Shop Class: Inside The Crazy World of an NHRA Top Fuel Pit Crew
Fix It Fast!
Think up two means of witnessing crazy power output from a four-stroke engine. First try standing near the tarmac while a B-29 Superfortress takes off about 100 feet over your head. Boeing’s WWII heavy bomber has four twin-row, 18-cylinder radial supercharged engines strapped to its wings pushing up to 3,700 hp—each. Best advice, cover your ears and hold your breath.
Next up, hang out a few yards from the Christmas tree while a pair of NHRA Top Fuel dragsters launch off the starting line. Your feet will vibrate against the concrete, followed by a numbing sensation in your chest. These nitromethane-burning powerplants are somewhat simple supercharged Hemi V-8s, but they twist out five-figure horsepower numbers.
The over-the-top raw power delivered to the rear wheels is incredible in itself, but the work involved in keeping these monsters tuned and in one piece between 4-second, 325-mph runs is likewise impressive.
Consider the brute force of the high-pressure air/nitromethane combustion inflicting damage to these engines. A comparison might be 250,000 miles worth of wear and tear on a street-production V-8, all condensed into a single 1,000-foot pass.
A Top Fuel engine burns more than 1 gallon of fuel per second, a tad more than a fullsize commercial passenger jet. The high oxygen content of nitromethane allows for an extremely rich air/fuel ratio. Compared to gasoline engines’ stoichiometric 14.7:1 mixture for efficient performance and emissions, a Top Fuel nitro-burn is closer to a 1:1 ratio.
Fuel delivery entails injectors situated in the supercharger, intake manifold, and cylinder head, fed by a fuel pump capable of delivering 100 gallons per minute. Combustion pressures and temperatures peak above 12,000 psi and 4,000 degrees Fahrenheit, respectively. Spark-plug electrodes melt down before reaching the finish line.
After all this force, speed, and hard-part damage take place, the pit crew gets to work—quickly. Every engine, following each run down the track, must be torn down, inspected, necessary parts replaced, reassembled, and fired in 40 minutes. Yep, 40 minutes, and there’s a minimum of three rebuilds en route to the final round of an event.
Pit crews consist of seven to nine members, each responsible for very specific tasks during every race. The crew chief is just that: a drag race–experienced administrator of the entire crew, stipulating jobs for each member to be performed using well-thought-out techniques. He has the last word in real-time decision-making and typically handles final tuning prior to launch.
The co–crew chief, or second in command, is another race veteran with a more hands-on job of crew supervision, as per the crew chief. He leads all crew activities, typically manages parts and supplies inventory and acquisition, and often oversees tuning and other crucial responsibilities between runs.
At the heart of the crew are specialized technicians dealing with designated sections of the engine, drivetrain, and chassis. There are lots of jobs that require attention between both runs and events; each technician usually holds the responsibility of several.
Through the entire process, the driver’s safety is every crewmember’s responsibility. When a failure occurs in a Top Fuel engine, we’re not just talking sluggish acceleration, a little smoke, or an oil leak. We’re talking about a potential explosion, shrapnel, and fire that can kill or maim the guy behind the wheel. That’s why inspection is such a vital part of the job.
DisassemblyThe dragster is positioned in a narrow area alongside the team’s trailer and jacked up off the ground, and teardown takes place with the use of wireless electric and pneumatic tools.
Technicians remove the blower and intake manifold off the top. Simultaneously, the oil pan is drained and removed.
Men on either side of the engine remove left and right valve covers and cylinder heads. By this time, the bottom-end technician has removed the connecting rod end caps, and the piston/rod assemblies are pushed up and out of the bores.
The engine is now disassembled down to the block, crank, and camshaft, which remain in place.
The crankshaft main caps are removed to inspect the lower bearing halves and crank journals. The top halves remain. The immense power from combustion on top of the pistons attempts to blow the crankshaft out the bottom of the block. That’s why most damage is inflicted on the lower main bearing halves, while the uppers suffer comparatively light wear. Bearings are replaced as needed.
The cylinder bores undergo inspection for scoring, scuffing, or cracks, which can be corrected with swift cylinder liner replacements.
Top Fuel V-8s use lifters, pushrods, and rocker arms to open their 16 big valves just like the second-generation Chrysler 426 Hemi they were modeled after. The legendary production 426 engines produced between 1964 and 1971 were rated at 425 hp. A Top Fuel engine requires nearly 900 hp just to drive its supercharger.
Servicing a Top Fuel dragster’s clutch is as important as maintaining the engine itself. There is no traditional transmission, aside from a Reverse gearbox. The crankshaft drives the flywheel and clutch (multiple friction and steel discs), which are connected directly to the driveshaft. Efficient acceleration is accomplished through clutch-slip at takeoff leading up to full engagement nearing the end of a run. This is controlled by an air piston limiting the centrifugal force application of weighted levers against the pressure plate at programmed engine speeds.
If a crankshaft or engine block fails inspection due to any type of extensive damage, the crew has the ability to replace the short-block in time between races.
Top Fuel engines are not water-cooled. Cooling comes from oil distribution, properties of nitromethane combustion, and the short amount of run time before and during a race. Eliminating coolant passages in the block and heads provides the strength needed to withstand 10,000 hp.
To accomplish all this in such a short period of time, as much work as possible is eliminated with exchange parts. Multiple previously inspected and prepared cylinder heads, superchargers, clutches, pistons, and rods are waiting for quick swaps. The number of runs on components is documented. Each has a limited lifespan and discarded following its determined number of safe races.
ReassemblyFresh piston/rod assemblies are installed in the bores and the end caps are torqued. Both cylinder heads go back on with new cooper head gaskets, along with lifters, pushrods, and rockers. Valve lash is set. The supercharger and intake manifold are bolted on top and the drivebelt is reattached. The oil pan and valve covers are installed.
Prepared clutch pack, flywheel, and pressure plate are installed; clearances are checked; adjustments are performed; and then covered up with a titanium bellhousing.
There’s lots of miscellaneous work happening as well, such as installing fuel lines, fittings, ignition wires, checking tire pressure, parachute install, safety straps to hold down the blower and cylinder heads in case of explosion, and so on.
Engine oil is poured in and 16 new spark plugs (2 per cylinder) are installed.
Warm-up!With the driver seated, an off-board starter motor is used against the blower’s driven sprocket to crank and fire the engine. First, the engine is spun with fuel pressure and ignition off to clear any fuel from the cylinders and prevent an explosion. Ignition on, primer fuel squirted into the intake, starter engaged, and the engine fires. Fuel pressure is then switched on to keep it running.
While running, crewmembers do visual inspections for leaks and monitor engine temperatures. Ignition timing and fuel pressure are checked and adjusted. The crew chief also scans computer data at this point. The driver confirms Reverse gear and correct clutch operation while spinning the wheels and warming up everything, including the rear drive axle.
The engine is shut down, drained of its oil, and filled again with clean and cool oil for the race. A second round of new spark plugs is installed. They don’t last long.
StagingWhen called upon, the dragster is towed to the staging area, where the driver is suited up and strapped into his or her seat. Shortly after engine restart, the driver takes the vehicle through the water box and wets the tires prior to the burnout. Tires stand tall and smoke, heating the rubber to make it sticky for maximum traction. Reverse gear is engaged, and the rail is guided back behind the start line.
Final idle adjustments are performed by the crew chief, and he waves the driver on.
Fuel pressure is dialed up to full, the clutch is engaged, and the dragster creeps up to the stage beam held back by a handbrake.
Three amber lights flash on the Christmas tree, wide-open throttle—and the quick trip starts all over again.