[Fot] Compression ratios

[Alexandre Camoletti]

HI John ! I milled 0.118 from my head (was 100% before, never skimmed) and
got 10.5 (corresponding to calculations).
But I made the chamfers in the chamber'side as per Kas' guidelines, so that
adds volume (approx. 2cc, as anticipated by calculation also).
So if you mill .118'' without chamfering from plain stock thickness then CR
may be above 11.
Then it depends how high the valves sit in the chamber, and what valves you
have (this can impact 1-2cc per chamber)
Also if you chamfer the plug hole, this adds volume.
Re headgasket, the volume it creates it often more than we think as you have
to calculate it not by multiplying the bore surface by gasket thickness but
the effective bore of the gasket itself, which often is quite a bit larger
than the round bore of the liner. Use school paper with squares to draw the
gasket bore on it, then count the squares and do the maths you'll get the
surface (each "non full" square count 1/2 square the small and big halves
will compensate each other quite well, this is the usual practice).
To be more precise I can check my handwritten chart if you wish, as I
calculated then measured all these parameters, it is in the shop with the
engine building file.
Let me know!
Alex

-----Message d'origine-----
De : fot-bounces at autox.team.net [mailto:fot-bounces at autox.team.net] De la
part de John Hasty
Envoyi : vendredi 26 ao{t 2011 15:43
@ : 'Friends of Triumph'
Objet : [Fot] Compression ratios

A while back, Mark Bradakis sent out a chart showing head thickness to
compression ratios for GT6 motors and in the chain of replies, Chris Marx
reported that the stock head thickness for a TR4 was 84.2 mm or 3.31 inches.
I note from Mark's chart that a GT6's head thickness of 3.31 inches = 10.75
compression ratio.  Question: are the various head thickness/compression
figures for the GT6 the same as for the TR4?  Or, better still, does anyone
have similar figures for the TR4?

John H. Hasty
Attorney At Law
Guthrie, Davis, Henderson & Staton, P.L.L.C.
719 East Boulevard
Charlotte, North Carolina 28203-5113
Tele: (704) 372-5600
Fax: (704) 372-4601
E-mail: jhhasty at gdhs.com
www.gdhs.com

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