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A strong, dependable block is
the cornerstone of every racing engine. It's the
foundation that supports all of your efforts to build
horsepower. Yet as important as the block is in building
a reliable and powerful motor, too many racers still
insist on using a "good old block" as the
starting point for a competition engine. In my opinion,
that's a major mistake. The truth is that there aren't
any good old blocks - at least when the subject is
big-block Chevrolet V8s.
The big-block Chevy and its
derivatives have become dominant in sportsman drag
racing. There are armies of Rat motors marching through
the staging lanes in the heads-up Super eliminators,
Quick 32 and fast bracket categories. It's amazing that
an engine that debuted 38 years ago is the powerplant of
choice in our sport, but it's tough to beat the
big-block's combination of performance, reliability, and
affordability.
While the technology of drag
racing has changed dramatically since the big-block
Chevy was introduced in 1965, some racers remain stuck
in the past. They still believe that an original
4.250-inch bore factory block is the ideal starting
point for a big-block racing engine. Unfortunately,
they're wrong - and that costs them time, money, and
horsepower.
The fact is that aftermarket blocks from Dart and
World and GM's heavy-duty Bow Tie blocks are vastly
superior to the original production castings. They've
got siamesed cylinder barrels that allow larger bore
diameters
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(up to 4.600 inches), stronger main bearing webs,
thicker deck surfaces and improved oiling systems. It's
simply throwing good money after bad to invest in a
decades-old production block for racing when these
modern alternatives are available.
The chief shortcoming of a
production Chevy big-block is its limited bore diameter.
The big-block's 4.250-inch cylinder bore diameter is a
compromise even with stock heads - that's why the
factory notched the tops of the cylinder bores for
intake valve clearance in high-performance engines.
Chevy engineers may have been concerned about the
long-term reliability of siamesed cylinder bores when
the big-block was designed. We know now, however, that
siamesed bores work just fine in everything from street
engines to Winston Cup and Pro Stock motors. Eliminating
the water passages between adjacent cylinders is the key
that opens the door to building big-inch
big-blocks.
Increasing cylinder bore
diameter improves engine performance in many ways.
Within reasonable limits, a bigger bore is like getting
free cubic inches. By that I mean that big-bore pistons
aren't significantly more expensive than comparable
small-bore pistons. The piston speed is the same
regardless of piston diameter, and you don't invite the
potential oiling problems and windage losses that come
with long-stroke cranks. Most importantly, a large
cylinder bore complements the big-block Chevy's
combustion chamber design and valve spacing.
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