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Adding a Custom Rollbar to the 1972 Corvette Scarlett Project Car

Safe and Sound

Jeremy D. Clough Feb 24, 2016
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It hasn’t escaped our notice that shoehorning over 600 horsepower into a stick shift car can make it a real handful. So far we’ve added traction control, five-point harnesses and a custom chassis to tame that power into something manageable. But if you’re going to put a car on the track where the goal is to drive to the limit, you have to plan ahead for what happens when you push it too far. This brings us to the rollbar.

There’s a lot of fab work and no small inconvenience involved in shoehorning in a ’bar, especially in a car with as little room as a C3, which already has about the least usable room of any Corvette. The first good reason to make those sacrifices is that many tracks require it. At the dragstrip, for example, once you start moving deep into the 11s, you’ve got to have one if you want to make more than that first pass that gets you thrown out. A well-braced bar also helps stiffen the chassis, which is always a plus, and the added weight in the rear can help with weight distribution.

There is, however, a fair amount of controversy about including full ’cages—and even ’bars—in street cars, and for good reason. If the driver isn’t helmeted and restrained in a crash, like they would be on the track, there’s a great chance their head will hit the ’bar. That’s about the same as getting hit in the head by a baseball bat, which is a pretty unattractive proposition. If you have a compelling reason to go ahead and install a ’bar anyway, it makes sense to reduce that risk in any way possible with bar design, padding, etc. It is, however, virtually impossible to eliminate all risks, and that’s something that bears serious consideration when you decide to put one in.

In our case, we felt the car’s intended track use required it, so we went ahead. Unfortunately, while safety is a hot topic in the Pro Touring world where Scarlett belongs, as of yet there aren’t many hard-and-fast rules on what’s required, leaving racers who want to be safe looking to SCCA, NHRA, NASA and other rules when they plan their builds. Similarly, we looked to the NHRA rulebook for general specifications and followed the basic design of a main hoop supported by a pair of uprights and braced by a crossbar that doubles as a harness mount. For material, we starting with seamless DOM steel tubing with an OD of 1 3/4-inches and a wall thickness of 0.120-inch that we MIG welded together, and to the frame to form the bar.

Since the C7 rear suspension on our Street Shop chassis requires modifying the back deck to make room for the bulkier A-arm system, we had already sawzalled out everything behind the seats, which left us with a large open area to measure for the bar, and to test-fit as we went. Even so, we raised and lowered the body off the frame several times to get the fit right.

Once the critical dimensions of the bar were set, we realized that our Corbeau seats sat higher relative to the bar than we wanted, which is a side effect of trying to shoehorn so much together in so small a space. In order to lower the seats (and therefore the driver’s head) below the bar, we started by cutting and re-welding the brackets that mount the seats to the floor of the car, which earned us an extra inch or so of room. We also learned the A4 seat is available with a shaved base that removes one inch of foam from the bottom seat cushion, which would buy us a little more space to work with. Had we known the rollbar specs when we originally ordered the seats, we’d have gotten the shaved version. Since we didn’t, however, we’ll have them modified to get the extra inch, and have a set of seat heaters installed at the same time.

With the bar finished, the frame goes to powdercoat, and once back, we’ll rebuild the back deck and storage trays around the rollbar and add larger wheels for our wider rear tires.

2 Autocad Bar Plans 2/20

01. Measure three times, cut once. After taking careful measurements inside the car to fit the bar as closely as possible to the interior, Tray Walden drew up the ’bar in AutoCAD. It may appear simple on paper, but the angles get fairly complex.

3 Seamless Dom Tubing 3/20

02. We started with 1 3/4-inch diameter seamless DOM tubing with a wall thickness of 0.120-inch, just a bit thicker than the 0.118-inch required for an NHRA ’bar. This allows a bit of wiggle room to allow for the tubing to thin as it’s being bent.

4 1972 Corvette Project Scarlett Rollbar 4/20

03. With the dimensions established, Tray started the bends in the middle of the tube with a slight “crown” that follows the inside roofline.

5 Rollbar Series Bends 5/20

04. This is the main hoop after the initial series of bends. After the shape was fit to the interior, the legs had to be cut to length. Note in this photo that the legs have been cut at an angle, which is necessary to fit it flush against the frame.

6 Main Hoop Checked Interior Trim 6/20

05. The main hoop was checked continually for fit with the inside of the car. While the interior trim pieces are removed in this photo, they were put in place for measurement purposes and later during the fitting process.

7 Crossbar 7/20

06. Once the main hoop was bent, we started on the crossbar. Since the crossbar is [itself] bent and also meets the main hoop at an angle, it was carefully set up in the mill at the correct angle before being notched with a holesaw.

8 Crossbar Prior Welding 8/20

07. Here is the crossbar in place on the main hoop prior to welding.

9 Hoop Crossbar Welded 9/20

08. This is the hoop with the crossbar welded in place. In addition to strengthening the hoop, the crossbar also serves as a mounting point for the seat harnesses. Note the concave bends on the crossbar; this provides maximum clearance for the seats.

10 1972 Corvette Project Scarlett Rollbar Downtubes 10/20

09. Once the hoop and crossbar were together, we cut the downtubes and welded them to the frame. As with the crossbar, they meet both the hoop and the framerail at an angle. Obviously, indexing the tubes correctly while the angles are cut is critical.

11 Thick Plate Welded Frame 11/20

10. We used a thick plate welded to the frame as a mounting point for the main hoop. The tubing for the hoop was welded all the way around its perimeter once we lifted the body back off the chassis.

12 Rollbar Mounting Studs 12/20

11. An obvious problem created by the rollbar is its interference with the ability to tilt out the rear window. Shortening the mounting studs made it possible to unlatch the top of the window, lift it upwards to free the studs, and then slide the window down and out of place.

13 Corbeau A4 Seats 1972 Corvette 13/20

12. With the structure of the bar in place, we put our Corbeau A4 seats in place to check their height, only to find they fit higher than we expected.

14 A4 Separate Base 14/20

13. We had ordered our A4’s with a separate base that screws to sliders mounted to the bottom of the seat. Once we began looking for places to remove height from the seat, this bracket on the back of the seat base was an obvious choice.

15 Seat Bolt Holes 15/20

14. After carefully removing the bracket from the base with a cutoff wheel, we used an awl to locate our seat bolt holes through the floor insulation and then laid out the pieces of the base and bracket we had cut off, clearancing them where necessary, and tacked it together.

16 Stock Seat Base 16/20

15. This is the first seat after rewelding the base (right), shown back-to-back with the stock seat base. It earned us about an inch. We’ll have the foam in the base shaved for another inch.

17 1972 Corvette Rollbar 17/20

16. After sorting out the seat height, we turned back to the rollbar, and added an additional pair of diagonals inside the main hoop for strength.

18 Seat Belt Harness 18/20

17. If you use seat belt harnesses that wrap around the mounting bar, you’re required to have some way to keep them from sliding on the bar. Tray, again, drew out a guide in AutoCAD and then burned a pair of them on the hi-def plasma.

19 Harness Guide Welded Crossbar 19/20

18. The harness guide was welded in place on the crossbar. We put them on the bottom to make them as unobtrusive as possible.

20 Rollbar Assembly 20/20

19. This is the finished rollbar assembly. Once the chassis goes to powdercoat, ’bar and all, we can start assembling the suspension, brakes and powertrain components.

Sources

Corbeau Seats
Sandy, UT 84070
801-255-3737
www.corbeau.com
Street Shop, Inc.
Athens, AL 35611
256-233-5809
www.streetshopinc.com

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