Project LSZ: Building a Cage

Update by Tom Suddard to the Nissan 350Z project car
Nov 1, 2019

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So far, we’ve LS1-swapped our 350Z and taken it drifting, autocrossing and drag racing. And while we had fun, none of those are the reason we built this car: Our goal is time trials, meaning racing against the clock on road courses against other fast cars. To do that, we’d need a roll cage. Back to the shop!

Cage Rules

Do we actually need a roll cage? According to the rule books, the answer is “not right now.” We’ve got our eyes on four time trials series with this build: NASA Time Trials, SCCA Time Trials, Gridlife Track Battle, and Global Time Attack. And they all allow fixed-roof cars in slower classes to run without a cage. Go faster, add sticky tires, etc., and the safety requirements all increase. So, while we’d be fine to get started without a cage, it would limit us in the future. Plus, if we ever make the jump to true wheel-to-wheel racing, we’ll definitely need a cage. 

And according to our sense of self-preservation? Yeah, we need a cage, and we need a good one. Why? Because our LS1-swapped 350Z is fast. And despite the advancements in track barrier design and the fact that this is a safe, modern car, there’s still a harsh reality here: We’ve never built a car that could hit a wall harder than this one, and it’s probably going to be us in the driver’s seat if that happens. We’ve always preached installing the absolute best safety equipment possible, and that approach has always kept us safe despite a few nasty crashes over the years. 

Meet the Master

So we called Kirk Racing Products, who’ve been building cages since 1981. They allowed us to see the process step-by-step as the company’s owner, Mark Stewart, caged our 350Z. Here’s how he did it:

Before we could add any bars, we needed to completely gut our 350Z’s interior and remove its windows to make room for the cage. We stripped everything except the wiring and the steering column from the car. Bonus points: Stripping the interior knocked 249 lbs. of weight out of the car, putting its pre-cage weight at 3013 lbs with a full tank of gas. 

The driver’s position is an important reference point when building a cage, since it affects the door bars, harness bar, dash bar and more. That meant we needed to pick a driver’s seat before installing the cage. So, we called Subé Sports, a racing equipment retailer that’s run by racers, and super knowledgeable about safety gear. Our question? “Is there a halo seat that will fit into a 350Z?” As they explained, despite being huge, these cars are actually tough to fit halo seats in, thanks to a wide tunnel and an inward-sloping B-pillar. Fortunately, they had a recommendation, and sent a Cobra Sebring Pro-Fit Standard seat. It’s FIA-approved, lightweight, and offers the halo protection we’re after. 

Next, we needed to mount the seat. We mocked it up with a modified 350Z mounting plate and brackets from Sparco. We’re tall and we like to sit upright and close to the wheel, which made seat positioning a balancing act of helmet clearance, pedal location, and ease of ingress and egress. After lots of trial and error while wearing our helmet and HANS, we found a good position for the seat. 

Prep-work complete, it was finally time for the cage. We trailered the car up to Kirk Racing’s shop in Mount Olive, Alabama, and went to work. The first step? Actually, more prep–Mark asked us to remove the car’s gas tank just to be safe, since it would be less than half an inch away from his holes for the main hoop.

Mark still builds every cage by hand, though he does work off of a cheat sheet of sorts. His black book lists measurements of every cage he’s ever built, meaning he already knew roughly what size and shape our car’s cage would need to be before we arrived. He starts every cage with the most important bar: The main hoop. That meant removing some extraneous sheet metal to allow access to our 350Z’s floor pan. Mark cleaned the paint, primer, and seam sealer away, leaving bare metal for our cage to attach.

Once he made room for our main hoop’s feet, Mark went to work making them. He makes custom feet for everything, and we watched him cut, bend, and trim each plate until it perfectly fit the car.

For the front feet of our cage, Mark built three-dimensional pieces that will attach to the car’s sill. Why not just bolt to the floor? The goal of custom cage building is always to keep the bars as far from the driver as possible. These attachment points are actually stronger, and provide plenty of surface area to meet the rules without taking up legroom or providing a fulcrum for a hard impact to break an ankle over. 

Feet complete, Mark bent the main hoop. He left the legs longer than necessary so he’d be able to trim it to fit tightly against the roof of the car. One main goal of roll cage building is to make the cage as large as possible, meaning it fits as tightly as possible against the body of the car. We chose 1.75” .120” wall DOM steel tubing after reading through the various rule books and assuming a worst-case-scenario race weight of 3400 lbs. This cage should be legal anywhere we ever want to race the car. 

Each joint in a cage needs to be welded 360 degrees, and that’s a problem for the main hoop, which is pressed against the roof. To give himself room to weld, Mark drills holes in the floor of the car, and drops the main hoop through them in order to weld the joints against the roof. Once those welds are complete, he raises the main hoop back up, and covers the holes with the cage feet he built earlier. 

With the main hoop trimmed to fit and tacked into place, Mark bent and fit the A-pillar bars. His goal was to keep them as far from the driver’s head as possible. Once those were tacked into place, he bent and installed a halo bar along the edge of the windshield, too. 

At this point, the main structure of the cage was tacked together, so Mark knocked the feet out from under the main hoop, dropped the cage through the floor, and fully welded every joint. He was careful to alternate joints, spreading the heat around to keep the cage from warping excessively. Once everything was welded, he raised it back up against the roof, slid the main hoop’s feet back underneath, and welded the cage, feet, and car together. 

Next it was time for the rear down bars, which meant more custom feet. Mark compromised a little bit when choosing the down bars’ attachment points to the main hoop, making them slightly lower than the top of the bar in order to give himself room to fully weld the joints.

We won’t call any of this easy, but Mark knocked out the next few bars so fast we barely remember watching him work. He installed the diagonal bars in the main hoop and down bars, then moved onto the harness bar. He chose its location after measuring our shoulders while we were seated in the car, making sure it would put our harness at a safe angle. He installed a straight dash bar, too, at a height we thought would work well for our steering column attachment (we’re not re-using the heavy factory dash bar).  

What’s the difference between a six-point cage and an 8-point cage? This step. Mark ran bars from the front cage feet to the firewall, adding another custom-made foot to each. These points aren’t required in any of the series we’ll be running, but they provide extra protection for the driver’s feet and ankles. We’ve been stuck on crutches before, and don’t have any desire to repeat that experience. 

Next, it was time for door bars. Mark started by installing the lowest bars, which run right along the car’s sills. The passenger-side was easy: Two bars, bumped out slightly, but not requiring the door to be gutted. Why? Because we’ll rarely be carrying a passenger, we didn’t need the extra weight and the loss of crumple zone that come with big door bars. 

Next up: The driver’s side. Mark asked us what we wanted: Something simple, safe enough to meet rulebooks, and light, or something bigger, stronger, and safer. We chose the latter, happily trading some extra weight for extra protection. Our driver’s door bars go out against the door skin, and up as high as we could get them without limiting ingress/egress too badly. This style of door bar is commonly called NASCAR bars, owing to their early use in that series. Note that our door bars don’t contain S bends, a frowned-upon technique to get around stubborn B-pillars. Our main hoop is far enough forward that we didn’t need them. What if it was further back? We could have used a hole saw to run the bars through the B-pillar if necessary. 

Every sundae needs its cherry, and every roll cage needs its gussets–at least in our opinion. These are another optional step, but add strength without adding a noticeable amount of weight. 

Success! After a few days worth of (Mark’s) work, we stepped back and admired our 350Z: It was caged, officially making it a race car! We loaded it up on the trailer, bought Mark a steak dinner, and hit the road home. Our next project? Finishing the interior, which we’ll cover in the next installment. 

Costs and Methods for Putting a Cage in Your Race Car:

We’re really lucky: Kirk Racing is only a day’s drive from our Florida home, meaning we could take the car there and have the best cage possible custom—built by an expert. The price for all this? A cage like ours would cost about $2500 to replicate in most cars. But we get it: Not everybody can make the drive to Kirk Racing, and everybody wants to save a little money where possible. Fortunately, there are other ways to add a cage to your race car:

Weld-in cage kits: Own a good welder? Patient? Love welding while upside down and crammed against a firewall? Then weld-in cage kits are for you, and Kirk Racing offers them to fit almost any car. What’s included? Every tube cut a tad long and pre-bent, meaning it’s up to you to trim them to fit perfectly and weld them together. These can be just as safe and just as custom-fit as the cage Kirk built for us, provided you’re slow, methodical, and a perfect welder. The price? Our cage would have cost about $1000 as a weld-in kit from Kirk Racing Products. 

Bolt-in cages: These pass tech in some organizations and they’re fine for track days, but we’d skip them if at all possible. While they can be nearly as strong as weld-in cages when properly designed, the fact that they aren’t custom made, and must leave room for bolts, sleeves, and assembly, means they can’t be as big or fit as well as custom-made parts. Case in point: Kirk Racing Products no longer sells six-point bolt-in cages for the 350Z, because it just wasn’t possible to provide enough room to easily get in and out of the car. They do sell a bolt-in four-point roll bar, though, which costs $595. In our opinion, there’s a great argument for bolt-in four-point roll bars for track day cars and similar, but as soon as you need a cage, it makes more sense to make the jump to welded construction. 

Locally-Made Cages: Can the guy down the street do as nice of a job as Kirk Racing? The answer, of course, is “maybe.” We’ve used local cage builders before with mixed results, sometimes getting crap, sometimes getting beautiful work that took two months longer than promised, and sometimes getting told they were too busy to help us. Our best advice here is to ask for recommendations, read reviews, and drop off your car with a copy of your rulebook’s cage requirements taped to the roof for the builder to read. Unlike Mark at Kirk Racing, who is a club racer himself, your local builder might only know what the local dirt track requires, and might build something that violates the rulebook without some extra help and guidance. 

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