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Re: [Healeys] compression ratio teaser

To: PG <britishcars@shaw.ca>
Subject: Re: [Healeys] compression ratio teaser
From: Chris Dimmock <austin.healey@gmail.com>
Date: Wed, 13 Jan 2010 03:43:04 +1100
Hi Paul, a standard 6cyl Healey has
1. dished pistons, and t
2. The tolerances used by BMC in the 1960's meant the pistons don't  
actually come to the top of the bore.

I didn't check your combustion chamber volume, I don't have a STD head  
lying around. But I suspect your calculation didnt account for:

1. you need to add the piston dish: and
2. Add an allowance (similar to the head gasket allowance) for the  
piston not being flush with the block deck
In order to get the correct std compression ratio
Are you coming to Australia again in the near future?

Now my divorce is finalised, I have that pair of Wolseley front shocks  
if you are still interested....

Chris
www.myaustinhealey.com
Sent from my iPhone

On 11/01/2010, at 5:16 PM, "PG" <britishcars@shaw.ca> wrote:

> Hi List,
>
> I'm having a tough time reconciling the calculated theoretical/static
> compression ratio of the later model Healey engines with the  
> published ratio
> of 9:1.
>
> Here is my math:
>
> Stroke              3.5"  (88.9mm)
>
> Bore:                3.281" (83.34mm)
>
> Calculated cylinder volume  Pr2*h:  485mm per cylinder or 2910 for the
> engine.  So far so good!
>
> For the compression ratio:
>
> Combustion Chamber volume:      53mm
>
> Gasket volume:                            2mm
>
> Therefore, calculated compression ratio becomes:
>
> (53+2) / (485+53+2) = 9.82:1
>
> Supposed to be 9:1 !
>
> Any of you geniuses see what I'm doing wrong??
>
> Paul
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