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Discussion Starter · #1 ·
Is there a difference . If not why are some called 719 , or 720. A +4 and a 102 mm piston = 719. Right or not? Just wondering ,no big deal.??????
 

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What's the difference (build wise and HP wise???)

Is it just 102.5 mm postons???
 

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There are no 102.5mm pistons.

719.1xxxxxx is the calculated displacement. The stock 660 is 659.7cc. Craycraft used to sell their 686cc kits as "690" and 727cc kits as "730". A polaris RZR 800 is 760cc.

They "WHY?" varies. Aesthetically we like round numbers. Also, rounding up sounds bigger, our culture views bigger as inherently better. Therefore if something sounds bigger, it's worth more.

A calculator and a chart here may help shed some light
http://www.raptorforum.com/forums/showthread.php?t=76577

741's are routinely called 740, 762 are often called 760. 779s are always called 780s.
 

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Same reason why yamaha calls the banshee a 350 and not a 347. Or a YFZ450 not a YFZ449.
 

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There are no 102.5mm pistons.

719.1xxxxxx is the calculated displacement. The stock 660 is 659.7cc. Craycraft used to sell their 686cc kits as "690" and 727cc kits as "730". A polaris RZR 800 is 760cc.

They "WHY?" varies. Aesthetically we like round numbers. Also, rounding up sounds bigger, our culture views bigger as inherently better. Therefore if something sounds bigger, it's worth more.

A calculator and a chart here may help shed some light
http://www.raptorforum.com/forums/showthread.php?t=76577

741's are routinely called 740, 762 are often called 760. 779s are always called 780s.
Just like the Raptor 700, it is a 686. If I remember right.
 

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Discussion Starter · #6 ·
Thanks for the inlightenment..... Makes since, i was just corious.
 

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I wish i knew there was this when i just did my last rebuild!
 

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Anyone can make non-typical pistons of any size you like. There have been some 103mm pistons made too. My point was that these kits in question do not contain 102.5mm pistons.

A 102.5mm piston with a 4mm over crank would be a 726. If you want to hit 720 with a 102.5mm piston you'd need to find a +3.25mm crank. A 102.065mm piston with 88mm stroke will net you 720.0cc


Sizes between 102 and 105 are typically used for two reasons:

1. People are too cheap and/or lazy to resleeve and don't have any concern about the reduced cylinder wall thickness.
2. Racing applications where there are specific displacement or other restrictions. Though these applications often see the use of larger OD sleeves anyway.
 

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Yeah I know what you were saying MD, I just had never seen any for sale until this one. I know you can get any size piston in any compression(for the raptor anyway) for around $300 but as a "off the shelf piston" anything other the 100mm-102mm and the 105mm are not to common.
 

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Yeah I hadn't seen those particular pistons before, but I was aware of the 103mm and some other custom batches of odd diameters.
 
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