Good information for anyone building, or considering building, a performance
engine.
Daryl
'66 R/G 1800cc Hot Rod :-)
----- Original Message -----
From: Jim
To: megasquirt-tuning@msefi.com
Sent: Friday, April 07, 2006 7:43 AM
Subject: How to tune accel param
A "quench" or "squish" area is any area where a flat area on the
piston crown comes into very close proximity to a matching flat area
of the cylinder head .
This area , in order to have the desired effect , must be VERY tight when
the piston is at TDC , one rule of thumb used goes like this :
When remachining your engine block you want to "deck" the block
(I think you may call it skimming ??) this is when you put the block in a
holding fixture which uses an expandable steel pipe that runs through all
of the Main Bearing bores and then machining the head gasket surfaces to
insure that they are square and equidistant from the main bearing bores .
Before performing this operation the pistons and connecting rods and
crankshaft are carefully measured so that the amount of material to be
removed from the head gasket surface can be calculated .
The end result is that the piston crowns will be perfectly flush with the
head gasket surface at TDC .
This results in the ONLY clearance between the piston and cylinder head
being the compressed thickness of the head gasket .
This is usually about .040 inches or 1mm , this is just approaching the
ideal clearance , ideal would be about half of that measurement but would
result in too much risk of the piston contacting the head at high rpm .
Head gasket manufacturers sometimes provide this compressed thickness
measurement right on the package , if they don't thier website or a phone
call will get you the specs. .
Another note of interest , sometimes "Steel Shim" head gaskets are
availible for your engine , the compressed thickness of these gaskets are
about half that of "composition" style gaskets , this may allow you to
reduce your quench clearance without machine work .
Here is a very good article I found with a quick Google search ,
it generally understates the advantages that I have seen .
http://chevyhiperformance.com/techarticles/94138/
And while it is referencing a Chevy V-8 , the principles apply to all engines
.
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'95 GM 4.3 Vortec V-6
Single Plane Intake w/ported GM Throttle Body
Ported Heads , stock roller cam retarded 8 degrees
MS-II V-3 , EDIS ignition
Cooling Fan and Torque Converter Control
250hp , 28mpg @60mph in a 2 ton wagon
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