Adam,
Compression ratio is:
(chamber volume + swept volume) / chamber volume.
With a 1600cc engine:
swept volume = 400 cc (1600 divided by number of cylinders)
If you have 40cc of volume up in the cylinder head:
400cc + 40cc / 40cc
440 / 40
or 11:1 compression ratio.
Now increase the chamber volume to 50cc (i.e. dig out
that dremel tool and start removing metal from the
cylinder head):
400 + 50 / 50
9:1 compression ratio.
Darn head cold... can't sleep!
Tom
Adam Bradley wrote:
> I know this is a very basic question but I don't understand how
> compression ratio is determined. For example, our R16 engines are 9:1,
> but there was a truck called the "Homer" that also uses the R16 engine
> but is only 8:1 (and has lower hp/torque, also single carb).
>
> I assume this means that on the compression stroke, the air is
> compressed to 1/9th (Roadster) or 1/8th (Homer) its original volume.
> Since both vehicles have the same bore and stroke, what makes the
> compression ratio lower on the truck?
>
> =====
> Adam
> '70 1600 SPL311-28181
> http://www.picturetrail.com/abend
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>
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