[Vwdiesel] Head gasket thickness

[LBaird119 at aol.com]

In a message dated 11/28/2007 4:12:47 PM Pacific Standard Time, 
vbriggs at stny.rr.com writes:

> Actually I think it's more thermally efficient at higher compression 
> ratio's, burning fuel more completely. They only lower it due to 
> mechanical restraints. Makes it harder to contain the magic smoke the 
> higher you get the cr.
> 
  Well, according to a diesel, class instructional book I have, 
the main reason they go with higher compression is for better 
starting.  I never did read the whole SAE paper on the 1.5 but 
I've had a couple people tell me that it says VW found 18:1 to 
19:1 to be the most efficient but chose 23:1 for dependable 
starting.  The same book covers an experimental, variable 
compression diesel, where the pistons are basically like big, 
hydraulic lifters.  As cylinder pressure increased, the pistons 
would compress more, giving lower compression.  The efficiency 
and power output was about double of the fixed compression 
version!  :-)
  Once you get to a certain point, pumping losses exceed the 
higher compression gains from an engine.  I'd suspect that 
number is somewhere between 16:1 and 19:1.  I know with 
Dad's pu, as the rings and all seated in, it LOST power.  Turned 
out it'd had the wrong head gasket, I replaced with the same 
back when that's what you did rather than measure.  We had 
700 to 750 psi compression!
  You could actually feel the sluggishness as compression 
increased and robbed power.
  


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