Ford has used quite a few different frame designs over the years. Two basic frame construction types are full-frame and unit-body (or unibody).
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The oldest frame design is fullframe. Typically, the frame rails are constructed of .120-inch-wall stamped steel that runs the length of the vehicle. At present, Ford still uses full-frame construction in its full-size cars and trucks.
The ladder frame is the oldest fullframe design. It typically consists of two long frame rails that run parallel for the length of the vehicle. The frame rails are separated by lateral supports. This design lacked strength in the early years. In 1932, Ford started adding diagonal cross-bracing (basically a big X-shaped frame structure) between the frame rails for strength. With the body bolted to the chassis, it became more rigid. From there, the ladder frame evolved until it was completely redesigned in 1965. Ford trucks continue to use the ladder frame today.
In 1965, Ford’s ladder frame was redesigned and given a new name—the perimeter frame. The front and rear frame portions were approximately 12 inches inward of the external body panels. The frames are referred to as portions, not sections. This is a full frame, made as one unit. The front and rear portions were not much different from the front and rear portions of the older ladder frame. The center portion of the frame was the difference in design. The center portion of the frame ran around the outside of the passenger compartment, usually only 1 to 2 inches inward from the external body panels. This design is much stronger in a side impact than the earlier ladder frames. This frame is also known as the “torque box frame” because it uses structural supports called torque boxes that kick the frame rails outward to the edge of the rocker panels.
Unitized body and frame construction is best described as body construction that incorporates body structure and chassis floorpan as a single structure. This single body and frame unit is made up of many different stamped sheetmetal pieces welded together. This makes the car lighter, keeps it rigid, and keeps cost down at the assembly plant. Ford has been labeled by some as the pioneer of unitized frame construction in the United States. The 1935 Lincoln Zephyr was Ford’s first try at the new frame design. By the 1960s, Ford and other American auto manufacturers were incorporating the unibody in full swing.
A subframe is the lower section of the unibody that is formed into a frame rail. Suspension components and engines usually bolt to the subframe, due to its increased strength compared to the sheetmetal floorpan. A subframe can also be a bolt-in section of a frame that has suspension locating points.
Full-frame constructed cars typically have bushings between the frame and the floorpan that they attach to. The factory bushings are usually made of rubber. These bushings help isolate the road noise and road feel to the chassis. For instance, when your tires hit the little reflectors that separate lanes on a highway, or they hit uneven pavement, the rubber factory bushings keep the jolt from being transferred to the body structure. That same design allows the frame to flex and twist under hard cornering.
Poly Compounds & Solid
As of writing this book, aftermarket companies are not offering body bushings for full-frame Fords made of poly compounds (commonly known as urethane, polyurethane, and Polygraphite). They also don’t offer solid body bushings made of aluminum. These body bushings would be the same shape as the factory rubber bushings, and they would be installed the same way too. They add serious rigidity to the frame and body by tying them together as one unit, and not flexing or distorting like rubber bushings. They also add more road noise and allow more road feel as vibrations transfer from the frame to the body. Almost all applications would be best suited with polyurethane body bushings rather than solid ones.
When building a car with a highpowered engine and a lot of torque, keep in mind that unibody cars tend to twist and flex. Forces from engine torque and flex from severe driving can cause fatigue in the body and frame structure, which makes the car more unpredictable on a road course or the street. To strengthen the structure of your unibody, you can install sub-frame connectors. Subframe connectors attach the front subframe to the rear frame. This reduces the torsional flex that the sheetmetal of the body structure usually absorbs and makes the car more predictable on a road course and the street.
Before installing subframe connectors in your car, be sure to inspect your frame and all of its components. If you install subframe connectors on a cracked frame, you will not be able to fully utilize the connectors. Repair any frame damage from rust, stress, or an accident before installing subframe connectors. Subframe connectors come in many shapes, sizes, and designs.
Non-Integral, Bolt-in Subframe Connectors
Bolt-in subframe connectors are the easiest to install, but they’re also the least effective. These connectors are only as strong as the bolts that connect them to the chassis. If you want to keep the option of returning your Restomod to stock one day, bolt-in connectors may be your best option.
Bolt-in connectors could be welded in, but they’re not intended for that purpose. If you’re going to weld them in, you may as well step up to stronger connectors that are meant to be welded. In most cases, bolt-in connectors greatly reduce the ground clearance, which can be a problem if your Restomod has a lowered suspension.
Non-Integral Weld-in Subframe Connectors
Non-integral weld-in subframe connectors need to be welded in place, but they don’t require serious modification to the floorpan, if any at all. They perform better than the bolt-in type, but depending on the car, they can reduce ground clearance. If your Restomod is like most, it’s lower than stock height and can use all the ground clearance it can get.
A few companies offer non-integral subframe connectors, including Total Control Products, Global West, Maximum Motorsports, and more. Depending on the application, these types of connectors are still less effective than the integral type. For instance, a non-integral weld-in connector that hangs down under an early Mustang ties the front and rear frame together. However, the frame can still twist, unless you weld a gusset somewhere in the center of the connector to the frame. To get a mental picture of this, which do you think is going to resist twisting (not bending): a straight bar or a U-shaped piece of round tubing? Obviously, the straight piece is stronger, unless you add a gusset or two near the center of the bend.
Keep in mind, the only complaint ever heard about subframe connectors is about reduced ground clearance. I’ve never heard anyone complain about a chassis being too stiff. Weld-in connectors are typically noticeable the first time you pull your car into (or out of) an inclined driveway, at an angle. Chassis flex should be reduced.
Integral Weld-in Subframe Connectors
Integral weld-in subframe connectors are the mother of all connectors. They require the most work to install, including cutting the floorpan and welding, but they’re also the most rigid. For all practical purposes, the strength you add with this type of connector is just short of installing a full frame in your vehicle. Integral weld-in connectors are typically stronger than the actual frames they connect. If done correctly, these connectors will not reduce your ground clearance either. Integral weld-in connectors protrude into the driver’s compartment, but with a little creative insulation movement, they can be hardly noticeable.
Currently, there aren’t any companies offering pre-built integral subframe connectors, but keep your eyes and ears open. If you want to build your own, you’ll need hand tools, a welder, and preferably an air compressor and die grinder. You can purchase the metal tubing down at your local metal scrap yard. Most homemade connectors are made from 2×2-inch square or 2×3-inch rectangle tubing with .120-inch wall thickness. Using any smaller tubing or thinner wall thickness will minimize the effectiveness of all your hard work.
Before you get started, remove the seats, carpet, insulation, and any parts you want to save from welding slag and hot ground metal flack. If you are welding near any windows, cover them. You would be really surprised at the damage welding slag will leave behind. Take all safety precautions. Safely elevate your car on level ground with car ramps or heavy-duty jack stands. Keep a fire extinguisher handy.
The most important part of a subframe connector is tying the front and rear subframes together, so locate them first. You’ll need to plot out the most direct route between the two subframes. Some front and rear subframes will line straight up, but some chassis have a front subframe that is narrower than the rear (or vice versa). When you plot out the subframe connector location on a chassis where the subframes line up, the connectors will run parallel to the rocker panel. Running connectors straight from the front to rear subframes will be the strongest. Make sure you connect the front and rear sections. If you fall an inch or two short of the actual subframe, the strength of the connector will fall short too. Figure out how you want the finished job to look. If you want the connector to be flush with the underside of the floorpan for ultimate clearance, then make your measurements to reflect your decision. If you don’t mind it sitting a little lower than the floorpan, for instance 1 ⁄2-inch, then figure that measurement into your lines.
Plot out the sections of the floorpan you will need to remove. Make sure to make the lines 1 ⁄8-inch narrower than the width of your tubing. Measure two or three times –cut once! Figure the cutting wheel or blade will also remove metal, so take that into consideration. Make sure the lines are straight. There are a lot of contours on the floorpan, so plotting out straight lines is easier said than done. You can use a straight edge to assist, or if you’re feeling punchy, get a laser level from your favorite hardware store and use the straight laser beam to plot out your lines. Make sure the laser is positioned straight over the floorpan for the most accurate results. If the floorpan curves upward more than the height of the tubing, leave the high areas when you cut the floorpan. Don’t remove more metal than necessary. This is a tedious process, but well worth the effort. Before cutting anything, make sure you don’t cut through a fuel line, a brake line, an emergency brake cable, or anything else important.
There are a few different ways to cut the floorpan. If you are tool-challenged and don’t have an air compressor, you can use a hacksaw. Use the type with a small handle and a blade sticking out of it. I’m not proud of it, but I’ve used this method and it’s not fun! Save yourself a bunch of grief and borrow an air compressor, a high-speed die grinder, and a cut-off wheel. In some cases, you can get away with a heavy-duty reciprocating saw. Almost anything is better than one of those little hacksaws.
Now cut the sections of metal from the floorpan. Trim the length of your tubing (subframe connector material). If you need to cut the connectors a little short (due to a strange angle), you can use 3⁄16-inch plate to make gussets to attach the connector to the subframe. Trial-fit the connectors to make sure they will fit before welding them in. Remove the connectors. For the ultimate strength of your work, you will need to weld every edge where the connector meets the floorpan and frame. For a clean weld, you will need to grind the paint off every edge of the sheetmetal with a grinding wheel. Clean the sheetmetal edges and the connector (bulk steel usually has oil on it from the manufacturing process and it will cause problems when welding). After welding in the connectors, use seam sealer to seal the elements out of the car. POR-15 products makes a seam sealer that inhibits rust called POR Patch; then use POR-15 to cover your work and keep it in good shape.
Front Support Systems
All manufacturers design braces into cars for increasing strength and keeping the car safe, without hampering the speed of the assembly line. Some of these braces are integrated into the chassis, and are welded to the car early in the process. The torque-box on the 1967 Mustang located under the left front foot well is a good example of a brace welded to the car for increased chassis strength. Bolted and welded braces are not extremely strong like separate pieces, but they are important to the strength of the chassis. If you’re used to driving your car with them, you’d probably notice if they were gone. So, if your car is extremely rusty and the torque box is non-existent, replace it.
The factory added braces to shocktower-equipped cars such as the Mustang and Falcon. Non-Shelby Mustangs sold in the US were equipped with a pair of small braces that tie the shock towers to the firewall. The one-piece heavyduty brace that replaced them was called the Export brace. It was produced to add extra support to the shock towers on cars exported out of the United States. Shelby American installed this upgraded brace on its cars to add rigidity. Reproduction Export braces are available through many reproduction parts suppliers. If you are installing an intake system on your engine that does not leave you space to use the Export brace, then you should modify the brace or customize it to fit your application. The Export brace is just one part of the complete front structure of any of the early shock-tower-equipped cars. The front frame rails, fenderwells, and fenders are all constructed of thin sheetmetal. They are strengthened by the stronger, thicker metal of the shock towers. The factory Export brace is important because it helps keep the upper shock towers apart. I’ve heard of old, beat-up Mustangs that have seriously fatigued and cracked fenderwell structures because they were driven without their Export braces. The shock towers can get weak enough that when the car is let down off of a jack, the fenders and fenderwells move inward as much as a 1 ⁄2-inch. That might not seem like much, but any movement that can be measured by your eyes is too much. If your shock towers can flex and compress under hard cornering, it can cause changes in suspension geometry and unpredictable handling. The movement also weakens the entire structure, causing permanent damage, such as bent or cracked frame rails.
Monte Carlo Bars and Shock Tower Braces
There are many Restomod candidates that would benefit from horizontal bracing in the engine compartment. Shock tower and strut tower cars will benefit the most from a Monte Carlo bar since the weight of the vehicle rests on the tower structures. Tying the two towers together increases rigidity and reduces fatigue.
Not to be confused with the Vshaped Export brace described above, shock tower braces and Monte Carlo bars are the braces that cross in front of the air cleaner assembly. The Monte Carlo bar mounts between the two front fenderwells, just forward of the shock towers. The Monte Carlo bar comes in many shapes and sizes. They differ for model year and option packages. Sometimes they are a straight bar, and sometimes they are curved in the middle to allow for some special-option carburetion. Monte Carlo bars are usually used in addition to the Export Brace to promote structural integrity through triangulation.
You can replace the Export brace and Monte Carlo bar with tubular steel bars, or just plain add one if you don’t have the any bracing to begin with. A few companies offer these in different forms. Two common manufacturers are Total Control Products and MPG Head Service. Both of these companies offer different levels for its kits. A lower level kit simply replaces the export brace with an adjustable tubular unit. The higherlevel kits offer the additional front tubular braces for improved strength and rigidity. The higher- level kits offer additional tubular braces for improved strength, rigidity, and full adjustability.
Strut Tower Braces
Late-model Fords have strut front suspensions, and they can be stiffened up with strut tower braces that are similar to the earlier models’ shock tower braces. Quite a few companies offer these braces. On the late-model cars, engine compartments are smaller and crammed full of accessories, so the braces are specific to year and model. For example, a 2003 Mustang brace may not fit a 2003 Mustang Cobra due to supercharger clearance. Some late-model Mustangs also came with bars that resemble a combination of the Export brace and the Monte Carlo bar.
What if you have a ’78 Ford Fairmont and you plan to turn it into a Restomod? There is a good chance aftermarket companies are not making strut tower braces for your car. Don’t let that stop you. You could design and fabricate your own by cutting some 3⁄16-inch-thick steel plate to fit on the top of both strut towers and then mount it to a strong point on the firewall. Tie all three plates together with some round, steel tubing. For design ideas, take a look at some Mustang strut tower braces before you start.
Some full-frame Restomod candidates came with C-section frames, also known as open-channel frames. These types of frames can be strengthened by a method called boxing. The object is to plate the open section of frame to box it. One trick is to use cardboard as a template for the boxing plates and then transfer the template onto the steel sheet. It’s best to use material of the same thickness as the frame. Then just cut out the plates and deburr them after you have welded them in. This process significantly increases strength, and it has been used by hot rodders for decades.
If your frame is already capped from the factory, you can add strength to it by welding up the seams. Factory-welded seams are not always the best quality. This should only be done with the frame out of the car. Before you pull the body off the car, measure the frame for straightness. Then measure it again with the body off. Welding the seams is an easy way to warp the frame if you don’t know what you are doing, so it’s a good idea to weld the seams with the chassis on a frame rack. You should only weld a few inches at a time to prevent putting too much heat into the frame. The heat causes the frame to expand, which causes twisting and flexing. If your frame twists and you keep welding, the frame will be twisted for eternity. This error can cause all kinds of suspension alignment problems, not to mention the inability to mount the body back on the chassis without serious emotional anguish. If you are not an experienced welder, pay someone else to do the job right.
Unfortunately, front wheelwells don’t always offer the clearance needed for tires of larger sizes. This is especially true when the ride height is reduced. Luckily, some full-frame Restomod cars have removable inner fenderwells. However, the structural integrity of the front sheetmetal and frame is reduced when the inner fenderwells are removed, and there may be more flex than desired. The inner fenderwells also protect the paint, engine, etc., from rocks that fly off of the tires. For these reasons, it’s usually a good idea to either modify them or make some new ones that will fit.
Whether or not you decide to keep your fenderwells, it’s a good idea to use some type of bracing to reduce flex. For instance, if you are going to remove the front inner fenderwells on your ’72 Gran Torino, you should add front braces to put some strength back in the front body structure. Front braces are also known as forward struts or hoop bars. These are more commonly found on extreme Restomods and drag cars. They can attach to a strong anchoring point on the firewall and run down to the frame structure next to the radiator. For the most rigidity, these bars can go right through the firewall and mount to a roll cage in the passenger compartment. This triangulates the front frame rails, which is especially important on extreme Restomods that are lacking the front inner fenderwells and shock towers. When you remove metal from the front structure, you will need to add bracing to put the strength back in.
If you decide to attach your front braces to the firewall, you should install some anchor plates to help distribute the load between the tubing and sheetmetal. The anchor plates should have the same wall thickness as the tubing used for the braces. A good rule of thumb is to make the anchor plate surface area about 21 ⁄2 times the size of the tubing diameter you are welding it to. For instance, if the round front-brace tubing is 1 inch in diameter, the plate should be at least 21 ⁄2×21 ⁄2 inches square. It’s not always possible to use such a big plate in tight spaces, but it’s a good rule to keep in mind. It’s best to weld continuously around the perimeter of these plates and plug-weld the plates to the host sheetmetal in a few places to further increase their resistance to fatigue.
Picking a strong anchor point is critical for strength and safety, so try to attach the bars near bends or corners in the attachment area because these areas are inherently stronger. As with any design, the structure is only as strong as its weakest link. If you anchor the braces to a weak area of the firewall, the brace will eventually break the sheetmetal. Also be aware that during a frontal collision, a poorly placed brace could easily come into contact with the driver, injuring or killing him. To avoid that hazard, anchor the brace to the frame in more than one location to make the strongest and safest design. If you are planning on running with any racing associations, you may want to check their rulebooks before going through the process of any serious fabrication.
The majority of Ford Restomod candidates are unibody cars and they do not have removable inner fenderwells. The metal is needed to keep the structure strong. Keep in mind that the front frame rails on a unibody car are nothing more than stamped sheetmetal.
RICK CARLILE’S 1965 CYCLONE
This may sound like a familiar story. A friend talked Rick Carlile into taking his car out to the track. The day was going to be an exercise in adrenalin-pumping fun. Just one track-day was all it took – Rick was hooked! Knowing track excursions are not easy on cars, Rick started looking for a car he could build for strictly track use. He wanted something out of the ordinary, so a track Mustang was out of the question. Rick got the opportunity to pick up a 1965 Comet Caliente for $500. The rest is history.
While Rick’s Comet Caliente isn’t a streetable Restomod, it definitely deserves some attention. Rick thought the word Cyclone would command more attention than Caliente, so he re-badged the car. Other changes to the exterior are the additions of Crites Restoration Products fiberglass front and rear bumpers and a Crites fiberglass Ram Air hood. The quality hood comes with builtin ducting to make the Ram Air ducts functional. Rick engineered a custom air cleaner system from an air-cleaner base, and a custom plate that mounts the filter in the hood ducting.
The 1965 is equipped with all the right mechanical elements to keep it going during open-track events. For power, Rick had the 525-hp 347 prepared by Gerolamy. It’s got a Ford Motorsports R302 block stuffed with Venolia pistons, Cunningham rods, a Moldex forged crank, Comp Cams flattappet cam, and Crane roller rockers. Bolted to the mill are World Products large Dart iron heads (turning the 347 into a 12.3-to–1 compression monster), dressed with Ferrara stainless valves and titanium retainers. A Jet Performance race-prepped 750-cfm 4150 Holley carburetor sits atop an Extrude Hone match-ported Cobra dual-plane intake. Lubrication is handled by a Fram HP-6 filter and mount, Canton 8-quart roadrace pan, and blueprinted Melling highvolume oil pump. A Setrab 25-row stacked cooler handles oil cooling. The David Klee race-prepped Ford Toploader 4-speed is engaged with a McLeod clutch, pressure plate, and aluminum flywheel. The transmission is solidly mounted with a McLeod scattershield, and it spins the 3-inch diameter aluminum driveshaft. The Ford 9-inch rear is stuffed with 3.70:1 gears mounted to a Detroit Locker, which turns the Summers Brothers 28-spline racing axles.
The interior follows the same racing plan, which only contains the essentials. You will find a Kirkey aluminum road race seat, Simpson 5-point harness, 13-inch Grant steering wheel, the essential AutoMeter gauges (clocked so the needles all point in the same direction during normal racing conditions), Safecraft fire system, video camera mount (for critiquing after the race), Longacre Hot Lap timer, and Wink mirror. Surrounding the interior is a 10-point roll cage, which protects the driver and ties the custom subframe connectors and entire chassis together for the ultimate in rigidity.
Handling the front suspension are TCP control arms, strut rods, and coilover kit (using double adjustable Aldan Eagle shocks). Front braking is accomplished by a Baer 13-inch track system using Hawk Blue pads and cooled by a 3-inch Cobra Automotive front brake duct kit. The rear suspension has 4-leaf rear springs with bronze race bushings, which are dampened by Spax rear shocks. The rear braking is accomplished by 11-inch x 2.5-inch rear drum brakes wearing Porterfield R-4 compound shoes. The body sway is controlled by a 11 ⁄4-inch front bar and a 7 ⁄8-inch Addco rear bar.
Over a decade later, Rick is still hooked on open-track racing events. His Cyclone seems to be continuously evolving and picking up speed, just like any true-blooded Restomod. A street version of this car would stick out in a sea of Mustangs and be well received by other enthusiasts, but not by the competition.
Rear Frame Rail
Tricks If you have to notch the frame to get clearance, it’s a good idea to reinforce the area that gets cut out with sheet steel that is the same thickness as the original metal. It’s also a good idea to use coldrolled steel rather than hot-rolled, due to the increased strength of cold-rolled steel. When working with frames or suspension systems, excellent welding and fabrication skills are required to do this work safely. If you aren’t 100 percent confident in your welding or fabrication skills, it’s best to have this work done by a professional welder/fabricator.
In order to narrow the frame rails on a full-frame car, the rails are cut off about 18 inches forward of the rear axle centerline and moved inboard. When figuring out how far to move the rails inboard, make sure you end up with enough clearance on both sides of the tire. Try for at least 1 inch of clearance on each side of the tire, or more if possible. If you are going to reuse the original rails, the end of the forward rails need to be capped with a plate that covers the entire open end and continues inboard the distance you want to move the rail.
Use 3⁄8-inch or thicker steel for these plates. Next, reattach the rear rails to the plated end of the forward rail, and then box in the areas ahead of and behind the plates with sheet steel that is the same thickness as the rails.
As you move the frame rails inboard, they are more likely to twist under suspension loads. You will need to add a fairly large X-member above the axle housing to prevent twisting. Use 2×3-inch box tube or something equivalent. The configuration should consist of a piece of tubing that attaches to the left side of the rear frame, a couple inches in front of the axle housing, and spans across to the right side of the frame behind the rear axle. Install a piece of tubing on the right side of the frame, in front of the axle housing, that spans across to the left side of the rear frame behind the rear-axle housing. Notching or cutting one of those tubes and joining it to the other tube will create a strong X-brace to strengthen your rear frame. When installing this X-member, make sure the axle won’t hit it at full bump. You may end up moving the X-member to just above and behind the axle for clearance.
There are several companies that make universal rails out of 2×3-inch box tubing. Chris Alston’s Chassis Works and Art Morrison Engineering are some of the best, but there are others. Similar construction techniques to narrow stock frame rails are used to install aftermarket frame rails. The majority of the time, when narrowing rear frame rails on leafspring rear suspensions, they are converted to coil-over suspension systems. If you use narrowed rear-frame rails, a narrower fuel tank or fuel cell will most likely be required.
Roll Bars and Roll Cages
Production bodies and frames were not originally designed to withstand the rigors Restomod guys put them through. Along with increased safety, the strength of the body and frame are increased with the addition of a roll bar or roll cage.
The following is an explanation of the terms used when dealing with roll bars and cages. Windshield posts are referred to as the A-pillars, and in succession, the next body posts toward the rear of the car are known as the B-pillars, then C-pillars, etc. Roll bars can be identified by the number of points that attach to the chassis or floorpan. A four point cage consists of the main hoop and two rear braces that run from the top of the main hoop to the rear-frame rails, or anchor plates that reinforce the floorpan above the frame rails. A six-point cage adds another set of bars from a point between your shoulder and elbow on the main hoop to a reinforced area on the floor near your feet. Another version of the six-point uses bars that run forward from the top of the main hoop, follow the A-pillars down past the dash, and finally terminate at reinforcing plates on the floor near your feet. It’s also common to combine the two versions of the six-point in one cage for more strength. An eight-point cage adds bars running through the firewall to the front frame horns, or shock towers on a unibody car. These two bars typically attach to the bars of the six-point where it passes the dashboard. Cages that are ten-point or more are basically eightpoint cages with extra bracing for strength and safety.
When planning a roll bar or cage, it’s a good idea to keep in mind that if you eventually want to race your car, your car will most likely have to pass a safety inspection and will need to be designed according to a rulebook. When building a Restomod, you’ll most likely need to abide by rules established by the SCCA and/or NHRA. Each has its own requirements as far as tubing material, diameter, thickness, placement, etc., so if you plan on racing in more than one venue, it’s a good idea to be sure you’re legal for all the rules that apply. If your design doesn’t follow exactly what is described in the rulebook, don’t hesitate to call the technical inspector and ask questions before beginning work.
Roll Cage Safety
Roll bars and cages are there for your safety as well as the safety of those around you. Once again, if you’re not extremely confident in your welding or fabrication skills, have this part done by an expert. An incorrectly designed or installed roll bar or cage could seriously injure you. If a bar breaks off in an accident, it could impale you. Make sure any companies or shops that you deal with have a good reputation and employ highly skilled workers. Again, if you have the slightest doubt about your design or welding abilities, have a professional fabricator do the job. Roll bar padding is another safety issue. An unpadded bar within arms-length or close to your head could cause a broken bone or worse. Also know that in an accident, seat belts can stretch as far as 12 inches.
If you are going to have a back seat for passengers, keep the passengers in mind when installing a roll bar or roll cage. On the street, passengers could easily come into contact with the bars too. If it’s possible that they could be in danger, don’t take the risk. Give them a ride some other day.
Roll cages and roll bars benefit from the addition of gussets. The gussets add strength by triangulating the mounting point and distributing the loads over a larger surface area of the tubing. Be careful of any sharp edges on gussets or any other object within reach of your limbs or head. Sharp, exposed edges are extremely unsafe and have no place anywhere in your car, especially in the passenger compartment. Take a little extra time and smooth any exposed edges or burrs.
Exposed sharp edges that can’t be reached with a file, sandpaper, etc., should be covered with some type of edge trim. Edge trim is available in a variety of different colors. Make your car as safe as possible. If your car gets damaged beyond repair in an accident, you can always build another one as long as you are still alive.
Weld-In Roll Bars/Cages
As with bolt-in roll bars and roll cages, make sure that you check the correct racing association rulebook that corresponds with your racing plans. It seems every sanctioning body has a slightly different idea of what design and tubing size is required to keep you safe. Some sanctioning bodies also requires the cage to be tied to the body for added strength.
Roll cages have been around for a long time, and there are some issues that keep surfacing. Two of the most common issues are headroom and door bars. Whether you plan to drive your car on the street on a regular basis or not, take entering and exiting the car into consideration. Some people choose cage integrity over ease of access. There should be a happy medium. On the one hand, you want the cage to be strong to absorb a hard impact; on the other hand, you need to be able to get out fast in case of a fire. An expertly designed and installed cage is not intrusive into the passenger compartment. The roll bar or cage should also be as close to the inside of the body as possible.
Buildings and roll cages have a few things in common, but the most important feature they share is the foundation. If the foundation isn’t strong, the integrity of the roll cage will only be good for visual effect—and as a weapon. The floorpan and the frame must be in good shape. A rusted floorpan is not a good place to anchor the cage. Fabricators prefer to anchor a cage to frame structures rather than sheetmetal, but this isn’t always possible. In the case of a unibody where the cage must attach to a sheetmetal structure, use large-load spreading anchor plates between the tubing and body metal. Again, use a rulebook as a guide to accepted practices. The rocker panels are typically made up of multiple sheets of formed steelsheet that are welded to create a strong structure. The steelsheet is also a good attaching point for the cage.
Roll bars and roll cage main hoops need to be anchored to the floor behind the front seats. In unibody cars, the rocker panels are the only place to anchor the main hoop. Most fabricators use 0.090- to .125-inch thick mild steel for fabricating anchor plates. The anchor plate is typically formed to take the shape of the floor area where it will be welded. Anchor plates need to be welded around the entire perimeter for maximum strength.
The main ingredient of a roll cage is the main hoop. The main hoop is the bar located just behind the front seats. All driver protection bars attach to the main hoop. Some racing rulebooks require the main hoop to be made out of tubing that is larger in diameter than the rest of the cage. In some rulebooks, the diameter of the main hoop tubing is determined by the weight of the car. Using larger diameter tubing, such as 2-inch, can cause headaches when attempting to bend it because most fabrication shops don’t have the proper dies. If the fabrication shop you have in mind doesn’t have the size of dies needed to bend your tubing, ask if they are willing to purchase them in order to do the job. A nearby shop may also be commissioned to bend the tubing. Either way, there are only two ways to do things: the right way, or over and over again. Build the cage strong and safe from the start because it might save your life someday.
All roll cages are not created equal. Cages designed for drag racing are generally not as torsionally rigid as road race cages. In road racing, it’s important that the chassis/cage be as rigid as possible so that the suspension can work under the extreme loads of braking and turning. Most road-racing roll bars and cages have a diagonal bar from the bottom of the right side of the main hoop, and running up to a point near the top of the main hoop on the left side. Adding this bar to the main hoop helps reduce twisting forces in the chassis, but more importantly, it helps keep the main hoop from trying to collapse downward in a rollover.
Bolt-In Roll Bars/Cages
Bolt-in roll bars and cages are for people who have commitment issues. Some people want to use their car for dual purposes. The car can be driven daily without the roll bar or cage, and it can later be installed on race days. Some people have plans to get their car back to “stock” condition someday. Yeah, right. Whatever your reason is, it’s your car and bolt-in roll bars and cages are perfectly fine when they are welded and installed correctly.
If you ever plan to race, make sure to check the rules to find out if they accept bolt-in roll bars and cages. Some bolt-in cages are not legal at drag strips. Some racing associations accept bolt-in roll bars and cages only for specific classes. Other sanctioning bodies require the use of large, hardened washers or metal plates that sandwich the floorpan sheetmetal. The hardware helps ensure the bar or cage is anchored securely to the floorpan and will be harder to pull through the sheetmetal. Some associations also require the use of fine-threaded grade-8 bolts with two nuts locked together. The doubled nuts ensure the first nut won’t come loose, causing the roll bar or cage to fail in an accident.
Tip In the process of designing your bar/cage, keep in mind that the joints need to be welded all the way around. It isn’t easy to do this with the cage tucked up against the sides of the body and headliner. First, you should form and install all of your floor-reinforcing plates. Lightly tack these in to keep them in position, but they will have to come out for the next step, so keep the tack welds small. The trick is to mock the cage together with light tack welds first, and then mark the floor around where each bar will attach with a Sharpie marker. Next, remove the cage pieces and floor plates. Now use a hole saw about 1⁄8-inch larger than the bar tubing and drill holes where you marked the floor. Deburr your holes and re-tack your floor plates in (they are coming out again shortly). Next, reinstall your cage bars and tack the cage together lightly. With the cage all tacked in, go around all the bars and put four or five tacks on each bar. Now remove the floor plates and let the cage slide through the holes in the floor a few inches. Voila! Now you can weld all the way around the tubes without having the sides of the body or headliner get in your way. When fitted tight to the inside of the body, a roll bar or cage will add considerable strength to your car and give it that wicked race-car look, while taking away as little interior space as possible.
For years, enthusiasts have resorted to tubbing to fit larger tires inside their fenderwells. To start off, there are two types of tubbing: tubbing and mini-tubbing. Both entail a ton of labor. Tubbing is what you generally see Pro-Street builders do. They remove the inner and outer fenderwells and replace them, along with making serious modifications to the frame rails. Mini-tubbing is the more recent style of getting more rubber under the rear of a car. You generally only remove part of the inner fenderwell to add a section for depth. With minitubbing, the frame may need a little surgery, but nothing major. The finished mini-tub typically looks like it came that way from the factory, instead of looking like a drag racer installed aluminum panels in his backyard. Now that you have an idea about the differences, we can read more about the processes of both types of tubbing.
Getting the widest tire possible under the rear fenderwell has been a goal since hot rodders figured out that wider is better for traction. It’s not easy getting 13-inch-wide tires under the stock quarter panels of an early Mustang, or any other car for that matter. Tubbing involves removing the fenderwells and the floor from behind the front seat to the taillight panel. After all the original sheetmetal has been removed, the frame rails are cut off about 18 inches forward of the rear axle centerline and moved inboard enough to get the necessary clearance for the new tires. New wheelwells can be purchased from any number of companies, or they can be fabricated out of either sheet aluminum or steel. Steel tubs are stronger, more durable, and generally provide for a quieter interior. This is why the majority of Restomod cars are built with steel instead of aluminum tubs.
Mini-tubbing is the process of cutting the wheelwell front to back at the largest diameter, and widening the well by adding in a strip of sheetmetal between the inner and outer halves of the well. Sometimes it’s also necessary to notch the frame rail slightly to clear the tire. This process is less time-consuming and less expensive than a full tub job. This is the process used when the wheelwell can be enlarged enough to clear the desired tire without having to move the frame rails, but some frame notching is usually necessary. When properly installed by an experienced builder or a professional fabrication shop, mini-tubs look like factory sheetmetal fenderwells.
Written by Tony Huntimer and Posted with Permission of CarTechBooks