Anyone try this?

 

Am not sure how many degrees im supposed too,i wouldent want to go past 6 degreesi believe 1 tooth is 16 degrees..

Someone on here has tried it and said it worked,but no real proof..

 

One tooth is not 16 degrees. That would mean there are 22 1/2 teeth.

degrees of one tooth = 360/# teeth total

Basic geometry


~HoundDog

 

so how many degrees are you retarding it if you do 1 tooth..?

 

how many teeth are on your sprocket?


~HoundDog

 

I have an 01 Raptor with a 11:1 wiseco piston (std bore), hotcams stage 1 cam, staintune full stainless exhaust (Australian built). And an opened up airbox, and rejetted.
I retarded the cam 1 tooth which equates to 17.1 degrees retarded in crankshaft degrees. The raptor has a cam sprocket with 42 teeth so 1 tooth change = 360/42 = 8.57 camshaft degrees hence multiply this by the 2:1 reduction which = 17.142 degrees crankshaft change. By retarding the cam the exhaust valve to piston clearance is reduced, but the wiseco comes with 1mm deeper valve reliefs in the piston compared to the flat top std piston. I checked the exhaust valve clearance by pressing on the exhaust valves while rotating the engine over near top dead centre and could feel a fair bit of clearance. I didn't measure this with a dial indicator though so i dont know the exact value.
The result. It flies. Conservatively i'd guarantee it' given another 500 rpm, but i reckon it's closer to 1000 rpm of top end power. It pulls hard and keeps revving instead of the power dropping off.
The jetting becomes much leaner at idle and i have wound out my mixture screws a fair bit and it now idles beautifully. I will fit 25 or 27.5 pilots when they come as i am now well past the recommended 3 turns max out.

I have noticed a little drop in bottom end power but the raptor has never had a shortage in this area anyway. If you have a wiseco or JE piston which has the deeper valve reliefs, and a stage 1 then you would be stupid IMO to not try this. If you have a stage 2 cam then you should only attempt this (to see if any benefit exists, it may not) if you are experienced enough to measure the exhaust valve to piston clearance with the springs removed and a dial indicator, as the stage 2 has more valve lift and might result in dangerously close contact.

By retarding the cam the top end increases as the intake valve closes later to take advantage of the momentum of the intake air and similarly with the exhaust. All i can say is that i am rapt with the quad now, and it has been one of the biggest gains in power that i have done. Same sort of gains as the piston and exhaust combined.
_________________

 

Well, there it is.

~HoundDog

 

what do you think Gary...

 

Excellent and informative! I do not doubt your word, but for curiosity's sake did you have a baseline before and after the change...such as a buddy too race? Have you hit the rev limiter since the mod? One time when I put mine back together it would not even run being off a tooth....I asume I was advanced?? How far off is your TDC indicator at the bottom now? Lets see.....effectively moving the cam 1 tooth toward (towards the front of the bike)with all else being equal will retard the cam? I am almost positive mine was off 1 tooth the other way when it would not run. Thanks gentlemen!

 

I think I saw Grant from australia post that on this or another forum.

I have always thought of this way - moving the cam gear counterclockwise advances it. If you turn the motor over the cam is "advanced in time" where the crank firing position and TDC have stayed the same. The cam is 1 toother "sooner"