How Does a Funny Car Work
Csaba Csere Car and Driver
The Funny Car's key component is an 8.1-liter (496 cubic inch!) V-8 developing about 11,000 horsepower and some 8000 lb-ft of torque. Oh, and it is capable of revving to 8500 rpm. The engine is a development of the legendary 426 Hemi V-8, using a block and heads machined from solid aluminum billets. This is possible because the engine has no water passages. Its usual running time is so short, it gets by without a liquid cooling system. The compression ratio is about 6.5 to 1.
The Mother of All Superchargers
When drag racers first started fitting superchargers to their engines, they repurposed Roots-type blowers originally developed by General Motors for a line of pre-World-War-II-era two-stroke diesel heavy-equipment engines. Those 6-71 blowers, so named because they force-fed six 71-cubic-inch cylinders, have evolved into the purpose-built 14-71 blowers used today (GM, by the way, never built a 14-cylinder engine). The blower uses 19-inch-long rotors nearly six inches in diameter to pump some 548 cubic inches (nearly nine liters!) of air per revolution. That's nearly four times the throughput of a Hellcat supercharger. Running at about 40 percent higher rpm than the engine crankshaft, the supercharger develops about 55 psi of boost pressure. At full power, the supercharger requires the better part of 1000 horsepower to do its work. Obviously, it gives back more horsepower in return.
The Funny Car burns a mixture of 90 percent nitromethane and 10 percent alcohol—and it gulps down some 20 gallons of that mix in a single run. Nitromethane has a number of key properties that make it the ideal drag-racing fuel. First, it contains some of its own oxygen, so that instead of the 14.7 pounds of air needed to burn one pound of gasoline, only 1.7 pounds of air is needed per pound of nitromethane. Even though nitro contains much less energy per pound than gasoline, its ability to burn richer means that it generates 2.3 times as much power. Its other key property is a high heat of vaporization, which means that it has a tremendous cooling effect as it turns from liquid to vapor. That's how the Funny Car engine gets by with no liquid cooling system and no intercoolers.
Lots and Lots of Fuel Injectors
Funny Cars use a continuous-flow fuel-injection system with a mess of injectors. The Dodge car has 32 of them: two in each intake port of the cylinder head, one in each intake manifold runner (shown), and eight of them upstream on the supercharger (which serve to cool and lubricate the blower). These injectors are fed by a 300-gallon-per-hour fuel pump with dual-stage operation. Only the manifold and blower injectors operate during idle, while all 32 flow during full-power runs.
An Ignition System That Could Almost Power a Welder
The engine uses two spark plugs per cylinder, and they are energized by dual magnetos. Those operate with some 40 amps of primary current to produce the very powerful spark needed to fire the super-rich and dense air-fuel mixture. Ignition timing is controlled by a crank trigger system that retards the spark during the launch to reduce engine power and not overwhelm the tires. As the vehicle's speed increases, the spark reverts to the maximum power advance of around 60 degrees.
No Transmission, but a Hell of a Clutch
The Funny Car has no transmission other than a simple device to allow the car to back up after a prelaunch burnout. However, the Funny Car does use a complex multiplate centrifugal clutch to achieve the gradual engagement needed to go from zero to over 330 mph without any ratio changes. There are some six driven plates, made from sintered iron, sandwiched between the flywheel; plus five steel floaters and a centrifugal pressure plate, making an assembly about 10 inches in diameter and 10 inches long. The driver's clutch pedal initiates the clutch engagement, but it's basically an on/off switch. The actual degree of engagement—and slippage—is regulated by the fingers in the centrifugal pressure plate, and force is provided by a pneumatic cylinder that is controlled through nine stages of pressure by a timer. Controlling the clutch slippage by varying the weight and travel of the arms on the centrifugal clutch, and the timing of the pneumatic cylinder is probably the most important tuning adjustment on the car.
It Has a Simple but Strong Chassis
This engine and all of the other components are attached to a spaceframe chassis fabricated from stout chrome-moly steel tubing. The differential and front and rear axles are bolted solidly to this frame, which is designed to be somewhat flexible; its deflection serves as a rudimentary suspension. The strength of the integral roll cage and the flexibility of the extremities are controlled by varying both the diameter and thickness of the tubing. The wheelbase measures about 125 inches—just under five inches longer than the production Charger SRT Hellcat sedan's dimension.
It's Got One Doozy of a Wing
The Charger Hellcat Funny Car's fully enveloping carbon-fiber body is designed to generate maximum downforce with minimum drag. Basically, it consists of a strong wedge that terminates in a large, boxed-in rear wing. The body tapers, so it's narrower in the rear than in the front.
As in All Racing, Aero Matters
By the time the Dodge hits the speed traps at the drag strip, Matt Hagen says, the car develops about 8000 pounds of downforce. It isn't clear if that figure includes the roughly 1000 pounds of downforce produced by the upward-firing exhaust headers (yep, the exhaust's flow is so voluminous and hot, it contributes to downforce), but downforce figures in the thousands of pounds are impressive either way.
Yes, there is some irony in the Funny Car's needle-shaped body and Dodge's "widebody" graphics mimicking the production Charger SRT Hellcat Widebody's wide-track design. Try not to think too hard about it.
Minimal Controls and Instruments
Inside the central cockpit, you'll find no instruments, as there isn't much for the driver to do but launch and steer (we'd add "hang on," but then that's obvious). There is a very short-travel throttle pedal along with a clutch pedal. To the driver's right is a hand brake, which operates single-piston brake calipers on all four wheels. To the left is a fuel-control lever that shifts from the idle to full-power fuel operation.
So, What's It Like to Launch This Puppy?
After the obligatory pre-race burnout to warm the tires (which lead a short, hard life), driver Hagen engages the clutch, which will be slipping liberally at these speeds, and uses the hand brake to inch the car forward into the staging lights. By now, he has switched the fuel system to "high" and is holding the car stationary with the hand brake. He launches the car just before all the lights come on by releasing the hand brake and flooring the throttle, which produces some 4.0 g's of acceleration. Now, Hagen is simply steering and holding on. If he has to release full throttle or touch the clutch, there is a problem, and the run is toast. Hagen says peak acceleration of 6.5 g's occurs at about two seconds into the run, when the clutch fully engages and the car is at about 200 mph. When he pops the twin drag chutes at the end of the strip, he briefly gets socked with 7.5 g's worth of deceleration.
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Source: https://www.caranddriver.com/news/g28472074/dodge-charger-srt-hellcat-widebody-funny-car-in-depth/
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