It's The Finishing Touches That Make The DifferenceLast month in the first chapter of "Installing a Prefab Body" we covered everything from stripping an old body off a car, to reconfiguring the rollcage, to trimming the hood. When we left it, Mark Davis and his students at the Carolina Motorsports Tech Center in Conover, North Carolina, had the Chevrolet Late Model Stock body from Aluminum Racing Products (ARP) in place and ready for paint-which is where we will pick up for Part Two. The heavy lifting is done; now it's time for the detail work. This story will cover the final touches: installing the windshield, windows, grille, radiator and radiator box, crush panels, and the rest of the body supports.
First on the list, though, was a new coat of paint. If you have time, this is actually a good point to stop the progress on the body and put on a new coat of shine. The windshield (although it was cut to shape in Part One) and windows were not in place, so there was no chance of overspray getting on them. Likewise, the window straps, grille, and other assorted pieces were not yet on the car, so they did not have to be removed or taped over. Mark Kerttula of PitPaint.com drew up a really racy scheme and handled the spraying duties. Many racers remove the body panels from the car before painting, but because Kerttula's design features several curving lines that run from the front bumper to the back, he felt it was easier to paint the body with it mounted in place on the car. This is the situation where not having a lot of pieces that require removal or taping off is a big plus.
After the Sherwin Williams paint was laid down, the car was loaded back up (very carefully, this time) and towed back to the Carolina Motorsports Tech Center. Davis says there is no specific order when it comes to the rest of the work required to get the car into racing shape. So, we began by installing the body brackets and fitting up the crush panels to seal the driver's cockpit from the underside of the car.
Brackets and Crush Panels There are many versions of brackets out there used to hold sheetmetal and fiberglass body panels in place, and they are all effective. In our case, we used lengths of 31/48-inch, 0.035-wall steel tubing. The chassis was built with attachment tabs welded in strategic locations, so we used them exclusively. Flatten the ends to create tabs and bend them to the angles you need. Davis prefers to put in no more brackets than necessary to hold the body in place. "If you have too many, especially on the corners, it can make the body too stiff," he explains. "When the action gets tight, there's going to be some bumping going on. Whether you are bumping somebody with your front bumper or getting hit from behind, you want a little give. If the corners of the car are too stiff, it can be too easy to get spun." From there it was on to what is universally accepted as the most hated part of race car building: crush panels.
"Building crush panels really isn't all that hard, but for some reason most people hate doing it. It just takes patience," Davis says. "When you start, you have to visualize what you want the finished product to look like, and try to think about how you want the panel to attach to the rest of the car. Don't cut a panel just to fill a hole and not have any overlap where you can pop rivet it into place. The final panel doesn't have to produce an air-tight fit, you can seal it off with a bead of silicone, but I try to make sure I have no gaps any larger than 0.010 of an inch."
When cutting crush panels, make sure you have a good supply of cardboard or, better yet, thick poster paper, on hand. You can cut pieces away and tape them back on as much as you like until you get the shape that's a perfect fit, and it's a lot cheaper than going through several sheets of aluminum. Once you are happy with your cardboard pattern, use it to trace the shape onto a piece of aluminum (or steel if you prefer) sheetmetal and cut it out. If this is your first attempt at building crush panels, you may want to give yourself a margin for error and cut a little on the outside of your markings. Use a bead roller to run a bead approximately 2 inches from the edge all the way around the piece. This gives the panel additional strength at the edges where it will have to attach to the car. Finally, a bead of silicone-especially on crush panels that separate the cockpit from the engine bay-helps keep carbon monoxide, dirt, and everything else away from your driver.
Can You See Me Now? From there it was on to the installation of the windshield and widows. Up front, the safety Lexan is 11/48-inch thick; for the rear window and side windows behind the C-pillars 0.060 Lexan is used to reduce weight. As mentioned in the first installment, NASCAR requires a stock roof for Late Model Stock racing, and the lip is recessed to fit OEM winshield glass, which is too deep for the Lexan we are using. So, for the tops of the front windshield and back glass, spacers had to first be pop riveted into place so the Lexan would sit flush where it meets the roof. This is not necessary on the side windows because they fit into ARP's fiberglass panels. Everything is then pop riveted into place (Davis uses only steel-shank rivets, available from Fastway Racing Products, throughout the car because of its higher shear strength).
The front and back "glass" must also be secured in place by two exterior straps. Our rules say they must also be bolted into place. We used thin aluminum strapping bolted into place with button-head screws to meet regulations and keep the exterior profile as smooth as possible. On the inside of the rear window, aluminum brackets were fabricated to hold the bottom of the rear window in the desired location. At speed, low pressure air rushing past the rear window will try to pull the thin Lexan out and cause it to almost bubble out. The brackets simply help the 0.060 Lexan maintain the desired shape.
The Cool Factor The most complex part of this install was the radiator, grille, and radiator box. The grille itself was easy: ARP makes an inexpensive grille insert that simply rivets into place once you have cut the marked opening out of the bumper cover. Davis likes ARP's grille design because it does not sit flush against the exterior of the bumper cover, but is recessed about an inch with a radius leading to the opening. That helps direct air into the opening instead of allowing it to slide off the sides. Davis says this design is effective enough that you can actually see a difference in engine coolant temperatures with no other changes.
"That radius leading to the recessed grille, from my experience, will lower the coolant temperature an additional 20 degrees under race conditions," Davis says. "That's a big deal to me, because now I have a cushion. To get the water temperature back to 220, I can put more tape on the car, which will give my driver more downforce. It's pretty simple: The more efficient you can make your cooling system the more you can close off the radiator opening. That gives you more downforce, which makes for a better-handling race car."
Continuing that quest for an efficient cooling system, we installed a 28-inch radiator from Fluidyne. This unit is made for Sportsman-level racing, so it is compact but very efficient. Of course, to get the most air to the radiator it has to be in the front of the car, which also makes it a prime candidate for wreck damage, so it needs to be mounted in such a way to make removal and replacement as easy as possible. Our radiator sits in a pair of brackets welded to the frame and is held in place at the top by a single bracket. In the event it gets damaged during a race, all that has to be done to replace it is remove the hoses, unplug the electric fan, remove the single hitch pin holding it in place at the top of the radiator, and yank it out. All the race team needs to get back on the track is a new radiator and a jug of clean water.
With the radiator in place and the grille opening cut, it was time to connect the dots with a radiator box. Throughout this buildup, Davis has reminded us that "air is the only thing you get for free, so you had better take advantage of it." When it comes to the radiator box, it's no different than the body. A box with straight walls does not direct the air where you want it to go or otherwise try to take advantage of how the incoming air strikes the radiator. For example, compare the size and location of your grille opening to the size and location of the radiator. After a tough race in traffic you should notice tire-rubber buildup on your radiator. That rubber gets to the radiator through the grille just like the cooling air; if it is concentrated in one area and not evenly distributed across the radiator, then you also aren't getting even cooling across the radiator fins. In other words, you aren't getting the most cooling power your radiator can produce.
An easy solution is to create a venturi in your radiator box. Davis does this by curving the floor and roof of the radiator box inward and then out-much like a carburetor throat. This not only increases airflow to the radiator, but it also causes the incoming air to follow the roof and floor of the box, increasing flow to the top and bottom of the radiator that normally do not see enough air. The sidewalls are flat since the width of our grille matches the width of the radiator. The box is attached to the bumper cover as close to the grille as possible with pop rivets. To allow easy removal of the radiator, the big end of the box is not attached directly to the radiator but to two tabs on the frame that the radiator sits in. This setup also minimizes the connections between the front bumper and the rest of the car. If the front end gets crushed, the radiator box probably will too. Simply rip off the front bumper cover and the radiator box should come with it.
Once the radiator system was installed, our bodywork was nearly complete. There's still a lot to be done on the car before it will be ready to race again-like a new engine, suspension components, and a driver's compartment upgrade-so keep an eye out in future issues of Circle Track for the continuing evolution of our NASCAR Late Model Stock.
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