If you are looking for a rear-axle assembly with ultimate durability, it's tough to beat t
We looked in the Strange catalog and found all kinds of pieces, including an excellent steel pinion yoke that will accept the stronger and larger 1350-style U-joint (PN U-1605; $89.95 Summit Racing), a Strange Pro Series limited slip (PN R5083, $518.95 Summit), a pair of aluminum, high-strength differential caps (PN H-1120, $89.95 Summit), an LPW aluminum rear cover with retaining bolts (PN R5203, $149.95 Summit), a Strange 1550 steel axle package with bearings (PN P3104, $396.95), and a pair of large Ford bearing housing ends that are required with the axles (PN H1143, $69.95 Summit). I'm assuming you'll use your existing gears with this upgrade. We included the limited-slip because it will accommodate the 30-spline axles that are a necessity to improve durability. If we include $300 for labor to weld the housing ends, weld the tubes into the housing, and install the internal parts, the total comes to a little more than $1,600. If you want to add a set of gears to this upgrade, you're looking at an additional $180, which pushes the total to almost $1,800.
Just to give you something else to ponder, we checked out the Strange S-60 conversion for your car. Strange has created a new Dana 60 housing that includes the upper and lower control-arm mounting fixtures to bolt directly into any '64 to '72 GM A-body. The S-60 offers the advantage of a much larger Dana 60 9.5-inch ring gear, the same large 3.150-inch housing ends, monster 35-spline axles that are 50 percent stronger in terms of torque capacity than the 30-spline GM pieces, and fully welded tubes where they enter the centersection. The knock in the past with the Dana has been that it is heavy. Certainly the larger-diameter ring gear will add some heft, but we're talking only 20 pounds over a comparable 12-bolt. We checked the price at Summit Racing (PN PRSAO5; $1,994.95), which could be only about $100 to $300 more than what you would have to put into your existing 8.5. In terms of durability per dollar, it's tough to beat the S-60.
One consideration is whether the Dana 60–style assembly uses more power to turn. We did that test back in the June '08 issue ("The Great Rear Axle Comparo," pg. 40) when we compared the 12-bolt with the Strange S-60 and the Ford 9-inch. We saw very little rear-wheel power difference with the Dana compared with the 12-bolt, mainly because the pinion offset (the relationship of the pinion to the ring gear centerline) is essentially the same between the two rear-axle assemblies. The big power absorber was the Ford 9-inch, on which we measured between a 5hp and 7hp loss compared with the 12-bolt above 5,000 engine rpm. So that leaves weight as the only other consideration, and if the brake package is the same, the S-60 is negligibly heavier. As for the cost of all this, you could recoup perhaps $300 to $500 by selling your existing 8.5-inch 10-bolt, at which point you'd be money ahead and have a rearend you can install, and you'd never have to worry about durability.
The Standing Mile
James Moore; via CarCraft.com: I'm building a car for land speed racing with the East Coast Timing Association (ECTA). I came across a four-speed Jerico transmission for cheap. It's been gone through and is a solid transmission. It came with a set of clutches about the size of a coffee cup coaster, and while I'm sure they're great, I know they're going to wear out quickly in the stop-and-go of the pits. Since I don't really need such an exotic (or expensive!) clutch setup, can you recommend something for me? The car it's going in is a gutted '91 Mazda RX-7 with a warmed-up small-block Chevy and an IRS out of a C4 Corvette with 3.08:1 gears. Right now, I'm estimating 400 to 450 rwhp out of the small-block to sort the bugs out. I saw in a story called "Poor Man's Jerico" that you guys were running a Centerforce clutch. Would something like that work for me, too? I've got a Centerforce Dual-Friction in my Mustang right now, and I like it a lot. What would you recommend for a clutch and flywheel setup?
We've used this Light Metal Clutch assembly and aluminum flywheel in our '65 Chevelle on a
Jeff Smith: This sounds like a real rocket, James, with 450 hp in a car that probably only weighs around 2,800 pounds. Given the mild power, the C4 IRS, and the reduced overall weight, a Centerforce Dual Friction 11-inch, single-disc clutch would probably be a good addition. The larger disc offers more surface area, which when combined with a given clamp load from the pressure plate and the coefficient of friction of the clutch disc can create the overall torque capacity of the clutch assembly. The reason oval-track and road racers use the smaller 8-inch multiple clutch disc is to reduce weight, which has a tremendous effect on the amount of power it takes to accelerate the mass of the clutch and flywheel assembly. To simplify that, it takes less power to accelerate a given mass with a radius that is 4 inches from the crank centerline than it does to accelerate the same mass where the radius is farther out, such as at 5.5 inches. We mention all this because Centerforce offers a couple of different options when it comes to the clutches. In your case, where the car will be used primarily as a race car, you might want to look into what Centerforce calls its Light Metal clutch assembly. First, you have an option of an aluminum 11- (or 10.5-) inch flywheel. It's no surprise that the steel flywheel weighs significantly more at 36 pounds compared with the aluminum's 15.5 pounds for the 11-inch-diameter wheels. While reducing the weight by more than 50 percent is dramatic, the effect is even greater with a larger diameter. Centerforce tends to reduce the weight of its steel flywheels to reduce the inertia, but there is still a major advantage to the aluminum flywheel. We won't get into the math because it can get complex, but the advantage is significant. The downside to an aluminum flywheel is that by reducing the mass, at low speeds it is difficult to accelerate lightly from a dead stop. That's why you see the NASCAR and IndyCars spin their tires when they leave a pit stop during a race, as it is very easy to stall the engine with a lightweight flywheel and clutch assembly.