DOES THE HDK SUSPENSION K-MEMBER HANDLE BETTER THAN A T-BAR SUSPENSION?
I was just reading something on the book of faces regarding coil over swaps and the negative affects of additional weight on the front frame rails. I know everyone has heard it before. "The front of these cars weren't meant to handle all the weight. The torsion bar cross member is under the car to hold the weight." This is actually something I've thought about and at the time of my swap I really wished I had a set of scales so I could do before an after corner weights. But I don't have scales and life went on. Prior to the light bulb just going off as I read on FB, my stance was my car has thousands of street miles and hundreds of autocross runs on the HDK and not a single panel gap has changed and my car hasn't folded in half like all the armchair quarterbacks said it would. However, I have new information now as it relates to this. When I was at the CAM Challenge in St. Louis,
@JBrian was there with his Gen 3 hemi swapped 71 Duster. He's running pretty much the same exact T-Bar setup I had prior to the swap. Part of the requirements at these national events is to weigh the cars to make sure they fit the rules. Guess what? Our front corners were damn near the same. In fact, our front right was exactly the same weight. So if the beloved torsion bar system transferred weight to the center of the car, how is it that our front weight was damn near identical? Let's get a little more finite. His car is 200lbs more than me (drivers in the cars) and all that weight showed up on the back of his car. However, he's got some stereo equipment and some other things that will generally add up to more weight. (I am still wondering where that 200lbs is though.) So I'll go ahead and give these people the benefit of the doubt and say the torsion bars are moving that weight to the rear tires. That equals 5% of the total weight of the car being moved to the back because of a t-bar. Perhaps, but I'm not convinced. 200lbs isn't going to fold the car in half because I don't have J bars.
That’s actually not an argument I’ve heard before. I know after doing the math on the HDK components vs stock and even stock with aftermarket stuff the coil over conversions were typically a little bit lighter as far as actual weight goes. It wasn’t a lot comparing like to like, especially with a manual set up on both it was only like 30 lbs or so.
Now what
@bjkadron was saying about where the suspension loads are carried in the chassis is a different story. But that’s not something you’d see on corner weights. The torsion bar suspension transmits the torsion bar loads radially into the K frame and torsion bar crossmember, where obviously the coil overs transmit their load vertically into the frame rails. The original chassis isn’t very stiff there- hood shake is an issue even on stock cars. So the concern would be more vertical flex between the frame rails and the firewall/rest of the chassis.
That said, if you’re doing any kind of racing the chassis gets reinforced anyway. With a coil over conversion adding j-bars or further triangulating the rails and firewall would help carry those loads.
The other thing I’ve heard would be the center of gravity, because of how the coil overs are arranged vertically vs the torsion bars which are down low. But that’s not the easiest thing to actually measure, not the height anyway with that kind of accuracy. And with the COG I wouldn’t suspect it would change much front to rear, as your corner weights show. The more interesting part would be if the height changed, if the coil overs raised the COG any compared to the tb’s.
But even with that, because the coil over system tends to be a bit lighter, I wouldn’t expect it to be a really significant change. The weight of the engine and transmission dominate that calculation. The hemi swap probably changes it more than any of the suspension changes.
Honestly, I think BOTH systems come down to tuning and set up. You can get good geometry with either system, if you tune the set up to your needs. My beef has always been the folks that claimed the coil over set up was somehow inherently better, which it isn’t. Both have pros and cons, but you don’t NEED coil overs to handle well. But that doesn’t mean they don’t handle well! It just means you can tune either suspension to handle well, and honestly getting either system to the same point is probably a similar amount of work.