Greg, check out the price of the pistons before you decide on a 2.0L or a
2.5L. The GT6 2.0L pistons are very expensive and will cost you well over
$100 (CDN) each. The 2.5L has what you will want for street duty and that
is low & mid range torque. General rule is "torque for the street,
horsepower for high speed only". Build for torque and you will never
regret it. With respect to the chamber volume for a 10.75 to 1
compression. Just do the math using the formula:
cylinder pressure = {[(1/4 pi) x bore squared x stroke] + chamber volume} /
chamber volume
fill in what you know, add the gasket volume to the cylinderhead volume.
Unless you zero deck the pistons, add the volume between the piston crown
to the block deck as well.
And hay, what kind of motor are you building that can run reliably on pump
gas with a 10.75 head. Its going to take a stout cam to keep things from
pinging apart. Have you thought of the intake manifold vacuum you will
have at idle (CV carbs???). What timing curve do you think it will take.
Planning on running propane??? Back to those pistons -- I assume you would
like to run forged units to handle the heat stress you will be subjecting
them to. I know of no source for 2.0L forged pistons. All I found were
OEM units made by AE (Hastings) in England. Perhaps a lister across the
pond can shed more light on what is available in the home land.
TTFN: Larry Quirk (another frozen Canuk)
----------
> From: WINDOWSEET@aol.com
> To: triumphs@autox.team.net
> Subject: Displacement
> Date: Wednesday, October 22, 1997 5:19 PM
>
> Hi, listers;
>
> I was doing some basic calculations on the displacement of my GT6+ engine
and
> came across something curious.
>
> Using the stock bore: 7.47cm (74.7mm) and the stroke: 7.6cm (76mm) I
> calculate a displacement of 332.9cc per cylinder and multiplying that
times 6
> cylinders gives a total displacement of 1997.45cc- just slightly under
the
> published displacement of 1998cc. It is obvious to me that the factory
didn't
> take into account the volume of the combustion chambers in calculating
> displacement. Is this common practice?Do most manufacturers publish swept
> volume as a measure of displacement?
>
> A GT6+ combustion chamber in a 10.75CR head has a volume of 30cc
according to
> the Competition Preparation Manual......so......a 9.5CR head should be
> approximately 26.5cc plus 4cc for the head gasket. Multiplied times 6
this
> would be 183cc which added to 1997.45 gives 2180cc.
>
> The reason for this exercise is that I am trying to calculate the proper
> combustion chamber volume for a 10.75 head if the bock is machined for
.040
> oversized pistons. Speaking of which, does anyone have any experience in
> using the .040 oversized pistons.....any block problems, like weak
cylinder
> walls, etc.
>
> Still trying to decide between a 1998cc engine and the 2498cc from a TR6.
> Some listers comments about high revving GT6 engine made me do some more
> thinking. In my mind it is still an issue of reliability, not necessarily
> maximum horsepower.
>
> Any comments or opinion will be appreciated.
>
> Greg Wolf
> 1970 GT6+ "Ian"
> Ann Arbor, Michigan
> Winnipeg MB Canada
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