Which engine is better in drag racing?

My short stroke engine is lacking power for drag racing how can I improve overall power output for 1/4mile?

• my underbone is a 125cc a kymco spike so far I've changed to a larger & lighter piston taken out weights in the flywheel to make it weigh less port and polish 200cc carbuerator harder compression springs & cluth springs, racing cdi, bigger intake valve, racing cams..I'm guessing i'm losing power because my exuast valve is stil original compared to the bigger intake valve & my exuast pipe is slim in diameter coming from the head...maybe you guys can confirm that or give me suggestions how to make it run faster thanks!

• Answer:

  Your exhaust valve size is more than likely just fine.The exhaust valve only needs to be 60 to 65 percent of the intake size.If you have had the cylinder head ported,then the exhaust pipe inside diameter needs to match the exhaust port inside diameter.The lenght of the exhaust pipe will be dependant on the rpm range the engine will be operating.I do not know about your make of bike,but a four stroke engine all operate the same way.You need access to a dyno to be able to fine tune the parts you have/are using to get the best possible performance.A change of 3 degrees on the cam timing makes a big difference in making alot of power or very little,for example.Too large a carb,will cause a loss of low end/midrange power,will not accelerlate well,and top /high rpm power may be less.Everything has to work together as a complete system,or you will be very disappointed in the bikes performance.