Shawn,
Getting back to my question about your compression. I tried to understand how
10.7:1 CR could be achieved primarily through proud pistons and am perplexed,
to say the least.
Using Goodparts compression tech article as a basis (right or wrong), it states
that removing .010" from the block decreases volume by 1.10 cc, while removing
the same .010" from the head decreases volume by 1.03cc. Not a huge difference.
According to the chart based on zero deck clearance, with an earlier 8.5:1 head
there needs to be approximately an 11.7 cc decrease in volume to reach 10.7:1
compression with a +.040 overbore (51.5 cc to 39.8 cc). If your pistons stand
proud .015" that would result in a volume decrease of 1.65 cc. This leaves
about 10 cc of volume still to be removed. If the balance were to come from
the head that translates into about .097" removed from the head. That seems to
be a decent amount of material and still leads back to my belief that head
milling is a much larger contributor to a compression increase than decking can
ever provide.
Is there something about your motor that voids any of this? Maybe my
calculations overlooked something? Larger Mazda pistons? Or...?
Thanks.
Greg Dito
CD6250L
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