Guy,
I have never heard of that computation for a
compression ratio. But I do know that 13.8 to 1 would
require a fuel octane of 104 or so.
Compression ratio is the comparison of total volume of
the area in your cylinder and combustion chamber of
the head at bottom dead center verses the volume at
top dead center. more technically described, here is
the formula from the Avonbar Racing Site:
Compression ratio
CR = Swept Volume + Total Combustion Chamber Volume
Total Combustion Chamber Volume
Swept volume = Bore x Stroke (pr2 H)
Total Combustion Chamber Volume = Cylinder head
Chamber Volume + Head gasket volume + Piston crown
volume at T.D.C. to Cylinder block face.
Example:
Swept Volume 249.63cc
Chamber Volume 24.2cc
Head Gasket Volume 3.4cc
Piston to block face volume 2.2cc
249.63 + 30.00cc 30.00cc = 9.32:1
Total Combustion Chamber Volume required for a given
CR.
= Swept Volume CR. - 1
Example:
Swept volume 249.63cc
CR. required 9.32:1
249.63 (9.32 1) = 30cc
John
> One question, when I did the compression test I got
> 190 - 200 lbs / sq
> inch
> Now at sea level STP is 14.5 lbs/sq inch so my
> compression ratio is
> 200 divided by 14.5 - yes?
> That gives me a CR of 13.8 : 1
> Seems high to me.
> Would this be the cause of blow - by, and my oil
> burning problem?
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