Recent notes on 87 octane use suggests that the Max's compression ratio may
not be the advertised 10.5:1. I installed Max heads on a 1300 Venture and
cc'ed the heads to measure true compression ratio. By my calculations, the
combination resulted in an estimated compression ratio of 9.0:1, which is
considerably less than the Venture's advertised 10.5:1. At the time, I had
a Max piston to compare. It is virtually the same as the Venture's, except
for a very slight "dome". My rough estimate of Max's true compression ratio
was about 9.7:1.
For your reference, I measured the Max head volume at 23-24 cc.
On a related subject, I was amazed by the deck height - this is the height
from the top of the piston at TDC to the bottom of the cylinder head (the
flat part that mates with the deck). I measured about 0.85". Generally
speaking, the Chevrolet and Harley motor builder sources I have researched
state that optimum deck height for a good combustion is about 0.40" and
anything over 0.65" causes the cylinder to loose the "squish factor" of a
quench type combustion chamber. This certainly indicates that there is room
for the longer connecting rods, but I wonder if much the same horsepower
increase would be available through simply and cheaply milling the decks of
the block. Comments?
Rey Kirkman
VMOA 439
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