Project Land Speed Racer 240SX: Chassis Prep and Roll Cage Fabrication
February 19, 2015
Project Land Speed Racer 240SX: Chassis Prep and Roll Cage Fabrication
By Chuck Johnson
Ah yes, the beginning of any good sedan type racecar build almost always starts with ruining a perfectly decent streetcar. In the case of Project Land Speed Racer 240SX though, I’m not sure if we are really ruining a perfectly good streetcar. Honestly, from the looks of things, it must have been owned by a series of wannabe dorifto hacks before falling into my hands. If anything, I think we saved it from a continued life of embarrassment running around with its “demon camber,” four corded tires, and doing a crap ass job at pulling off that coveted hellaflush style.
God damn, give me a gun, let me shoot this car, and put it out of its misery. Or better yet, anyone have that flamethrower attachment from Call of Duty Black Ops? Let’s roast some marshmallows! Ok never mind, there are already too many S13 chassis in the junkyard and the 240SX seems to be making its home on the endangered species list somewhere between the Bug Eyed Frog and the Zululand Black Millipede. We’re gonna have to do the “right thing” and save this one… That is, save this one to claim our small piece of history with.
To start off the build of Project Land Speed Racer 240SX, we needed to prepare the chassis for the roll cage construction. This is probably the most therapeutic part of building a racecar, especially if you don’t care about how the interior comes out. In our case we started out caring, methodically removing the interior panels with the intentions of selling them for a few bucks. About half way through though, the beer kicked in, we came to our senses, and just started tearing, ripping, and gutting out the interior. It just wasn’t worth spending our precious free time getting flaked on or haggling over a few bucks.
Fortunately, we sobered up from our rampage just in time to carefully remove the interior wire harness, which runs throughout the cabin and under the dash. We disconnected it at the super multiple junction box, which is on the driver’s side underneath the dash. Since it would be months before we reassembled the car again, we also made sure to label all of the important connectors using masking tape and a sharpie.
We found several interesting modifications to our wire harness. Surely, this one was performed by a highly skilled electrician.
With the interior panels and wire harness out of the way, we bought 20 pounds of dry ice to remove the sound deadening on floorboards. When you do this part, be sure to use gloves, as the dry ice will burn bare skin. Also, make sure you are in a well ventilated area unless asphyxiation via carbon dioxide is your thing. Whatever floats your boat dude. For an older car, the S13 240SX has a lot of sound deadening, which is a bit annoying. On the flat surfaces, it helps to crush the dry ice up into smaller chunks with a hammer and then chisel the sound deadening up once gets cold enough. On vertical surfaces like the transmission tunnel, we taped pieces of cardboard in place to hold the dry ice against the sound deadening.
There is also a softer, gooier type of sound deadening that Nissan places around the wheel wells and inside the quarter panels of the S13. This type of sound deadening is impervious to the dry ice method. Instead, we used a torch to heat it up and a putty knife to carefully scrape it off. Let me emphasize the word carefully here. Molten sound deadening on your skin is a painful thing and you can come up with some pretty creative strings of cuss words when this stuff gets on you. The thing is, it sticks to your skin like molten magma and when you attempt to remove it, you end up peeling off your own skin along with it. [Insert elaborate strings of cursing here.] Sounds painful, huh? It is. Please, don’t ask me how I know this.
Going back to that term “carefully” again, make sure you wear safety glasses as the steel bristles will fly off at high very high speed and stick into things like arms, legs and eyeballs. Since this website isn’t available in braille, please wear your safety glasses.
Once we removed the large pads of sound deadening, we used a wire wheel attached to an angle grinder to remove the residual sound deadening and also the adhesive seam filler in the joints of the interior. Many of the cars I’ve seen at the track neglect this step and also don’t paint the interior. Honestly, that looks like crap. But hey, if you like driving a car that looks like a theft recovery, that’s your business.
Speaking of doing it right, every time we build a racecar we learn something new. It’s the small details that make a difference. This time we learned about spot weld drill bits, which allow you to drill out the weld without drilling a hole through the body. In the past, we used to remove unneeded brackets by drilling out their spot welds. The problem with this is the car ends up looking like Swiss cheese later on. This might not harm a car functionally in road racing, but when you race on a dirt lakebed like El Mirage, it’s critical that every hole in the car is sealed to prevent the driver’s compartment from filling up with dust and blinding the driver mid run. This might sound strange, but it happens in land speed racing.
With the interior prepped, we dropped off Project 240 LSR at Pierce Motorsports, located in Torrance, California. Jim Pierce’s experience as a fabricator is wide in breadth having prepared vehicles for rally, off road, and road racing. What’s more impressive is that Jim’s driving resume mirrors that of his fabrication experience. Jim has seen seat time in everything from the Baja 1000 to Prescott Forest Rally and NASA and SCCA endurance and sprint racing. With experience in off road and rally racing, we knew that Jim was capable of building a cage to withstand the most common type of crash in land speed racing, the high speed flip.
At Bonneville, there are no other cars on course with you; however, there is one giant wall to hit. It’s the giant white one made of salt below that you’re racing on. At high speeds, the common crash in land speed racing begins with the car becoming unstable, the front end lifting off the ground, and then the car going airborne. The car becomes airborne sometimes by 10-20′ and then comes down on its roof. Check out the video below, for a wicked example.
In general, the SCTA rule book can be described as straight forward in some areas, yet ambiguously complex in others. When it comes down to it, the rule book is up for interpretation just like any race series. However, it’s important to realize up front that it’s only the chief tech inspector’s interpretation of the rules that counts at the end of the day. To avoid any disputes when the car was finally built and ready to race, we made sure to keep Steve Davies, the SCTA chief tech inspector, in the loop during the construction of our roll cage.
The SCTA rules require that all cars weighing over 2,500 pounds and competing in classes where the record exceeds 175 MPH, use a minimum of 1-5/8″, .120″ wall mild steel tubing or 1-1/2″, .120″ wall E4130 Chromoly tubing. The rulebook goes on to state that these tubes must terminate into ¼” thick floor plates that have a minimum perimeter of 22″. To give you a relative comparison, NASA requires that cars weighing between 2,500 to 3,000 pounds use 1-1/2″, .120 wall or 1-3/4″, .090″ wall tubing and use a minimum of an .080″ thick floor plate. Remember the video? This is the reason for SCTA’s larger diameter and wall thickness requirements in comparison to road racing.
To make sure we satisfied the SCTA rules, Jim Pierce constructed the main structure of the roll cage from 1.75″ x .120″ wall, DOM mild steel tubing. We chose DOM mild steel alloy over Chromoly for its weight and cost benefits. Chromoly has chromium and molybendum, which gives it improved strength properties over 1018 alloy steel. Inch per inch, and pound for pound, there is little difference in weight between chromoly and mild steel tubing. The weight savings in a chromoly cage comes from the fact that the added strength of chromoly allows the cage to be built with a smaller diameter, thinner walled tube. In land speed racing though, a heavier car is actually desired as it is more stable at high speeds. Many classes in land speed racing have restrictions on the use of aerodynamic aids, so land speed racers often address stability by adding weight, sometimes getting very creative in doing so.
This crew of this Dodge SRT4 filled the factory intercooler with buckshot (bee bees from shot gun shells) and then used the factory fuel tank to hold 12.5 gallons of water. After all the weight additions, the car was reported to weigh in the neighborhood of 4,000 pounds!
Chromoly needs to be TIG welded and then have each weld normalized or heat treated for its strength to return in the weld area. If the normalizing is not done correctly, the weld area will be weak and brittle, which is obviously not a good thing. All this highly skilled TIG welding and heat-treating adds to the labor cost of a Chromoly cage making it much more expensive than a mild steel cage. Although I’m not exactly in my college years anymore and barely getting by on the frugal nutrients of top ramen, I would actually like to get done building this thing and go race so the reduced cost of the mild steel cage was a plus.
Roll cages in land speed applications usually mimic that of drag racing. Actually, if you trace drag racing back to its roots you’ll find that it’s the other way around. Many of the NHRA rules actually spawn from land speed racing. Hence, the similarities in roll cage construction. Nonetheless, knowing that I might have somewhat of a road race bug that may need to be itched again later on in life, Project 240 LSR’s cage design is closer to that of an overbuilt road race cage instead of the typical drag race or land speed cage.
The heart of the cage’s structure is a 1.75″diameter, .120″ wall main hoop, diagonal brace, and harness bar. The main hoop and diagonal brace’s function is to protect the driver from roof collapse in case of a flip or roll over. However, it cannot do this effectively without additional lateral support.
Equally sized rear legs known as “kickers,” coupled with upper and lower X’s help displace and distribute loads on the main hoop to other portions of the cage structure and uni-body frame. In the same sense, A-pillar bars extend forward, perpendicular to the main hoop, terminating next to pedals.
Additional tube bracing and “taco gussets” triangulate the main hoop, A-pillar, and roof spreader bar to strengthen the different junctions. In addition, dimple dyed, steel gussets tie the roll cage to the uni-body structure on the A and B pillars to stiffen, and ultimately strengthen, the chassis and cage assembly.
The A-pillar bars are tied together with a roof spreader bar and a diagonal roof bar which triangulates the roof area. Combined, the A-pillar bars, roof spreader, and diagonal roof bar outline the stiff envelope of safety that encapsulate and protect the driver.
Since the S13 chassis has such a low slung windshield and A-pillar angle, additional bars were welded in place to provide the A pillar bars additional support against collapse. Also note the tube gussets that triangulate the main hoop and A pillar bar. The main point here is to ensure that the main hoop and A-pillar do not collapse if the car were to land on its roof during a high speed crash.
The SCTA rule book states that the roll cage structure must protect the driver from all sides. This is a commonly overlooked or under interpreted rule, as the roll cage should not only provide side protection, but also protection below the driver’s rear end. Note how the hump in the floor board for the catalytic converter had to be clearanced to accommodate the butt protection bar.
To satisfy the SCTA tech inspectors, Jim Pierce fabricated door bars with an uninterrupted X design that connect the lower portions of the main hoop and A pillar bar. A huge gusset ties the intersection of the two bars together. To increase the envelope of safety, the door bars have been pushed out horizontally, protruding into the door. This little bit of area will act as a nice cushion in case the car lands on its side after becoming airborne.
To completely encapsulate the driver, a sill bar running snugly parallel against the uni-body frame was incorporated into the cage. This “snug” fit is one of the ways that I evaluate how well a cage was built. I’ve seen a lot of cages that I can stick my arm through the gap between the main hoop and B-pillar. In my opinion, that’s just a sign of a lazy or inexperienced cage builder. Jim Pierce prides himself on making cages where you can barely slide a credit card between the cage and the chassis. Remember, the cage should be spread out as far as possible to maximize the envelope of safety. Also, a well-built cage that butts up against the car’s interior is also a good way to stiffen up a chassis in race series that limits how many point cage you can have.
With the cage construction complete, we then turned to painting the cage and interior. Painting is all about good prep work and an investment up front will go a long way towards ensuring that your paint job will look good in the end. The first step is to mask any areas that you don’t want painted. Aluminum foil works great for quickly covering tricky things like pedals, wiring, and brake lines. It also helps to lay masking paper on the floor boards to keep the over spray from settling on the floor board while the cage and other areas are painted. If excessive over spray builds up on a surface it makes it difficult to get a smooth paint job down the road.
After the masking is complete, the next step is to degrease the surface. This is especially true for the roll cage as steel tubing usually has an oily layer on it to give it some corrosion resistance. MEK does a great job of breaking down the oil and grease. If you live in a state full of hippies like we do here in California, MEK can be pretty hard to find. As a substitute, denatured alcohol will work nicely.
We degreased the cage surface with denatured alcohol and then roughed up the surface with sand paper and scotch brite. For good measure, we then degreased one more time before we laid down the first coat of primer. On the bare metal surfaces of the cage, we used self etching primer which will help prevent rust down the road.
We ended up spraying the whole interior with primer, but it’s really not necessary. In fact, it’s an unecessary pain in the ass. To save some time and money, just scuff the factory paint with some sand paper, degrease, and then paint it. Simple as that.
After the primer was dry, we blew off the painted surfaces with compressed air to knock off some of the loose overspray that had built up in the interior. We had to sand down the more persistent, rough areas of overspray with fine sand paper before applying the top coat.
Once we laid down the primer coat, we began applying the top coat, working from the roof to the floorboard. When selecting a paint for a top coat, its best to choose a hi-gloss paint that is easy to clean and easy to touch up. Also, think about driver comfort when selecting the color. A lighter color will reflect heat and ultimately lower cabin temperatures whereas a dark interior color like black can make life a bit more uncomfortable for the driver. The most common colors we”ve seen used for a racecar interior are gloss white and battleship grey. We decided to be a bit different this time around and chose a matte silver for our interior. We like the color, but hope it cleans up as easy as a high gloss paint.
With the cage build complete, we’ll next turn our focus to prepping the suspension with some trick KW coilovers and SPL links. Stay tuned for the next installment of Project Land Speed Racer 240SX!