My current understanding of compression ratios suggests that this high a
ratio may not be the problem it is normally assumed to be, depending on the
cam timing. Static compression ratios are calculated from bottom to top
dead center. However, there is also a "theoretical" dynamic compression
ratio, calculated from the timing of the opening of the intake valve to top
dead center, solved graphically using the correct rod length and throw.
This will of course give you a lower number, that is generally not quoted,
and rarely talked about. In one of his books Vizard quotes a cam designers
rule of thumb that most street engines have dynamic ratios of about 8.5,
while racing engines generally run about 9.0 and therefore require racing
fuels. It has also been said that most engine failures are associated with
to high a dynamic compression ratio. This theoretical compression ratio
does not include corrections for intake tuning effects and overfilling.
I
----------
> From: Patrick McMullen <pmcmull@ibm.net>
> To: Chris Kantarjiev <cak@dimebank.com>
> Cc: fot@triumph.cs.utah.edu
> Subject: TR-6 compressor mod
> Date: Monday, January 11, 1999 7:27 PM
>
> I would definitely use the lower compression head. You do not want high
> compression with forced induction. Unless you're planning on running
> water injection or modified fuels. The stock camshaft would work as
> well. Stock cooling systems will be pushed to the limit. Absolutely
> need a good header system. Minor ignition recurving.
> I believe the one example I read about was in California. I think his
> name is Richard Taylor? He also built a TR-6 with a turbocharger.
> Loves to tinker with the 2.5 litre engine! All my back issues of Six
> Pack are in storage so I can not access them for names and addresses.
>
> Pat in NC
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