[6pack] TOO MUCH COMPRESSION?

[Ted Schumacher]

John, quick math shows you about 9.8.  You are right on the border of 
too much.  Years ago this was not a problem. We would run 10.6 or higher 
on cast pistons.  Problem is today's gas burn hotter so you have the 
issue of increased pressure (compression ratio) and increased burn temp 
on the piston head.  Not good.  I suggest you redo the calculations for 
compression ratio to see what you really have. (CR=V1 + V2 divided by 
V2). V1 is the volume of the cylinder. V2 is the volume of space above 
the piston at tdc.  Make sure to include any dish in the piston and the 
volume of the head gasket in V2. A simple fix is too have the piston 
coated. Top coating is for heat and skirt coating for "slippery".  We 
build a lot of engines and this is a very viable alternative. No need 
for custom made gaskets, etc. Ted


John Mc wrote:
> Just a general question to those who may know better than I.  I've just completed a port & polish & modified
> the combustion chambers on my TR6 head and have calculated the compression as being close to 10:1 (bore 78,
> stroke 95, Combustion chamber 39cc, Piston dome -6cc, head gasket bore 79.3, compressed gasket at 1.11 and
> zero deck clearance). Given that this is a fairly hot street car, is this too much?  Are the modern fuels up
> to it? I have the opportunity of fitting a second head gasket to reduce it down to about 9.1:1 but would like
> some advice first?  Another related question, are there thicker head gaskets available for an overbored
> (2.7litre) engine?  If so, I think that would be better than using 2 gaskets.  All opinions welcome.  Thanks.
>
> John Mc
> '71 TR6 PI
> '76 Dolomite 1850
> '76 Dolomite Sprint
> '64 2000 Estate
> "Fast is First"
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