****I saw this on another forum, and wondered what you guys thought??? - Ken


I have just finished a weekend with a big smile on my face.

Basically ever since i have had my Raptor, although i love the midrange grunt, i have been dissapointed with the top end power and drop in power at the top end.

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.

 

been idscussed and thrown out,it was on BT and no one i know has tried it..may cause damage ..

 

I tried the mod in question and and my engine did not want too turn over.....not even when being pulled by a truck....LOL. Apparantly a clearance issue with my 10.75/1 JE piston. THats a myth busted.

 

Probably the reason your engine wouldn't turn over is because the decomp pin not being timed right. I had problems with hard starting (like what you are describing) when my timing chain got stretched to the max. JMHO

 

THis was'nt hard starting....I probably should have elaborated that I heard clatter when the engine would barely turn over when being pulled with the truck at approx 30+ mph in 5th gear and dumping the clutch. Lucky I did'nt bend anything. Not sure what I was thinking...[img]i/expressions/face-icon-small-tongue.gif[/img].

 

OOOOooo sorry, yeah thats a little different than hard starting....but just a little.[img]i/expressions/face-icon-small-wink.gif[/img]

 

Does anyone have their decomp pin removed, my cam keeps on shredding the decomp pin keepers on the cam wheel themselves, i want to just remove it in general, how bad is the hard starting and if i shouldnt remove it, how come my decomp keepers keep shredding off. I just ruined my second set, what do i do.

 

What part are you talking about?

 

If the decomp pin keepers(surrounding the flyweights) are bent outward too much towards the head, they will scrape & will get mangled. Make sure they are bent in parallel to slightly inward towards the weights so just enough clearance is available that the weights can open & close. Any more clearance & they tend to stick out too much & can scrape the inside of the engine case.