Summary: C.R. & HP & Healeys
Okay, regarding shaving the head of my big Healy vintage
race car to increase the compression ratio:
Roger Garnett says (along with some other helpful comments)
> Well, you really ought to do some reading
So I got out Vizard's book on Tuning the A-Series Engine
(yes I know the big Healey 6-banger isn't an A-Series, but
for those who aren't familiar with it, the book is a virtual
cornucopia of useful information on engines and techniques
to increase their performance -- the examples just happen to
be centered on the A-Series and some of its quirks).
And among other things - he states that an increase in the
C.R. from shaving the head is better than an increase from
changing the piston design. Specifically he says going to
less of a dish, or to a flat or domed piston, gives poorer
results assuming the same C.R. It seems the perfect shape
for a combustion chamber is spherical, and the closer one
stays to that shape the better.
To all of this James Fuerstenberg adds:
> I know a few folks who vintage race big healey's and
> no one is running less than 10 to 1...a fellow I know
> who runs around 10.5 to 1 considers that conservative...
> the fast guys are running more like 12 or so to 1.
Okay, a few reference points are ALWAYS helpful and
appreciated.
> You do not need much hp to walk past someone on the
> straight. Just a couple of hp will make a big
> difference when you are both flat out on a long
> straight...a better exit from the corner will
> enhance this.
Which sounds like James has seen me in action. But he's
right, my driving could be better (although I think I am
improving). Still, those few extra hp would be nice until
I can get through and out of the corners more consistently.
Plus, Matt Silveira describes
> a book called "Automotive Math" available at, where
> else, Pep Boys. The book is published by HP BOOKS.
> There is a formula in there for calculating Compression
> ratios, HP and HP to compression ratio and vice-versa
> as well as gearing, tire combos, etc.
I think I'll head for PEP Boys this weekend and check
it out. Of course, Vizard's book also talks about
calculating compression ratios, but does not specifically
relate C.R. to horsepower that I've found yet.
And finally, Barry Fox warns
> make absolutely certain of the amount to be removed.
> Too much and you find the push rods are now too long
> (been there, done that...its a long story, if anyone
> wants the gory details, contact me directly).
OUCH, that's certainly some good advice.
With these comments and cautions, but mostly Vizard's
comments, I'm starting to lean toward taking a bit off
the head. But first, that trip to PEP Boys . . .
Y'all have a good weekend, you hear?
-- Dave L.
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