so how much do you think i would expect to pay in labor if i did it all at once?

 

o and can i get a high comp piston without doing a big bore? and does anyone have advice on big bores? good bad? how big and is it worth the price? and what does it cost?

 

It doesn't take too long to swap anything on the 450R, but the 400EX takes a little longer due to swapping sleeves. I would say roughly 4-5 hours, so about $300 or so for labor costs, maybe a little more.

 

Also, keep in mind that 11:1 is about as high of a compression ratio you'd want to run and stay on pump gas. If you go higher than that you will have to mix premium pump gas and race fuel. So if you're not racing that'll get old real quick.

 

so whats does a high comp piston do? sorry for allt he dumb Q's and if 11:1 is the highest i wanan do befor i run a mix or gas and race fuel, then y can a yfz 450 run off pump gas, its running 11.4:1 ratio?

 

There's not a big difference in 11:1 vs. 11.4:1 . more compression=more power. But there are things to consider. Octane makes fuel stable under compression, so the compression ratio you choose needs a fuel with at least the octane rating necessary to prevent pre-ignition. Pre-ignition is when the fuel mixture ignites from heat and compression before the spark plug fires. Not good for an engine. And depending on how high you choose to go you need to think about a stronger connecting rod, crank, etc. If you're not racing I think the best thing to do for now is go with a 416-426 bore and no higher than an 11:1 compression ratio. It is possible to gain power through mods and still have a reliable motor. But keep in mind that an all out race engine is made for just that. You can reach a threshold where it's not worth modding a 400ex in terms of $$$. And the big bore high compression stroker motors are not meant to idle.