13:1 or 12:1 Compression

[Coondog #77]

Im looking to rebuild my 400ex. I want to bore it to 426cc and get a bit more power from it. My decision is whether i should go 13:1 or 12:1 compression. I know that a lot of you are going to tell me to go for the gusto and do 13:1, but keep in mind im on a minimal budget. I cant afford to rebuild a motor every 6-9 months. any suggestions and no im not selling my quad to get a 450.

[Jeremy]

and no im not selling my quad to get a 450.

Damn!

I'd just stick with the 12:1 then so you can stick with pump gas.

[Coondog #77]

i can afford gas no problem. How often do you rebuild your motor Jeremy?

[Jeremy]

Ummm....I don't really have a set interval. You could easily get a whole season out of a build with just re-ringing the piston halfway through the year if you're on a budget and keep up with your maintenance.

[Coondog #77]

so its just the rings that need to be replaced every so often. The person i talked to made it seem like a new piston, and junk. that makes me feel better. i maintian my quad better than my truck. its easier and "cheaper for the most part".

[Jwilson84]

if buying gas is not a problem id get the 13.1 probally a little more power in the 1 point compression probally gunna need about 95 or so maybe 100

i hope pistons last more then 6 months..lol i dont want too put a new one in that soon, like said i think maintainance is key i change about every 5 hours or so almost every ride...lol

[sic06suz450]

If i were you I would leave it stock. 400ex is such a reliable bike the way it is..and they arent THAT slow. You gotta remember your bike is air cooled and when you try to add power to it, it is gonna make it run hotter and you will have no way to keep it cool so it will need rebuilt more often depending on the conditions. So if anything I would either keep it stock or at most do the 12.1

[Morgan@RE]

400exs are VERY touchy. The 440 I had way back in the day would blow a head gasket if you looked at it wrong. The sleeves in the cylinders drop pretty often, thus causing a blown head gasket.

The less compression you build a 426 with the more reliable its going to be. You have to remember that they are air cooled, and heat is not something you want in a 400 motor. Ive seen dropped sleeves, warped heads, the threads pull out from getting soft, have to install 7/16 stud kits. Gets real expensive real fast if not done right, and you have to back track and fix things.

Come to think of it, I built a 11:1 426 about 3 years ago, and it STILL runs hard enough to keep up with some mild 450s.

[Coondog #77]

400exs are VERY touchy. The 440 I had way back in the day would blow a head gasket if you looked at it wrong. The sleeves in the cylinders drop pretty often, thus causing a blown head gasket.

The less compression you build a 426 with the more reliable its going to be. You have to remember that they are air cooled, and heat is not something you want in a 400 motor. Ive seen dropped sleeves, warped heads, the threads pull out from getting soft, have to install 7/16 stud kits. Gets real expensive real fast if not done right, and you have to back track and fix things.

Come to think of it, I built a 11:1 426 about 3 years ago, and it STILL runs hard enough to keep up with some mild 450s.

I chose 12:1 i dont have money to rebuild every year. Im going to get a Four Stroke Tech secondary oil cooler so that i keep every thing chill motor wise. I will never go 440 or bigger its not economical. Thanks for the help guys.