DOES THE HDK SUSPENSION K-MEMBER HANDLE BETTER THAN A T-BAR SUSPENSION?

[JBrian]

I have been following this thread carefully and to say it has been extremely informative would be a huge understatement!

Torsion bar suspension vs CO /rack and pinion.

Here's what I have observed.

Both systems can perform extremely well but, for the vast majority of us, to make the torsion bar system work requires replacing or modifying most of the TB system anyway.

It ends up being a long way from stock to get the performance these guys are getting.

Its useless to use TB and factory K-Frame without removing it and rewelding all the seams and installing the required gussets. Boxing LCA's , replacing Upper control arms with Tubular , experimenting with T-Bars , Installing a better sway bar, upgrading shocks, upgrading steering box to Firm Feel specs or going with a Borgeson replacement.

In a nutshell, the members on here who are running TB based suspension have addressed all the shortcomings and ended up with exceptional handling cars.

The aftermarket has also responded and companies like HDK and RMS have executed fantastic handling and durable systems as well but using a well designed and executed bolt in platform that is much easier to implement for the average enthusiast.

I am not in the Autocross expert category as the posters on here but I do have track time on road courses. (Just came back from 4 days at Barbour Motorsports in Alabama) so I get how a well engineered suspension system is needed if you want to be competitive.

As for my experience?

9000 trouble free miles on my Alter-k-ation RMS suspension, normal tire wear, no breakage (Drag racing and "spirited" winding back road excursions ) .

I have no doubt the HDK system would perform the same.

I'm going to agree with your assessment. I would guess if Tim and I ran the same wheel/tire combination, with Tim driving both cars back to back, it would be splitting hairs to see which car is quicker. And if Tim's Duster is quicker, how much? Both setups can work well. And one more issue. The Borgeson box, which is great on the street is way to slow on autocross slalom course sections and real tight slower speed turns. It's livable for most of the rest of autocross courses.

HDK: Is it lighter? It defiantly has better header clearance and maybe oil filter clearance on a GEN III Hemi? How about tire clearance? I'm not sure how tight the 265/35-18x9.5 30mm offset would be on my car. I'm sure it's going to rub the inside frame rail on my hub, but how about the outside fender?

Tim would know more than I. Who wants to sponsor an autocross day to get answers?

 

[72bluNblu]

I'm going to agree with your assessment. I would guess if Tim and I ran the same wheel/tire combination, with Tim driving both cars back to back, it would be splitting hairs to see which car is quicker. And if Tim's Duster is quicker, how much? Both setups can work well. And one more issue. The Borgeson box, which is great on the street is way to slow on autocross slalom course sections and real tight slower speed turns. It's livable for most of the rest of autocross courses.

HDK: Is it lighter? It defiantly has better header clearance and maybe oil filter clearance on a GEN III Hemi? How about tire clearance? I'm not sure how tight the 265/35-18x9.5 30mm offset would be on my car. I'm sure it's going to rub the inside frame rail on my hub, but how about the outside fender?

Tim would know more than I. Who wants to sponsor an autocross day to get answers?

The Borgeson is 14:1, the racks are 12:1? I mean that difference is like a 1/2 turn on the steering wheel lock to lock. And that assumes you're actually getting the same steering angle from both, I don't know about the HDK but IIRC the RMS doesn't have as much steering angle.

"like to like" the HDK is about 30lbs lighter. So that's manual steering to manual rack, or power rack to Borgeson. It's dramatically lighter than with a factory mopar power steering set up, but I don't think anyone that was trying to be competitive would run one of those.

Tire clearance isn't improved for 18" wheels, the limits for those are the frame rails, fenders, and possibly the UCA's depending on the style being run. But given that the HDK can run the same tubular UCA's as a torsion bar car the like to like comparison for 18" wheels would be the same. The offset on the wheels might be different depending on the hub to hub width on the HDK, but the room for wheels on the car is the same. I believe the HDK has better wheel to suspension clearance for wheels smaller than 18" because the torsion bar set up runs into outer tie rod clearance issues. But I think most folks doing competitive autoX stuff with these cars are on 18's anyway for tire selection.

I'm running 275/35/18's on my Duster, they're +35 but the DoctorDiff 13" brakes kick my track width out 5mm a side. After pushing and rolling the fenders I have some room to the outside, my QA1 tubular LCA's don't have steering stops so the limit on that is the frame rail regardless.

 

[Super-Cuda]

The Borgeson is 14:1, the racks are 12:1? I mean that difference is like a 1/2 turn on the steering wheel lock to lock. And that assumes you're actually getting the same steering angle from both, I don't know about the HDK but IIRC the RMS doesn't have as much steering angle.

"like to like" the HDK is about 30lbs lighter. So that's manual steering to manual rack, or power rack to Borgeson. It's dramatically lighter than with a factory mopar power steering set up, but I don't think anyone that was trying to be competitive would run one of those.

Tire clearance isn't improved for 18" wheels, the limits for those are the frame rails, fenders, and possibly the UCA's depending on the style being run. But given that the HDK can run the same tubular UCA's as a torsion bar car the like to like comparison for 18" wheels would be the same. The offset on the wheels might be different depending on the hub to hub width on the HDK, but the room for wheels on the car is the same. I believe the HDK has better wheel to suspension clearance for wheels smaller than 18" because the torsion bar set up runs into outer tie rod clearance issues. But I think most folks doing competitive autoX stuff with these cars are on 18's anyway for tire selection.

I'm running 275/35/18's on my Duster, they're +35 but the DoctorDiff 13" brakes kick my track width out 5mm a side. After pushing and rolling the fenders I have some room to the outside, my QA1 tubular LCA's don't have steering stops so the limit on that is the frame rail regardless.

To add to the information being discussed , here's the specs on the rack used by RMS.


https://www.flamingriver.com/pub/media/wysiwyg/pdfs/power_rack_and_pinion_specs.pdf



This from Borgeson's site.

Upgrade Your Mopar with Modern Quick Ratio Steering​

Transform your classic Mopar’s handling with Borgeson's advanced quick-ratio power steering conversion box, designed specifically for 1962-1982 Mopar models. Engineered with a responsive 14:1 steering ratio and just 3.5 turns lock-to-lock, this upgrade delivers precise control, enhanced responsiveness, and modern driving feel. Borgeson’s power steering box directly bolts to your original K-frame, conveniently utilizing the stock pitman arm for seamless installation. Benefit from increased exhaust clearance, effortless steering input, and a substantial 10-pound weight reduction compared to factory equipment. Available with comprehensive installation components—including pump kits, steering couplers, and adapter fittings—Borgeson's Mopar steering solutions ensure straightforward installation and lasting reliability. Discover improved comfort, agility, and performance—upgrade your Mopar’s steering today with Borgeson's precision-engineered power steering conversion.

 

[Dartsun]

Adding a borgeson box in my B Body was one of the best improvements I've done on my car. The old firm feel was decent but also over boosted.

 

[72bluNblu]

To add to the information being discussed , here's the specs on the rack used by RMS.


https://www.flamingriver.com/pub/media/wysiwyg/pdfs/power_rack_and_pinion_specs.pdf



This from Borgeson's site.

Upgrade Your Mopar with Modern Quick Ratio Steering​

Transform your classic Mopar’s handling with Borgeson's advanced quick-ratio power steering conversion box, designed specifically for 1962-1982 Mopar models. Engineered with a responsive 14:1 steering ratio and just 3.5 turns lock-to-lock, this upgrade delivers precise control, enhanced responsiveness, and modern driving feel. Borgeson’s power steering box directly bolts to your original K-frame, conveniently utilizing the stock pitman arm for seamless installation. Benefit from increased exhaust clearance, effortless steering input, and a substantial 10-pound weight reduction compared to factory equipment. Available with comprehensive installation components—including pump kits, steering couplers, and adapter fittings—Borgeson's Mopar steering solutions ensure straightforward installation and lasting reliability. Discover improved comfort, agility, and performance—upgrade your Mopar’s steering today with Borgeson's precision-engineered power steering conversion.

I'm a bit curious on the math on that. The factory boxes that were 16:1 are advertised at ~3.5 turns lock to lock. So, all things being equal, a 14:1 ratio should be more like 3 turns lock to lock.

As for the MII racks, I've seen them advertised at 2.7 turns lock to lock like the ones you posted, but also all the way up to 5 turns lock to lock for some of the manual MII racks (with 3.3 (15:1) and 4 also in there depending on manufacturer). So it would really depend on which rack was being used. 2.7 lock to lock would be roughly 12:1. Maybe 13:1?

The Hotchkis Challenger was using a factory power steering box with a 1.5:1 quickener, so that would have been at 12:1.

A quick, rough measurement on my car shows a total steering travel at ~6", so steering angle shouldn't be too dramatically affected with those racks if the whole travel can actually be used when it's on the car. Back when I had stock LCA's and steering stops my wheel and tire set up did just kiss the frame rail, so I may be short a smidge on that travel. But when I looked into steering stop height across a bunch of various lower ball joints I found it was all over the map, so that distance might vary quite a bit because the steering stop height on the lower ball joints was not a tightly tolerance item. I looked into it because another member with the same tire size but more backspace on his wheels than I have said they were hitting the steering stops with room to spare to the frame, where mine were basically hitting the frame and stops at the same time.

 

[DionR]

Feels like a manufacturer spec of 2.7 could still be more like 2 turns lock to lock if the turning radius is large in the actual application. I know my brother's Speed Freaks kit required limiting the steering to keep the tires off the frame, no idea what his turns lock to lock ended up at.

I guess my thought being, lower number of turns lock to lock might not really mean a faster steering if it just means you get to the limit sooner. And I don't think just asking how many turns is a useful comparison.

The other factor is steering arm length, among other things. A shorter arm at the spindle will make the wheel turn faster than a long one. And frankly, the stock A-Body arm is probably longer than a lot of the M2 based suspension arms. It's one of the things that push us into 18" wheels if we want wide tires, among other things.

Too bad there isn't a longer pitman and idler arm like the E-Bodies have an option for.

 

[72bluNblu]

Feels like a manufacturer spec of 2.7 could still be more like 2 turns lock to lock if the turning radius is large in the actual application. I know my brother's Speed Freaks kit required limiting the steering to keep the tires off the frame, no idea what his turns lock to lock ended up at.

I guess my thought being, lower number of turns lock to lock might not really mean a faster steering if it just means you get to the limit sooner. And I don't think just asking how many turns is a useful comparison.

The other factor is steering arm length, among other things. A shorter arm at the spindle will make the wheel turn faster than a long one. And frankly, the stock A-Body arm is probably longer than a lot of the M2 based suspension arms. It's one of the things that push us into 18" wheels if we want wide tires, among other things.

Too bad there isn't a longer pitman and idler arm like the E-Bodies have an option for.

Yeah the true ratio is tied to the actual steering geometry so that's probably why the advertised ratio numbers for the aftermarket boxes/racks don't quite line up with the lock to lock number of turns compared to factory. Although given that the total steering distance is similar I wouldn't think you'd need to limit it a ton if the track width was similar, and with the HDK I would imagine most folks have the hub to hub about as wide as it can be, so, pretty similar to the factory numbers.

You can get fast ratio pitman and idlers for A-bodies, they just don't clear the vast majority of the exhaust systems out there. I think the Schumacher Tri-Y's for 440 in an A-body are the only ones known to work.

Although now I think a 1.5:1 quickener and an EPAS system would take care of the ratio issue. Heck you could do a 2:1 quickener if the EPAS motor would keep up. But that would be like ~1.5 turns lock to lock, which would ridiculous on the street.

 

[HemiDenny]

Who wants to sponsor an autocross day to get answers?

What do you need?

 

[Mopar_Taxi_Guy]

Although now I think a 1.5:1 quickener and an EPAS system would take care of the ratio issue. Heck you could do a 2:1 quickener if the EPAS motor would keep up. But that would be like ~1.5 turns lock to lock, which would ridiculous on the street.

Hotchkis 76 Dart Build

 

[Super-Cuda]

Hotchkis 76 Dart Build

Awesome Racecar!!

Great to see a Mopar morphed into such a track warrier!