For the typical street/strip motor, hot rodders have been aspiring to match towering horsepower peaks with excellent low and midrange torque for decades. Get that curve flat enough, and you've got yourself a broad and flexible torque plateau opposed to a narrow and finicky peak, which aptly describes the performance of the 461ci big-block Olds we recently built for our '65 Cutlass project car. While its 514 hp is more respectable than delectable, the Olds' maximum torque output of 540 lb-ft-which extends from 4,100 to 4,600 rpm-is both remarkably stout and astoundingly flat. Furthermore, the big-block Olds kicks out 494 lb-ft at just 3,000 rpm, and averages over 500 lb-ft throughout its entire operating range of 3,000 to 6,000 rpm. Sure, it's not terribly difficult to eclipse 500 hp with a run-of-the-mill small-block Chevy in the current era of easy horsepower, but it's the gobs of twisty stuff-and how cheap and easy it is to attain-that sets this 461 Olds apart from the pack.
Searching for a core locally...
Searching for a core locally proved fruitless, so we tracked down a nice 455 on eBay for $500. The motor was pulled from a '71 442 and displayed minimal wear upon teardown. The seller kindly stripped it down to the bare short-block before shipping it out.
While all these numbers look great on paper, they work even better in practice. The Tremec TKO-600 five-speed trans, 3.73:1 ring-and-pinion set, and 26.7-inch tires the 461 will be paired with match its torque curve perfectly. Assuming a shift point of 6,000 rpm, the big Olds will never fall more than 100 rpm outside of its broad torque peak on the 1-2, 2-3, and 3-4 shifts. Not only does that bode well for our '65 Cutlass' autocrossing endeavors, all that torque makes for an extremely well-mannered street combination that packs a devastating wallop from right off idle all the way to redline. Using a stock crank, a .030-inch cleanup bore, Edelbrock aluminum heads, a Mondello single-plane intake manifold, and a COMP hydraulic flat-tappet cam, the combo is as simple as it gets.
To transform our stack of parts into a thumpin' big-block, we hit up the expert engine builders at the School of Automotive Machinists in Houston, Texas. Although many readers recognize SAM for its perennial success at the AMSOIL Engine Master's Challenge, its primary objective is teaching students how to build performance street and race motors. Under the tutelage of school director, Judson Massingill, and head instructor, Chris Bennett, SAM's students carefully machined, balanced, assembled, and dyno tuned our 461 Olds from start to finish. The graduates the program churns out are hot commodities amongst the upper echelon of racing, and in fact, the student who ported the cylinder heads for our big-block Olds is now working for Warren Johnson's Pro Stock team. Considering that the Olds 455 and the Olds brand have both kicked the bucket, the young 'uns were psyched by the opportunity to work on an engine platform that precedes their time.
Piston and rod selection for...
Piston and rod selection for Olds motors is somewhat limited, but the parts that are available are very high quality. The stock-length 6.735-inch Eagle steel rods used in our 461 are good for 850 hp, and they were paired with 4.155-inch SRP forged pistons. Thanks to the Olds' tall 10.625-inch deck height, the pistons have a meaty 1.750-inch of compression height.
Back in the glory days of intra-GM rivalry, Buick, Oldsmobile, and Pontiac built a triumvirate of 455s. Unlike their high-winding 454ci Chevy counterpart, the BOP boys settled upon their own unique combinations that emphasized torque over horsepower, and this focus on low and midrange grunt is clearly evident in their engines' basic architecture. With a 4.125-inch bore and a 4.250-inch stroke, the 455 Olds' under-square dimensions loudly telegraph its stump-pulling intentions. Granted, the 4.250-inch stroke-one of the longest ever used in any muscle car engine-doesn't increase torque output much at all, it does shift the torque peak lower down in the rpm range and broadens the area under the curve. In comparison, the over-square 4.250x4.000-inch Chevy 454 is more inclined to turn greater rpm and make its power higher up in the rev band.
The combination of a long stroke, lots of cubic inches, and modestly sized cylinder head ports set the stage for making gobs of torque in a hurry. Torque monsters, by nature, don't need to turn high rpm, so the Olds 455 features beefy 3.000-inch main and 2.500-inch rod journals to increase journal overlap and enhance crankshaft strength. While larger journals increase bearing speed and friction, its adverse effects are fairly insignificant in a low-rpm motor like the 455. Since big horsepower at high rpm was never a likely scenario with a 455, the block casting is quite a bit lighter than a Chevy 454 as well. Rumored weight differences between the two vary greatly, but conservative guesstimates claim that the Olds weighs in at 50-75 pounds less than a comparable big-block Chevy.
SRP offers off-the-shelf big-block...
SRP offers off-the-shelf big-block Oldsmobile pistons for both .030- and .060-over applications with -5cc valve reliefs. The 4032 forgings have a silicon content of roughly 12 percent, which tends to be more brittle at high temperatures than a 2618 alloy piston. The advantage of a 4032 alloy piston is that it expands 15 percent less, which allows running tighter piston-to-bore clearance for reduced blowby and piston slap.
Since the 461 Olds is more...
Since the 461 Olds is more street than race, we matched the pistons up with a set of 1/16-, 1/16-, 3/16-inch JE standard tension rings. SAM set the top ring gap at .026 inch, and the second ring at .028 inch.