YZ 450 big bore

3 replies to this topic
  • highmark00700

Posted April 20, 2011 - 12:00 PM


I have a 03 yz 450, I'm thinking of putting a 478 big bore on it. All the kits I have found have a 12.5:1 piston in them. I would like a 13.5:1 piston. I can get a aftermarket 98mm piston in 13.5:1 but not in a kit. I can't decide what to do, stock bore high compression, big bore stock compression or a big bore and order a high compression piston from someone else. Anyone have any dyno numbers of stock bore w/ high compression piston vs. big bore w/ stock compression or high compression? I don't mind running race fuel so that's not much of a factor, I'm just curious what the best power for the money will be?

  • wags450

Posted April 20, 2011 - 03:07 PM


What are you going to do with it? What kind of riding?

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  • highmark00700

Posted April 20, 2011 - 07:35 PM


Mostly sand dunes and track riding once and a while.

  • wags450

Posted April 21, 2011 - 01:39 PM


Its always cool to have and I have 2 thoughts on this from past experience

1. High compression is a cool thing to have more power for the dunes/track if done right and race gas smells good.

2. Its nice to be able to put 91 octane in with the stock compression but have the power of the big bore.

I have had both with the 450 motor in my YFZ450's for the sand dunes. To be honest I couldnt tell the much of a difference side by side in identical bikes except one cost more to ride because of gas. Lower compression was more reliable and lasted longer. Save the money go with the pump gas piston and put a hotter cam in it.

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