General engine questions: Compression ratio and Displacement

[Larry" <rocco16v@netzero.com (Larry)]

> I understand Displacement to be the total amount of fluid (air or water,
> etc.) that the chamber will hold at it's largest position: full down
> dead center. The difference between TDC and it's opposite isn't used
> when calculating displacement. It's just how much air the cylinders
> hold.


No. Engine displacement is the swept volume of each piston times the number
of pistons.You disregard any volume above the piston when it's at TDC.
one-half the Bore, squared X pi X stroke X number of cylinders

>
>
> > With all that: Is this math right?
> >
> > A = displacement
> > B = volume when cylinder is at the top
> > C = Compression Ratio
> >
> > C = (A+B)/B = A/B + 1
> >
> > Compression ratio is increased by increasing displacement,

Yes, unless you conpensate.

If on the other hand you keep the
> same stoke but change the height of the top of the piston you have
> increaed displacement but not compression. (This is very simplified
> btw.)

No.  There are only two ways to increase displacement of a cylinder;
increase the bore or increase the stroke.


> > Increasing the compression makes your engine more efficient as it then
> > squishes the fuel and oxegen closer together before it is ignited. So
more
> > fuel is burned. Am I right about this as well?

I'm not sure just what the dynamics are, but don't think "More fuel is
burned" since there is not more fuel TO be burned....(see below)

> Well, I think of it as holding a increased amount of fuel (and of course
> air too) in the 'same' area as a low compression motor leading to
> greater power. If the increased compression results in a smaller space
> than the lower compression motor _then_ you are getting the same power
> from less air/fuel, and therefore more efficiency.

Increased CR does not increase amount of air or fuel taken in during the
intake stroke.  Only more displacement or supercharging does this.

Larry  sandiego16V