During the 1960s, all of Detroit's entry-level cars-including pony cars-relied upon the simple leaf spring to perform rear suspension duties. Leaf springs have been around a long time, and go back to a time before cars even existed. Horse-drawn buggies had leaf springs, much to the relief of their occupants. Over time, more sophisticated rear suspensions and suspension aids were developed, including the triangulated four-link, torque arm, ladder bars, truck arms, double-wishbone independent, torsion bar, Watt's link, and Panhard bar. If you flip through the ads in PHR, you'll see plenty of great upgraded rear suspensions that use many of these technologies, but is there still a place for the lowly leaf spring? We think so!
When we bought Project Nova...
When we bought Project Nova it still had the stock monoleaf six-cylinder rear suspension and 8.2-inch 10-bolt rear. Our 523hp Dart SHP 400ci small-block could completely toast one tire through the top of Third gear! Fun, but not fast-or safe.
Two clear advantages to using a leaf-spring suspension in a car that already has one are cost and simplicity. Upgrading the factory leaves with beefier ones is as easy as swapping parts. And those parts will cost less than most other options. From a functionality standpoint, a leaf spring performs three different duties: It locates the axle laterally, it fixes the axle's position around two planes of rotation, and it performs its requisite duties as a spring. That's a lot of stuff for one part to do. In more sophisticated rear suspensions, those duties can be performed by as many as four different parts. Asking one part to do all those duties has its disadvantages, namely being that a leaf spring is by necessity a compromise between competing needs.
Notwithstanding, there are serious advantages to a leaf spring. With few parameters to tune, a leaf spring with the optimal spring rate, ride height, and shock valving can get you amazingly close-in terms of lap times-to suspensions costing many times that. A few years back, we tested an optimized leaf-spring setup in our 1976 Chevy Camaro project car, then swapped over to an aftermarket triangulated four-link, and found that the expensive four-link conversion had just the smallest edge over the leaf setup in the timed slalom and skidpad.
At Classic Performance Products,...
At Classic Performance Products, our new 3.08-geared Moser 12-bolt (see "12 Bolts To Glory," Dec. '10) finally met up with our '68 Nova and a pair of beefy multileaf springs and KYB Gas-Adjust shocks.
In planning our '68 Nova project, we remembered how well the leaf-spring setup worked on the g/28 Camaro, and we wanted to revisit that. When we asked Classic Performance Products (CPP) to help us with the Nova, we knew they had a leaf-spring system that was designed for hard autocross and road-race use. Project Nova was conceived with the idea that all the improvements should be easily reproduced by the average reader in a garage environment, and a hot leaf-spring setup fit that bill perfectly.
The '68-74 Nova and the '67-69 Camaro/Firebird share identical suspension architecture in the rear, and it's important to take note that across these vehicle lines there is a variation in the leaf springs and rearends between cars originally equipped with straight-six and V-8 engines. Six-cylinder cars like ours originally had monoleaf springs and monoleaf axles, and even though the engine had been swapped to a V-8 long prior to our Dart SHP 400 transplant, the spring and axle was still a monoleaf. Monoleafs do not have locating pins that lock into the axle spring perches, so when we decided to upgrade our stock rearend to a Moser 12-bolt, we ordered it with the necessary V-8 spring perches.
Even though a factory V-8 multileaf is better equipped to handle the increased torque of a factory V-8 (and will do in a pinch), it's not really up to the 523 hp (and 523 lb-ft of torque) of our Dart-based small-block, which would wrap a pair of OE multileaves into an "S" the second we hit the gas. The CPP Sport multileaf spring kit (PN 2407C, $375) is stiffer than a typical V-8 multileaf, and is 11/2 inches lower than stock. When coupled with the increased damping ability of the CPP-supplied KYB shocks (PN KY-1107, $39 each) these should put us right in the ballpark for the small-block's power, and the increased grip of our 255/40R17 Nitto NT01 R-compound rear tires.