We think it's safe to say that the best-performing hot rods have the best-matched parts. There's no doubt that picking the right combination of parts for a given application is crucial to getting optimal performance from our road-burning Chevys. This concept is especially important when it comes to choosing a clutch-and-flywheel combination. This system is the vital link between engine and transmission, and picking the right components for maximum performance requires that you account for a host of variables. In the following case study, we'll touch on the mysteries of flywheel inertia and explain why lighter proved to be better in the form of Centerforce's Light Metallic Clutch (LMC) Series. Our subject for this experiment is Patrick Wilson's '67 Chevelle. To make a long story short, the Chevelle ended up needing a new clutch after various activities during a recent cover shoot (no one from CHP drove-honest).
Our selection process began with a consultation between Steve McClenon of Hotrods to Hell (the builders of Wilson's Malibu) and Centerforce clutch guru Will Baty, who stated, "We like customers to call us." Baty wanted a full rundown before making a recommendation. Wilson's Malibu weighs about 3,000 pounds, and its 409ci small-block puts out 507 hp at 6,100 rpm and 495 lb-ft of torque at 4,600 rpm. The gearbox is a Tremec TKO II five-speed and the failed clutch was a Centerforce Dual Friction unit running a 14-inch steel flywheel. Baty asked about the Mali's intended usage, and was told "weekend toy." Most importantly, however, Baty was told about Wilson's recent change from 3.42:1 to 4.11:1 rearend cogs, looking to mellow out the Mali's extreme top-end rush.
Based on this information, Baty recommended Centerforce's patented LMC Series clutch along with a 13-inch aluminum flywheel. The LMC pressure plate features a 7075-T6 aluminum friction ring and cover (the "Light Metallic" part of the equation) mated to a high-carbon steel heat shield. The LMC also uses a dual segmented-style disc for maximum holding capability. Its puck-style clutch pads increase the clamping pressure (measured in psi) by concentrating it into a smaller area. Centerforce's flywheel is also 7075-T6 aluminum and is equipped with a riveted-on steel heat shield and a replaceable steel starter tooth ring. The new clutch/flywheel assembly was a whopping 27.1 pounds lighter than the one it replaced. So the question is, why the diet?
Inertia. Webster's says, "Inertia is a property of matter by which it remains at rest or in uniform motion unless acted upon by some external force." Baty says, "Inertia is your friend. It helps the car move when it wants to die. The action of letting the clutch out pulls the motor down, trying to kill it." This is also known as the moment of inertia. When inertia is overcome, the weight of the flywheel keeps the motor running. "There's this mass on the back of the crank," Baty explained. "As soon as it gets in motion, by revving the motor and engaging the clutch out, it's locked down." In short, this weight helps get a vehicle moving, but becomes dead weight that the engine must turn once it is moving. So why did Baty recommend the LMC?
"After the change from 3.42 gears to 4.11s, there was so much inertia it was real easy to break the back tires loose," Baty stated. (An epic understatement if we've ever heard one.) "A heavy flywheel gives the car a mechanical advantage," he continued. "We killed some of that weight, and a little bit of bottom-end torque." Why, you ask, would we want to kill bottom-end torque? In short, with 500 lb-ft of torque on tap and 4.11:1 gears, the Malibu has pulling power to spare. (Low gear ratios are a substitute for torque, according to Baty.) Even the mildest of launches was prone to ignite the hides. This car simply doesn't need the mechanical advantage provided by a 36.6-pound steel flywheel. "With the lighter unit," Baty said, "it's like starting in Second gear. It's easier for the car to take off. In fact, we almost made it too easy."
Now, we're not suggesting that a featherweight clutch/flywheel combo is for everyone. As we did here, the clutch must be matched to the vehicle. "In general," Baty told us, "the lower your gear ratio, the lighter the flywheel that can be used. But it all has to work in conjunction." In other words, a heavier car with 3.08:1 gears probably wouldn't be a candidate for the LMC setup. Even if the engine's torque output was high, such a vehicle would more than likely still need the mechanical advantage provided by a heavier flywheel. Doing otherwise would create lots of clutch slippage-and "clutches don't like to be slipped," we were firmly told.
So Baty's recommendation made Pat Wilson's street beast easier to launch. But Wilson got even more than he bargained for. At the same time we reduced flywheel inertia for easier launches, we also took a load off the engine throughout the rpm range. "The lighter flywheel doesn't create more horsepower," Baty explained, "but now the engine is happy. It doesn't have to rotate all that mass. The horsepower is there, and the engine doesn't have to work as hard. We killed a bit of low-end, but once it's up in the gears, this car's an animal. It's more responsive, free revving, and acceleration is improved." HTH's Steve McClenon agrees. "The smaller-diameter flywheel gives a slightly different feel," he commented, "but the car feels like it has 100 more horsepower. I see nothing but plusses with this setup."
The car's owner agrees too. "I think it's fantastic," Pat Wilson told us. "There's less pedal effort than I expected. It's crisper. It took me about five lights to come away smoothly. I'd say the new clutch is about 20-percent grabbier, but it's easier to drive. And that flywheel thing...the engine bounces off the rev-limiter, so I just mash the pedal and shift. I drive it every day now. It feels a lot more powerful."
We'd say we've found a match.