In my pre-driving teenage years, I had older friends who were hooked on installing steep rear gears in the late-1960s and early-to-mid-1970s used cars they owned and modified. They liked to blast from stoplight to stoplight, not to mention doing burnouts to show off for the rest of us whenever the opportunity presented itself.
Given their examples, you’d think that when I got my license and my car, I’d want to do the same, but instead, I became a proponent of more reasonable rear gearing that provided lower rpm on the highway. Part of it may be due to the fact that like most teenagers, my car was my daily driver, not a purpose-built hell-raiser that didn’t have to get me to work and school each weekday. Yet many of those friends had been in the same situation, so go figure.
I learned early on that the intended use of the car was important when contemplating a rear gear choice. My first car was a 1967 Chevelle SS 396 with a swapped-in low-compression 454, a four-speed, and a 3.55-geared 12-bolt Posi. Around town it had punchy throttle response and was quick, but I preferred to cruise on the open highway and on long winding backroads whenever I could. And under those conditions, my opinion was that the cruise rpm was a bit high.
My favorite car magazines of the day told me that when choosing a rear gear ratio, the engine’s performance characteristics (Does it like to produce power at high rpm or is it built more for making a lot of low-end torque and mid-range power?), transmission type, converter stall speed if the trans is an automatic, vehicle weight, and tire height should be considered.
The jury is out as to how many of my friends who were in love with 3.73s, 3.90s, and 4.10s paid attention to any of those factors. As for me, I never did change the rear gear in that car, because it didn’t annoy me enough to put the cash and effort into it. I was also too busy fixing other areas.
In the early 1990s, when I got my 1977 Trans Am, it was equipped with its original 400, a Turbo 350, and a 2.41-geared Safe-T-Track. You read that correctly, 2.41 rear gears. It was seemingly ready for the Bonneville Salt Flats right from the factory, except for the fact that its Pontiac engine only made 180 hp in stock form that year. The engineers likely chose the numerically low gear ratio for fuel economy reasons. It certainly negatively affected acceleration, yet running low rpm on the highway without an overdrive was pretty comfortable.
A later swap to a four-speed and 3.23 rear gears woke up the performance of the car considerably. Yes, highway rpm increased as well, but I rationalized it by deciding that 3.23 gears provided a good balance of performance and economy.
Currently, my 1967 Buick has its original 400, an M-20 wide-ratio four-speed in place of the stock close-ratio M-21, and swapped-in 3.08 rear gears. An easy excuse for not having more performance-oriented gears is that I bought the Buick this way. However, I haven’t been in any rush to change them even though I know the 3.08s do little to exploit the acceleration potential of the 400. Again, I don’t mind the decently low cruise rpm on the highway when compared with 3.55s or numerically higher cogs.
I realize that installing an overdrive transmission and a numerically higher rear gear will grant me the best of both worlds, but that will take time and money. My ’67 GTO has a mild 455, 200-4R overdrive automatic, and a 3.55 Safe-T-Track, so I’ve already experienced the satisfaction of torquey performance combined with low highway rpm years ago when I could drive that car regularly. It’s currently in need of restoration. Though I could swap its trans and rear into the Buick in the meantime, I still really do like shifting gears for myself in the GS.
Is your vintage ride geared more for higher-rpm performance or lower-rpm long-legged open-road cruising? Which do you prefer and why?