and exhaust.

If you want to go the full hog....

Get the base of the inlet ports build up by a cyl head guy. Then get him to flow your head, measure the compression ratio, cam lift and duration ,deck height, bore stroke, header pipe length and diameter etc etc. He will stick all that info into his computer and u tell him where u want max power and torque. His computer will then advise ideal lobe centres. Then you just get the sprockets pressed off and refitted at the ideal place, or buy a slotted sprocket kit from Falicon.

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If you want more power in 'chug chug' mode, add another base gasket or two.

How does this increase power? I see how it might lower the compression ratio, if nothing else.

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lower compression helps torque in the very low rev range. Thats one reason why 426's don't 'chug' as well as XR's etc etc.

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Get the base of the inlet ports build up by a cyl head guy. Then get him to flow your head, measure the compression ratio, cam lift and duration ,deck height, bore stroke, header pipe length and diameter etc etc. He will stick all that info into his computer and u tell him where u want max power and torque. His computer will then advise ideal lobe centres.

it does make alot of sense to have an engine tuned like that. i would be afraid of 1) the cam gears slipping after that, 2) having some guy take a rotary tool to my head. :devil:

i would be interested in getting the engine specs measured, telling him where i want the power, then getting a slotted sprocket kit for both cams. :thumbsup:

i would get a set of hotcams, but they're made for more mid and top end. :awww:

though, i might just get the sprocket kits from falicon and experiment. i guess im not ready to go full hog... im really looking for an easier way, and less $$$.

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