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8,000HP Top Fuel Engine

Among All Engines Of Drag Racing, The King Of The Hill Is The Supercharged And Nitromethane-Fueled Monster. So We Thought We'd Take An Inside Look At An . . .

By , Photography by Jon Asher

They are considered the kings of the sport-the supercharged and nitromethane-sniffing internal combustion beasts that literally stomp the ground and push a 2,300-pound land rocket on 1,000-foot runs eclipsed in 3.77 seconds at speeds approaching 325 mph. The violence that emits from the headers of these 500ci monsters is quite literally deafening. If you've never experienced the raw power of a pair of Top Fuel cars blistering the dragstrip, the initial sound pressure shock wave blasts you in the chest and assaults your eardrums. Standing within 30 feet of a Top Fuel car at WOT feels more like an explosion or some kind of uncontrolled crash of noise, pressure, and caustic, yellow-orange gas that instantly burns your nostrils. Top Fuel engines are power personified-a barely contained internal combustion evolution of mythical proportions that snarls and breathes fire and often wreaks havoc on those who presume to exercise control.

So let's take a look at what is responsible for all this violence. What you'll discover is that while a Top Fuel engine appears quite tame on paper, it's the synergy of fuel, spark, and boost that makes it violent.

Inside the Beast
There was a time when all you needed to race Top Fuel was a front-engine dragster chassis, a junkyard 392 Hemi, a Jimmy blower, and enough money to buy some nitro. There were very few limitations except on your nerve and creativity. Today, the kings of the sport are limited on almost every level with the intent to tame this very powerful beast. One of the first limitations was on displacement, now topped out at 500 ci. This creates the odd situation where many big-inch street engines would be illegal for use in Top Fuel. Ironically, our Kaase Boss engine in this same issue would not pass tech due to its 521 inches. In spite of the limitations, there's still plenty of room for tuning. Dale Armstrong has long since retired from active Top Fuel racing as crew chief of the famous Kenny Bernstein-owned Budweiser King Top Fuel car, but in the '80s there was still room for major innovation, and many of Armstrong's creations-such as the first use of onboard data logging-is still a Top Fuel standard.

Top Fuel is also a place where myths abound, especially in regard to ignition systems. Just 30 years ago, Armstrong says fuel engines ran on far less fuel, making them leaner, which turned spark plugs into glow plugs, which continued combustion even after the ignition system failed completely. But with today's fire hose-like delivery of fuel, Armstrong says, "You couldn't do any of this without a strong ignition system." Armstrong was in fact the man who pioneered the use of twin magnetos and two spark plugs per cylinder back in the '80s and who went so far as to add a third spark plug and mag that the NHRA immediately banned. The tremendous amount of fuel present in the cylinders demands an immense amount of current flow to spark the combustion process. The popular MSD Super 44 magnetos are so powerful that they deliver 1.2 amps of electrical energy across the spark plug gap each time a plug fires. This is four times the electrical energy delivered by a hot street ignition system at 300 milliamps (0.3 amp). Think of those MSD magnetos as the equivalent of an engine-driven arc welder and you get the idea.

How much liquid is injected into the cylinder at max revs? According to Bill Miller, owner of Bill Miller Engineering (BME) in Carson City, Nevada, his Top Fuel engines inhale as much as 80 gallons of fuel per minute at peak torque, which is equivalent to 1.3 gallons of fuel per second! "You can't pour it out of a gallon gas can that fast," Miller comments. After peak torque-between 6,000 and 6,300 rpm on a Top Fuel engine-fuel flow is reduced because the engine's volumetric efficiency suffers due to a lack of time. "At the higher engine speeds, all that liquid fuel acts like a choke that blocks the airflow," Armstrong says.

Typical Top Fuel Engine
Displacement: 496ci
Block and head: Aluminum Brad Anderson or Alan Johnson
Bore x stroke: 4.310 x 4.250
Compression ratio: 7.0:1
Cylinder head: Hemispherical
Intake valve: Titanium 2.45 inches
Exhaust valve: Inconel 1.92 inches
Rocker ratio: I = 1.73:1, E = 1.53:1
Camshaft: Mechanical roller
Duration: 290 to 300 degrees at 0.050
Roller lifter: 1.6875 inches in diameter
Valve lift: 0.800
Supercharger: Roots style, 14:71
Boost pressure: 65 psi maximum
Ignition: Twin 44-amp magnetos capable of 50,000 volts
Ignition timing: 52 to 55 degrees BTDC
Fuel pump: Mechanical, 100-plus gal/min
Injection: Mechanical, total of 42 injectors
Fuel: 90 percent nitromethane, 10 percent methanol
Oiling system: Wet-sump
Oil capacity: 12 quarts, 70W oil
Maximum rpm: 8,250 rpm
Maximum hp: 8,000 equal to 16 hp per ci

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