There's a lot to love about a vintage muscle car. We can swoon over the seductive styling, the purposeful simplicity, and intangible raw element of power that seems to emanate from these classic American machines. While a classic muscle car fits in your garage like a jewel in a case, bringing that beast onto the streets in a usable fashion often presents an entirely different concept of reality. Technology has been steadily moving forward in the decades that have elapsed from those automotive glory days, and taking to the streets in old iron is enough to drive the point home.
Our project Satellite is a perfect case in point. Although currently far from achieving the status of artful garage decoration, the visual, spatial, and auditory elements are all there. With a high-winding 340 small-block working through deep gears, the sounds and action were ready to thrill, however, put this machine to use and reality sinks in. On the wide-open expanses of asphalt where such a machine should thrive, it did nothing but disappoint. Even with the "compromise" rear gear ratio of 3.55, the hydraulic and mechanical realities of nearly 10 percent torque converter slip and gear ratio had the engine trying too hard, and going nowhere fast.
A sustained 4,000 rpm on the wide-open highway is enough to get you thinking about those reciprocating engine components needlessly eating away at themselves. Cutting down the pace to a more sustainable level brings nothing but humiliation as the old Mopar chokes the flow of cheap imported tin moving down the road. And, what reward for all the misery? There was nothing to show for all the open-road drama but excessive noise, engine heat, and vibration from the overworked drivetrain. There is a definite disconnect between the promise of sweet performance, and the reality of highway inadequacy.
Gearing UpNow this shortcoming is not without its cure. The real problem lies in the fact that the OEM transmissions of the era were limited to three forward gears, with tightly spaced gear ratios cumulating at 1:1. In practical terms, what this means is that the limitations of the transmission ratios present a choice: gear it for acceleration, or gear for outright speed. Making this choice via the rear axle ring-and-pinion ratio presents the enthusiast with no correct answer. Consider the alternatives. Taking the path of a low gear ratio will provide the rocket-like acceleration expected of a performance machine, but at the expense of any real semblance of utility on the road. Gear it for high speed, and the muscle has just been removed from your muscle car. Strike a compromise gear ratio and try not to be overly disappointed when the car simply does nothing very well. When it comes to gearing using the old '60s drivetrain technology, we really have a strict A or B choice, with opposite goals and outcomes.
OEM manufacturers solved this paradox decades ago with transmissions featuring deep overdrive ratios, wider ratio spreads, and lock-up torque converters. In examining each of these characteristics, their individual advantages are clear, but more importantly these features work together to a cumulative advantage. An overdrive alone will drop the rpm at speed, but the lockup torque converter is what really makes overdrive gearing shine in an automatic transmission application. Taking a 30 percent cut off the transmission input shaft speed puts a standard hydraulic torque converter down to a speed well below its efficiency range, making for lazy operation, inefficiency, and excessive heat. The lock-up with the overdrive solves this problem. A wider gear ratio spread brings the entire package together, allowing a moderate final drive ratio (with the associated lower driveline speeds), while providing far greater gear multiplication on the initial hit to get rolling in a hurry.
Keisler's A-41 is based on...
Keisler's A-41 is based on a modified 4L60E, engineered specifically for the Mopar retrofit application. The trans can take some punishment, with units available to handle 450, 550, or 650 lb-ft of torque.
Our 904 Torqueflite was working...
Our 904 Torqueflite was working great, but the 1:1 top gear ratio and normal torque converter slip, working through our Satellite's 3.55 rear gear ratio, made the car a pig on the open road when compared to any new car. We were happy to see the archaic transmission go.
Stock Mopar torque converters...
Stock Mopar torque converters carry an integral starter ring gear, while the Keisler system uses a GM-style flexplate with the ring gear built in. All of the required hardware came packaged in the A-41 transmission retrofit kit.