HDK coil over system - spring selection

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Buschi340

Buschi340

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for stock K-Member. Have it already and also the qa1 shock multiple adjustable.

My question is about selectiong the correct spring. I know I have too weight the car. The whole car or just the front?
From that Point i can follow the qa1 instructions and calculate the rate with weight and angle...

But - can I have a longer length than the 12" Shocks to give more travel in expanding for weight Transfer ( drag race some times ). regular spring just longer or high travel spring? Hope that doesn't effect streetability too much?

what about springs with multiple spring rates they offer? any good or not recomendable?

car is a 72dart with 6.1 HEMI

Coil-Over Springs | Street Performance, Drag Racing & Circle Track Racing Coil Springs | QA1 Suspension
 
Buschi340 said:
for stock K-Member. Have it already and also the qa1 shock multiple adjustable.

My question is about selectiong the correct spring. I know I have too weight the car. The whole car or just the front?
From that Point i can follow the qa1 instructions and calculate the rate with weight and angle...

But - can I have a longer length than the 12" Shocks to give more travel in expanding for weight Transfer ( drag race some times ). regular spring just longer or high travel spring? Hope that doesn't effect streetability too much?

what about springs with multiple spring rates they offer? any good or not recomendable?

car is a 72dart with 6.1 HEMI

Coil-Over Springs | Street Performance, Drag Racing & Circle Track Racing Coil Springs | QA1 Suspension
Click to expand...


I dont have kit you do but I do have coil overs. I've got a big block up front so I'm running 375 lbs front springs and 200s in the rear. To accurately figure out what you need, you'll need your entire vehicle weight and then the front and rear weights, you can do it though just with the entire vehicle weight if you know your weight bias front to rear. also, you'll need to know what your rear spring rate is, as this plays a vital part in weight transfer. There's a good tool online you can use free to help get you right.

Spring Rate Calculator « Ridetech – Tech


As far as increasing travel with a longer spring, it doesn't work that way. The suspension travel is limited by the control arms and bump stops. A taller spring would also require a taller shock/coilover. you'd have to design the control arms to work with the taller spring.

Assuming this is strictly a drag car, I wont get into how sway bars factor into affecting your spring rates.

as for multiple spring rate springs, I personally dont like them. but thats just me, others do like them. I just like knowing what exacting my spring is doing, it's easier for my mind to wrap around when adjusting things. When I was big into roadracing and auto x with my cousin years ago, we simply bought different springs, coil overs are easy to change springs on and we also used spring rubbers to change things up too. All depends on how much playing you wanna do.
 
You need to know your ride height in order to pick the correct length shock. You want the shock to be as close to the middle of travel at ride height. As far as,Springs go. The best why is to have your corner weights and a cross section weight to pick the right spring rate for you intended purpose.
 
Buschi340 said:
for stock K-Member. Have it already and also the qa1 shock multiple adjustable.

My question is about selectiong the correct spring. I know I have too weight the car. The whole car or just the front?
From that Point i can follow the qa1 instructions and calculate the rate with weight and angle...

But - can I have a longer length than the 12" Shocks to give more travel in expanding for weight Transfer ( drag race some times ). regular spring just longer or high travel spring? Hope that doesn't effect streetability too much?

what about springs with multiple spring rates they offer? any good or not recomendable?

car is a 72dart with 6.1 HEMI

Coil-Over Springs | Street Performance, Drag Racing & Circle Track Racing Coil Springs | QA1 Suspension
Click to expand...

One of the drawbacks of the coil over conversion with a stock K is the limited space available utilizing the factory pivot points and shock mounts. The 12" coilovers work with the HDK because of the relocated / lowered LCA pivot point....required by the rack / pinion

based on other builds, I think a good place to start with your application is 450lb springs.....I usually install them with all the weight (not in mock up mode) on the car as it will be driven.....put the car at the ride height you desire....(in the recommended ride height range of the shock mfg) and measure how far the spring compresses. It should compress approx 25-33%. If you have to crank the pre-load beyond 33% of the uninstalled spring height to get it in the mfg range.....you have too soft of a spring. If you do not have to crank the preload up to 25%....you have too still of a spring.
 
12 Inch shock thats what i have. Travel is of course limited by the shocks. Me stupid :D
Well, i can't go into a shop here and make experiments with different springs. For doing that I Need a german spring supplier :) Will check that out. so i will have to weight my car first and see where I end up. Thanks guys....
 
Are you using the factory LCA?.....because I only remember selling you support hoops and upper shock mounts.

No problem.....I am just a little confused.
 
I have one of Denny's stock k coilover conversion kits, and I don't see any way you could make a factory LCA work. I'm pretty sure you're going to need the LCA's, pins they mount to, and rear support brackets.
 
JDMopar said:
I have one of Denny's stock k coilover conversion kits, and I don't see any way you could make a factory LCA work. I'm pretty sure you're going to need the LCA's, pins they mount to, and rear support brackets.
Click to expand...

Me either.....but I am wrong all the time. Just ask my wife. :)
 
Guys have been running coil overs on stock lowers for years, how would it not work? Bolt coil over to lca, if you want, tap the pivot pin and put a plate on it, done!
 
You are right JR, The Motown Missile in 1972 used factory LCAs with coil overs.

What I ( and perhaps JD) meant was you cannot substitute the factory LCA in the HDK coil over conversion ( unless the frame is modified /notched for spring clearance ). There simply is not enough room for a 2.5" od coil spring using unmodified factory LCAs.

We wish you could, be a lot less $$$$

Good catch.
 
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I could not get the coil spring to clear the frame thru the full travel of the shock.

Secondly, utilzing the factory pivot shaft did not provide for what I felt was needed for any kind of sufficient rear support

I am confident some of the hot rodders out there can make it work.....just not the way I chose to do it.
 
if i remember right you told me in the PM it will work good with the factory LCA without modifications. hmmm......i told you I want to use the factory LCA.

Pivot shaft of the control arm? the factory design? rear Support because the of the missing Torsion bar? significant issue?
 
I have to dis agree with you...... I have not been shy about my opinion of supporting the rear of the LCA when removing the torsion bars. Additionally, the main reason / function for making tubular LCAs is to move the shock mount outward for spring clearance. While I do think they look pretty, there is no function in pretty.

sorry for any confusion....but I think you have me mixed up with someone else.
 
well, in another thread you wrote with the braces and UCA it is a simple Torsion bar delete. Not mentioning the necessarity of LCAs.

Anyway, I trust you and maybe i understood something wrong. Its all in english :D

So I don't try to make this working and do continue Shopping end of this year....
What do i Need for the lower part? LCA, bump stop ( for UCA ), this Pivot for the arm to k-member. thats it? PM me if you want... what about the sway bar? Provision for that?
 
I will send b you a PM tomorrow. ...got a long trip to Carlisle as a passenger

Can you supply me a link to the post you speak of regarding a simple torsion bar delete?
 
i don't wanna argue abiut that. I am pretty sure I did ask you in the PMs if I have to move something on the lowers. It was never been spoken that the lowers has to be removed for HDKs. I like your LCA, no question but this raises costs and I see Problems with our car inspections to allow such an upgrade. the lowers looking significant different to stock and thats what our car inspectors want. And i probably need a certificate of material and that it officially a replacement for the stock LCA. ( upper and coil over itself is ok because you can find that in old chevys for example). If yours would look like stock or at least half way similar.... ( Germany can be complicated regarding licenses and car Upgrades )

The link is but thats not what i really meant.... HDK Tubular Coil Over for Stock Steering
post 129 for example: I do not see any clearance issues with the HDK coil-only package compared to your factory set-up...... the torsion bars are just gone.
 
No problem.......no argument. I just want to understand for my own piece of mind.

I see now where the misunderstanding might have occurred. In that post I was answering a question by Airwoofer on any clearance issues with his snout bars and he was not asking about anything else at that time. (that is how I read it anyways)
2 posts above (Post 127).....same thread

I will pm you later when I am on the road.
 
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