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Sun, 3 Dec 2000, 09:08 AM

The Science of Body Mounting
Photos & Text by Bill Walters

Why Does it Take 80 hours to Prepare Today's Nitro Flopper Bodies?

As automotive technology slides into the next millennium, drag racing continues to be the perfect motorsports test bed for mechanized deep thinkers who want to see their ideas put to the ultimate test. Every part on today's nitro burning Dragsters and Funny Cars has been developed through years of research for maximum efficiency and durability under the most extreme conditions imaginable. This season there has been a renewed emphasis placed on the importance of aerodynamics in the Funny Car class. More specifically, designers, engineers and crew chiefs are looking for a body that provides the most down force with the least amount of drag.

Dunn' Pontiac Firebird
Both the 2000 Pontiac Firebird and the 2000 Chevrolet Camaro body style have become popular this season for their advanced aerodynamics. After one glimpse of Jim Dunn's awesome looking Mooneyes Pontiac Firebird at the season opening NHRA Winternationals and it was easy to see the dramatic changes that the new Firebird shell had undergone. A wider front end, a narrower roofline, and a rear spoiler area that resembled a pick up truck were easily evident. And the ground clearance when the car launched it's seven thousand horses was equally impressive as the car appeared to almost scrape the track as it lifted the front end.

As more Funny Car bodies became available this year, many teams began the switch to the new styles. John Force unveiled his 2000 Mustang body at the race in Columbus without even testing the new shell, as he intensifies his heated season long battle with Jerry Toliver. On the other hand, Toliver's WWF team actually uses both the Firebird and the Camaro bodies. Crew chief Dale Armstrong literally uses the eighty-pound shells as a tuning aid, swapping bodies depending on the down force required by each track they race on.

When I overheard that Team Nitro Fish was sending their new 2000 Camaro body to Indianapolis to be "mounted", I became curious. When the team told me it would take "80" man-hours to complete the project, my jaw dropped. How could something as simple as preparing a body to ride on the chassis take so long? I decided to find out just what was involved in the science of mounting a Funny Car body.

How it Works

Mounting a body involves putting the body on the chassis in the correct location to comply with the rules regarding such things as front overhang and ground clearance. A major consideration is getting as much spoiler on the car as possible, and that spoiler height is relative to roof height. You want to mount the body as low as you can and still be within the rules. The NHRA requires three inches of ground clearance under the front of the car and two inches under the sills down the side of the car. The body is allowed forty inches front overhang, measuring from the center of the front wheels to the front of the body.

The new generation bodies have taller roofs, which clear the roll cages better. With the old bodies you virtually had to set the roll cage against the roof. The new bodies have more of a crown in the roof, which allows you to add more spoiler height and lets the roll cage clear the roof area. That enables fabricators to concentrate on maintaining the ground clearance requirement and the front overhang dimension while mounting the body.

The side dimension on the new bodies also became critical as the sills became lower to the ground. While designers tried to keep the new body as low to the ground as possible as the car goes down the track, the new shells were scraping the ground at the rear of the sills when the car would squat during a launch. The new Firebird has the sill cut away and running uphill, especially on the right side of the body, which squats lowest when the car leaves the line.

Sarver's Pontiac
I talked with Keith Burgan, a noted drag racing builder and fabricator who came over from Australia over a decade ago and now runs a successful business in Indianapolis. Burgan mounted the Chevy Camaro body for Team Nitro Fish and has also worked with the John Force team on the new 2000 Mustang body.

"To do the complete package, by the time you mount the body, do all the interior sheet metal, the spoilers, the windows, the latches, and all the peripherals eighty hours is pretty close to the mark," said Burgan. Some of the things that affect the amount of time involved with mounting the body include things like the exact configuration of the spill plates on the spoiler package. Little things like having a spoiler that is removable so the car fits in the trailer must be considered during the mounting process."

The new spoiler packages are catching so much air on the rear deck that there has become a noticeable increase in the amount of struts and cables used to support the tremendous load.

Burgan continued, "the NHRA has a minimum requirement for the rear spoiler. They require a strut from the center of the lateral component forward to the deck lid, with a doubler underneath the deck lid. Then they require a cable connecting the spill plates together. What's been happening now with the newly designed bodies is that the loading is so high that the side spill plates are actually flexing from all the air building up on the back of the deck. Many teams are adding extra aircraft strength cable wires to help spread the load on the rear deck. Now a lot of the teams are actually using 5/16" tubing for support."

A look at the cable and struts.

Past to Present

The early body mounts back in the seventies and eighties were much simpler that today's aerodynamic wonders. There wasn't near the download on the bodies back then as there is now and that has required a drastic increase in tube structure underneath the body. Back in the seventies there was a single tube across the back of the car extending from one quarter panel to the other, and that was bolted or fiber glassed into each side and that was it. The tremendous down force created on today's Funny Cars as they travel at over 300 mph when they near the speed trap, reaches five thousand pounds, and that has forced the designers to add extra tubing across the body on the bottom surface to support the increased load.

The rear deck area is probably the most critical area to consider when mounting a body due to the excessive loading. The rear deck design must be well engineered and laid out, and the welding quality has to be good because that's where the majority of the load is. Even the hood area on the front of the new generation cars can be exposed to extreme stress. Many of the new body styles have up to four lateral struts under the front of the body.

A look at the underside of a body.
So the time to mount the body has increased as the down force created has increased, requiring more structural support. The supports are usually small diameter tubes that are bonded into the surface of the body with carbon fiber, so you can use thin wall tubing.

"Today you have a tube that connects the quarter panels down low behind the rear wheels that kicks up to where the chassis and body interface," Burgan continued. "Then you have tubes going up to support the spill plates and the entire rear deck area. The body structure is relatively thin, actually a multi-layer sandwich with an inner and outer shell with foam in between. Five thousands pounds down force on one area of a shell that only weighs eighty ponds creates some incredible stresses."

Different fabrication shops use different mounting methods for the tubing. Some mount them with bolt on cads while others glass tubes into the body or glass pads on to the body from the inside. Some bodies have bolt through pads, evident by the diamond shaped patches all over the body. These pads bolt to the support tubing underneath and are a popular choice by the Victory Chassis company. On the other hand, noted builder Murf McKinney uses a different style bracket which actually clips in place to the body, and once they've finished with the mounting process they bond the pad into the body from the inside. While the bonded bracket pad looks better esthetically, the bolt on bracket pad is easier to fix if it is damaged due to excessive tire shake or a pressure overload on the pad.

The Mounting Process

I'll try to give you a rather simple idea of what is involved in the process of mounting a chassis. Various shops have different ways to do it, for example some builders like Murf McKinney keep a mock up chassis in their shop to mount bodies on.

Builder Burgan explains, "because I do mounting work on many so different brands and chassis, I normally make a fixture for the different cars if I don't have one."

Burgan begins the mounting process by setting the car on the ground and setting the tire pressures. "You need to have as many of the engine components as possible in the car, because the chassis does flex." Burgan explains. " You want to have the chassis basically loaded, but obviously you can't have everything in there."

Burgan then makes a fixture that bolts to where the weight mounts are located on the front of the chassis, and that holds the body three inches of the ground, which is the minimum height. "I shim the car with a two by three structure that will bolt onto the weight bar and actually comes back onto the frame and is supported there. On that I mark the forty inch minimum overhang dimension, as well as the center line.

Next Burgan uses more tubing as spacers to support the sills. He sets the body over the car and sets it at the front for required overhang, and also at the top, then centers it all and clamps it in place.

"The rear bumper is checked next for a minimum height requirement," Burgan continued, " and work is begun in that area of the body to begin the basic rear structure, and partly because it is easily accessible. When that is done you can pick the whole body chassis up and put it up on stands, off the ground, and once you've done that you can crawl underneath it and do the front structure."

When the car is up in the air, it has little saddles that fit over the frame rail that are connected to what is called the tubular tree. Once you have it supported everywhere, you make it so the body hinges in the back and then you go to the front and do the latch mechanism, which attaches to the cross member that supports the underneath of the body.

After you've got the tube structure done you begin work on the sheet metal, which is an angle or t-section frame that sits around the top chassis rail, and is notched to clear the roll cage. It comes down to the bell housing area and it has a bridge across it to connect the two sides, and that's what all the sheet metal attaches to on the chassis side of things. You make the sheet metal and attach it to that and then you have to bond flanges into the body for the firewall, the side sheet metal and the rear bulkhead. You grind the inside of the body so there is enough of an area to attach the composite material, so that it bonds correctly. You need to use an epoxy that is strong enough that it won't tear out, but not so brittle that it is easily damaged during severe tire shake. If the epoxy is too brittle it will fracture and then somehow the bulkheads fall out of the body.

Usually Burgan's next procedure is to put the car back on the ground and re-check the tire pressure and do the rear spill plate and spoiler. The trick is to make the spill plates a little too tall in the beginning. The highest point of the roof is the reference point for the height of the rear spoiler and the spill plate. The rear spoiler can be four inches above the roof and the spill plates can be five inches higher. On a level surface you can measure from the roof to the floor, and then measure up from the floor to get he correct spoiler height.

When asked what was possibly the hardest part of mounting today's Funny Car chassis, most agreed that crawling around the front of the chassis to do the tube structure ranked as the most difficult procedure. "You're trying to weld small diameter thin wall tubing in place and trying to get good quality welds that will survive while working in a tight confined area," said Burgen. "It's especially bad if your doing a body mount on a car that's in a rush and is still partially assembled." Other things to consider are making sure the body clears the fuel tank, which was a problem with the Camaros. Also you must be careful if you have a tall driver with a tall roof cage, although most of the new body styles have cured that problem.

By the time you purchase a new body at around $8.000, and then pay for a mounting process in the $10.000 to $12,000 range, and to top it off, add paint and decaling, your looking to spend close to $30,000! So think about that the next time you see your favorite fuel flopper melt to the ground, as hours of work, money and technology go up in smoke.

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