Around here, the unusual is highly favored. As such, this 1963 Pontiac Le Mans joined the stable. What makes this car unusual is its extremely unorthodox driveline design, undoubtedly so for an American car in its day. Four distinctive components contribute to this: First, the engine is a 195ci four cylinder that is, pretty literally, one half of Pontiac’s solid performing 389ci V8. Second is the driveshaft, which consists of an enclosed torque tube with a flexible torsion bar driveshaft. Third is the rear mounted transaxle, consisting of the transmission and differential mated as one unit. Finally, fourth, is the independent rear swing axle suspension design.
The engine, known as the “Indy Four” (it is frequently misrepresented as the “Trophy 4”), was a compromise engine design that came about as a result of budgetary constraints along with a need for an economic (MPG) small engine configuration. The Tempest (the Le Mans was a trim level for the first two years of production that morphed into a series for ’63, but is a Tempest) was Pontiac’s answer to the compact car market along side Chevrolet’s Corvair, Buick’s Special and Oldsmobile’s F-85. As such it was meant to be an economy car. The Indy Four was able to be constructed on the 389 assembly line as it shared many components with its V8 sibling. When viewed from the right side, the engine really looks like a V8 as the cylinder bank’s 45º angle is identical to that of the V8, as is the head and valve cover. However, when you walk around and gaze at it from the left it presents a massively different picture. If the half-of-a-V8 engine design wasn’t unusual enough, the displacement absolutely was. Since the four cylinder we think of today was mostly popularized by foreign automobile manufacturers, we usually think of them in metric sizes. At 3.2 liters, this four cylinder is massive. To put it in perspective, a VW Beetle, built the same year, had a 1.2 liter four, and VW/Audi currently offers a 2.0 liter turbo four in some of their models. Both of those engines put together equal this one’s displacement! Inline four cylinder engines have some inherent vibration properties that become more pronounced when their displacement exceeds 2.0 liters. This can be counteracted by the use of balance shafts, however the Pontiac did not utilize them and vibration was a given. If you Google these cars or this engine, there are many contemporary articles written about the engine and it appears that a certain mythology has been cast upon it. This seems to have fed upon itself, finally culminating in the stuff of legends. I don’t know how many people who have written of its “agricultural sounding four” or how it “would rattle the fillings out of your teeth with vibration” have actually driven one of these cars, but first-hand experience dictates this car is smooth, powerful and its lack of exhaust burble is the only real giveaway that it doesn’t have a V8. Road & Track said as much in their original 1961 road test. This particular example is equipped with the high performance version of the Indy Four complete with 10.25:1 compression and a 4-barrel carburetor along with an aftermarket 2 into 2 header. Rated stock at 166 HP, it isn’t crazy powerful, however its healthy 217 ft lbs of torque makes for a deceptively potent street driving experience. It really is easy to forget it’s “just a four cylinder.”
Indy Four – Half of a V8
Aiding in the reduction of its inherent vibration is the unique torque tube driveshaft assembly. The torque tube, essentially a long rectangularish box-like tube, is bolted to the engine and the rear-mounted transaxle tying them together into one unit. This allowed the vibrations of the engine to be distributed throughout the driveline to reduce their intensity. Contained inside the tube is a solid torsion bar-like shaft that runs in a slight downward arc, rather than in a perfectly straight line. Somehow, this arrangement earned the non-Pontiac moniker of “rope drive.” Evidently, the nickname stuck, but it couldn’t be more inaccurate. The shaft is nothing like rope, nor is it even like stranded cable, which sort of resembles rope if you squint. Torque tube designs were used by Porsche in their 924, 944 and 928 series automobiles to power their rear-mounted transaxles.
Does this solid steel shaft look like rope?
That brings us to the rear-mounted transaxle. Transaxles are transmissions and differential units merged together into one unit. This car has a four-speed manual version, however there was a three-speed manual and two-speed automatic. Putting the gearbox in the rear of the car encouraged an optimal 50/50 weight distribution across the chassis for handling purposes. Similar concepts were utilized in the 1950s by Italian manufacturers such as Lancia, Cisitalia, Maserati and others – particularly in early grand prix car designs. The aforementioned Porsche models employed the rear-mounted transaxle for the same reason.
In the day, contemporary VW, Porsche and Corvair automobiles had a rear-mounted transaxle just ahead of their rear-mounted engines. All three of these vehicles had swing axle rear suspension systems and, thus, the Tempest followed suit. Endless pontificating has been done on the properties of a swing axle design. Ralph Nader made it the basis of his Corvair-damning book “Unsafe at Any Speed.” However, VW cranked out millions of automobiles through the 1967 model year using this design and uncountable swaths of us who drove and/or rode in those cars are alive and well to tell the tale. Yes, there are undeniable handling characteristics of the swing axle that one ought to understand prior to operating a car equipped with one, but then I’d argue that we all ought to understand the handling characteristics of any automobile we drive – sadly, that doesn’t seem to be the case. Anyhow, Google “swing axle” if you want to join in on the fun.
The wacky angle of an unloaded rear wheel
The Le Mans is a big hit here because its unusual driveline configuration is so similar to the Italian cars from our past. Moreover, according to a 2004 Hemmings Motor News article, there are roughly 600 Tempest/Le Mans cars in drivable condition today. Considering GM produced somewhere around 370,000 of these cars, their current scarcity is remarkable.