Building on Spec

By Scott Lear
May 11, 2010 | BMW | Posted in Safety | From the May 2007 issue | Never miss an article

Our latest BMW project car is quickly becoming a full-fledged race car. We feel a little like football coaches, training a shrimpy Melvin to become a mighty Thor. We’ve whipped our car into shape, cutting out the excess flab by removing the comfy bits. Now we’re ready to strap on a helmet and some shoulder pads.
As much as some automotive steroids would help to turn our 1989 BMW 325i into a powerhouse, the number of allowable modifications for NASA’s Spec E30 class is strictly limited. This helps to keep racing costs down and promotes a level playing field, at least as far as the cars are concerned. It’ll all be up to the sack of meat behind the wheel to get to the finish line first.

The inner structure of the sunroof came out after some coaxing.

Since that’s the case, why not put some effort into keeping the driver alive? After all, you wouldn’t send a quarterback out on the field with just some spandex and a pat on the butt. NASA seems to share this opinion. While the performance modifications are tightly regulated, one area where NASA’s allowable upgrades don’t skimp is on safety equipment. Participants are allowed to construct a very sturdy roll cage with eight attachment points. The cage must be complemented by a good race seat, harnesses and even head restraints for side impacts. Building a safe race car is pretty straightforward, but it’s no place to pinch pennies. The bill for our safety equipment will consume the largest portion of the project’s entire budget.

Let the Sun Shine In

We used a piece of sheet metal as a lightweight replacement for the sunroof panel.

The Spec E30 class rules allow for the removal of the sunroof mechanism, a move that adds a little more driver headroom. Removing the sunroof hardware can also help lower the car’s center of gravity.
While unbolting the sunroof panel and associated motor and cables is pretty straightforward, there’s more to it than just turning some wrenches. The sunroof assembly has an inner roof panel that should be removed to get the most headroom and allow the roll cage’s bars to be as high as possible. This makes for a much safer roll cage as it increases the amount of room between the cage and the driver.
To remove this inner panel, you must first drill out several spot welds that are located around the sunroof opening itself. You can then use a propane torch to cook the glue that holds the inner panel to the roof’s outer skin. By slowly heating the joint and pulling down on the panel, you’ll eventually free the offending part. Once the inner assembly is out of the car, you can devise a way to firmly mount the original sunroof panel back in place. You might notice, as we did, that the panel is actually quite heavy. We decided to replace it with a piece of 20-gauge steel that we pop-riveted into place. While this is neither as pretty nor as elegant as getting the steel panel back in there, the extra two pounds of weight loss isn’t so bad, either.

The steel base plates for the roll cage tie into the sill and floorpan.

While the sunroof was out, we had just a few more details to take care of before we could install a roll cage. Since we were planning on putting in a bar that runs along the firewall, we had to remove the dashboard. This was easy, requiring the removal of just a few bolts on each A-pillar and the disconnection of a bunch of wires, including those for the instrument cluster. Some careful tugging and our dash was soon on the ground. Removing the dashboard would also allow us to run the forward down bars closer to the A-pillar and thus farther away from the driver, again maximizing the size of our safety cell.

Cagey Behavior

The rear of the cage ties into the trunk, directly over the springs.

We then loaded the BMW onto our Trailer World aluminum trailer and pointed the rig toward Mount Olive, Ala., for our appointment with Kirk Racing Products. Our tow vehicle for this trip, by the way, was a new Nissan Titan that we had on short-term loan. It certainly is a big, capable truck. It didn’t blow our Pathfinder into the weeds, however, and the Titan is almost too big for daily use.
Once we reached Mount Olive, Kirk Racing Products owner Mark Stewart met us early in the morning so we could go over the basics of our cage. Mark estimates that one of the most time-consuming portions of a cage installation is the fabrication and attachment of the floor and sill plates that the rest of the cage will weld to.
Mark’s installation process begins with the use of an air-powered sander to clean off the paint and undercoating at each point where the cage will contact the body. The plates are then cut and fit to each point and tied into multiple planes if possible. For example, the main tube’s mounts are welded to the floor panel, the sill and the rear seat ledge. These three points of attachment should eliminate any possibility of the cage punching through thin sheet metal in the case of a serious roll.

Mark uses a industrial-sized MIG welder for all of his cage work.

Good cage builders strive to get the largest cage possible into the car, allowing for the most room around the driver. This makes the cage more comfortable and helps the driver get in and out of the car; this design approach also helps reduce injuries caused by flailing arms, legs and melons contacting the cage itself. To that end, Mark carefully bends each tube—we went with 1.75-inch-diameter, 0.095-inch wall DOM steel tube—so that it matches the curves of the unibody, in some cases pressing against pillars and panels ever so lightly.
Next, Mark makes sure that each of the connecting bars on each particular hoop is backed up by one on the other side. For example, the bar that runs above the driver’s head and the one that runs down to the rear spring perches both meet the main hoop at the same place. The goal behind this design theory is to create a strong cage that can take a hit without any one bar placing undue stress on the other bars it is welded too. The installation of the cage starts with the main hoop, which is the one located behind the driver. This is bent and cut to fit, then placed inside the car. The floor plates are then fitted and welded in with Mark’s trusty Millermatic 251 MIG unit. The main hoop is then tack-welded to the floor along with a diagonal brace.

We added forward attachment points that go to the footwell.

At this point, Mark switches gears and starts working on the front forward tubes that run down along the A-pillar. Once these bars are properly sized and shaped, he then makes their mounting plates and tack-welds the forward tubes to the main hoop. Next Mark cuts the crossbar that runs along the top of the windshield and then tacks the bar into place.
With support now in place up front, Mark breaks the tack welds on the main hoop and the front floor mounts and pivots the forward assembly down so he can completely weld the crossbar in place. The forward assembly is then fitted back into position and solidly welded into place. At this time, the main hoop is also fully welded to its floor mounts.
Next, Mark builds the rear down tubes and X-brace, carefully cutting the rear seat’s back panel so that the bars can pass into the trunk area and attach to the rear spring mount. With the rear of the cage nearly complete, Mark welds in the horizontal harness mount bar and adds gussets to the main hoop and down tube connections.

We were amazed at how patiently Mark works with the various tubes and plates. At every single step, he takes his time to analyze the angles, lengths and bends needed to create this mathematical sculpture. After each bar is meticulously measured and cut, he uses a large cutoff wheel to carve out a precise fishmouth that will ensure an accurate fit—no hole saws or drill presses for Mark.
As a result of his precise methods, Mark’s cages require little to no filling in their joints to make up for improper fit. Each weld is a connection of strength, not a cosmetic cover-up for poor sizing.
The next step is to make the seventh and eighth points for the cage, the bars that go forward to the foot wells to provide foot protection. The floor’s surface is cleaned of any paint, and then the mounting plates are welded in place. Two short bars are then welded in to form a triangle that extends forward from the bars at the A-pillar. The dash bar is bent and welded into place, passing over the steering column and bending forward to mimic the curve of the firewall.
Mark then starts work on the door bars. A sill bar is first bent so that it curves outward along the inner edge of the door and along the sill itself. This is welded into place so he can start working on the X-shaped door bars.
We decided to build our cage without NASCAR-style door bars, opting instead for side-impact bars that are X-shaped and curve outward, pressing against the inner door panel. While NASCAR-style door bars do allow for more room right next to the driver, there are several compromises that are made.
First off, the driver’s door needs to be completely gutted and the window removed. This creates logistic and odor problems for a car that is stored outside. Secondly, in the event of a serious side impact, the NASCAR-style bars will immediately transfer energy to the car itself, with no dissipation of energy. This can lead to higher shock loads on the driver’s body than necessary. By keeping the door intact along with its original side-impact beam and panel, there can be some initial, slower deformation that bleeds off energy before it reaches the driver.

The cage was painted using fillable rattle cans (below); it takes a contortionist to get the back side of the tubes painted.

The cage was painted using fillable rattle cans (below); it takes a contortionist to get the back side of the tubes painted.

Mark adds that while both designs are legitimate, using a sill bar and a well-designed X means there’s not much chance of cage deformation. This design has been successfully used in professional rallies, and its only real downside is the lack of room, especially in narrow cars.
At the end of the job, Mark had us refit the seat and climb into our race car-to-be. He then welded in a slick little dead pedal to the left side’s foot protection bars. Mark also measured our shoulder height and welded in the harness mount bar. Touches like this really set a custom cage apart from a mail-order kit.
Mark quoted us a price of $1600 to $1800 for our entire roll cage, based on our desire for eight attachment points and a rear X-brace. When the sparks were done flying, we wound up closer to the latter price point but felt that we got a great deal in the bargain. Mark’s work is first-class, and he’s a pleasant and honest businessman. We literally drove past some competent cage builders to reach Mark’s shop, and we don’t regret that decision one bit.
We bid Kirk Racing goodbye and loaded the newly caged BMW back on the trailer for its trip back to our Florida home base. We still had some work to do.

Don’t Forget Your Coat

After the whole thing was painted, we used Lamin-X film to protect it from chips; here you can see the X-bars for the door opening.

Our BMW was in need of paint work before we applied any of the requisite numbers and sponsor logos. We also had to paint the bare steel tubes that made up our new roll cage.
We had Higgs Auto Paint, our local paint supply shop, mix up a batch of BMW’s Salmon Silver in a catalyzed enamel. This was injected into DuPont’s Nason Fill-In reducer cans (Part No. 441-37), essentially giving us a custom color in a large rattle can. Each $6 can holds 4 ounces of unthinned paint, so we had eight cans mixed up from a $30 quart of paint for a total cost of about $70.
On a calm and sunny day, we donned our masks and painted the roll cage, starting in the far back corner and working our way toward the front portions so we wouldn’t paint ourselves into a corner, both literally and figuratively. The outside of the car, including the hood, roof and trunk lid, was given a fresh coat of paint.
To provide a little eyeball appeal, we also had Higgs mix up a quart of Delphin Grey using the same rattle can technology. This was used to paint the wheels and portions of the front grille. A pair of stripes were masked off on the sides of the car and sprayed this same darker gray. The stripes are reminiscent of those on the Lotus Cortina, albeit more subtle in hue.
In all, the cosmetic freshening of our race car set us back a hair under $200. That’s cheap in this age of $5000 paint jobs, but it’s more than good enough for a wheel-to-wheel racer. If we end up having to replace fenders and doors as the season progresses, we’ve also got a quick and easy way to match the paint and fix cosmetic issues. We don’t want to be thinking about our paint job when we’re going three-wide into a corner.

Personal Guard

Our freshly painted cage is a wonderfully strong outer shield, but a few more key safety items will mean the difference between a survivable accident and chunky salsa. We can’t very well sit on the bare metal floor and brace ourselves against the cage while driving, after all.
Next to a helmet and driving suit, the seat and harness are the objects closest to a driver’s squishy and delicate inner bits when racing. The car and the cage will be taking the impacts in an accident, but from a momentum point of view, a body is an independent agent inside the car. And as the car decelerates, the first solid objects the driver will be hitting are the seat and the harness. It’s important to make sure that these components are up to the job of providing maximum protection against injury.
As an added bonus, a good seat and harness combination make the act of racing much easier since the driver’s body is held securely in place regardless of the g forces endured. Autocrossers who commonly run R-compound tires on cars with stock seats and belts are perhaps the most intimately familiar with how tiring it is to try and steer while hanging onto the wheel in an attempt to keep from ending up in the passenger seat. A deep-bucket racing seat tightly holds the driver, allowing full attention to be focused on the subtleties of car control at the limit.
The throne we chose for our car is the Cobra Evolution S GT. The Evolution S is FIA approved and features integrated head restraints to save our necks (literally). Since we have two drivers of varying widths, we opted for the 50mm-wider GT version. Thanks to composite Kevlar construction, the GT still weighs in at just 19 pounds. Our seat was $1049.95 from Subè Sports. Yes, less expensive seats are out there, but when it comes to personal safety we like to be well-protected.
We learned a fun fact while shopping for seats: A seat doesn’t retain its FIA certification unless it’s paired with mounting brackets of the same make. A set of Cobra competition alloy side mounts were $135 from Subè Sports. To eliminate any adaptation frustrations, we opted to use E30 Floor Mount Adapters from VAC Motorsports ($180). These killer pieces are CNC machined from thick 6061 T6 billet aluminum and will allow us to fine tune our mounting location without drilling more holes in the car.

We used the VAC Motorsports E30 Floor Mount Adapters to mount our Cobra Evolution S GT seat, which made the whole task easier.

To hold us snugly in the seat, we called up Impact Racing for a six-point cam-lock harness ($210) and some mounting hardware. The main questions you should hear when ordering harnesses are: How many sub straps would you like? Do you want to pull up or down to tighten the lap belts? With dual sub belts, pressure is distributed more evenly, and there’s a bit more room to, ahem, maneuver. Remember that part about keeping your squishy and delicate bits safe? We’re all about the dual sub belts. Pull-up or pull-down belts are mostly a matter of preference, but make sure that if you choose a pull-up belt there’s no chance of the adjuster getting caught on anything and accidentally releasing. (See our harness safety tips from expert Joe Marco elsewhere in this issue.) The NASA regulations require a window net, so we called up HMS Motorsport and ordered a 16x16-inch Schroth net and mounting hardware for $199. Because our Cobra seat has built-in head supports, we don’t need a right-side net. To make the cold steel bars of the roll cage a bit softer on our noggins or knees—should the worst happen—we ordered a box of high-density roll bar padding from BSCI. The padding is SFI 45.1 approved, installs easily thanks to built-in adhesive, and comes in lengths of 3 feet at about 18 bucks per length.

We’re using an Emergency Suppression Systems fire bottle that comes with dual nozzles and can be refilled at home.

Our last major safety item is a fire suppression system. Like many safety gizmos, this one falls into the hope-I-never-have-to-use-it category. Still, it’s cheap insurance against a type of injury no one wants to endure.
Emergency Suppression Systems’s 2.3-liter Racing System sells for $349.95. That gets you a pull-handle setup with two nozzles for dual-zone coverage. Most people mount one for the driver and the other in the engine bay. The ESS system uses AFFF concentrate as the fire retardant, and it’s field rechargeable. A recharge kit for the 2.3-liter bottle costs $54.95. Pull the handle, and the AFFF concentrate blasts out of a pair of T-nozzles under high pressure, making a fire-killing mess that you’ll be happy to see should the need arise.

Eyes Forward

Now that the safety gear is in place, we’ll start on the rejuvenation of our BMW’s suspension, including all of the allowed modifications for this fun class. We still have shock absorbers and springs to install, an engine to tune, and a race car to sort. You can see the latest progress on this and all of our other projects at


  • Bilstein: shock absorbers,
  • BSCI: roll bar padding,
  • Carbotech Performance Brakes: brakes, (877) 899-5024,
  • Cobra: seat and side mounts,
  • Emergency Suppression Systems: fire system,
  • H&R Springs: springs, (888) 827-8881,
  • Higgs Auto Paint and Body Supplies: paint and supplies, (386) 252-4848
  • HMS Motorsport: Schroth window net,
  • Impact! Racing: harnesses, (317) 852-3067,
  • Ireland Engineering Motorsports: anti-roll bars, (626) 359-7674,
  • Kirk Racing Products: roll cage, (205) 608-1156,
  • Momo: steering wheel, (800) 251-7625,
  • NASA: sanctioning body, (510) 232-NASA (6272),
  • Redline BMW Performance: project support, (954) 783-7003,
  • Web site and support,
  • Subè Sports: seat vendor,
  • Team Dynamics: wheels,
  • The Tire Rack: Goodridge brake lines, wheel studs, (888) 981-3952,
  • Toyo Tires: rubber,
  • VAC Motorsports: seat mounts, (866) 714-2002,
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