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Prepping our Roadster Shop Chassis for our 1971 Wagon Project

Time to start adding performance parts to our Roadster Shop Fast Track chassis

Steven Rupp May 19, 2019
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Our two-ton wagon project is chugging along and with the new Roadster Shop Fast Track chassis assembled it was time to start filling it with performance parts. Yeah, we know it's a four-door station wagon, but we have big plans for our '71 Chevelle, including open road racing, standing mile, and even trying to embarrass some cars at the autocross. We've embraced the fact that our Chevelle will tip the scales at an estimated 4,500 pounds, so the only place we're trying to save weight is in the unsprung areas.

The beauty of working on a full chassis car is that when the fame is away from the car it's incredibly easy to install parts. Given this, we want to have the complete driveline installed along with most of the hard lines before sending the chassis to its new home under the wagon.

Of course, the main actor in our play is the ProCharged LS3 stroker built by Shafiroff Racing in New York. It pumped out 987 hp without breaking a sweat, and while we're going to dial it down for pump gas, the potential for 1,000 hp is only a pulley and some octane away. Backing up the LS is a Magnum six-speed kit from American Powertrain. Nothing beats rowing gears and the Magnum is the best choice out there. Working our way back, the next item to figure out was the driveshaft, which for the wagon is longer than average at 55.5 inches. After talking with GForce Performance Engineering we opted to go carbon-fiber. Why? Well, the length we need, combined with the power output of our engine, would have required a 4-inch aluminum driveshaft, but that was too large for the shaft loop in our chassis. By going with carbon we could run a smaller diameter and still have the strength and, more importantly, make our critical speed numbers. There's a lot of science behind driveshafts, so expect a more detailed story in the future. Sending the power to our wheels is left to the Strange Engineering rearend. We chose 3.70 gears, but there's a chance that, after driving the car, we may opt for 3.50 gears. We won't know what's best until we hit a track or two. The case is their heavy-duty aluminum piece, which knocked 10 pounds from our unsprung weight. For a posi we're running the track-proven Detroit Truetrac from Eaton. It's a lot of puzzle pieces that all have to fit together, but, more importantly, work together.

Once the chassis is appropriately kitted out we will slide it under our wagon and see what needs to be cut, clearanced, or otherwise modified to meld the two together. We also need to add a fuel tank since the stock one, located in the driver-side quarter-panel, isn't going to cut it. Nobody makes a tank so there will be some creative cutting going on to get a 22-gallon Fuel Safe unit mounted properly. But those are tasks for another day. For now let's start getting our chassis ready to roll under our wagon.

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With our frame powdercoated and fully assembled it was time to start installing all the components so we could roll it under our '71 Chevelle wagon body. First up was confirming that the low-profile Holley oil pan (PN 302-2BK) on our Shafiroff LS engine would clear the rack. We did this using a plastic mock-up LS we have, which is a ton easier than using the real deal, along with the engine plates and Energy Suspension mounts that came with our Fast Track chassis.

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First up was mounting our American Powertrain TREMEC Magnum six-speed to our stroker LS mill. To mate the two we're using a Quick Time bellhousing (PN RM-8020). By checking out how much of the input shaft protruded past the face of the bell we can confirm our pilot bearing and make sure everything is going to play nice together. When doing this math be sure to factor in the steel scattershield that sandwiches between the bell and the block.

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With the Quick Time shield in place, we secured the Centerforce DYAD lightened billet steel flywheel using the included ARP hardware. Using a prybar between the teeth of the flywheel and the trans dowel pin kept the flywheel from turning while we torqued the bolts to spec.

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The DYAD DS is a twin-disc clutch that can handle up to 1,400 lb-ft and there's a specific order to which everything goes together. It's also balanced so we made sure to keep all of the red marks lined up. To keep the discs centered you can use a splined plastic tool, but we had an old Magnum input shaft that worked even better.

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Next up was the main unit that features their centrifugal weight system for better clamp load along with their ball bearing-actuated pressure plate for lighter pedal effort. It's almost too pretty to hide away in a bellhousing.

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Lastly, we installed the Quick Time bellhousing. The spun steel construction offers a ton of safety without a lot of extra weight.

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For hydraulics we like to keep it simple. Typically, we use a GM clutch release bearing, but it has a plastic inner collar that can be problematic under hard use. Centerforce's solution is an OE-style bearing (PN 601810) that has an internal steel collar and came equipped with a steel-braided hose (with protective heat shield) that will make installing and bleeding the bearing much easier. This was bolted to the front of our Magnum transmission.

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The Magnum six-speed from American Powertrain was then put in place and bolted to the bellhousing and then to the Roadster Shop chassis by way of an Energy Suspension polyurethane transmission mount. The trans came equipped with American Powertrain's White Lightning shifter, which offers independent adjustable spring bias for better centering and faster shifts.

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With the Shafiroff LS3 stroker and Magnum trans installed, our driveline was off to a good start, but there were still a ton of boxes to check off before it was ready to slide under our wagon.

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The Baer rear floater, inside the Strange Engineering housing, came outfitted with 1/2-inch ARP wheel studs, but our front SKF "Corvette" wheel bearings are 12mm. To avoid the catastrophic problem of mixing up front and rear lug nuts at the track we came up with a solution. First up was hammering out the stock 12mm studs.

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ARP now offers 1/2-inch wheel studs that are specifically designed with the correct knurl to replace the 12mm studs found in modern bearing packs. They come in a standard (PN 100-7731) and longer length (PN 100-7730). We chose the longer version to match the studs in our Baer floater.

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Our wagon is destined for some hard driving, so having an oil cooler isn't really on the optional list. Adding one is easy thanks to Earl's new LS Side Mount Oil Cooler Adapter. It mounts to the side of the pan (retaining the stock oil filter location) and has a 180-degree thermostat built in along with two 1/8-inch pipe ports for pressure and temperature sensors.

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Back to the driveline, we prepped our Strange Engineering third member for installation. The wagon is heavy and with an engine capable of putting out 1,000 hp we wanted a stout unit. Inside the HD Pro case (PN N2300) are a set of Motive 3.70 gears (PN RS07890370) and a 31-spline Detroit Truetrac posi unit (PN N1979).

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The key component of their third member is this HD Pro aluminum case, which offers a 10-pound savings over an iron unit, along with larger oil channels for better lubrication. Chrome-moly studs are encapsulated by billet aluminum main caps for even more strength, and the unit was topped off with a high-strength pinion support and billet 1350 yoke.

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With the third member in place we were able to measure for a driveshaft and call the guys over at GForce Performance Engineering. Originally we were going to go with an aluminum shaft, but given the length of the driveshaft, two-plus ton weight of the wagon, and high power of the ProCharged engine we would have had to run a 4-inch diameter driveshaft to stay on the safe side. Our first problem was that the driveshaft safety loop in our frame was 4.25-inches wide, which wasn't enough room. The problem with a 3.5-inch shaft was one of critical speed, not necessarily strength. The best option became one of their high-tech carbon-fiber shafts. This allowed us to drop the diameter under 4 inches, yet clear all of the math hurdles in terms of strength and critical speed.

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We were a bit surprised that nobody made off-the-shelf long-tube headers to fit the Roadster Shop chassis. There were mids and Roadster Shop often stitched together pipes for their customer cars, but that was it. Given our power output, we really wanted long-tubes, so Ultimate Headers (who make headers for most all of the chassis companies out there) worked with Roadster Shop and came up with 1 7/8-inch long-tubes to clear the Fast Track chassis. The headers were beautiful with the cast flanges and thermal-coated tubes. Best of all, they fit perfectly and are now an on-the-shelf part number.

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While we were waiting for parts, Motor Trend Tech Center Manager Jason Scudellari got busy building stainless hardlines for the fuel system. Of course, some of this might change once we get the body in place, but at least we had a head start.

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Using a combination of 1/2-inch stainless tubing and -8 AN fittings from Earl's we will have plenty of fuel capacity to feed our blown LS.

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On the engine side we used one of Earl's OE EFI Quick Connect (-8 to 3/8) fittings (PN AT992086ERL), which had an integrated 1/8-inch NPT port for a small mechanical fuel pressure gauge.

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Back on the chassis side we were able to install the front Baer brakes that would match the rears that came with our floater kit. The massive XTR calipers are track bred and, along with the slotted Extreme+ 14-inch rotors, we should have no problem slowing down our massive wagon.

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The extra-large Baer brakes still fit inside our 18-inch Forgeline GF3 wheels, but while we were able to make the rearend perfect for our existing wheel offsets, the modern sealed bearing design of the front suspension meant we needed new front wheels to fit inside our wagon's fenders. It might be time for some fresh Falken RT615K+ tires as well.

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It's been a long path to get to this point, but all the major players are in place on our chassis so it was time to roll it under the wagon and see where everything fell.

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Of course, first up was removing our highly modified factory chassis. And since we're not ones to waste, we found a bone stock '72 wagon for all of our old parts to move to. Hey, it's the coolest form of recycling.

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With the firewall painted black we could get ready to put the chocolate with the peanut butter. Now, with Roadster Shop's SPEC chassis we know it's mostly a bolt together deal, but the higher-performance Fast Track chassis requires some tunnel fabrication and, of course, we need to ditch the gas tank in the driver-side quarter-panel and come up with a better solution. But that's another story for another day.

 

Photography by Steven Rupp

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