For the older cars, they add an extra spark plug. Twin plugging is very
common in the Porsche street/race cars with CR greater than 10:1.
Induction and cam overlap may have some influence also.
Olin Brimberry
Raleigh, NC
- -----Original Message-----
From: owner-healeys@autox.team.net [mailto:owner-healeys@autox.team.net]
On Behalf Of PG
Sent: February 15, 2007 3:13 PM
To: 'Healeys'
Subject: compression Ratios
List, hear is some food to dwell on:
I was reading some articles last evening and a question popped to mind.
Why is it that the Porsche 2007 911S has a compression ratio of 11:8 to
1
and yet does not have detonation whereas an older English motor with
compression of 10:5 to 1 has issues?
Is it that the advertised compression numbers are "static" compression
and
because of valve timing, in particular, the closing of the inlet valve,
that
the dynamic compression on the Porsche might be substantially less than
the
11:8 to 1.
Also, could it be combustion chamber design, better cooling etc etc.
Any thoughts
Regards,
Paul
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