I am looking into going up a little bit in compression. Wondering what the best way to go was. Obviously there are pistons and yes, there are different pistons from a couple of companies. At least a couple of companies sell them.

Why cant be machine the head or the cylinder? or even both at a fraction of the price. From what I'm told there is a great deal of room between the stock pistons and the valves. why not bring it in a little for that 1.3:1 boost in compression?

also, 11:1 is tough to run pump gas unless cams are moving enough air. Has anyone run 11:1 and not used the cams? CAMS ARE PRETTY PRICEY!

 

I am running the ron-woods 11:5 piston with stock cams and valve springs,and it runs pretty good, I would think for a trail rider it would be a perfect set-up. great bottom end and mid range,and then the top is thier but not "arm-pulling".


If you "Deck" the head, definatley have it done by someone with lots of experience,cause you only have 1 shot!!!







Bigger.

 

Call Ron Wood racing at (949)645-0393 and talk to those guys. They have always been cool to me with good advise. They do tons of rotax stuff.

 

Bigger hit it on the head - you only get one shot. you can bolt in pistons, and always have the option of changing back, or going farther, and if you up your compression to like 13:1 and then get tired of hunting down race gas down the road its nuts and bolts away from reducing it.

 

Good Point Bigger and Hightower

 

BigDaddy, when I bent a valve awile back, Knutz had my head decked by someone here in Vegas.

It only raised the compression 1/3 of a point.

But if you're looking for high compression MrHorsepower sells one that's 14/1.

 

Are there any thinner head gaskets for stock guys that want to get a little more compression? And If you deck the head you could always get a thicker head gasket to go back. So you have options unless headgasket don't come in different sizes.

 

Hey BigDaddy, Im with you. Ive been thinking about doing this for a couple of weeks now. Not only would you save a lot of money, but higher compression domed pistons are not as efficient as flat tops due to squishband. I have decent knowledge of engine top ends, and am a machinist at a factory. I think if one was to take their time measuring clearance of exhaust valves there shouldnt be a problem. BUT, if one later wanted to install cams with more lift and duration.....OUCHIE....If I do this I will try to mill cylinder only, then maybe the cylinder base gasket could be shimmed back up, a lot less pressure down there!!

Like I said, I dont think I would have a problem pulling this off..But if I shave .020" off the cylinder, what would that make my compression ratio? Wouldnt you have to know the cc's of the combustion chamber to figure this?

 

Hey big Mike, there is one thing to remember , these aren't 2 stroke bikes. Your valves will hit the piston if you mill the head. You haave to run a piston with valve reliefs built in. I have a 12:5:1 piston laying around but i want to make sure my rig hold up first before I give it up. It is the only back up I have. If you are skeptical about more commpression, don't be. Spend the $250.00 for the piston and headgasket and do the work yourself you won't regret it and if you need help I can talk you through it.

 

High compression is awesome. Great boost in power. It is amazing what a climber this engine is with high compression and cams. I have been running 11:1 mostly because my Weekend Warrior has a fuel station and I don't see putting race gas in it and filling up my wife's and daughter's quads with race gas when they don't need it. Too expensive.

I still have a stock bore 11:1 piston collecting dust since I went to the 102mm bore. For sure the higher compression and cams netted more of an increase than the larger bore.

It is much easier to just do it right the first time and fork out the cash for the piston rather than messing with the head. If someone still wants a head to experiment with, I think I know someone that has one to sell [img]i/expressions/face-icon-small-wink.gif[/img]