A Tempest on the Track (Part 3)

Credit for original photo: Thomas A. DeMauro / High Performance Pontiac / Hot Rod
While my first two track-car posts haven’t elicited any comments here, they have sparked some conversation on the Facebook posts I made to drum up readership. Jon Wood replied with the following: “The torque tube wall thickness was increased from .050 to .090 for the 326. The rope shaft and torque tube were used with the SD421 Tempests, and they held up fine. The automatic transmission is pretty sturdy, the 3 spd manual leas so but suitable for a stock 326. The 4 spd manual was not very sturdy.”

So, the ’63 drivetrain is the only one designed to be robust enough for the three-hundred plus foot-pounds of torque the LS1 would output. Would I then opt for the ’63 over my previous choice of a ’61, or would I stick with a ’61 and swap in the beefier torque tube? Since I’m dreaming, I’ll go with the latter.

As promised, I’m moving on the wheels, tires, and suspension with this post. Interestingly, according to Wikipedia, the first-gen Tempests all came with a unique-to-GM "four-on-four-and-a-half" bolt pattern. Fortunately, this is pattern is the same as that found on early Mustangs, so the aftermarket supports it. The stock Tempest could be had with a six-and-a-half inch width if you ordered air conditioning. The stock tire on these was called 6.5X15. This system has gone the way of wide whitewalls, so the modern equivalent is P175/75R15. I’m going to want to keep the same outside diameter (25.3”) since I like the fit in the wheelwell and the speedometer will still be accurate. I’ll go a little wider than stock (7”) and much larger in diameter (17” - shorter sidewall for good handling). With a fender massaging and the right offset, I’m figuring I can get away with 205/50R17 tires. It’s a popular size with plenty of high performance options out there.

On to the suspension. The front end is pretty straightforward sixties’ GM with unequal length a-arms. I’d put in stiffer springs that lower the front a couple inches, bolt on performance shocks, and fit a beefy sway bar. The rear, however, is a bit trickier. The trailing arm suspension was only offered on two American cars, the first-gen Tempest and first-gen Corvair. The design is basically the same as that used on VW Beetles and, with much success, on early Porsche. GM improved the scheme in the Corvair for 1964 by installing a transverse leaf spring and softening the coils at each wheel. What this did was tie the left and right side wheels somewhat together to minimize the tuck-in that could take place under adverse cornering conditions. There’s a lot written out there about the Corvair suspension, but suffice it to say the transverse spring is an improvement, and I’d implement on my Tempest somehow. The rear end would also be lowered with the overall spring stiffness (coils plus transverse leaf) being higher than stock.

I’ll finish up my dream build in the next post where I’ll address body modifications.