1980 Pontiac Firebird Turbo Trans Am: The Chicken and the Snail

From the October 1979 issue of Car and Driver.

It’s not gas distress that makes Ponti­ac’s bird of performance burp fire all over the Trans Am’s hood. It’s a turbo­charger, installed by Pontiac to ruffle the Firebird’s pinfeather and boost its potency to 205 horsepower for 1980. The decal fowl is now on a new flight plan—out of a rather primitive past to a future where speed and efficiency are precisely matched in importance. We should all tip our hats to the engineer and bean counter who’ve joined forces to keep the Firebird flying high, even if it did take a little heat under its tail to maintain altitude.

The turbo Bird must carry around its old, heavy body for two more model years in spite of the fact that all the medium-to-big engines fit for this sort of duty are out of production. Faced with two “easy” alternatives to kick off the Eighties—building stone-slow Firebirds or borrowing engines from another GM division—Pontiac avoided both, and in­stead allotted more than a few engineer­ing dollars to discover some fresh horsepower. The biggest engine this di­vision builds, a 302-cubic-inch V-8 (la­beled a 301 by marketeers), was origi­nally conceived in 1977 as a smooth-­running, fuel-efficient station-wagon mover, but with lots of redevelopment it’s risen to the task at hand with turbo­charging. Though others have bolted the hardware together in almost exactly the same fashion as Pontiac did here (Buick’s turbo V-6 comes closest), the Trans Am’s new turbo V-8 does distin­guish itself as the biggest of its kind ever to see large-scale production.

In case you hadn’t noticed, turbocharging is the universally accepted per­formance panacea for the times, and at the core of this particular system is an AiResearch TBO305 blower. Buick’s V-6 and Ford’s inline-four applications use the same basic unit, which features an integral waste gate controlled by intake-manifold pres­sure. Pontiac’s design is notably differ­ent in two respects, however. First of all, boost pressure is set higher than others have ventured (9 psi), and second, the compressor housing has a larger flow capacity to suit the requirements of the Trans Am’s larger piston displacement.

A Rochester Quadrajet carburetor feeds the turbo’s hungry mouth through a carefully designed cast-aluminum ple­num chamber. Air is picked up by a four-inch-diameter duct just above the front air dam, flows unimpeded to the carburetor, where fuel is added, and then turns through 90 degrees in the plenum to enter the turbo compressor in a horizontal stream. All passages are as smooth in shape and as generous in area as possible to minimize power-lim­iting restrictions. Heat is also detrimen­tal to a high-mass flow, so the normally aspirated 301 engine’s exhaust cross­over has been omitted from the turbo engine’s intake manifold. Instead, there’s a water jacket surrounding the plenum chamber. It heats the charge to maintain cold drivability, but once the cooling system reaches 217 degrees Fahrenheit, the thermostat shuts off flow to keep fuel-air mixtures as cool as possible.

Nine psi worth of overpressure is a rather ambitious undertaking for an engine certified to run on 91-octane fuel, and realizing this, Pontiac has taken sev­eral precautions to avoid the mechanical destruction all too common when a tur­bocharger blows an engine the wrong way. Detonation is the principal enemy. It can be combatted by at least three means: by adding water injection, which Pontiac has avoided for a number of good reasons; by enriching the fuel-air mixture, which is unfortunately contrary to efficiency goals and therefore used sparingly; and by retarding ignition tim­ing. A side effect of using a later spark to limit detonation is the fact that it also sacrifices power. This is why Pontiac has adopted a very sophisticated spark re­tarder, pioneered by Buick in its 1978 turbo Regal. The system relies on an accelerometer-type transducer bolted to the intake manifold to listen for vibra­tions characteristic of unscheduled com­bustion. Upon hearing the first few rat­tles of detonation, the transducer tells an electronic module first to back off spark advance, and then immediately thereafter to restore just enough to keep ignition timing at the threshold of detonation. This happens continuously every few milliseconds, so the engine runs with optimum spark advance all the time.

Several internal modifications have also helped the 301 stand the gaff of nine pounds of boost. Extra material was added to the block’s bearing webs and top deck, and main-bearing-cap bolts have been increased from seven-­sixteenths to one-half inch in diameter. Crankshaft fillets receive a pressure-­rolling treatment to make this part more fatigue-resistant. Pistons are cast-alumi­num, but they’ve been redesigned (along with the wrist pins) for greater strength. The compres­sion ratio has been lowered to 7.5:1.

So far, this is standard turbo-engine practice, but all these conventional com­ponents were screwed together and di­aled in to produce some very un-turbolike behavior. Pontiac’s objectives were to match T/A 400 acceleration, to reap all the fuel-economy benefits offered by trimming piston displacement 25 per­cent, and to keep drivability up to GM’s usual high standards. Translated into street language, this means Pontiac wanted its turbo motor to act like a much bigger normally aspirated engine all the time, except at the gas pumps.

In driving this new-world T/A, you’d swear Pontiac was trying to keep its tur­bocharger a secret. After a big buildup on the hood (rebulged for clearance and redecorated for flash), the instrument panel has neither a boost gauge nor even so much as an idiot light to tell you there’s anything special happening ahead of the firewall. The exhaust rum­bles the same sounds of the mellowed-­out, catalytic-convertered V-8 we’ve heard for years. Nailing the gas pedal only further confuses the issue: what you feel is the tug of an eager 350 cubic inches or so, doing its best against a 3700-pound curb weight. And don’t try to listen for the whistle of a turbine wheel spinning up to tell you good things are going on at the other end of the throttle linkage. Pontiac pays AiRe­search a few dollars extra per unit for turbochargers just to buy them without the tiny rotating imbalance that makes them whine the haunting melody turbo nuts learn to live by.

Pontiac’s plan goes further. There is no surge in the T/A’s torque curve to tell you the booster’s just been lit. As soon as you hit the throttle, the turbo­charger goes to work and pumps up full boost by 3500 rpm. Likewise, this car lacks an acceleration lag and the attend­ant steep rush to the redline you get with Buick’s, Ford’s and, most assertive­ly, Porsche’s turbos. So the blown T/A is more in the Saab Turbo class of per­formance: soft-spoken but aggressive. It works hard all the time to keep you from knowing it’s working hard.

There are, however, limits to the tur­bo’s enthusiasm. By the time the engine reaches 4000 rpm, the show is essential­ly over. So much spark has been backed out by the anti-detonation electronics that the horsepower curve droops like licorice in the sun. For maximum accel­eration, you’re best off leaving the shift­er in “D” and letting the transmission make the moves Pontiac programmed into its hydraulic heart.

In hard-number terms, 60 mph hap­pens 8.2 seconds after the stoplight goes green, and a quarter-mile is over in 16.7 seconds. The speedo registered 86 mph at this distance in our testing, and will crank up to 116 mph if you happen to have a cross-county straightaway, as we did, to let it all hang out. Referenced to 1979’s performance peak—a 400 T/A four-speed—acceleration times are longer by 1.5 seconds, and about 10 mph has been lost from both quarter­-mile and flat-out speeds.

As you can see, a few performance points have been lost for 1980. These sacrifices are predictable with tightening emissions and fuel-economy stan­dards, but the amount of bullet-biting we’ll have to accept in this instance goes beyond the pale. California will catch no more than a glimpse of the new turbo engines as they’re built into cars at GM’s Van Nuys assembly plant and promptly loaded on trucks and trains bound for the other 49 states. A rather cruel and unusual predicament. Even if you do happen to live where the turbo is certified and decide to step up to buy one, your gears will forever after be se­lected by Turbo Hydra-matic whims. That’s right, synchromesh fans, the four-speed’s been banned from turbo­charger duty. Or any T/A duty for that matter, since Pontiac plans to offer but one manual transmission to serve the whole Firebird line for 1980: a three­-on-the-floor as base equipment behind a 231-cubic-inch V-6.

All of which makes the Trans Am’s former greatness seem really great this year. Fortunately, most of the non-en­gine past glory is intact. The all-disc brakes are second only to the Corvette’s for pure, made-in-America stoppability. The wonderful WS6 handling pieces still work road magic, although there is substantially less oversteer to play with now that much of the powertrain’s punch is gone.

Chalk the loss up to this year’s tight­ened emissions laws if you’re planning any correspondence with your elected representatives. Pontiac says heavy, stick-shift models are all but impossible to drive smoothly enough to pass the new hydrocarbon standard. And four-speed turbo-T/A prototypes with cali­brations aimed at certification were sup­posedly so abysmal to drive that Ponti­ac’s chief engineer, Steve Malone, pulled the plug on their development.

That’s not to say you’ll never see the turbo matched to a four-speed in the Trans Am. The folks at Pontiac realize this is their image leader, and they’re not all convinced the T/A can lose its four-speed, big-motor macho all at once and save face with a turbocharger. Final judgment awaits—at discothèques, drive-ins, and cruising loops across the nation, where the flaming hood bird is as much a part of the Saturday-night scene as tight slacks, Super Fly shoes, and gold neck chains. Until turbo fever plays here, the T/A’s mystique won’t be secure.

Source: www.caranddriver.com