400ex best bore size?

[Trent Finnessey]

So I’ve got a 400ex with a dg Slip on a air filter and a stage 2 hot cam, I want to put a big bore kit on it... either a 416 or a 426 NOT a 440! Only because I hear the 440’s overheat all of the time and cause lots of problems. I’m looking for 3 things, 1. price (with kit is cheaper), 2. Reliability (obviously witch kit is more reliable) and 3. Which kit give better power, I’m assuming the 426 give it more power but if the 416 give it say 35hp for $450 and the 426 gives it 37 for $600 I’m probably gunna go with the 416....  Thanks!

[MarkinAR]

Stock bore with high compression will almost always outrun the big bore.  The thing about larger bore size is higher torque, but not necessarily more power.  You gain CC's, but it takes more to push that much more air thus minimizing the larger bore size.  And of course the larger bore comes at a cost of cylinder wall thickness, thus more heat.  If i were building a runner for flat out hauling as* in a straight line, i'd go high compression small bore. If i were doing trail riding and needed torque at lower RPM, go 416 and add a larger oil cooler.  In either case though, you need to bump to good head studs and some machine work so it doesn't blow the head off.  Now that I think about it, I might still go higher compression, head studs, and drop a tooth on the front so it would rip around the trees.  Like any engine being built though, it's mostly preference over anything else.  A 400ex is not going to compete with a Banshee in a straight line, and it will struggle to pull like a 450 around trees, but it's still my favorite all purpose sport quad.