Piston compression ratio

[250R Baja Rider]

Guys,
I am installing a stage 2 cam and valve kit on my raptor soon.
Since the motor will be opened for the first time in 2 years, I wanna put a new piston.

The question is what compression ratio piston should I use to use pump gas and still have a reliable top end.

My riding is mostly desert riding when mid and top end is used for long periods of time.

I would appreciate your inputs :D

[krt400ex]

10.5:1 - 11:1 is right where u want to be for running pump gas. for ur situation i would go with a 10.5:1 because it will run a little cooler. with the heat of the desert a 11:1 is pushing it a little.

[F-16Guy]

10.5:1 - 11:1 is right where u want to be for running pump gas. for ur situation i would go with a 10.5:1 because it will run a little cooler. with the heat of the desert a 11:1 is pushing it a little.

True for the 400ex, but every engine is different. The compression ratio you can run on pump fuel is determined by a number of factors, including displacement, cooling method (water or air), combustion chamber design, bore and stroke, and even the octane available in your local area (I can only get 91 in Phoenix). I don't know much about Raptors, so I would probably go to BlueTraxx or a similar forum that specializes in Yamahas and find out what they're running. Most of the people around here are Honda riders, but you might find someone who knows if you keep asking.

[krt400ex]

Originally posted by F-16Guy
True for the 400ex, but every engine is different. The compression ratio you can run on pump fuel is determined by a number of factors, including displacement, cooling method (water or air), combustion chamber design, bore and stroke, and even the octane available in your local area (I can only get 91 in Phoenix). I don't know much about Raptors, so I would probably go to BlueTraxx or a similar forum that specializes in Yamahas and find out what they're running. Most of the people around here are Honda riders, but you might find someone who knows if you keep asking.


u gots a point. but what i said is a base line, but i don't know that much about yamahas. try the yamaha section of this site

[250R Baja Rider]

Thanks for your inputs....

I'll check bluetraxx