Piston question

[sportracer07]

Does anybody know right off what size the stock piston is, 86mm or 85mm?

[Grimzella]

stock bore 85.00 mm 400ex

[sportracer07]

Well i bought the 4 whlr torn down and the motor was in a box, so all i had to do was assemble everything, he already had the piston, its a wiseco 86mm,, so would that make my ex a 416 or 420 or what?????

[F-16Guy]

406.

[sportracer07]

Ok thanks, and do you guys think that it would run good with a hotcam, or is it not built enough to help, the piston is an 11:1, what mods could i do cheap to help out.

[F-16Guy]

Yeah, a stage 2 HotCams cam will give you a nice performance gain. Why was the motor in a box?? Sounds like something isn't right. Check the crank bearings and rod really well before assembly. If it still has stock head studs, you should definitely consider sending the cylinder to GT Thunder to have HD studs installed. If the bottom end is tight and the top end looks good, have the studs installed, get new rings and a cam, and throw it back together.

[sportracer07]

I got it from my best friend ,he traded for it and didnt feel like messing with it and knew i was lookin for a quad, so we did some trading around, but he had already torn it down to see what it needed, and ordered the new piston and had it bored out, it has been together since last summer and running strong, i just happened to find the piston box tday and it made me curious.

[F-16Guy]

That's great! Yep, it would be a 406 (405 and change, really).

[sportracer07]

whats the difference between the stage 1 and 2 hotcam, and do you think the stage 2 might be to much for it , with no more than i have done???

[F-16Guy]

The lift is really close on both. The stage 2 has more duration (valves open longer), which will give you better mid-to-top end power vs. the stage 1. With an 11:1 piston, you will see gains everywhere in the powerband - from low, to mid, to top. I have a stage 1 cam in mine, and it has tons of low and midrange power, and a nice increase in top end over stock. Both cams have more duration and lift than stock, so with an 11:1 piston, you'll see gains across the board with either. The difference will be where the power peaks. The stage 1 will give you peak output earlier in the RPM range, and the stage two later in the range. The reason I recommend the stage 2 is that this engine has a ton of torque to begin with, so there's no chance of killing the bottom end power with too much cam duration, especially with a high compression ratio piston. The stage 2 will help develope power in the upper RPM range, where the 400ex usually falls off.

[JOHNDOE83]

the stage 2 helps alot, before I got mine, when drag racing my friends yfz450 we would be neck and neck till fifth gear then he'd pull away fairly quick....after the cam we'd hit fifth and be dead even, till he hit sixth gear then he was gone...lol... he only had a pipe and filter

[sportracer07]

Thanks for the info guys, looks llike i will be getting a stage 2 hotcam as soon as i can>