[Healeys] compression ratio teaser

[Chris Masucci]

Hi Paul,

Couple of things I would suggest.  

First, the specified volume of the combustion chamber may not match reality.
It may be off by a small amount, and unless you measure it you have to go by
the factory spec.  It can add up to a small amount, and even different
valves will change things slightly.

Second, assuming flat top pistons, do they actually come up right to the top
of the deck at TDC?  You need to measure protrusion of the piston to figure
final combustion chamber volume.

Cheers,
Chris
BJ8

-----Original Message-----
From: healeys-bounces at autox.team.net [mailto:healeys-bounces at autox.team.net]
On Behalf Of PG
Sent: Monday, January 11, 2010 12:17 AM
To: 'healey'
Subject: [Healeys] compression ratio teaser

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
Healeys at autox.team.net
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