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The '400 SBC Trick': Larger Bore, Shorter Stroke

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History of Chevy's NASCAR Engines: Small Block Evolution Details Up Close With a Legend (SB2 & R07)

What happens here

The quest for increased horsepower led to the desire for larger cylinder bores and shorter strokes, as this configuration allowed cylinder heads to 'breathe' better. The Chevrolet 400 SBC engine was identified as a suitable candidate due to its larger factory bore. However, the standard 400 SBC came with two-bolt main caps that were weaker than the four-bolt caps of a 350 SBC. Engine builders modified the 400 block by installing custom billet main caps (sized for the stronger 350 mains) using spacers, and then line-boring the assembly to precisely fit a 350 crankshaft. This ingenious adaptation allowed racers to combine the desired bore size with improved block rigidity, laying the groundwork for future high-performance small blocks.

Goal: Explain the modifications to the 400 SBC engine for enhanced airflow and durability.

Tools and materials

  • Billet Main Caps — Providing stronger main bearing support for the 400 SBC block
  • Chevrolet 400 SBC Engine Block Chevrolet — The base engine block chosen for its larger bore
  • Rottler F69A Machine Rottler — Line-boring the main caps for precise crankshaft fitment (shown in background)
  • Spacer Custom-made — Adapting the 350-sized main caps to the 400 block

What they say

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400 Main which was a little over 200 000 bigger but uh put the spacer in the block cap on it that was the correct size for a 350 crank and line board it like say about 400s for two bolt so we've been splayed caps on them like that that worked out for good quickly when they come out with the bow tie block later on that quickly evolved that's what everybody did used a bigger bowl shorter stroke is that the same Arizona was running the 180 degree headers and stuff on his cars yeah you were building these engines back then we didn't build these engines we did this block work and cylinder head work were the cylinder heads you were using like a factory like a Corvette head or do you remember what it was from the very first ones were Factory type he had quickly evolved in what they referred to as the bow tie cast iron head required an extension from out of work so it was all done by hand the heads were very fragile it was a given

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