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Old 07-20-2009, 12:03 PM
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Question about compression.

I know this might have been brought up a few times before but can't find anything.

I understand that in a gasoline V8 engine a compression of about 10.5:1 is pushing the limits of pump gas.

But what puzzles me is why does my motorcycle (2008 Kawasaki Ninja ZX-6R) came from the factory with a 13.3:1 compression and ran on premium gas without any problems what so ever, also my new motorcycle (2009 Kawasaki Ninja ZX-14) runs a 12:1 compression on premium.

I also know that diesel motors (the ones I work with) run almost 18:1 then are turbocharged to insane amounts of charge PSI. I understand that this is because of the differences in firing methods.

What makes these motorcycle engines allow a higher compression then a V8 or other factory car will allow?

Hopefully someone is able to answer this, been reading alot and now I'm puzzled.

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Old 07-20-2009, 02:14 PM
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Combustionchamber design, aluminum heads and block dissapate heat much faster.And the engine is far more lightly loaded.
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Old 07-20-2009, 04:42 PM
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As already stated, aluminum, chamber design, and vehicle weight is a huge one on a bike as they are so light.
Also, cam design plays a role, as most bikes have redlines in the 9000-14000 RPM range.
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Old 07-20-2009, 05:59 PM
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Static compression isn't the only thing in play here. How much PSI you make at low rpm is an important factor too. Quench also is important. The cam plays a huge role in high compression engines using pump gas. The combination of the engine is key. If you lived during the 70's, you saw plenty of low compression, no quench, sorry camed engines from the factory ping themselves half to death and get sorry fuel mileage too......btw, how much cranking psi do you have?

Last edited by cranky1; 07-20-2009 at 06:36 PM.
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