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So yet another reason for the performance drop after 69-70...???

I was always under the impression it was 72 and up, and not all 440's, just a random majority. I've seen more than one 71-4 steel crank 440's with an internal balancer. Wouldn't all the 6-pack rod 440's been external...???


When the compression ratio dropped in '72 or so the pistons got light enough to internally balance a 6 pak rod motor. The imbalance was only 6.5 in-oz(compared to cast crank LY rod 440 at 12.9 in-oz) so it didn't take much weight reduction to go to internal balance.