[DeTomaso] Compression ratio estimate
Pantdino
pantdino at aol.com
Wed Aug 14 00:22:49 EDT 2013
Given that both valves are not closed from bottom dead center to top dead center, of what significance is the mechanical CR anyway?
Seems like what matters is the psi at the time of ignition.
I know I must be wrong or they wouldn't tear down engines to determine it.
Jim
-----Original Message-----
From: JDeRyke <JDeRyke at aol.com>
To: boyd411 <boyd411 at gmail.com>; detomaso <detomaso at poca.com>
Sent: Mon, Aug 12, 2013 11:45 am
Subject: Re: [DeTomaso] Compression ratio estimate
Boyd, in a word- no. That's why in spec-racing classes that require a max.
compression ratio, they still do tear-downs. If there was a dependable way
around it, those guys would have found it.
The clearances inside the motor must be physically checked; there are
simply too many possibilities for changes- both by the factory and 'other
people'
to assume or infer anything. Cam lift & lobe center spacing, piston design,
block & head work including valve jobs & gasket changes- even wear- all
will alter any compression tests.
Unless you are the original owner and know for sure that NO machine work
has ever been done (which is either sad or scary), the way that always works
is to pull the heads and measure the void volume using Archimedes' Principle,
and ratio that against the measured bore & stroke. There are no short-
cuts.
Gasket sets are available and you'll learn a lot from a winter tear-down.
Enough others on this Forum have done this that you can't get into much
trouble. An engine stand and an overhaul manual are invaluable for this. You may
even save some money and will certainly gain some power! Good luck- J Deryke
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