1993 Ford Mustang Notchback - All Cooped Up
In Order To Run 9s The Right Way In Safe And Legal Trim, Project Fox Gets A Custom 10-Point Rollcage.
From the February, 2010 issue of Popular Hot Rodding
By Stephen Kim
Photography by Stephen Kim
As the adage goes, don't buy a $10 helmet unless you have a $10 head. Despite the sad state of the devalued U.S. dollar and the shameful popularity of shows like The View, most heads are still probably worth at least $11. Surely, safety equipment is something that should never be taken for granted, and nothing enhances survivability in a performance car more than a quality rollcage. A vicarious lifestyle of trying to dupe the tech inspector might seem cool when you're 17, but as any racer will tell you, walking out of the car under your own power is the number one priority. Going fast comes second. Besides, lifting after the eighth-mile marker-or getting booted off the track after just one pass-is as lame as it gets. So if you have the power and grip to warrant one, don't be a cheap, inglorious loser. Get a cage.
Over the past several months, the skilled craftsmen at Bill Buck Race Cars in Austin, Texas, have installed the suspension and built a stout 8.8 rearend for our '93 Mustang project car. However, their true specialty is in custom chassis fabrication, as evidenced in high-profile drag machines, such as Mike Murillo's 2,900hp Outlaw 10.5 Mustang. While Project Fox won't make anywhere near that much power, its 775 ponies are more than adequate to reach our goal of 9-second e.t.'s. According to the NHRA rulebook, cars running quicker than 10.00 or faster than 135 mph in the quarter-mile must be equipped with a 10-point rollcage, so we had Buck build us one out of chrome-moly. Of course, there are very stringent stipulations in terms of how the cage must be built, which Buck graciously explained to us during the build.
Granted, a bolt-in cage would have been sufficient for our needs, we felt the additional strength of a custom weld-in unit was well worth the extra expense. Given that every car and every application is slightly different, a custom cage allows for a tighter, more polished fit. "It's hard to quantify exactly how much stronger a weld-in cage is than a bolt-in cage, but just about everyone agrees that welds make for a more solid structure. Bolts are designed to handle tensile loads, not lateral loads," Buck explains. Nonetheless, custom cages require additional labor, and opting for chrome-moly tubing instead of mild steel only makes matters worse. However, since Project Fox's big-block conversion will certainly tack on its own share of extra pounds, minimizing the weight gain associated with a cage is hard to dispute. "In a typical 10-point cage like this, chrome-moly will be about 40 pounds lighter than mild steel. Most people only think about weight savings, but chrome-moly is also stronger," Buck says. As you'll see, building a custom cage isn't a job for a novice, or even those who are somewhat competent with a welder. It takes time and a whole lot of practice, so in most instances it's best left to a pro fabricator.
|THE COST SO FAR
|'93 notchback Mustang
|Sold old wheels, tires, engine, trans
|532 big-block Ford
|Phoenix TH400 trans
|Strange 8.8 rearend
|Comp Engineering rear suspension
|AJE front suspension
|Bill Buck custom 10-point cage
Since no one wants to accidently...
Since no one wants to accidently light their car on fire with a welder, it's a good idea to gut the interior whenever installing a custom cage. A 10-point cage features down bars that run from the halo bar to the floors, so the dash must also be removed. The process can take the better part of an afternoon, so ripping out the interior at home before dropping it off at the chassis shop is a good way to save a few bucks.
Chrome-moly itself isn't any...
Chrome-moly itself isn't any lighter than mild steel. The weight savings comes from the fact that it has a thinner wall thickness. Like a crankshaft, chrome-moly is an alloy, and is therefore stronger than mild steel. Consequently, the NHRA mandates 1.625x0.118-inch tubing for mild steel cages and 1.625x0.83-inch tubing for chrome-moly cages. Despite its thinner walls, 4130 chrome-moly tubing features a 106,000-psi tensile strength compared to mild steel's 63,000-psi rating.
The main hoop acts as a foundation...
The main hoop acts as a foundation for the entire rollcage, as it serves as an attachment point for the door bars, halo bar, trunk bars, shoulder bar, and kicker bars. Per NHRA specifications, it must be within 6 inches of the driver's head, a minimum of three inches above the driver's helmet, and at least as wide as the driver's shoulders. Buck measured from the center of the headliner toward the B-pillars to determine where to bend the bars. Buck shoots for 1/8-inch of clearance between the hoop and the headliner to prevent rubbing and squeaking. On a street car, the position of the hoop may need to be tweaked slightly to prevent covering up the dome light.
Much like a brake line bender,...
Much like a brake line bender, tube benders used for rollcages have degree indicators to help measure how much a tube has been bent. Getting a tube to fit tightly against the contours of the interior is often a case of eyeballing, and trial and error. Chrome-moly tubing requires significantly more force to bend than mild steel.
On unibody cars, any point...
On unibody cars, any point where the rollcage intersects the floor or trunk must have a 6x6-inch steel plate (0.125-inch thick) welded to the body. Since floors are seldom flat, NHRA rules allow bending the plates to follow the contours of the body. After grinding away the paint, the mild steel plates were welded to the floor. Chrome-moly joints must be TIG welded.
At the four attachment points...
At the four attachment points for the main hoop and A-pillar bars, Buck cut a hole slightly smaller than the reinforcement plates using a plasma cutter. By temporarily tack welding the bars to the plates, Buck can later break the welds, remove the plates, and drop the entire cage downward. This opens up access to the joints near the headliner, enabling full 360-degree welds in tight spots.
To further enhance strength,...
To further enhance strength, Buck positioned the reinforcement plates for the trunk bars right on top of where the factory framerails run underneath the trunk. The driver side plate had to be bent to follow the contour of the spare tire well. Buck says that bending the plate does not compromise strength.
With the plates welded down,...
With the plates welded down, the trunk back bars were tacked to the main hoop. Although Project Fox will run modestly sized tires, Buck likes to position the trunk bars as far inward as possible just in case customers decide to tub their cars later on.
Building a custom cage is...
Building a custom cage is just as much about adhering to the rulebook as it is about packaging. The trunk bars were moved as far back as possible to create extra headroom for rear passengers. Buck notched the package tray area with a plasma cutter to make space for the bars, which also enables reinstalling the speakers in the factory location.
The longest and most complex...
The longest and most complex piece in the entire rollcage is the A-pillar bar. It stretches from the main hoop, over the doors, down the A-pillar, and to the floorboard. It requires compound bends on multiple planes to get just right. In order to improve visibility, Buck moved it to within 1/2-inch of the windshield.
After breaking the tack welds...
After breaking the tack welds holding the main hoop and A-pillar bars to their steel reinforcement plates, Buck dropped down the entire cage through the floor. Without doing so, it would be nearly impossible to lay down 360-degree welds on the joints between the main hoop, A-pillar bars, and trunk bars. Afterward, the cage was raised for final welding to the floor.
Not only is chrome-moly harder...
Not only is chrome-moly harder to bend than mild steel, it's also much more difficult to weld. The tubing joints must fit much closer together, and the TIG process is more labor intensive. Buck suggests working slowly with chrome-moly, as the tubing is very thin and easy to overheat.
With the anchor points of...
With the anchor points of the cage firmly welded in place, the next step was adding the shoulder bar using the same 1.625x.0.83-inch tubing as in the rest of the assembly. It serves as a support for the seats, and an attachment point for the seatbelts. Per the NHRA, it should be no lower than 4 inches from the driver's shoulders.
Fox Mustangs are notorious...
Fox Mustangs are notorious for chassis flex, so Buck's a little antsy about relying on the stock floors for stiffness. Consequently, he fabbed a set of custom subframe connectors, again using 1.625x.0.83-inch tubing. They were attached to the body using 2x2-inch steel plates. Subframe connectors become mandatory at 8.50 and quicker, so that's one less thing to upgrade if beefing up the cage becomes necessary later down the road.
For an ultra-tidy appearance,...
For an ultra-tidy appearance, Buck capped the ends of the subframe connectors, which also helps keep out road debris. Since the factory metal is zinc-coated for corrosion resistance, which gives off potent fumes, good ventilation is extremely important when welding to it. Again, proper heat control must be exercised, since it's easy to burn a hole in the thin stock metal.
The door bars, trunk bars,...
The door bars, trunk bars, and A-pillar bars help limit front-to-back movement of the main hoop. Likewise, a set of kicker bars triangulate the main hoop to keep it from moving from side to side. They're typically attached to the floor, but Buck welded it directly to the subframe connectors using a factory drainage hole in the floorboard.
With the seats mocked in place,...
With the seats mocked in place, Buck marked the location of the seat belts on the shoulder bar before welding on a 1/4-inch-thick tab as an attachment point. Angling them slightly ensures that the belts will pull on the tabs properly.
Unlike a six-point rollbar-which...
Unlike a six-point rollbar-which is good for 10.00 in the quarter-a 10-point cage features a halo bar attached to the main hoop, and two A-pillar bars than run through the dash and attach to the floor. The difference in material and labor between the two is substantial, as a 10-point cage requires more tubing and removal of the dash.
All it takes is some humidity...
All it takes is some humidity to rust up raw steel, so a cage should be painted immediately. While the cage was dropped down, Buck cleaned it with degreaser and added a coat of black Rustoleum paint. He advises against using lacquer thinner, as it contains oil.
Per NHRA rules, the door bars...
Per NHRA rules, the door bars must pass halfway between the driver's shoulder and elbow, and is designed to keep occupants inside the car. A testament to his patience and master fabrication skills, Buck bent up a complex set of bars that clear the bulky seat bolsters and the stock door panels.
Now that the cage is complete,...
Now that the cage is complete, Project Fox has officially entered re-assembly mode. Stay tuned in the issues ahead as we install the fuel system and interior, then finally shoehorn the big-block between the frame rails.