We still have the original stock 50mm top end on our eton viper 90...I was looking at some of the big bore cylinders for sale at the different performance places and have a few questions....
First of all how much of a power increase will I get with going with a bigger bore?..
Will a 90cc or 96cc motor make much more power than the stock 82cc motor?
.Is there an advantage to buying a "kit" that includes the cylinder and piston and related parts or can I just bore the stock cylinder out and buy a larger piston?
How far oversize can the stock cylinder go?

I will be adding a stock apex pipe and a larger carb as well..

 

I know the ports were much larger on WRH's kit. I think porting makes a bigger difference than the 8cc's. It also shaves some weight, since it's aluminum.

 

Your cylinder can go to 52mm guaranteed.
The 105 big bore LT80 kit (which is 96cc's w/stock stroke) does not need the sleeve as the stock sleeve can be bored to 54/54.5 (the big bore size). So there is a fair chance that your cyl can bored to 54mm.
Legs is correct!
Porting is where you get what you really want and still be at a reliable 82+cc motor.

 

You are probably right about the CCs not adding a significant amount of power..I have never worked on such a small cc engine so I wasn't sure how noticeable it might be?....However I do recall running our viper next to a polaris 90 and the polaris seemed to have better bottom end torque..It was a true 90cc versus our vipers 82ccs.

 

Thanks for the info LT80....Do the stock ports just need some cleanup or do they need to be enlarged and reshaped etc?..I have yet to tear one of these things down so I have not even seen the stock ports..

 

You will get more torq with a bigger cylinder than a stock bore.....but you will get more rev's out of a stock bore! ...... Torq is always a good thing to have . You can bore a stock cylinder to 54mm.

 

IMO, the exhaust needs to be raised and the transfers widened. That's the simple answer.