High Compression 400ex

[300EXRD]

Hey i'm thinking about putting a 12:1 piston in my 400 is there any problems with it? are they reliable? I do a lot of trail riding ,so
keep that in mind. Also does anyone have any good cam ideas
or other power adding ideas. thanks for the help

[BLEEDRED]

With a comression ratio that high you are going to have to run higher octane fuel...higher than pumped gas. Many people also have trouble with blowing head gaskets with that high of compression which is a result of their head studs pulling out. So make sure you build in some security with heavy duty head studs.

Is is reliable...if done properly in can be, but keep in mind that the stock CR for a 400 EX is 9.1:1. Granted Honda is safe with everything, but you are really jacking up the CR going that high. You would probably need to look at replacing the rod and make sure you replace all the fastners inside the engine when you do the build.

[TC426EX]

12:1 is fine, thats what Im running but there are other things youll need to do if running this compression... For 12:1 I would definitely install a Heavy duty rod like the carillo or sparks... Oversize Head studs will be a necessity, not an option... Also, you will have to run race gas in it all the time, so take that into consideration. As far as a cam goes there are a multitude of options. If you wanna keep the cost down go with a drop in like a hotcam. There are more expensive drop in cams like the TC 926 XC cam and sparks aggressive drop in cam. Other than that most other cams require the hardened rockers, HD springs, etc.