The crankshaft is held to the block by Main Bearing Caps. Traditional pushrod V8's had 2 bolt mains, which meant that there was 2 bolts holding each cap on. High performance, or heavy duty engines often had 4 bolt mains, meaning there was 4 bolts per cap, for added strength. The new Ford Mod engines have a minimum of 4 bolts per main cap, and the DOHC 4.6 has 6 per. It just means it's that much better equipped to handle high power output.
Take care,
-Chris
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