What It Takes to Run Top Fuel.


For all of you people that dig drag racing and wondered what Top Fuel is like here’s a little ditty I put together so you can see what a Top Fuel engine is like, how it’s built, and how expensive top fuel cars are to campaign. To do it on your own is next to impossible unless your last name is Trump.

  The cylinder block; Top fuel is so hard on parts that the block has to be robust in the exponential form to withstand the internal forces.  It has been estimated that these engines produce between 7000 and 8000 horsepower. No one really knows because a top fuel engine would shake a dyno to pieces in short order. There’s just no dyno’s that will handle one of these monsters. Besides that these motors are way too expensive to sacrifice one on a dynamometer. Back to the blocks, they are forged units. John Rodeck has pioneered top fuel hemi blocks for years.  Rodeck says that the block is first forged with a massive 8000-ton hydraulic press using a single die done is three strokes to produce the basic structure. After that, machining takes the block from 250 pounds down to around 100 pounds.

   After initial machining the block is heat treated using a specially made Rodeck-designed oven that bakes multiple blocks in one shot.  Then the blocks are bolted down in a specific way and final shaping and head bolt holes are machined to tolerances of plus or minus .0005” inch. That’s really tight! The block is them moved over to another CNC machine and it’s finished up. It takes approximately 12 hours to finish a block. Each block is custom made to the customer.

 Crankshafts: Bryant Racing Crankshafts produce fuel profile crankshafts on a billet assembly based on bearing spacing off of Chrysler’s 426 Hemi engines. The cranks are machined from 4330BM Timken steel. It takes Bryant 60 hours to produce a fuel crankshaft which includes post-manufacturing treatment process. These cranks along with having stress-relieving, and nitriding processes done are also cryogenically treated (frozen).  Each crank goes for around $3800.00 each. This also depends upon what the crew chief specifies on the crank being made.  A typical crankshaft usually will run anywhere from 12 to 15 passes. High dollar teams replace them after 12 runs.  This is assuming the crew chief gets the tune ups right. If he doesn’t he can kill a crank in one pass. Yeah these motors can be that hard on parts.

  Pistons: Pistons in top fuel motors are the sacrificial lambs of the engine parts. Nitromethane is just so violent it takes it toll on the pistons. Bill Miller Engineering makes some of the best fuel pistons on the planet. The pistons are made from an aluminum alloy 2618-T61. The front four pistons are down .030” compared to the back four, which makes average overall compression run about 6.8:1. The pistons are subjected to a low temperature hard anodizing process. Pistons made this way last about twice as long as they have in the past. How long is that? Well a piston can last from one run to 5 depending on the tune up. Teams usually buy pistons 40 at a time, price on that quantity is $62.50 per piston, or $2500 for a 40 piston lot. Nothing cheap about these engines. BME also manufactures wrist pins. Top fuel and funny car nitro engines produce forces on the wrist pins of as much as 50 tons. There are very few materials what will withstand this sort of force. BME uses VascoMax C-300 an exotic thusly expensive nickel-cobalt-titanium steel  “superalloy” with very high tensile strength, (294,000 psi) and an extreme fatigue endurance limit (one billion cycles at 125,000 psi).

    I’m not gonna go into the entire engine assembly, I wanted to get into some of the more astonishing data about these engines. Just know that the rest of the pieces in one of these motors is designed and built like the above pieces, with corresponding prices per unit piece as well.  Cylinder heads for example are usually Alan Johnson pieces which are a true work of art. They are CNC machined and ported so the heads are repeatable for each customer. Most feature a 2.45” intake valve and a 1.90” exhaust. These are the AJPE Stage VI Hemi Heads. Set up for a 4.187 bore diameter. A set of bare heads goes for $6850.00.  A fully assembled and finished set of heads goes out the door for $9000.00.

Camshafts: Ok here’s where the fun starts. Crane Cams makes top fuel cams on a 2.125 diameter base. The intake duration at .050” lifter rise is 298 degrees, and the exhaust is 296 degrees. Lobe centers are 112-114 degrees. Lobe lift is usually between .478 and .500” lift at the valve depends on what rocker arm ratio is being used. On the intake side they can run from 1.57 to 1.75:1. The exhaust side runs between 1.52-1.65:1. So doing some simple math let’s take the .500 lift cam lobe and multiply it by 1.75 on the intake side and 1.65 on the exhaust. Multiplying .500 X 1.75 yields .875” lift on the intake valve and  1.65 X .500 gives us .825.” That’s got the valves darn near an inch off their seats!  Push rods are huge. Big block Chevrolets back in the early days of 427 big blocks uses some 7/16 diameter pushrods on the L88 motors. Top fuel pushrods are 9/16” in diameter! Opening pressure on the exhaust side of a running top fuel motor is tremendous. In fact some teams are using solid steel pushrods on the exhaust sides.

 

If you think your SUV gets poor mileage then read on! 

  Fuel Delivery:  Because nitromethane only contains roughly ¼ the energy content of gasoline you have to wash a lot more of it thru the motor. Nitromethane brings its own oxygen into the engine with it unlike gasoline which has none. Gasoline’s stoichiometric air fuel ratio is 14.7:1. Or 14.7 parts of air to 1 part of fuel. Nitromethane’s Stoichiometry is 1.7:1. This means we can run it just about direct one to one air to fuel ratio. This takes a tremendous fuel system.

The fuel pumps are made by Sid Waterman. They are driven off the front end of the camshaft. The one of choice is called a “Mega Bertha”. These are billet assemblies set up in four sections. These fuel pumps can deliver more than 112 gallons of fuel per minute at 600 psi!  Most teams run them at 92 gallons per minute, and during a pass this equates to 1.3 gallons of fuel per second!  Top fuel dragsters carry 18 gallons of nitromethane on board, and more than 8 gallons of it are used up during the burn out and the staging process. Most of the balance is used up during the pass!  So these cars are burning almost 18 gallons of fuel in less than a quarter of a mile! Top fuel and floppers are limited to 1000’ under throttle.

And you thought your SUV got shitty mileage? To get this amount of fuel flow into an engine takes lots of injector nozzles. Usually 32 or more nozzles are used. 8 injectors are in the hat, another 8 located in the intake manifold and 16 more located in the intake ports. An onboard computer is used to sequentially turn on these “down nozzles.” It is linked to the clutch and other data sending areas. And you thought dragsters were simple?

In order to light off this sort of mixture takes one hell of a sparker. MSD’s 44 Pro Mag is the only one being used today. Not that it’s a bad one on the contrary it’s a great unit. Personally I don’t think the old Vertex and Schiefer Magnetos of yesterday would light off the fuel cars of today, just isn’t enough  spark energy in these older units. The MSD Pro Mag 44’s produce around 44 amps of current along with extremely high secondary voltage. Fuel motors have sixteen sparkplugs not 8 like a normal V8. So they run two front driven magnetos. If you have wondered why there are two red headed Pro Mag 44s in all the fuel and floppers that’s why.

Top Fuel and Top Fuel Funny cars are the hardest accelerating cars on the planet. They are every bit as sophisticated in their own right as a formula 1 car or any other race car for that matter. There’s nothing that sounds like a 500 inch hemi motor on 90%. Nothing has the throttle response, the sound, the idle it’s the ultimate form of the reciprocating spark lit, piston engine. No other engine on the planet makes anything even close to the power of what a fuel motor is capable of. It’s often trick to equate how many horsepower per cubic inch a motor can make. Chevrolet was the first American V8 to make a horsepower per cubic inch when the 283 cubic inch 283 horsepower fuel injected small block came out. Top fuel nitro motors make 16 horsepower per cubic inch! Sixteen times as much as the little 283 did back in 1957!

Just a little information for you.

Dave

References are:

Drag Race Technology: Top Fuel: So Much Power, So Little Time by Wayne Scraba.

Equipment Manufacturing:

Bill Miller Engineering

Bryant Racing Crankshafts

John Rodeck

Crane Camshafts

Sid Waterman

Alan Johnson

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