The one compromise to originality was the installation of a modern MSD distributor in place of the factory ignition. To closely simulate the as-installed arrangement, the engine was installed with a belt driven water pump, and the head pipes were bolted to the manifolds. The engine was loaded onto Westech's SuperFlow engine dyno for the numbers. How would the various changes factor in terms of the power at the crank? Naturally, the crew at Westech had a dyno test in mind for this in-house project, and we were eager for the results. The balance was tipped with about one point less compression, but with a more modern cam profile, an upgraded valve job, and top-notch machining, assembly techniques, and replacement parts. We had essentially a mildly revised version of this engine, using all stock major components. That's the true compression ratio, and it is still high enough to make good power, but is a lot safer with today's gas and iron heads."īack in 1966, the stock L72 big-block was rated at 425 gross horsepower. With the pistons fitting at 0.005-inch below the decks, and a 0.051-inch-thick head gasket, the final ratio in my engine worked out to 9.86:1. This reduced the dome volume another couple of cc, down to 14 cc. We found when building the engine that the valve to piston clearance on the intake side was not enough, and had the piston's valve relief notches fly cut 0.080-inch deeper to give a safe clearance. 2300, which have a dome volume of 16.8 cc. For this build, I used a set of SpeedPro forged pistons, No. With the small early chamber, the trick is to use a smaller dome to cut down on the compression ratio.
Rick explains, "These earlier 427s used closed chamber heads that measure around 100cc stock, and I wasn't going to consider anything but the numbers-correct heads. Piston dome and chamber volumes are the key contributors to compression ratio with a given engine combo, and here the obvious choice to dial in the ratio was to select the appropriate piston. All of these changes add up to performance and reliability through higher quality in the build, instead of making big changes to the engine's original combination." All this stuff was never done from the factory, but we're just optimizing the assembly, and making sensible upgrades where the original parts are going to have to be replaced in a rebuild, like in the pistons, rings, and cam. I'll file fit and gap the rings for a better combustion seal than stock, I'll use modern forged pistons with coated skirts. If a better aftermarket Comp valvetrain will add engine reliability and performance, deal me in." Rick goes on, "I'll blueprint the bottom end and have Steve assemble it like a race engine, checking clearances, making sure everything is at the best specs for a balance of power and reliability. The cam isn't making a permanent alteration to the engine, and it is pretty transparent when in there it just works better. As Rick puts it, "You're always going to be changing parts in a rebuild, and if a modern Competition Cams' version of the stock cam gives me a similar feel, sound, and vibe to the original, but with more power and rpm, I'll take that upgrade. To meet these goals, some changes to the pure stock combination were deemed acceptable. For 1970, the 454 replaced the 427 as Chevrolet's premier big-block, putting an end to the period recognized by the mighty 427's dominance. Exotic it may be, but don't expect to find one sitting under a tarp, as factory production was little more than one-off.
For 1968, big-block options were unchanged, but in 1969, an addition was made to the lineup, which constitutes the Holy Grail of factory big-blocks, the all-aluminum ZL1. The L88 was designed as a racing powerplant, with a serious 12.5:1 compression ratio, an 850-cfm Holley carb, dramatically beefed internals, and aluminum heads. The top dog 427 was the legendary, under-rated, 430hp L88. Closing out the ranks of "Tri Power" 427s was the L89, which was essentially an L71 with aluminum versions of the large port rectangular heads. The milder 400hp L-68 was based on the L-36 engine, while the 435hp L71 otherwise shared specs with the L72 of the previous year. Choices in 427 big-blocks were expanded in 1967, with three new "Tri Power" engines, adorned with an induction consisting of a trio of Holley two-barrel carbs.
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