Rey I assume you mean .085", .065" and .040" when you stated your measurements.
You are right about squish being more effective with the piston up higher. But
you also have to verify that you have plenty of valve to piston clearance to
enable decking of block or surfacing heads to up the compression. I've never had
a V-Max engine apart so I can't comment on the stock engines clearance here and
the potential to raise comp. ratio.
There is another factor, that is valve timing change after surfacing heads. You
will alter this just by cutting the heads so if doing so I assume one would have
to make the timing gears adjustable to return valve timing to where it should
be. Furthermore, does the stock timing chain tensioner have sufficient room to
take up the looser chain following these mods?
Some of the guys out there who play with these engines can hopefully put us on
the right track please.
Sam Blumenstein #795
Rey Kirkman wrote:
> 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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