Pontiac inline-4 engine

Pontiac inline-4 engine
1962 Pontiac Tempest LeMans
Overview
Manufacturer Pontiac Division of General Motors
Also called Trophy 4
Production 1961-63
Layout
Configuration OHV inline four

The Pontiac inline-4 engine is a 195.5 cu in (3.2 L) inline four cylinder engine[1] produced by the Pontiac Division of General Motors Corporation between 1961 and 1963.[2] Created from one bank of Pontiac's powerful 389 cu in "Trophy V8",[3] its single application was in the first generation Pontiac Tempest. It was dubbed by Pontiac the "Trophy 4",[4] playing off the racing success that had earned the 389 the company nickname the "Trophy V-8" after just two years of competition.

History

The Pontiac inline-4 engine is a short-stroke, 45-degree inclined[4] inline four created from the right bank of the 389 V-8 for the debut of the Tempest in 1961. With an identical bore and stroke of ​4 1⁄16 in (103.2 mm) and ​3 3⁄4 in (95.2 mm), its 194.4 displacement is precisely half of the 389. Known as the "Trophy 4", it shared most of the 389's tooling and up to 120 of its parts. This degree of commonality enabled it to be produced on the same lines as the V8, allowing substantial cost savings. A drawback was that the 195 weighed much more than a purpose-designed inline-4: at about 540 pounds (240 kg), it was exceptionally heavy for any form of four-cylinder.

The brainchild of auto industry legend John DeLorean,[5] then the head of a design team responsible for the birth of the Tempest line, the 195 produced 110 hp (82 kW) (gross) at 3800 rpm and 190 lb⋅ft (260 N⋅m) at 2000 rpm with a single-barrel carburetor (as fitted with manual transmission using regular gas, and 120 hp (89 kW) with premium); 130 hp (97 kW) with regular gas (and 140 hp (100 kW) with premium), as fitted with automatic transmission; and 155 hp (116 kW) @ 4800 and 215 lb⋅ft (292 N⋅m) @ 2800 rpm with the optional four-barrel carburetor and automatic transmission.[4] A "power pack" option for the 1962 four-barrel carburator increased rated power to 166 hp (124 kW).[6]

1962 Pontiac Tempest convertible

The Trophy 4's drivetrain featured a rear-mounted transaxle connected to the engine vvia a torque tube,[1] giving the four-cyliner Tempest a near-perfect 50-50 front/rear weight balance.[5] As the driveshaft ran at engine speed, rather than the transmission output speed, it ran at a higher speed and lower torque than a conventional driveshaft for a rear wheel drive car. This allowed it to be made unusually small in diameter: a 5⁄8 inch (16 mm) solid rotating shaft inside a pressed steel square tube. Uniquely, the shaft was also bent downwards into a curve, which had the effect of making the critical speed of such a flexible shaft higher than the engine's maximum rpm.[7] The curve of this thin driveshaft gave it the nickname of the 'rope drive'.

A downside of the 195 was engine vibration,[1] as an inline four-cylinder engine suffers from inherent secondary imbalance resulting from its 180 degree crankshaft. In its design, the two outside cylinders move together simultaneously, as do the two inside cylinders. Due to geometry, a piston descending from top dead center will always move quicker through the first 30 degrees of crankshaft travel than a piston moving upward from bottom dead center, meaning that more mass is moving downward than is moving upward, causing a shaking in the vertical plane. Modern engineers consider the installation of twin counter-rotating balance shafts necessary for engines much larger than 122 cui (2.0 L). The V8-based design of the 195 lacked balance shafts due to cost.[3] The 195 was instead cushioned by flexible rubber engine mounts designed to isolate the engine from the rest of the car, and its forces were further dampened by the Tempest's unusual drivetrain (which distributed forces by the engine being bolted directly to a rear-mounted transaxle via the solid outer tube of its driveshaft). The timing chain in the 195 was originally the same as the 389, but was prone to stretch and break from engine vibration; a special high-strength version was developed as a replacement.

The 195 was dropped when the Tempest was upgraded from a compact to an intermediate for the 1964 model year.[1]

See also

References

  1. 1 2 3 4 1961-'63 Pontiac Trophy 4, Hemmings Motor News August, 2010
  2. ↑ "The Trophy-4 didn't last long, getting the axe after the 1963 model year, but it remains the most memorable of cut-down engines" http://autoweek.com/article/car-life/cut-down-engine-week-pontiac-trophy-4 Cut-Down Engine of the Week: Pontiac Trophy 4
  3. 1 2 Cut-Down Engine of the Week: Pontiac Trophy 4, Autoweek
  4. 1 2 What's It Worth? 1962 Pontiac Tempest "Trophy 4" Convertible ..Johnny D Decides To Put The Transmission In The Back, Vintage Auto Appraisal
  5. ↑ Pontiac '62 manufacturer's catalogue
  6. ↑ "Drive Shaft Curves Like A Bow". Popular Science. September 1960. p. 56.
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