We’re seeing many hot rods with great looking drilled and/or slotted rotors behind big billet as well as forged wheels. There’s no question that they look trick, but what is the straight story on how they work? Are they better than plain rotors, or worse? In the real world of street driven cars, will they help my stopping power? Rather than listen to a lot of opinions, let’s look at the science behind these questions by getting info from the experts at Wilwood brakes and ECI.
Mike Skelly of Wilwood offered us a little history on the origin of drilled rotors. As road racing tires allowed greater track speeds in the 1960s, race teams began seeing a great loss in brake capability. In that era of organic and asbestos based pad friction material, a problem occurred with the adhesives used to fasten the pad to the steel backing plates. As the temperature of the pads increased, the adhesive would break down and cause a layer of gas to form between the rotor and the pads. That vapor layer retained heat in the rotor and acted as an “air-bearing” high-pressure area between the pad and rotor. By drilling holes in the rotor surface, those gasses were able to be dissipated into the vented center of the rotor, no longer interfering with the pad to rotor friction. Racers also liked the idea that the rotating mass of the rotor was reduced, causing a small advantage of less inertia during acceleration and braking.
Slotting the rotor is felt to have its greatest effect removing worn off pad debris from the rotor surface. The relatively sharp edges of the slots are also considered as an aid in resolving the pad glazing that can occur at high temperatures. Fresh pad material is then exposed for better braking action at the cost of faster pad wear due to the constant renewing of the pad surface. The conclusion is that slotting may improve braking, with little chance of loss.
Since asbestos based brake pads were outlawed in the nineties, new materials and bonding adhesives have been developed. The now common ceramic based pads do not produce the outgassing problem in any conceivable street use, so there is no real function-based reason to use drilled rotors. Slotted rotors may still be useful in their ability to remove pad glazing but consequently produce faster pad wear. That spells more brake dust on your wheels, which can be corrosive to aluminum wheels, as are many of the chemical cleaners used to remove that dust. Since most hot rods are not driven hard enough to get hot enough to glaze the pads, slotted rotors may offer little in the way of better brake function.
Heat damaged brake rotor
It’s important to recall that a major function of the rotor is to transfer heat out of the brake system. The laws of Physics tell us that energy can be moved and converted to other forms of energy, but never destroyed. That means the kinetic energy (rotating mass) of the rolling wheel and tire are resisted by the brakes, which convert that motion energy into heat energy. That heat is then dissipated into the air by the cooling of the caliper body and rotor. Think of the rotor as the radiator for the brake system. That’s why brake fluids with higher temperature tolerances were developed, and why vented rotors are common today.
Following that heat transfer logic tells us that a rotor with more mass can absorb more heat energy than a lighter rotor of the same design. That is an advantage of larger diameter rotors, along with the greater leverage of increased size. The problem with regard to our question of drilled and slotted rotors is that those practices act to reduce the mass of the rotor, reducing the desired heat transfer. Some rodders have correctly stated that the rotor surface area is increased by drilling or slotting, but the issue in heat transfer is mass, not surface area. It does seem that a greater rotor surface area may allow a faster cool down after the heavy braking has stopped, but the issue is more about heat transfer during braking due to rotor total mass.
It is the experience based opinion of every single brake expert I have consulted, that the loss of rotor mass due to drilling and slotting creates more brake loss than any possible gains due to degassing or faster cooling of the surface area. There is no better authority on hot rod brakes than Ralph Lisena at ECI. Ralph agrees that practical street driven vehicles rarely encounter the high heat conditions that make drilled or slotted rotors beneficial from a strictly functional stand point.
For the street, you want a heavier, larger diameter rotor. As a case in point, the ’73-’87 Chevy pickups offered a light duty one-inch thick front rotor, and a heavy duty option that was one and a quarter-inch thick. Since both were ttwelve-inchdiameter cast iron vented rotors, using calipers of the same piston bore and using the same pads, the conclusion we draw is that GM engineers agreed that the larger rotor mass would produce the desired better brakes for heavier loads.
So we seem to be back to the idea that the major issue in brake system heat transfer is the rotor mass. Outgassing of heated brake pads is not an issue in any conceivable street application. Therefore, drilling the rotors may cause a very small loss of braking power, rather than an increase. But, we may be over thinking a small issue. The consensus among experts is that there will be little effect either way in the real world. So, if you like the way they look, go for it. You’ll have the racy look, and the car should stop just fine. In fact, I just got thirteen-inch Wilwood rotors for my own ’57 Chevy “Smokey Yunick” Tribute AutoCross car. I’ll run it hard in the Goodguys AutoCross series, so we’ll take Wilwood’s advice to run slotted, but not drilled rotors.
Article courtesy of Goodguys Rod & Custom Association, written by Brent Vandevort.
For 1958 the tagline at Plymouth was “The Star of the Forward Look,” and for once this was no idle ad agency boast.
The tagline for this 1958 Plymouth campaign (below) was “The Star of the Forward Look,” and in this case we’re inclined to agree. As well as any single Chrysler product could, the ’58 Plymouth exemplified Virgil Exner’s Forward Look design theme, which began with the 1955 models but really took off in 1957. In that year the entire Chrysler Corporation product line sported low, sleek rooflines and the most dramatic tail fins in the industry, throwing the General Motors styling team into a panic. (See our feature on the 1957 Plymouths here.) For ’58, Plymouth received a minor facelift with quad headlamps—which the front end had clearly been designed for in the first place—and now the look was complete.
In watching the clip below, you could be forgiven for assuming that the Fury Hardtop Coupe was the only Plymouth offered that year. But actually there was a broad product lineup with the Plaza as the base model, the Savoy holding down the midrange, and the Belvedere (and Fury) at the top of the heap. Available engines included the trusty flathead six with 132 hp, a pair of 318 CID poly-head V8s, and the Golden Commando 350 CID V8, while the Powerflite (two-speed) and Torqueflite (three-speed) automatic transmissions included standard push-button controls.
Actually, in ’58 Plymouth was the star of the show at Chrysler Corporation from more than one angle. With model year production of almost 444,000 units, Plymouth continued to hold down the number three slot in the Motor City sales charts, trailing only Ford and Chevrolet. And meanwhile, Plymouth sold more cars than the rest of the Chrysler divisions combined, demonstrating the size and scale of the “low-priced three,” as the category was known in the U.S. auto industry at the time. Video follows.
Article courtesy of Mac's Motor City Garage.
Here’s the selling story for the Ford Motor Company’s middle-luxury Mercury division for 1958.
This 1958 Mercury commercial takes us back to that familiar time when the American automobile was sold by the inch and by the pound. Bigger was better, and “longer, lower, and wider” was another way to say “new and improved.” Cars kept growing all through the 1950s, and by ’58 they had nearly reached their zenith in size and weight. In this spot, a wacky stunt featuring rodeo star Wag Blessing is used to demonstrate (purportedly) that the Mercury has “the solid, comfort ride of a big, heavy car.”
Indeed. Through a good part of the decade, the Mercury brand was marketed under the tagline “The Big M,” and the 1958 models were true to form. The senior Park Lane, introduced at midyear to compete with the Buick Roadmaster, rolled on a 125-inch wheelbase, sporting an overall length of 220.2 inches. (Wheelbase for the rest of the line was 122 inches.) Two new V8s built on Ford’s MEL architecture were offered in 383 and 430 cubic-inch displacements, and there was a Super Marauder version of the 430 boasting three two-barrel carbs and 400 horsepower—one of the most powerful engines of the ’50s. Along with much of the industry, Mercury had joined the push-button transmission craze—read about Merc-O-Matic Keyboard Control here.
Despite the ambitious product lineup, 1958 was not a banner year for Mercury, nor for the Motor City’s middle-luxury class in general. Sales tanked as the nation suffered through its first real post-World War II recession (at the time, labeled the “Eisenhower recession”). Production for the Mercury brand slipped more than 50 percent, prompting a complete rethink of the division’s product strategy and Turnpike Cruiser styling theme. But for the moment, let’s enjoy the rough-riding demonstration by Wag Blessing. Video below.
Article courtesy of Mac's Motor City Garage.
In 1965, there was still one passenger car in the United States that offered a standard L-head engine: the Rambler American.
The basic L-head engine design—with its valves in the block, not in the head—enjoyed a long and productive life in the Motor City. From the age of the Model T (1909-27) all through the depression years, the L-head (also known as a side-valve abroad and as a flathead in American slang) was by far the industry’s favored layout. There were always other valvetrain configurations, of course, but the popular L-head was simple, rugged, and with its minimal component count, inexpensive to manufacture.
That changed after World War II, when the availability of high-octane gasoline drove the shift to high-compression, overhead-valve engines, led by the Cadillac and Oldsmobile V8s of 1949. (Read about the ’49 Rocket V8 here.) Soon the entire industry went overhead. From there, a few manufacturers pressed on with flathead engines for their low-priced models (Chrysler through 1959, for example) but by 1965, excluding commercial and industrial engines, there was only one civilian passenger car left in the U.S. auto industry with L-head power: the modest Rambler American.
The ’65 Rambler American’s flathead six, which displaced 195.6 cubic inches and was rated at 90 hp that year, was closely based on the Nash 600 engine introduced way back in 1941. While the artwork above is a bit cartoonish, it nicely illustrates the Nash 600’s key features. There was no intake manifold as such; rather, the intake ports were integrated into the cylinder block and head and the carburetor bolted on top. Meanwhile, the exhaust manifold was simply a stamped steel tube, more or less, that clamped to the side of the block. Though the exhaust tube was prone to corrosion and blowout it was easy enough to replace, and overall, the Nash six was a marvel of simplicity and ruggedness. When Nash was merged with Hudson to become American Motors on May 1, 1954, the little L-head six carried on. From its original displacement of 172.6 cubic inches, it was enlarged to 184 CID in 1953 and 195.6 CID in 1955.
Through all these years, Nash and AMC also offered overhead-valve sixes and V8s, but the L-head six served as the company’s low-price leader, allowing AMC to offer the compact Rambler American at an extremely low price—at times the automaker advertised the lowest-priced car in America. To shave costs even closer to the bone, the L-head ultimately sported a tiny industrial air filter instead of a proper silencer (below). But nothing is forever, and when American Motors introduced a new and advanced 232 CID straight six in 1964, the little flathead’s days were numbered. For 1965, the side-valve six was available only in the Rambler American 220 and 330 series, the company’s most basic and stripped-down models. And then it was gone.
Article courtesy of Mac's Motor City Garage.