cyl heads and compression?

[dardal@xxxxxxxxxxxxxxx]

Mikey, I think yo are close.  Compression ratio is a geometrical engine
parameter defined as the total volume of the cylinder (total clearance volume
plus swept volume) divided by volume of cylinder when the piston is all the way
up at TDC (also refered to as clearance volume).  The clearance volume is
determinded by the chamber size, piston shape, and of cource head gasket
thickness.  If the piston is dished, it adds to the clearance volume reducing
compression ratio, if its domed, it subtracts volume, increasing compression
raio (all these are obvious of course).  So, theoritically, you can have the
same compression ratio with an infinite combination of head chamber volume,
piston shape (domed or dished) and head gasket thickness.  Practically, we are
restricted by the cylinder heads and piston types available my manufacturers.

All the above need to be taken into account when trying to estimate the
compression ratio of the engine you are about to rebuild. 

D^2

Quoting mike sutton <mikanlin62@xxxxxxxxxx>:

> In light of recent events, I must say that I am not trying to make the world
> conform to my point of view but nonetheless , the  following sentence was
> posted today  - 7/16/04 -  and I have to disagree with it, and will explain
> why after the sentence.
> 
> ".......Combustion chamber shape (open vs. closed) has almost nothing to do
> with
> compression ratio....."
> 
> When you squeeze a volume of a gas ( meaning air not fuel ) into a space
> that is smaller than it was before, it gets compressed to a higher pressure.
> A given volume of air that exists in an open chamber cylinder head and then
> compressed into a closed chamber head has to yield a higher compression .
> If you look at the reverse, and take a dished piston and replace it with a
> flat top piston or piston with a dome, does not the compression ratio
> increase?  You have decreased the space that a given volume of air has to be
> squeezed into.  If you went from a 86 cc cylinder head volume to a 74cc
> volume, you have done the same thing.
> 
> If this is not the case, then the Mopar Performance B/RB Engine book is
> incorrect, as well as most other engine build up and modification books as
> well.  I will defer to the mechanical engineers on this, as I may have not
> used the correct terminology on what I am trying to say.  Maybe combustion
> chamber shape is not as good of a term as volume in this case ......can we
> get a ruling, or did I misread this one entirely?
> 
> Mikey
> 62 Crown Coupe
> 
> ( with larger chambered heads to drop the compression a bit and avoid pre
> ignition and detonation on regular gas - or not? )
> 
> 
> 
>