[Healeys] FW: Compression ratio for a fast road 100

[PG]

Hi Tom,

Depending upon the octane you run, you will likely NOT get any detonation
issues.   Generally, detonation only occurs at compression ratios over
10.5:1.  I run a compression ratio of 10.2:1 with 91 octane fuel and have no
issue.   Occasionally, I purchase race fuel (octane 118) so that I can
advance my ignition timing and take the car for a good run.

Can't understand why you would loose any smoothness to the engine.....  This
is more a factor of the camshaft than the compression ratios.

With respect to a 9.5:1 compression ratio being a "track car".   Nonsense.
Most modern cars today are running higher compression than in the days of
old....especially with the advent of variable timing.   Track cars are
running compression ratios or >11:1 with high octane fuel.

Overall, a compression ratio of 9.5:1 would not be aggressive.  

The downside of increasing your compression might be along the lines of
disappointment.   I've never been a fan of trying to improve a cars
performance on a piecemeal basis.  An engine is a coordinated piece of
machinery; changing one thing without changing others has limited impact.
The biggest limitation of an engine is it's ability to breath......  just
because you increase the compression ratio does not mean that the engine
will be able to flow the intake and exhaust properly to accommodate.

DW forged pistons are expensive and I think there are a lot better ways to
get a bigger bang for your buck.....I would focus on the breathing of the
engine (intake and exhaust).  The three things I would do are:  change the
camshaft too something with a mildly larger overlap, spend some money
getting the head ported, install some exhaust headers, purchase a lightened
flywheel and get the crank/flywheel dynamically balanced.  This will give
you a much improved engine.....Now, if you add the 9.45:1 compression
pistons, you'll notice it and the engine will be able to take full
advantage.

Paul