From the May 1973 issue

Just when we had fast cars relegated to the museum sections, Pontiac has surprised everyone and opened a whole new exhibit. How it ever got past the preview audience in GM's board room is a mystery, but here it is—the car that couldn't happen. And the list of reasons why it couldn't is both long and well known. Compression ratios have plummeted like the Dow Jones in 1929, while factory-sealed lean carburetors are the norm, along with soft ignition and valve timing. It's all summed up by the equation of the year in Detroit: EGR (Exhaust Gas Recirculation) to fight NOx (Nitrous Oxide), at the expense of bhp and mpg. Until now, the realization that exhaust emissions will be Ivory pure in the very near future was hardly an encouraging sign.

The conclusion was inescapable: truly fast street cars would be gone with no chance for an amnesty. But Pontiac has defied all that. Nineteen hundred and seventy-three, unobtrusively perhaps, is the year of the fastest Firebird ever. And it's certified by Uncle Sam to be free from any bad manners. The SD-455 passes the same emission tests after a 4000-mile break-in as does every other production engine. If this were an all-new engine, it would then have to complete a full 50,000-mile certification program. However, since the Federal government recognizes the SD-455 as part of the 455 engine family, the SD version doesn't have to run the durability tests, but can use a deterioration factor defined by a standard 455 four-barrel engine. It is only that kinship to a volume engine that makes it a reality.

And just how fast is this 1973 "Last of the Fast Cars" from Pontiac? One does not jump into that consideration without a bit of meditation to insulate the mind against time-inspired overload. First of all, you must temporarily purge your thought waves of the small displacement engines that have occupied center stage since the neurosurgeons came down on Super Cars. Let your concentration wander over the truly fast cars of today, the 454 Corvettes, 911 Porsches, Panteras and Jaguar V-12s—but only briefly, because they are merely mid-14-second quarter-mile cars.

You must reach a plateau of concentration where the machinery is even swifter. Go all the way back to 1968. Think of the Street Hemis, the L88s, the Boss 429s. When that era of unconcerned euphoria is locked in, sit back and get yourself comfortable to savor this progression of "performance" as determined in 1320 feet. Relish it as you would a Cuban cigar. And no fair looking ahead to the specifications page. We've checked with our lawyers, and they say it's okay to tell you . . . if you can keep a secret.

HUMPHREY SUTTON

On the seventh of February, 1973, our test Firebird Trans Am SD-455 swept through the quarter-mile at Orange County International Raceway in Irvine, California in an elapsed time of 13.751 seconds and at a terminal speed of 103.56 mph. That is fast. That, in fact, is outrageously fast even within a five-year-old frame of reference. And it was done in a street legal car—a 1973 street legal car—with a full tank of gas (3854 lb. curb weight), street tires and, wait for it . . . automatic transmission.

There was no cheering throng in the shut-off area, not a single pat on the hoodscoop for the over-achiever 1973 Trans Am. There should have been. The event was easily on a par with Don Garlits' recent five-second runs in a fuel-burning dragster. It proves that once again, blindingly fast acceleration can be yours right off the assembly line.

The secret password is SD-455. Simply check that option code on the order blank, and your Firebird will bristle with under-hood muscle. That is a rare quality these days, especially in a car which has the one-dimensional appearance of a Super Car, but which less ostentatiously has incorporated the subtle improvements that have traditionally sold high performance sport cars.

It is almost a car of bigger than contemporary life dimensions. Among Sporty Cars, only the AMC Javelin and the Firebird offer engines over 351 cu. in. Since all Pontiac engines must be considered a "big" block, the 455 is not new or unusual in the Firebird chassis. But the SD-455 is a whole new breed of car, not just an engine. And you can credit guys like Special Projects Engineer, Herb Adams (sneaky insight: take a look at who has built the Pontiacs occasionally entered in Trans-Am or NAS-CAR Grand National competition the last couple of years), as well as Senior Project Leaders, Skip McCully and Tom Nell. They understand . . . in the face of adversity. The naysayers seemed to be everywhere. The front line of resistance consisted of the bean-counters who swore on a stack of Venturas that Pontiac would lose millions with a production SD-455.

They were supported by a handful of emissions engineers who predicted that certification of a performance engine to 1973 standards would be impossible. As a final reserve, there were the antediluvian members of management . . . men who still scratch their heads over the '64 GTO. Opposition came, was strong, pervasive, almost overwhelming; but Adams, McCully and Nell, in their naive dedication, have won out. They'd much rather think about winning in NASCAR or NHRA than merely chasing hydrocarbons. But if those are to be the rules of the game, they will still play . . but with their own entry. So, in the end, enthusiasts get a stay of execution, and the engineers again have a thoroughbred engine to fret over—all 100 percent legal in government eyes.

The outside of their Super Duty engine is cleverly disguised to look exactly like a standard Firebird 455 V-8. That means a massive lump of cast iron, with its water pump the only piece of aluminum in sight. But the source of strength lies not far below its expanse of turquoise paint. To begin with, there is a strong base of operations. The block is reinforced with thicker bulkheads, 4-bolt main bearings and more material in the camshaft and lifter area. The connecting rods and pistons are forged, and the crankshaft is an iron casting. (A forged crank would be stronger, but Pontiac bypassed the expense with special treatments for the casting. Outside surfaces of the crank are nitrided, and a pressure rolling operation is applied to the journal fillets. That mashes down surface fibers to eliminate minute tensions that often grow into cracks.) Pontiac tests have shown the crank to be one stout piece of iron. Our performance tests show no reason to contradict that claim in any way.

For extra insurance, the engine is assembled with generous clearances. Also, an 80 psi oil system is on hand to keep the lubricant flowing while the engine pumps out all its horsepower. And that power flows off the crankshaft in astounding quantities, an impressive total of 310 net horsepower. The secret to that power, if it is a secret, is that the engine can inhale all the air-fuel mixture it needs. That is really the only avenue to performance these days, since the SD-455, like all those "performance" engines, must squeeze its power out of 91-octane fuel (which limits the compression ratio to a low 8.4 to one) intake and exhaust systems have made up for the low compression ratio. Cylinder head design is unique to this engine, with intake ports of the "constant area" design. Normally, intake passages must wend their way to a combustion chamber, twisting past pushrods, head bolts, water jackets and other incumbent hardware. Avoidance is only part of the problem. In addition, enough material must be left over for sufficient wall thickness in case the casting cores shift—and they do in production.

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