Ham also chimes-in on the weight of his differential. “We removed the chrome-moly rear from my own Camaro. It weighed in at 212-pounds, loaded ready to go. Our first unit weighed in at 212-pounds. Our second-generation rear comes in at 206-pounds.”
The expense of adapting this “bigger is better” theory can be put into context by examining a season of overall expenditures to maintain a “first-gen” Pro Mod differential. A typical racer can funnel through up to $20,000 in gear sets, bearings, spools, and more if they are campaigning hard over a season-long competition series.
What is a modular rear end housing? As demonstrated by the TSP Racing components, the term modular is described as “an object composed of standardized units or sections for easy construction or flexible arrangement.” A modular differential contains multiple sections that can be exchanged or replaced to alter overall width, mounting points, or internal components.
Looking at those maintenance expenses can reasonably justify the up-front costs of upgrading to these new differentials. “Obviously, large-scale rearend failures can add up to even greater costs overall,” Carmack adds. “Especially when a failure like that can take out everything from driveshafts, transmissions, and even damage the lower-end of your engine.”
“The Top Alcohol Funny Cars probably put out 3,000- to 3500-horsepower on a weekly basis with our 11-inch ring gear and rearend,” Chrisman expresses. “We use that same ring and pinion in our Pro Modified housing. We currently have 4:29- and 4:56-ratio gears of our own design.”
Justin Carmack describes the material used to machine his new housing design as a "proprietary aerospace aluminum alloy." With no more specification than that, he describes the aluminum as offering the overall strength of chrome-moly steel combined with the weight of aluminum.
The investment by these companies to create a totally new ring and pinion unit is no small expenditure. Chrisman demonstrates, “We may make some 5:14 gears for the 1/8-mile guys down the road, but to engineer, tool, and manufacture an entirely new ring and pinion set can cost as much as $100,000 for every gear ratio you create.”
These comparatively massive ring and pinion gears that these rearends now house have another strength advantage surpassing just the increased girth: the larger size offers better contact angles along with more significant tooth contact between the two gears.