Royal Scamp
Unsprung Hero- A-Body Coil-Over Coversion
This is the first installment of the “Royal Scamp” street\strip A-body build. The main objective for the Scamp is going fast, after all this is supposed to be a 10-second street machine. One of the key elements to building a street machine is reducing weight while adding adjustability and reliability. Let’s face it, torsion bars just are not the most reliable suspension design. They are heavy, awkward and prone to breakage, especially when subjected to the stresses of a high-powered launch (and the subsequent return to earth) down the drag strip.
A torsion bar functions on a similar principle as the coil spring, but instead of rolled into a coil, the spring bar is left straight and mounted laterally with the subframe. As the lower control arm moves up and down, the torsion bar twists in the middle (the ends are secured by large socket-like fittings in the frame and control arm), resisting the movement. The best thing about a torsion bar is that they are easy to change out and easy to adjust. As the vehicle ages, the bar eventually stretches and bends, which requires periodic adjustment for proper ride height. This also means that it is easy to lower a torsion bar car by simply loosening the adjuster.
The biggest problem with torsion bars is reliability and spring rate. Coil spring breakage is fairly rare, but finding busted torsion bars is fairly common. Adding the additional weight of a big-block to the car will only compound things. The Scamp will have some serious torque on tap, and the thought of breaking a torsion bar is not pretty. Then you have the problem with torsion bars and the lack of variable spring rates. We could swap in some big-block torsion bars for load capacity, but then the front end won’t lift as much during the launch, which will reduce the weight transfer. Slant-6 torsion bars release faster for a better launch, but the car will be harder to control on the street. The only real solution is a coil-over conversion.
This is one of those tricky swaps, where you can either spend $5K on a tubular K-member for a simple bolt-on, or you can do it low-buck and get many of the same benefits. It may not look as pretty, but it only costs a fraction of the price. We decided to keep the cash in our pockets and go for the home-brew method. It is more fun than just bolting on a kit and it leaves the budget intact for other projects.
There are several key elements to this swap so pay attention. The parts you need to order are critical. The part numbers listed here are QA1 components that we sourced from Summit Racing (except for Reilly Motorsports, we ordered those direct). They had everything in stock, even though it was not all listed in the catalog. We spent some time on the phone with Bob Reilly at Reilly Motorsports researching the components. They manufacture the AlterKtion tubular K-member as well as the tubular A-arms and strut rods we used in this swap.
You need the following components to make this work-
QA1 adjustable coil-over shocks- single or double adjustable, we opted for the doubles (576 potential settings), but this depends on your intended purpose and tuning needs. The main point is to get the right shocks. We used part #DDR-5855P, which are QA1 Proma Star 17” ext, 11.625 collapsed double eyelet shocks.
SS100SDM eyelet to stud adapter- This is the key component. Whether you use QA1 shocks or something else, you have to have an adapter. The adapter converts the upper eyelet mount to a stud mount like the factory shock. Yes, the rubber will wear out faster and you will have to change it, but for a weekend car like this, that could take 3-5 years. For a daily driver, you will be changing it once every 1-2 years.
Coil-Over Spring- We used the QA1 10-450 spring, which has rate of 450 lbs./in., and is 10-inches long and 2.5-inches in diameter. DO NOT use the 12-inch spring, it is too long. The 2.5-inch diameter barely fits, so nothing larger will work there either.
Tubular Upper A-Arms- The stock A-arms won’t clear the coil spring, they need to be swapped out. We used a set of Reilly motorsports tubular arms, which not only clear the coil-overs, but also add a fair amount of adjustability to the castor and camber, all of which mean greater tuneability at the track.
Adjustable Strut-Rods- These components are not required for the coil-over swap, but they are a good idea. Our strut rods came from Reilly Motorsports and allow you to the tune the movement of the lower control arm. Using a rod-end and solid bushings, the play in the factory version is removed, leaving you with only the movement you want. Beside, our stockers looked more like an ocean wave than a straight bar.
The installation was simple, but as we are working on Mopars that do not have a great reputation for tight tolerances, trimming some stock components was necessary. We used an ESAB Handi-Plasma to make quick work of the offending material, but a sawzall or oxy-acetylene torch works too. If this is your driver, you need to plan ahead as getting the entire job done will take two days, including adjustments. As with any front suspension work, the car needs an alignment afterwards.
*Tech tip
Torque specs
Don’t forget to torque all the suspension components. If you do not have a service manual handy, here are the basics-
Pivot shaft (lower control arm) 145 lbs
Strut to lower control arm 105 lbs
Cam Bolt (upper control arm) 65 lbs
Ball joint stud upper 55 lbs
Ball joint stud lower 85 lbs
steering knuckle bolts (upper) 55 lbs
steering knuckle bolts (lower) 100 lbs
The torsion bar design is not horrible; it works, just not as well for a dual-purpose vehicle like a street\strip machine. While we could make concessions and use it, the best solution was to change it out.
The adjuster needs to be released to remove the tension on the bar. Once the adjuster is completely loose, the tension on the bar is gone.
A spring clip on the frame side retains the bar, remove it before attempting to drive the bar out.
We used this handy torsion bar clamp to drive the bar out of the sockets. We sourced it from John’s Cuda Shop via his Ebay store. This works much better than destroying a pair of vice-grips.
The bolts on the suspension have been in place for 30+ years, they tend to resist removal. We sprayed each fastener with JB80, the best rust-buster on the planet.
The brake caliper and rotor were removed to gain access to the lower ball joint bolts. While replacing the lower ball joints is not required, they boots were split and for the minimal price, it is just a good idea.
The upper ball joint was separated from the spindle using a pickle fork. We tried our ball joint separator, but it would not fit in the tight space.
The upper control arm is retained by these offset washer bolts. The offset washer rides between two tabs on either side of the bolt and as it rotates, the arm is moved forward and backward in the slot. This is part of the alignment adjustment and should be retained.
The lower ball joint bolts to the spindle and the lower control arm as well as the steering arm. It is not rebuildable.
Once all of the front end components were out, we hired BS Blasting to remove all the old paint, undercoating and grime from the underside of the Scamp. For this task, they used recycled crushed glass as the blast media. Once we are ready, they will come back out and soda blast the body. Nice and clean.
The strut rods were cut with the plasma torch. You won’t be reusing them, and they were bent anyway.
We fogged the inner fenders with some Extreme Chassis Black we got from Eastwood. This stuff resists chips and is very durable. It looks good too.
We sprayed the Reilly Motorsports tubular arms and strut rods with the Extreme Chassis Black as well, since they ship raw steel. The rod ends were threaded in two threads out from the bottom, then the jam nuts were tightened. This is the suggested spec for 99% of all A-bodies.
The QA1 shocks come in separate pieces. This is an exploded view of the assembly. It is very simple. The spring mounts (and the locking nut) thread onto the body, the spring slides over the shock body, then the upper spring mount slides over the shock arm and the shock is compressed till it all fits together. The ride height is adjustable too. The instructions suggest anti-seize on the threads, but this is only needs if you plan to make frequent height adjustments. On a road car, this actually creates problems as the anti-seize will collect rocks and grit, making it harder to adjust. You can also opt for the Torrington bearings, which ride between the lower spring mount and the spring to make adjusting the height easier.
This is what makes this swap possible. The eyelet to the left was removed from the shock and the stud mount replaced it.
We pre-assembled the spindles for a dry test fit. In hindsight, we should have done this BEFORE we painted.
We placed the spring in position and discovered that the spring won’t clear the lower bumpstop bracket. Whoops.
We cut the bumpstop off and still had some clearance issues with the pinch weld at the top of the subframe. We marked it and cut it away as well. Reilly Motorsports assured us this does not affect the strength of the subframe, though we did spot weld it for peace of mind. We also clearanced the tab for the upper control arm as well (upper right hand corner). A few minutes grinding it clean and we re-sprayed it.
The upper A-arm uses rod ends, which require these spacers. There are 4 short and 4 long spacers (use 4 on each side). For most cars, the long spacer goes in front of the each rod end. We had to tab them into place using a hammer. Depending on your castor needs, these can be moved around.
The shock was bolted into the upper mount and then the lower. Don’t forget the steel bushing inserts.
Then the rest of the spindle assembly was completed. Don’t torque it yet.
The strut rods were assembled by measuring and marking the rod end at 3\4-inch. This is the starting point and this equates the stock rod length. Thread the bar to this mark.
The rod end mounting bolt was tightened and then the assembly went in the front mount. Don’t torque it yet.
Then the control arm end bolted up. The adjustment for the rod end requires the car be capable of loading the suspension, which we can’t do yet. We will get this knocked out as soon as the rear suspension is in.
All done for now. With adjustability, reliability and some weight savings (about 30 pounds total), the front suspension is ready for hard launches down the track. The shock are capable of being 90\10 to 10\90, so we can unload the front suspension and get the car hooked off the line.
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