Re: It is complicated - combustion chambers count

Posted by MarkB_MI on March 27, 2006 at 19:09:08 from (64.31.11.99):

In Reply to: It is complicated - combustion chambers count posted by jdemaris on March 27, 2006 at 07:18:23:

JD,

The reason it's called "displacement" is because that's what it is: the volume displaced by the pistons as the engine goes through one complete combustion cycle (2 revolutions for a 4 stroke engine, 1 revolution for a 2 stroke engine.) The volume of the combustion chambers is not "displaced", and is not used to calculate displacement.

Combustion chamber volume is, however, used to calculate compression ratio. Compression ratio is the ratio of the volume of the total cylinder volume when the piston is at bottom dead center to cylinder volume at top dead center. In other words, (Displacement + CCVolume)/CCVolume.

Now if we choose to include combustion chamber volume in total displacement as you suggest, there's an obvious problem: If we increase the size of our combustion chamber, displacement goes up, and so should horsepower. But any hotrodder will tell you that horsepower will decrease as you increase the combustion chamber volume because the compression ratio drops. Keep displacement and combustion chamber volume separate and everything makes sense: Bigger chamber, lower compression, less power. Smaller chamber, more compression, more power.

Replies:

• Words change over time jdemaris 20:12:47 03/27/06 (2)
  • Re: Words change over time MarkB_MI 03:41:34 03/28/06 (1)
    • That is rediculous jdemaris 05:58:35 03/28/06 (0)

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