I have noticed that there are different compression ratios w/ the 440 bore kit for the 400ex? If I was to run 12.5:1 would I have to run race gas or could I still use #92 octane pump gas? Are there any draw backs to running a 440 kit?

 

From what I've heard, running compressions over 11.1 will require running race gas, or a mixture of it.

 

there is no way you should run pump gas with that compression. i think it is recommended when your compression gets to a true 10.5:1, you should start mixing race gas. however, i run a 10.8:1 piston and i run on 93 octane. however, i don't know if that is a true comrpession ratio. drawbacks of the 440 are you need to resleeve the cylinder and the 440's also produce more heat than others.

 

I have a curtis sparks 440 kit with a 12.5:1 in I run 110 octane.

 

Okay, So if I do get a 440 kit, I am told that I will have to get an exhaust kit that is 440 compatible, a larger carb, and a new cam, this is coming from "Boss" in Dirtwheels magazing dialed in what exhaust, carb and cam should I get? I want to increase the power across the entire power band.

 

If you took a poll of members here it would tell you to get the following:

Sparks X-6 exhaust.

Hotcams stage 2

Keihin FCR 39 carb.

I would buy a 89mm Ross 11.5:1 piston. You can get an 89.5mm which is a true 440 but you have no room for overbore like the 89. That would run on a 50-50 mix of Race gas and pump premium. You would then drop 2 teeth on your rear sprocket.

 

Also look into getting your head ported.

 

This is a dumb question, but what is head porting?
I ride good, but I am no mechanic...[img]i/expressions/face-icon-small-blush.gif[/img]

 

I have to be able to run pump gas

 

the head is the part of the bike above the cylinder. this will contain valves and valve springs. air flows into the head. if you port the head you either make it larger, smoother, or change the shape of the holes or ports. this can make your bike flow air better. if you want to run pump gas, you can order a 10.8 ross or je piston. these pistons are actually designed for the xr400 dirtbike so the ratios will be a little less than 10.8. you can run a true 10.5:1 ratio or possibly alittle higher on pump fuel.