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Big Bore vs High Comp Piston

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What are the pros and cons of each? I will be replacing the piston and would like to know what kind of things to expect from each?

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I'll be interested in the responses as I'm about to piston change and have been thinking about a big bore also.

My guess is the big bore will give more of what the X is known for - strong bottom/mid with not much top end ?

If this is the case thats OK as it's what I liked about the X over the WRF

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I tried both the je 13.5 hi-comp piston for a season and last season tried the 280 athena big bore kit. The high comp piston seemed to give a little extra power everywhere. Not lots though. the big bore was by far the best mod for power I've done. Very happy with it and can't see me going back to stock bore now. there does seem to be peaple on this site that have tried it and weren't as happy as me , some even going back to stock bore. I think there set up wasn't right . I'm running the 04r cam and pink wire ccc modes and drilled difuser. Not very loud and lots of jam everywhere but overrev... The overrev just kills the motor quicker anyways.

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I've got a new Wiseco HC piston in my mine and i can really notice the difference throughout the powerband, extra power everywhere. I'am surprised sometimes when the front wheel comes off the ground. I went this route cause I heard that a big bore can put extra stress on the rod and crank that it wasn't designed to take and it was only an extra 100$ as opposed to 6 or 7 hundred that a big bore kit costs.

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I disagree with the extra stress on the motor. my bike won't even hit the rev limiter anymore were most of the stress comes from(untra high rpm). Now the extra stress is probably equal to the stock bore screeming . I have had a crank failure with the stock bore after three years of riding....We'll see how long I get now with the big bore, on my second season now.....I personnally think it will last much longer , beause you end up riding in a much lower rpm range than stock bore. And the extra power is way more than a high comp piston, my 2 cents...Cheers

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I've not used a big-bore set-up, but for racing applications, I have used the JE high compression piston for 3-1/2 years and am very pleased with it. It provides a nice boost everywhere and still allows the engine to rev-out like stock with proper jetting and air-box mods. I don't scream it--don't have to--she runs like a scalded-dog. I also use oxygenated race fuel which isn't necessary with the HC piston, but the two seem to go together really well.

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Don't knock it til you try it. Like I said I've done both and the big bore is way more power...usable power at that. It still screams and wants to be ridden hard. But you can ride it a gear or two high and still pulls very hard. Why do you think all the off road pro's are running big bores????

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A few quick questions for my own curiosity,

1) are the big bore kits balanced with the standard balance factor?

2) why run a crank until failure? isn't easier and cheaper to prepare for it and replace?

3) does anyone have dyno charts run on the same dyno of the differences being discussed or is it all seat of the pants?

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I have read a few comments indicating less top end after the big bore.

Is this more to do with choice of cam ?

X cam is bottom end on a 250 - more so on a 280 ?

Would the 05R cam be a good match for the 280 for strong bottom/mid ?

Normally engines dont loose their ability to rev from a bore increase, its usually from extra stroke.

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They don't rev as much becuase the piston is heavier.. I don't run the crank until failure...I run it until the brass starts to appear in the oil filter which is a sign of the crank starting to wobble and crub off the side shims of the crank. Its not blown yet but will be shortly after this starts happening.I have on 04 r cam that pretty much has the most radical profile for top end and I still can't reach the rev limiter. The bottom seems to work well with this came.. It pulls down low much harder than stock or ccc moded or hi-comp piston. Done them all. I'm sticking with the big bore. No replacement for displacement.

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