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850 vs high compression 750

  • Thread starter Thread starter crapwacker
  • Start date Start date
Need criteria and context...

But just making a guess here (you're not drag racing), I'd much rather ride the machine that hasn't been modified.

So the 850.
 
It looks to me that if you put 850 cylinders and pistons under a 750 head you will get close to 10:1 compression. The stock CR for the 750 is 8.8:1 with a 187cc cylinder so if you increase the swept volume to 212cc it should bump the CR up to about 9.8:1.

So as far as the original question is concerned it is more like "high compression 850 vs high compression 750".;)

Brian
 
gssuzukixxx said:
It looks to me that if you put 850 cylinders and pistons under a 750 head you will get close to 10:1 compression. The stock CR for the 750 is 8.8:1 with a 187cc cylinder so if you increase the swept volume to 212cc it should bump the CR up to about 9.8:1.

So as far as the original question is concerned it is more like "high compression 850 vs high compression 750".;)

Brian
Click to expand...

I don't get it? Compression should stay the same as, the 750 and 850 head are the same.

Unless you get high comp wiseco oversize 750 pistons.
 
Coady said:
I don't get it? Compression should stay the same as, the 750 and 850 head are the same.

Unless you get high comp wiseco oversize 750 pistons.
Click to expand...

Well compression ratio is the ratio between the volume of the cylinder + combution chamber when the piston is at the bottom of the stroke vs the volume of the combution chamber when the piston is at TDC. So if you keep the combution chamber volume the same and increase displacement then you will increase the CR.

I know that people say the 750 and 850 heads are the same but the 850 head would have to have a large volume for the 2 motors to have the same CR.

Brian
 
gssuzukixxx said:
Well compression ratio is the ratio between the volume of the cylinder + combution chamber when the piston is at the bottom of the stroke vs the volume of the combution chamber when the piston is at TDC. So if you keep the combution chamber volume the same and increase displacement then you will increase the CR.

I know that people say the 750 and 850 heads are the same but the 850 head would have to have a large volume for the 2 motors to have the same CR.

Brian
Click to expand...

Sorry I meant to say "larger combustion chamber volume for the 2 motors to have the same CR."
 
I have always figured that the extra compression is a significant part of the extra responsiveness of the 1000 over the 850. Do both...
 
gssuzukixxx said:
Well compression ratio is the ratio between the volume of the cylinder + combution chamber when the piston is at the bottom of the stroke vs the volume of the combution chamber when the piston is at TDC. So if you keep the combution chamber volume the same and increase displacement then you will increase the CR.

I know that people say the 750 and 850 heads are the same but the 850 head would have to have a large volume for the 2 motors to have the same CR.

Brian
Click to expand...

Both heads are the same. Both stock Cr's are quoted at 8.8-1. But the bores on the 850 are 4 mm larger!! How could that be?

Could it be that the piston crowns are shallower on the 850 pistons????
 
Yes, I never thought about the piston crown when I made my posts. Brain wave turned out to be a brain cramp.

Sorry about that.

Brian
 
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