Tech Note On: MAIN CAP ATTACHMENT
Motown Cast Iron Blocks

Prior to the availability of aftermarket blocks, performance enthusiasts were faced with the dilemma of scouring junkyards looking for 4-bolt main blocks or trying to fit 2-bolt blocks with aftermarket cap kits. Now you have a choice between standard 4-bolt main blocks with nodular iron caps and splayed billet caps. Rest assured that the 4-bolt setup will provide excellent reliability for most applications. For the serious performance enthusiast, the splayed billet setup is preferred for several key reasons. The illustration below shows a cross-section of a block casting, and the relationship between bolt holes and the “meat” of the block. As you can see, the splayed bolts have a much better “anchor” due to available material thickness. The multi-directional clamping of the splayed bolts also helps improve bottom-end durability.