Quote:
Originally Posted by Uncle Bob
Well, your first reply caused me to remember I had downloaded rumble seat's (rest his soul) pdfs in the past, so checked to see if anything explanatory was there. It appears these are pre-war 81a heads as well by his reckoning:
"The 81A heads (24 stud) came in either aluminum or cast iron. Both were rated
the same at 6.2:1 C/R. Both have right and left heads. The aluminum heads have
combustion chambers of 82cc for the right head (part #6049) and 84cc for the left
head (part #6050). The cast iron heads have combustion chambers of 79cc for the
right head (part #6049) and 81cc for the left head (part #6050). Interesting....
same C/R with different cc’s.... wonder if flat top versus semi-dome pistons
account for the variation?"
The larger chamber size for the aluminum is consistent with the 21 stud ('37-8) being lower compression than iron heads (supposedly for truck app, but I have a passenger engine with them, so.....?)
As for the original idea of the thread, you've demonstrated the effect of less common knowledge being useful in recognizing seemingly unusual market pricing.
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The few CC's in variation that were noted had more to do with manufacturing tolerance and perhaps the accuracy of the inspection process.
Both the cast iron and aluminum heads (6.2:1) had a factory dimensional tolerance of 78 - 82cc's.