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Hey guys, I'm new to the forum and just looking for some suggestions. I recently bought a very clean used 2007 Honda 400EX. I would like to get a little input on possible upgrades to beef this sucker up a little bit! Anybody got any suggestions on exhausts or jet kits or anything that will help with performance? Please be specific about what upgrades you might have done and the results. Thanks! Land vehicle All-terrain vehicle Vehicle Car Automotive tire
 

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The gains from exhausts are pretty slim so it's a choose which ever you like situation. Put a uni filter in and either take the air box lid off or drill some holes in it. As for jetting, that's trial and error. Jets are only a few bucks so buy a bunch of different sizes and see what works best. I'm sure someone on here can get you in the ball park of correct sizes. If you really want to add some oomph get a stage 2 crank shaft and a higher compression piston. Doing those will really wake that engine up. 11:1 is about as high as you can go with stock bore and still run pump gas.

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The gains from exhausts are pretty slim so it's a choose which ever you like situation. Put a uni filter in and either take the air box lid off or drill some holes in it. As for jetting, that's trial and error. Jets are only a few bucks so buy a bunch of different sizes and see what works best. I'm sure someone on here can get you in the ball park of correct sizes. If you really want to add some oomph get a stage 2 crank shaft and a higher compression piston. Doing those will really wake that engine up. 11:1 is about as high as you can go with stock bore and still run pump gas.
Didn't you mean Stage 2 CAM shaft?
 

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You many consider changing the gearing of you want more pep down low, other than that I always felt every little bit helps....I have full exhaust, choke delete and jetted, stage two cam, port and polished head, 11:1 piston, auxiliary oil cooler (no more power, but insurance that the extra power made won't overheat anything) and running a Unifilter without a lid. Future plans include a FCR carb, heat wrapped exhaust and air scoops.

I've always looked at it like not one of these mods will make a huge difference, but enough put together will.

After all, race cars don't just use a race piston and the rest stock....
 
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