don't waste your bore sizes for 10cc. the horsepower gain will be nil.

 

<< Milkbone how do you like those shaved fenders? and is that 416 a revver of a bike somewhat like a 2 stroke.RGB XR400 cam here also. >>

Milkbone??? Anyway, yes it revs up much faster than stock. The JE piston is Aluminum as compared with steel for stock. It felt about half the weight. I have ridden a Banshee. Mine doesnt rev as quick; but is pretty close. I can now start at dead stop in 2nd gear with light throttle and it will pull the front to the sky! Several ATV Web sites I have visited show a 416 with mods like mine putting out app.37 hp at the wheels. A stock 400ex puts about 27 hp to the wheels. I have also modded the: Headpipe,Silencer,Carb, And Intake for more flow.

 

were did you get the aluminum piston and the 416 bore kit i would like to have it because the 440 kit is to big a it sounds to me as if the kit will blow up my crank shaft

 

Go to Exriders.com and look for the link at top of page. It is Marcums ATV. He has some very good prices. Click on 400ex and scroll to ENGINE. He has both the 416 and 440 bores in JE and Wiseco. I prefer JE. Most aftermarket pistons are Aluminum for reduced weight. You can go to a 440 kit for about $200 more, but you will have about $50 more at machine shop for resleeving. Hope this helps--MB

 

You won't find any steel pistons. The stock piston is a cast aluminum alloy. It weighs 288 grams. Most of the aftermarket pistons are forged aluminum alloy. Forged pistons usually weigh a little more than cast ones, but not much. The heaviest piston's that I've seen for the 400EX are the JE and Wiseco 89mm/440 ones. They weigh 307 grams. the Ross 89mm one weighs 300 grams. Something else to consider- the factory pin is quite heavy- 74 or 75 grams. Most of the aftermarket ones are lighter, the lightest I've found is a special alloy by Ross @ 62 grams. A dollar bill, by the way, weighs 1 gram. Not a lot of weight.

I've been researching 440 kits for my bike. When you spend hours on the phone with the different mfg's and the machine shop, the better choices become clearer.