440ex Compression How High Should I Go?

[bill222]

I am doing a 440 kit into my ex and am wondering what compression to run 11:1, 12:1, or 13:1? I already have a larger capacity oil tank. What gas will be needed for the compressions? And which is the best suited for my racing/freestyle riding?

[Jnblaster05]

umm 11:1 is the lowest u can go on pump gas i have 11:1 but wish i had gone with higher like 13:1 cause i still put 100 octane in it cause it makes it run so much better its crazy but its all on whether uhave access to race gas and wanna pay the extra money for it

[drew416ex]

yeah depends on what fuel you want to run. More compression gives you more low to mid power also.

[HondaRaceReady]

Can't high compression kill the starter motor and ruin the engine? It wont be able to start a bike with 13:1 compression. It takes a real **** of a kick to start 13:1 so I know it takes a lot of power.

[Jnblaster05]

see im no expert but it depends on your cam like i have a stage 2 so it has no decompression on the motor like it dos stock so its definitley not good on the starter like if its not starting right away u dont wanna keep crankin on it

[drew416ex]

well lets say you have a big web cam. Cant think of the model number right off hand but it has so much valve overlap that you lose a lot of compression which is the point of getting a piston that big. If you have a 12:1 piston with a hotcam stage 2 and a big web cam with 13:1, the 12:1 will actually have more cylinder pressure because that cam has a lot less over lap. Yes the 13:1 is harder on your starter, connecting rod, etc but its not as hard on it with a bigger cam. So all of this also depends on the cam you will be running.

[blue_ex_rider]

I havent been able to find a 440 pistion with a 13 to 1 compression unless maybe cp makes one or you can special order one i would guess but you have to get 4. but I know Je ross and wiseco dont make a 13 to 1 compression you can get a 12 to 1 though. i have a 12.5 to 1 pistion that i ordered from sparks that is an 89 bore that i have never ran before It was like 210 for the pistion and i put 30 more in ti to have it skrited I never used the pistion put it on the rod and that is it. That is the highest compression pistion i could find ina 440 kit and i would be willing to sell it to you for 90 bucks shipped. if your interested i can gets pics just let me know.