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I was looking at a few things lately and I just want to make sure that I am understanding right. My CX500 is actually 496CC? not 500 correct?
 

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correct. Like most if not all motorcycles. the listed CC's is not the actual CC's
 

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I have a 650 and it's actually something like 676!



Larry
 

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In this vintage era, it was common to nameplate either a rounded up or down number, so the bike could be sold in certain regions of the world for a class size. This was mainly due to the regulations imposed by each region/country for either importation, or other taxation. It probably still exists to some extent, and each part of the world will have it's own rules.



There are other scenarios too, as I've noticed, for example, in the racing classifications for the Salt Lake Flats there is a range of actuals that are quite a bit off of what the true CC is.
 

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And because its 496cc I got a cheaper insurance rate. At 500cc the rates went up!
 

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Depends if its been bored out......could be a true 500
 

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In this vintage era, it was common to nameplate either a rounded up or down number, so the bike could be sold in certain regions of the world for a class size. This was mainly due to the regulations imposed by each region/country for either importation, or other taxation. It probably still exists to some extent, and each part of the world will have it's own rules.



There are other scenarios too, as I've noticed, for example, in the racing classifications for the Salt Lake Flats there is a range of actuals that are quite a bit off of what the true CC is.


That theory still holds true to this day with most mfgs.
 

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My FJ 1200 is actually 1188cc. I think most manufacturers do it. Yamaha's FZR1000 was actually 1002cc.. I expect its because swept volume is cylindrical rather than cuboid too.
 

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This holds true for a lot of cars too. My 3 cylinder Geo Metro is billed as a 1.0 Liter (1000 cc's, and yes, I know there are bikes that are bigger than it!!), but it's actually a 996cc. Think about it, 3 goes into 996 an even number of times, but wont go into 1000. It's probably easier for the engineers to save or add a few cc's for symmetrical purposes rather than splitting the two or three ccs amongst the cylinders. Even my 88 Honda CRX isnt truly a 1500, I think it's like a 1496 or something like that.



With our bikes you could have two 250 cc cylinders, but maybe whatever material or available parts they were working with would only allow for two 248 cylinders without some sort of major modification or engineering redesign. I dont know, but just taking a semi-educated guess here. Seems logical. I do agree that the 500 label is mostly due to class/taxation purposes as well, plus its a lot easier to say your bike is a 500 rather than a 496.
 

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^Well, it probably just easier to keep to conventional measurements than to use decimal sizes in order to get it dead on the cc ratio. Remember pistons are round, which makes getting a precise volume a little more difficult. Not even close to impossible, but not really worth the trouble.
 

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There's a reason for the "metric" measurement of displacement to almost always be "close", and the "American" measurement to be spot on.



Taxes.



Euroland, Asia and just about everywhere in between, where they use the metric system long before the US would even recognize it, started taxing vehicles by displacement about the time the 2nd one came off the assembly line, building for the tax break line and shaving a piston or thickening a gasket to just squeak below the next tax bracket. The norm of rounding to the nearest liter can also be attributed to the relatively small unit a cc is, it's 1000th of a liter, so a couple cc's here and there don't represent much, even less in the early days of less than efficient engine designs.



The US has never taxed displacement, and up until the last 25 years or so, always used Cubic Inches to measure displacement. There was no rounding up or down, as can be witnessed by the many engines referred to by their displacement, the 327, 318, 351 etc.



1 cubic inch = 16.387 cubic centimeters.



While not taxed, horsepower was a major factor in insurance rates for vehicles in the US, manufacturers have fudged official HP figures downward to assist in sales. Ford did this famously on the S Cobra Jet engines, officially rated at around 375HP for insurance purposes, they were actually delivered with around 450HP.
 
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