12:05 Garage- ’70 Duster build

racerjoe said
I did a thing, which may surprise a bunch of people.... My car is now setup with an HDK coil over K member.... you know, for science. Can it handle better than the stock K?

The stock K setup owes me nothing. It's done great and I likely didn't reach it's limit because I'm not a pro driver. Thanks to the help from people on this forum, I was able to source all the parts that can make a t-bar suspension work in ways the auto designers of the 60s could have never imagined.

I've read so many negative comments about coil over setups, but I can't create an opinion without experiencing it myself. So lets start with the 3 common items why people say coil over setups aren't good.

1.) The shock towers aren't meant to hold the weight of the car: Denny has addressed this with his hoops that connect the shock tower to the chassis. It's very robust. That $hit ain't going nowhere!
2.) Coil over setups don't have enough travel: Since Denny's kit uses the shock tower (with his special bracket for the coil over) the coil over I'm using is 16-7/8" at full extension, which is bump stop limited to 16.5". The stock shock is 15.5". The suspension travel distance between the stock setup and Denny's is very similar. I feel like the stock suspension can droop further and the HDK compresses further. I failed to measure the stock K before I took it apart. Other brand coil over setups do use a shorter shock so this statement won't apply to the others.
3.) Aftermarket Ks don't have enough camber gain: This statement is true. THe HDK does have less camber gain. However, is this even important? I don't know enough to see the benefits and hope someone can educate me. Here's the way I see it. Camber gain is the increase of camber as the suspension compresses. In a hard stop situation when the car nose dives, wouldn't I want to keep the tire as flat as possible? Camber gain would have a negative affect on this. I realize it may help in a turn, but that's where caster comes in. Why not set an aggressive caster so the tire tilts in on the turn when the body rolls. Again, I'm not an expert on this particular topic, so I don't know if it is good or bad.

The spindle/hub assembly you see below is a drop in for the Mustang 2, but uses a C5/C6 corvette hub and brake configuration. I didn't have enough GM parts on my car, so I chose this over the standard M2 spindle. My wheels wouldn't work with the standard C5 brakes since the rotor and caliper are extremely close to the face of the hub. Converting to the radial mount Wilwood allows for lots of adjustment. I was able to shim the bracket very easily to accommodate the brake rotors I was previously using.

I'll elaborate more on this soon. I drove the car a few miles to check my home alignment and also let the springs settle so I can adjust ride height if needed. So far brakes are good, steering is a rack, so that's an obvious difference. More to come....

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:eek:

But seriously, I’m interested in hearing your opinion on the swap. Not very many people have done as much as you did to make the most out of the torsion bar suspension before doing the swap to coil overs. And that’s always been my gripe, people do the conversion thinking it’s necessary to handle well, which isn’t true.

All things being equal, I still think the chassis being designed to carry the suspension loads radially through the K and torsion bar crossmember VS vertically on the forward frame rails is the biggest issue, and one that is not addressed by Denny’s hoop reinforcement. The Mopar chassis has flex between the frame rails and cowl (“cowl shake”) and running coil overs up front increases the vertical load on the rails, making that problem worse. IMO that calls for additional bracing between the cowl and rails. Stiffening the shock mounts to carry the coil overs is necessary too for the HDK, but additional reinforcement is needed in the form of “J” bars or something similar to USCT’s shock tower to cowl reinforcement. That’s true for all of the conversions, regardless of how the coil overs are mounted.

The HDK retains the factory amount of suspension travel, but some of the competing coil over conversions do not, so while travel may not be an issue with the HDK in particular it is still a valid issue with the others.

Another issue, and I don’t know if it’s relevant for the HDK to be honest, is turning radius. It is an issue on some of the other conversions. The rack used doesn’t allow the same amount of turning angle. Not a big deal on a cruiser, but for AutoX it can be an issue on tight courses.

Camber gain is important, and the torsion bar system is a good one for that. It isn’t an extreme amount by any means either, so again IMO less would not be advantageous. But most of the geometry changes between the torsion bar system and the coil over conversions can be filed under pros/cons, they both have things they’re better at. And some of them are made better/worse by other factors in the set up that can make them more specific to a particular car. Most are pretty minor, so, most drivers aren’t going to notice much.

The weight savings of the entire system depends very much on options. It’s not as much as most people think, I’ve documented it several times. And more than just weight, it’s worth noting that the layout of the coil over system will tend to raise the CG, especially vs a manual steering stock set up. The coil overs are the heavy part, and they’re mounted high.