Chevrolet's 1955-57 performance saga is one that will never be forgotten. In the eyes of most historians, it lacked nothing. If Chevrolet had to do it all over again, hardly anything would be changed. But when 1958 showed up, a lot had changed. To most, it was initially not for the better.
Gone from the passenger-car regular production-option order pages was the high-performance 270-horsepower 283. The now-290-horse fuel-injected engine was available, and supposedly a few were built, but we've never come across a documented factory-build '58 fuelie. In their place were two smooth-idle hydraulic-lifter big-blocks. Coded "W-motor" 348s, each weighed in at 125 pounds (or more) heavier than the small-block. Both engines, due to the camshaft profile, lacked high-rpm revability and power over 5,000 rpm. It looked like Chevrolet had taken the AMA antiracing edict a little too seriously.
Many performance enthusiasts have always wondered why Chevrolet dramatically increased the size of its '58-61 models. With its sales success in 1955, 1956, and 1957, why mess with a good thing? To make a long story short, they had to stay ahead of the competition. At this point in time, big was the status quo. Lore had it that the bigger and classier your car, the more successful your peers and neighbors thought of you. So Chevrolet had no choice but to offer "more" car.
Chevrolet stylists (we believe) seldom thought about performance. Nor do we believe they considered what adding 500 or more pounds does to vehicle driveability, performance, handling, and fuel economy. But hey, glamour was key in 1958. It was Wowsville for sure. Stylists were instructed to create more eye candy, and they delivered big time in 1958.
The first of the new Turbo Thrust 348 engines produced 250 horsepower. It had a Rochester 4GC four-barrel carburetor and pumped out 355 lb-ft of torque at 2,800 rpm. It added $59 to the sticker price. The second was a Super Turbo Thrust 348. It had three two-barrel carburetors and produced 280 horsepower at 4,800 rpm with 355 lb-ft of torque at 3,200 rpm. It added $70 to the bottom line.
Under normal driving, only the center carburetor operated. But when the throttle was opened 60 degrees, the front and rear carburetors opened. The three two-barrel carburetors each flowed about 225 cfm, while the Rochester 4GC four-barrel carburetor flowed about 450 cfm. The extra 225-cfm Tri-power airflow somehow equaled 30 horsepower. Both engines featured the same heads and hydraulic lifter camshaft. Chevrolet publicly limited engine rpm to 5,400 due to hydraulic lifter bleed-down at about 5,500 rpm.
The standard transmission in 1958 was a manual column-shift three-speed. Two optional automatic transmissions were also offered, a Turboglide and a Powerglide at $231 and $188, respectively. Two manual transmissions were also offered: a standard three-speed and an optional BorgWarner four-speed. Both had an iron main case and tailshaft housings. A Positraction differential was also available for $48.
Where's The Beef?
The '58 Chevrolets were nine inches longer than the '57. A 348 Impala hardtop weighed in at about 3,675 pounds, and with automatic transmission it had a 0-60-mph e.t. of 10 seconds. Three months into the model year, dealers all over the USA screamed for a high-performance engine with some moxie. Other brand dealers were laughing and giving them the raspberries.