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Tube & Pipe

Fabricating tubes to do 320 mph

By Russ Olexa

Handling up to 10,000 hp, a custom steel-tube frame for a top fuel dragster or funny car literally tries to tear itself apart during each race.

As the back wheels of a top fuel dragster reach speeds of more than 320 mph in a quarter mile, they try to catch up to the front wheels, bowing the frame up to 6 in. while trying to break the car's tubes, welds, sheet metal and other metal components.

But it's these components, when properly built as an integral system, that keep the driver safe. If a horrific crash destroys the dragster, often the driver walks away from the car with minor injuries.

Building a frame to withstand this kind of punishment while still being light enough to set world speed records is imperative for the sport of drag racing.

McKinney Corp., Lafayette, Ind., is a premier builder of tubular chassis for the drag racing industry. The company builds both top fuel and funny car frames for well-known racing teams like John Force, Big Daddy Don Garlits, Darrell Gwynn, Kenny Bernstein and Joe Amato. Many frame purchasers like Connie Kalitta, Shirley Muldowney, Don Prudhomme and John Force are legends in the field of racing.

Along with building chassis, the company supplies hard-to-find fasteners, fittings cables and other essential components that are required to build a lightweight yet strong car.

Founded by Murf McKinney in 1981, the company has grown into a self-sufficient manufacturing and research and development center. The company's facility has slightly more than 23,000 sq. ft., is staffed by 31 employees and is equipped with state-of-the-art CNC machinery including waterjet, press brake and punching equipment.

Bitten by the bug
McKinney got the racing bug in the mid-1960s from his oldest brother, who raced a dragster, and from hanging around with local racers. He says, "When I graduated from high school I bought a funny car and started racing on my own. Over the years I drove for some people, had my own cars and worked for some other racers as a hobby. In 1981 I had a chance to get on the receiving end of the advertising money. It looked like my chance to stay and survive in the sport that I liked."

When they call a particular dragster a funny car, it's because when these cars were first introduced in the 1960s, they had their wheelbase altered to shift the weight forward for better traction, and they looked, well, funny. Now they are at the top end of racing along with the top fuel cars. They're almost as fast but have more of a passenger car appearance.

Building the fastest drag racing cars takes more than just weekend racing. McKinney says, "Because I was a racer and drove the cars, I had ideas about how to make them better. We used a scientific approach instead of just trial and error. We have the latest finite element analysis software to model the cars and see where all the stresses are so that we can design the parts around the loads. It's word-of-mouth advertising that got me to where I am today because we give racers the best car with the greatest value and leading-edge technology."

Building a tubular chassis
To make sure the chassis does what it's expected to do, every component from a simple bracket to a complete chassis is computer designed to save weight and to have the necessary strength to last for years of racing. Using a stress-analysis program, McKinney's designers can analyze the forces that affect performance. This approach allows the company to maximize strength and minimize weight in every part it manufactures.

Before constructing a frame, every piece of tubing that comes in measuring 1 in. in diameter or larger is tested. The four main rails on a bare 300-in. wheelbase chassis for a top fuel dragster are 4130 steel tubing, 1.25 in. in diameter, having a 0.049 in. wall thickness. The tubing on the rear of the top fuel car is heat-treated to add even greater strength.

The front half main rails for a 125-in.-wheelbase funny car are 1.25 in. with a 0.58 in. wall thickness. Hoops that enclose the driver in the safety cage are 4130 steel that is 1.625 in. in diameter with a 0.83 in. wall thickness. This tough steel along with the structural design of the chassis are the keys to keeping the driver safe and the car light.

But what stresses do these cars take? Todd Morris, senior engineer, says that they have data to support the actual torque values during a run on both the rear wheel and engine, but the data is closely guarded and expensive to obtain. He mentions, "It's a debatable question that we've hammered around for probably the last three or four years. We've gone full circle from just doing stress analysis on the chassis in-house to actually getting on-track data and strain-gauge data on the chassis through different sources and through the tire manufacturer. We try to use all this input to get all the different methods to align and correspond. There's nothing like real world numbers to use. So we've come up with numbers for an engine that exceeds 8,000 hp to 10,000 hp and 5,400 ft. lbs. of torque at the motor. Then multiply that through the rear end gear ratio for the torque at the rear axle. It is a tremendous amount of torque, but the racers also have things that dissipate the heat energy and affect torque such as clutch slippage, tire slippage and the bowing of the chassis."

After the tubing is cut, it's set up in a jig fixture to build either a funny or top fuel car. Once the frame is jigged up, the welding begins. The company uses seven Miller Dynasty welders. Although cheaper welders are available, Bob Dreher, fabricator and welder, says that they want one of the best to do their frames.

He says, "We use manual-pulse TIG welding. This puts a lot less heat into the tubing. It's been great for us. We'll jump around to different parts of the car and weld a quarter or half a tube here and go somewhere else, just trying to even out the heat from the welds so we don't get too much heat in one area. This is especially true when we get back toward the rear end mounting because that becomes critical when we line the engine up with the rear end. We really have to be careful as to how it's welded, because just a little bit of pull one way or the other and the frame becomes a headache to make sure everything lines up."

When frame tolerances are an issue, the company found that it's best to take more time up front when welding to let the heat dissipate and keep the temperature low. In the long term, this will ensure repeatability and consistency.

McKinney adds, "Fabrication of the tubes is critical. The fixture jigs for the chassis tubes are leveled off to about 10 thousandths of an inch. A car's rear end mounting has to be precise. The driveline is so closely coupled to the rear end that you don't have much error there for misalignment, and you don't have a drive shaft that's 4 ft. long with a U-joint on either end. You only have one spline joint to slip together there. We do all the welding we can, and then the last thing we do is mount the rear end. Welding is done in multiple stages. We go through the heat and cool cycle during welding, then we position the rear end and do the minimum requirement of fabrication and welding to mount it and do a final check. We actually have a fixture with dial indicators on it for this. We dial in that drive line accuracy within thousandths of an inch."

McKinney adds, "All our chassis are custom built. We are virtually making the parts this morning that we'll use this afternoon. We work on a pull system. As we need parts, we start with the raw material and manufacture it on an as-needed basis."

McKinney builds his cars to the SFI 2.3M specification, which is required by all sanctioning bodies worldwide. A complete car, from start to finish, takes about 350 hours to produce.

From hand work to CNC punching
After welding the frame, other parts such as sheet metal are added according to the customer's needs. On the outside and inside of the top fuel rail, sheet metal is used for various components. One called a puke tank acts like a pressure relief valve collecting oil that gets pressurized and forced out of the engine's valve covers during a race. It's made of thin-gauge aluminum. Race track personnel don't want any oil spilled on the track because the next car could run over it, lose traction and spin out of control. Sheet metal also surrounds the driver, encasing him in a protective area.

Dreher adds, "Just a couple of years ago, our sheet metal was all hand cut and bent manually, taking three or four days for some parts." The company owners realized that they had to do it faster and more efficiently.

McKinney remarks, "Because we work with such exotic materials such as titanium and magnesium, which are expensive and low volume, the first part has to be good and has to be done with minimal setup time. Often these parts are one-of-a-kind. We try to design and build around standard components, but this business is an evolutionary process. What we're using today may not work or be the proper thing to use six months from now. So we can't build a lot of inventory because it turns over way too quickly."

CNC equipment is expensive but necessary says McKinney. He adds, "The market that we serve is a narrow, vertical market. There aren't very many people that do what we do, so it's specialized niche marketing. The practices that we use in this niche market are the same practices that they use in aerospace, in sheet metal shops and job shops. This is a labor-intensive business. We can't afford to pay highly skilled craftsmen to sit and file and make a pile of dust all day when we can do it with machines in a fraction of the time that it takes that craftsman to hand-make a part. So we need the CNC equipment to do this."

The company ended up purchasing a Trumpf Trumatic 2020-R. Dreher says, "Now with the CNC punch, all the little holes for the rivets and other attachment areas are punched in. All the things that we used to do by hand that might take hours or days is done in minutes or hours now. Then we have to deburr the part and do some manual operations. But the punch has just saved so much time. The part accuracy is greater as well because it's done on a CNC."

Along with the Trumpf punch, McKinney also has a Bystronic PR? 100 IPC press brake and a Jet Edge 30 HP waterjet that give the company the part repeatability and accuracy it needs. McKinney adds, "A lot of our bolt-on parts are in the +/-0.003-in. range for machined components."

Some of the accessories the company builds are produced from 6061 aluminum tubing with varying diameters and wall thickness and from titanium for parts like wheelie bars. McKinney offers a catalog for all of these parts. The company makes between 24 to 30 chassis per year, which is a mixture of top fuel, fuel funny and alcohol funny cars.

What is the cost for a frame and components? A top fuel chassis is around $55,000 and a funny car chassis is about $40,000, plus the body, which is another $30,000. This is before an engine, tires and other accessories are added. An engine can cost another $50,000, and you need several because top fuel and funny car engines rarely go beyond one race without rebuilding. But like any sport that is at the top of the class, advertisers foot the bill through endorsements. It becomes a business that travels at well over 300 mph in a quarter mile. Now that's a thrill. FFJ

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