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1967 Mercury Cougar - Street-Friendly Comp CageWe show you how to combine safety and style for the ultimate streetable rollcage From the November, 2011 issue of Popular Hot Rodding By Christopher Campbell Photography by Author
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Though not quite an oxymoron, we should preface this story about our ’67 Cougar by saying that street friendly is a relative term here. Max Effort’s ethos through and through is pushing a street-legal muscle car as far as possible on the road course, and to make that a reality we need a ’cage that’s designed to function on several levels. This CAD rendering by Filip... This CAD rendering by Filip Trojanek at CorteX Racing looks like a design for a full tube-chassis car (and it could be), but it’s actually the model for Max Effort’s rollcage. Some of the bars represent structure to be built while others stand in for unibody structure already in the car. The design was shown to increase the rigidity of the Cougar/Mustang body by 500 percent. Essentially, once the ’cage is in the body, it just becomes decoration. First and foremost is safety; building a car with high levels of performance potential necessitates planning ahead for the worst possible outcome. If something goes wrong, we want to walk away. Or at least limp. To extract every ounce of capability out of our CorteX Racing suspension system, we also need to create a ’cage that is designed to make our unibody chassis as rigid as possible. Flex and twist are your enemies when you’re generating high g-forces, as they literally change the geometry of the chassis. Factory unibodies function a bit like monocoques by using the panels and the tub of the car as structure, but are typically quite weak in terms of deflection, especially in vintage cars. What we want is a ’cage that essentially becomes the load-bearing skeleton of the car. On the street side, we want to do all of the aforementioned without making ingress and egress too much of a contortion act. The real trick to making a true competition ’cage feel more streetable, though, is to minimize the imposing look and feel by integrating it so well into the interior that it looks almost graceful and natural, and less pure race. That’s no easy task since it requires balancing safety with style, but fortunately for us that’s a skill something Ryan Kertz at Kertz Fabrication excels at. Ideally we should have the... Ideally we should have the correct seat and steering column installed, but since we’re planning to build in a lot of adjustability for different drivers it won’t be much of an issue. For now we’re sitting on a block to approximate height and driving position while Kertz takes measurements. It also helps if you make engine sounds. Kertz is a high-level race car fabricator, so strength and safety are always paramount in his plans for any rollcage. Nevertheless, he’s also one of the few such metal benders who also believes in creating a ’cage that feels custom tailored to a car rather than just assembled for strength. What’s the difference? Organic flow. Any number of ’cage configurations can be strong, but there are certain guidelines that must be followed to create one that feels like it was intended just for a particular car. The good news is that it’s all stuff that can be learned and applied to any ’cage, and Kertz has agreed to show us some of his tips and tricks for installing a totally sano structure. While this particular ’cage for Max Effort is more than most rodders will need or perhaps want, the same concepts will apply to pretty much any endeavor. If you’re looking for a trustworthy place to build a beautiful and functional ’cage for your ride, give Kertz a call. Trust us; it would be worth the effort to get your car to his shop at Infineon Raceway.  Here’s why that much effort...  Here’s why that much effort was necessary; when designing a ’cage for ideal rigidity, Trojanek employs stress analysis to fine-tune the placement of the bars to maximize strength while minimizing the amount of steel needed. The value of the ’cage is 12,000 ft-lb per degree—meaning it takes 12,000 ft-lb of force to twist it 1 degree.  Kertz doesn’t use the conduit...  Kertz doesn’t use the conduit skeleton method; he prefers to simply take careful measurements for the main hoop and sketch out the plan. Always try to picture the ’cage as a complete unit, then work backward and figure out how to break it down into manageable pieces.  Those measurements are then...  Those measurements are then transferred to a 1:1 scale sketch on a sheet of cardboard for accuracy. The main hoop is by far the most time-consuming part of the rollcage and also the most critical to bend correctly since every other bar ties into it. Get it wrong and everything else will be off as well.  This upper section of the...  This upper section of the main hoop is especially challenging since it requires two bends to get it to conform to the body and hug tightly to the panels. Kertz uses a short length of pipe here to help visualize what he wants to do, then takes measurements from the body and quarter window and notes the angles required.  Once you’re satisfied with...  Once you’re satisfied with the numbers, it’s time to cut steel. Our main bars are 1¾ x .095 DOM and we also have some 1½ x .065 DOM to save weight on less critical bars designed for rigidity. Always buy more tube than you think you’ll need to account for errors or additions. We recommend Tube Service as a good source.  From there it’s back to the...  From there it’s back to the cardboard sketch to check accuracy of the bend and double-check the angle before trial-fitment.  A barrel grinder makes quick...  A barrel grinder makes quick work of burrs and is also ideal for fine-tuning cuts that are just a little bit off. This one needed just a touch more depth.  Using a JD Squared Model 3...  Using a JD Squared Model 3 tubing bender that he fitted with a hydraulic ram for easy one-man bending, Kertz shaped the main hoop using the angles he measured inside the Cougar. Actually he has to bend just a touch more than is needed to account for slight bounce-back in the tube. Once he releases tension and the tube is in its final shape he rechecks the angle and then measures the ram to ease repeatability on the other side of the hoop.  Fits like a glove; careful...  Fits like a glove; careful measurements paid off and the main hoop fit perfectly on the first try. Note the slight rearward angle the hoop is mounted at; Kertz looks for natural lines in the car to align the bars with. The rearward angle of the main hoop matches the rake of the quarter window glass. The blue tape shows our next bars.  After a few minor adjustments,...  After a few minor adjustments, the result was a near perfect coupling.  Don’t make any permanent welds...  Don’t make any permanent welds until the entire ’cage is finished; Kertz lays light tacks just sufficient to hold the bars in place while he measures.  Here’s another good reason...  Here’s another good reason for only tacking tubes to the car; Kertz recommends building as much of the ’cage outside the car as possible for ease of construction. The entire main hoop will be finished before he slides it back into Max Effort.  The remotely operated ram...  The remotely operated ram also allows Kertz to step back and eyeball the progress. Just out of frame, we’re holding the other side of the hoop.  One of the things separating...  One of the things separating pros from amateurs when it comes to ’cages is precise fitment. To fill in the hoop with the harness crossbars, Kertz uses a JD Squared TN-100 tubing notcher fitted with a hole saw on his drill press. These things can make both simple and complex notches when used correctly; like the one necessary for the crossbar.  These bars won’t need further...  These bars won’t need further adjusting, so Kertz TIG welded them completely once he was satisfied with the fitment, since making these welds on a table is much easier than making them in the car.  Solid welds with appropriate...  Solid welds with appropriate penetration might be the most important part of the whole process. Though the perfect stack o’ dimes is indicative of a welder with good rhythm, it’s the heat signature and coloration around the weld that we’re really concerned about, since it tells the quality of the weld. This one is perfect.  It may seem like a lot of...  It may seem like a lot of work, but here’s the result of that preplanning: two flawlessly formed A-pillar tubes that flow perfectly with the lines of both the roofline and the A-pillars.  Want to know how Kertz lays...  Want to know how Kertz lays TIG beads that look like art? We’ll explain all those hieroglyphs on the front of this Lincoln TIG machine in an upcoming issue.  Correctly formed A-pillar...  Correctly formed A-pillar bars are as difficult as the main hoop, but in a slightly different way; A-pillar bars require bends that are correctly clocked to flow along the roofline then down the A-pillar itself. For mock-up, Kertz tacks a smaller-diameter tube into a piece of the 1¾ x .095 DOM that is roughly the shape he needs for the down tube, and then slides another section of 1¾ x .095 DOM over the inner tube.  This is the junction of the...  This is the junction of the main hoop, A-pillar bar, and a roof crossbar made from lighter 1½ x .065 DOM. The theory here is to triangulate most of the bars above the driver’s head to create the strongest structure possible at that point. We’ll be replacing the headliner, but to avoid melting it as he tacked, Kertz placed a sheet of aluminum between it and the bars.  Here’s the finished main hoop...  Here’s the finished main hoop in its final location, but still only tacked into position to allow some flex for maneuvering our next challenge: the A-pillar bars.  Inside the car, the separate...  Inside the car, the separate pieces can rotate independently, allowing Kertz to easily determine the clocking needed for the best fit and flow. Ideally we want this bar tucked tightly to the roof and barely visible from outside the car. He adjusted this tube several times in the bender, then set the clock and tacked the two pieces together.  A good eye is useful, but...  A good eye is useful, but a digital level is always right. Kertz double-checked the A-pillar bars on each side to ensure they were level relative to one another.  The integrity of the ’cage...  The integrity of the ’cage is paramount in this project, so Kertz removes the outer edges of the dash to allow the A-pillar bar to slide into place unimpaired. We’ll rebuild the dash around the tube afterward.  With his mock-up tube, measurements,...  With his mock-up tube, measurements, and notes as reference, Kertz grabbed a fresh length of tube and created a new A-pillar tube. One of the cardinal rules of ’cage building is that every length needs to be a single piece of tube—no butt welds or splices allowed.  Here’s a challenge we’ve always...  Here’s a challenge we’ve always wondered about: How do you weld all the way around the joint, especially when it’s tucked so tightly to the roof? There’s no TIG that’s going to fit in there, no matter how good a welder you are, and it’s never acceptable to leave a joint like this.  The answer is you simply create...  The answer is you simply create more room! Kertz removed the mounting plates, then used a holesaw to cut a hole in the floorpan just large enough for the ’cage to slide through.  Relatively speaking, these...  Relatively speaking, these bars are a piece of cake; there are no bends involved, just intersections. For aesthetics, the split bar should maintain a perfect consistent centerline on either side of the intersection. Start with a notch cut just a bit too small, and sneak up on the fitment by using the barrel grinder to open it up. A long straight-edge is ideal for verifying that the inclination of the two sides matches.  The last thing we need to...  The last thing we need to address is the engine bay. Without the factory shock towers we’ve lost most of the unibody’s upper strength, so loads would be mostly carried by the framerails.  Just like that, we’ve got...  Just like that, we’ve got an extra 6 inches of headroom, plenty for Kertz to lay a strong TIG bead all the way around the joint.  Here’s the completed door...  Here’s the completed door bars on the driver side. The gussets don’t add much strength, but they add a ton of style! The killer ovals were made by a Rad Rides oval punch set. They’re currently pondering a new production run; email or call Troy and the boys now, and tell ’em they gotta make more of these things!  To solve that issue and create...  To solve that issue and create a far more rigid frontend, Kertz ran a bar through the firewall that ties the A-pillar bar and dash into the front suspension’s mini tower and then the framerail itself. The two shorter bars make a geometry that Trojanek found to be beneficial to overall rigidity in his testing.  Our door bars will be a basic...  Our door bars will be a basic X-style for maximum strength and safety, as well as meeting standards for many race classes. We still want functioning standard latches and regulators, however, so some minor adjustments were necessary. Kertz used a tape measure to determine where the intersection of the X should occur.  To strengthen the cowl section...  To strengthen the cowl section of the unibody, Kertz ran a straight bar behind the dash tying the two lower bends of the A-pillar tubes together. There’s still plenty of room to reassemble the dash to stock, but it’s a good thing we had no plans of running A/C or stock vents.  Here’s the view from inside...  Here’s the view from inside the engine bay. We weren’t building to any specific road race class or NHRA specs since Max is mostly an open track car, but we will technically be legal for the American V8 Super Car Series.  Those measurements were then...  Those measurements were then transferred into tape to double-check clearance and placement.  To wrap up the triangulation...  To wrap up the triangulation of the cab section, Kertz ran a down bar from the back of the main hoop, again tying into the upper bend for triangulation. The diagonal follows the same theory and ties into the bottom of the passenger-side down bar at the mounting plate. We got lucky; the optimum angle for the bars just barely missed the package tray. Obviously, we won’t be running a rear seat.
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