Frame or chassis options for A bodies

[DionR]

Being I have owned Tbar cars and while I fully agree with 72 bluNblu that they do work, honestly in my opinion that are not as fast as a good coil over kit. One only needs to look at vintage porsche's to see that if one wants to go fast, they all convert to coil overs.

With all due respect, I think that is a little bit of an oversimplification and not an apples to apples comparison.

I find it hard to believe that a Porsche TB suspension has many similarities to an A-Body TB suspension, besides a long straight spring. Just a thought, but if the aftermarket coilovers on a Porches also corrected some geometry inadequacies, then it might have less to do with the torsion bar and more to do with a different suspension design.

For example, the early Camaro has a horrible front suspension design that requires huge spring rates to get the required wheel rate. If a new coilover kit relocates the lower shock mount so the spring is more effective, the car suddenly turns faster lap times, but it might be less about the "magical" coil over and more about a better design.

Can't argue that losing the TB gains room, but beyond that I don't see what the advantage is.

And don't miss that most of the aftermarket kits I've looked at don't seem to have the support for the lower control arm that the factory suspension gives. Not much bracing and no triangulation so when the wheel hits a bump the lower ball joint moves backwards. Maybe it's no better than a factory setup with a worn out strut rod bushing, but it's at least designed better and just needs to be upgraded to be executed effectively. The pictures above are a decent example of this, with a long control arm and a relatively narrow mount at the pivot point. Lot's of leverage there to move the LBJ backwards and forwards and disrupt the handling. Maybe it is beefy enough for this, but it is working against the laws of physics, rather than with them.

I'm struggling to think of a fast A-Body with coilovers...maybe Wracks? But there are 3 listed below that are TB and leaf spring cars, and the Green Brick isn't even one of them.

But you don't need it. lilcuda's '68 Valiant has lapped portland international raceway as fast a C06, hitting 160mph down the straight, it's a torsion bar and leafs car. Tomswheels ran the Goodguys autox faster than some $150k Camaro with his '69 cuda convertible, and he was still running $14 Gabriel shocks. I'm guessing the $150k Camaro was a bit easier to drive though. And his Valiant is faster than that and still a torsion bar and leafs car, it won SCCA CAM events, finished 2nd to M. Pozzi at San Diego, 5th in the CAM nationals west, etc.

Heck I heard Tom was selling his car, you could buy his for less than it would cost to go to a full chassis. Or to even build his car...

I wonder what Tom would have done at the CAM nationals with the motor out of lilcuda's car. Pretty sure he was down significant horsepower to most of the people he ran against, and still finished 5th.

Shame he is selling it. Still don't agree with the reasoning, but it's his car and he can do with it as he wishes...

 

[DionR]

I think you need to read through this thread...

 

[blown71duster]

Honestly, I wouldn't get anything from magnumforce ever after seeing one of their other previous tubular k-frames that had an unsupported rear lower control arm mount actually broke on I believe more than one car while they were backing up,

The next question you need to ask is if they actually strength test any of this stuff before they send it out. It's a friggin k-frame and lower control arms. If it busts, you're in a world of hurt. I've never even seen it mentioned so who knows.

.

I really don't understand the bashing on magnum force being weak, that was the one thing I liked about their Transformer frame . It is very well built .Same with the lower control arms ,very well built. It is not something you want if your looking for a lightweight piece for a drag car. It weighs a lot more than a stock K.


Some people just flat out don't want a torsion bar stock setup , no matter how good they can be made to handle.

I am sure Andy the O.P. will find something aftermarket that he will be more than happy with.

 

[goldduster318]

I really don't understand the bashing on magnum force being weak, that was the one thing I liked about their Transformer frame . It is very well built .Same with the lower control arms ,very well built. It is not something you want if your looking for a lightweight piece for a drag car. It weighs a lot more than a stock K.


Some people just flat out don't want a torsion bar stock setup , no matter how good they can be made to handle.

I am sure Andy the O.P. will find something aftermarket that he will be more than happy with.

I don't intend on getting into a heated debate about this, but since you asked:

I was referring mostly to the original style designs that left the rear control arm mount unsupported, just to flop around back there. I see the transformer has a tie bar back there and a double shear mount now, no doubt for that very reason.

At the end of the day that k-frame is a pretty poor design. There's no pilot to the frame as evidenced by the absolutely huge slots, so I am unsure how you actually ensure it doesn't move after it's installed. No doubt it's extremely difficult to install this in exactly the correct orientation.

The second issue is that unless I am not seeing something beefing up this area it has a pretty amazing stress riser in the areas circled in the attachment. Remember that lateral loads have to be transmitted back to the areas where the bolts are as there's only the clamp loads from the plate on that plane and the bolts transferring that energy to the car body.

It's basically a bunch of steel plates welded together except for in the area in front of the steering rack which is probably where it matters the least. Therefore it has to be much heavier than it would be if it was made out of tubing. Tubing in general is much stiffer than plate, especially to twisting. So the only way to compensate for that is to increase thickness massively. Not sure the wall thickness. I hope it's not something thin like 1/8".

This is also the same guy that sold kits for years where he'd hook coil-overs to the stock shock mounts without reinforcements. No doubt that those towers were not made to hold the car up.

I'm not sure any of the aftermarket coil-over k-frame kits are designs without some kind of fault. The alter-k-tion is probably a better design than this still but not really that rigid since it's only tied together with one square tube crossmember.

It would be interesting to see how these things deflect under shock loading from a pothole or whatnot.

The factory k-shape not only is resistant to to twisting in all directions, but the LCA is also partially supported by the torsion bar and torsion bar crossmember. So, suspension loads are spread out pretty well over the front of the car. They are also transmitting the forces from braking and acceleration on the lower control arms through the strut rods to a spot much closer to the front mounting bolt. It's pretty well done.

If you weld up the stock k-frame, gusset the steering box mounts and motor mount areas, beef up the LCA pin areas,and put the stiffening plates on the LCA, you've got a stiff platform. They also seem to hold up well even with the questionable welds.

 

[blown71duster]

The frame is 3/16 thick , I don't feel like there is any strength problems , just my opinion though.
We are happy with it and that's really what matters, if you love your stock setup that's ok too, just not what we wanted for this resto-mod.

 

[dukeboy440]

Hey Everyone, thanks so much for the replies and understanding of the question as I have been away from my cars for some time.

Did not know that these options were available, so its exciting to see.

I have several A-body cuda's and am interested in converting one to a fun street/track day car and honestly I thought that in order to get the rigidity, I would need to fully replace the frame.

Can anyone give some feedback on any of these options as to quality, cost to product considerations, ending benefit? Why one over the other?

Best

Andy

You might try the guys over a lateral g forums too. Lots of guys over there including chassis and race car builders for road racing. There's many many ways to achieve a great handling mopar without spending 15 to 20 grand on a chassis.

A good set of torsion bars and rear leafs will improve an abody greatly.

However, if you're wanting a track car, you want adjustiblity in your suspension, the more, the better. Think of it like a tool box, the more tools the better and once you learn more about how to tune, you can shave seconds off a lap time just by making a slight adjustment. While the torsion bar setup on mopars is very good when tuned properly, just ask Jim Lusk who's done amazing things with his, i wanted more.

I recommend a GTS, Gerst Tubular Suspension front K frame. Yes, there's others out there such as the Hemi Denny and RMS, QA1, AJE etc. All have their good points but I chose to GTS because I felt it had more adjustibilty built in than the others and properly addresses ackerman, bumper steer and the camber issues A bodies are known more. Regardless of which kit you chose, do your research, call each builder and talk to them and figure out what'll work best for you.

As for the rear, again, adjustability. SS leaf kits, caltracks etc work great in most cases, but for a track car, adjustibilty is limited. I want to be able to finely tune my roll centers as well as load and unload each tire in a predictable way. Leafs dont give me that.

Anyway, enough of my rant. Best advice I can give is research, research and more research before spending any of your hard earned cash on anything. The guys here and over at Lat G are great.

 

[joes68340s]

Something I have watched over the years is the aftermarket k frames might gain you coil overs and rack an pinion you cant run a very wide tire up front not much more than a 235. Stock suspension modded fronts can get up to a 295 tire.

 

[Woods74]

This thread doesn't suck.

 

[dukeboy440]

Something I have watched over the years is the aftermarket k frames might gain you coil overs and rack an pinion you cant run a very wide tire up front not much more than a 235. Stock suspension modded fronts can get up to a 295 tire.

depends which ones, the HDK and the GTS are amongest the narrowest/closest to stock track width.

 

[72bluNblu]

Something I have watched over the years is the aftermarket k frames might gain you coil overs and rack an pinion you cant run a very wide tire up front not much more than a 235. Stock suspension modded fronts can get up to a 295 tire.

Not true, on either account really.

Wracks71 is running 18x9's with 275/35/18's on the front of his Duster with his RMS Alterkation (his specs are listed at this Hot rod mag article, scroll most of the way down the page http://www.hotrod.com/cars/featured/1312-2013-muscle-car-of-the-year/. I suspect with the proper wheel and backspace it would be possible on the HDK and others as well. That's basically as much tire you can run on an A-body because of the frame and fender clearance.

A 295 on the front of an A-body would require serious fender modification regardless of the type of suspension. I have 275/35/18's on 18x9's on my Duster which still has it's torsion bar front suspension, but there's pretty much no room to the fenders or the frame at my ride height. I know Tomswheels was running 285's on 18x10's on his Valiant, but he also pushed his fenders out with a jack. I suppose 295's would be possible by doing something like that, but at that point you're basically flaring the fenders. And you could do that with any of the coilover conversions too, as long as you didn't mind the bodywork.

Maybe on some cars a 285 would work with the right amount of trimming and fender lip rolling, if the 285 was on the narrow side (actual tire width depends on brand and model of tire). I have 295's on the back of my car, it's a BIG difference compared to the 275's I have up front. I know, I tried- the 295's were outside of the front fenders. ;)

Also, for the "coilovers are the only way to go fast crowd", go back to that Hot Rod article. You'll see that the Hotchkis taxi, a '70 Satellite 4 door, ran over a second faster on the autocross than Wracks's duster did. That's a big car with torsion bars and leaf springs coming in faster on an autoX course than a fully coilover converted duster. Not only that, the Taxi was the 2nd fastest car on that autoX, faster than all but one of those other fancy rides. And that Satellite is at a huge disadvantage, pun intended, because of it's size. Wheelbase and weight are very important in autoX. Yeah here's that link again http://www.hotrod.com/cars/featured/1312-2013-muscle-car-of-the-year/

 

[67autocross]

Just my 2 cents on the Hot Rod Magazine test.....unless the same person is used like Motor Trend does with Randy Pobst when they test, the results mean nothing.
The same car could win a competition like this or finish last just by changing drivers.

 

[Woods74]

Just my 2 cents on the Hot Rod Magazine test.....unless the same person is used like Motor Trend does with Randy Pobst when they test, the results mean nothing.
The same car could win a competition like this or finish last just by changing drivers.

Not the point; it's about hardware capability.

 

[72bluNblu]

Just my 2 cents on the Hot Rod Magazine test.....unless the same person is used like Motor Trend does with Randy Pobst when they test, the results mean nothing.
The same car could win a competition like this or finish last just by changing drivers.

Sure, driver skill is always a factor. But here's the thing. A torsion bar suspended, leaf spring equipped, 4 door B body came in 2nd place. That car has a 116" wheelbase. Think about that. It averaged over a second faster a lap than a coilover equipped, 4 linked A-body with a 108" wheelbase. A full second. On an autoX course. We aren't talking a mile long course. 1 second in a course that's being run in 48 to 54 seconds.

And really, read that article. Take a look at the suspension set ups on some of those other cars. Look at those cars! These aren't grocery getters, most of them are purpose built track day machines. And we aren't pulling drivers off the street, most of those drivers frequent track events. All those cars have a minimum of several thousand dollars into suspension set up. Heck most of them probably have $10k in suspension work. Maybe more. And they were slower than torsion bar/leaf spring car.

Yeah, the driver is always part of it. But so is physics, and a 4 door 116" wheelbase car has some serious disadvantages in the physics department. And yet it still managed to be faster than a whole handful of cars with some really fancy suspension. I mean, fully subframed Camaro's vs a '70 Satellite 4 door? I'm not saying that coilover set ups can't be fast. They can. But you don't need them. And it doesn't have to be just the Hot Rod article. Look at what Tomswheels did with his Valiant in the CAM class. I mean, 2nd only to Mary Pozzi at SCCA San Diego? Not bad considering Tom's '67 Valiant was probably giving up 250+ horsepower to Mary's '73 Camaro.

The point is torsion bar cars can be fast too. Faster, in fact, in the right hands.

 

[ssba]

If I was going to put a A-body on a track I would go torsion bar leaf. Leafs are great for acceleration and traction and the torsion bars work well with the leafs.
Some of the things I would pay attention to:
You need to know what your car weighs how it is distributed and
the center of gravity. The lower and closer to center
the weight is in your car the faster and flater your car can go thru a turn.
You may not end up with 50/50 frt to rear but you can get real close if you keep this in mind
while choosing and placing parts in your car. Shoot for a center of gravity close to12".
Solid greasable bushings frt and rear. Delrin is a good choice for most as aluminum would hammer out and need replaced more often. Steel in the front leaf spring eyes. They can be drilled to lighten them some.
300 lb/in. front torsion bar rate. 125 lb/in. rear leafs. 450 lb./in. front sway bar. No rear bar.
8" &10" width wheels. 4.10 - 4.88:1 gear.
11.75 front disk 11" drums rear brakes.
16:1 manual steering box.
Lower front roll center to 3 or 4 in. 5°+caster 1°-camber 3/32" toe out.
Control fluid weight. Oil pan and fuel tank baffles.
This would be stiffer than you would want on the street. You would need to glue all your
dash screws in place. And check the car often for loose fasteners and stressed sheet metal.
Run over a dime and you could tell if it was heads or tails.

 

[goldduster318]

[ame="https://www.youtube.com/watch?v=yfVC2qOJ_lU"]Tire Rack - HOT ROD Unlimited Tests 200-Treadwear Tires on a 1970 Plymouth - YouTube[/ame]

Video of the same thing with Kevin's car. It beat their 2012 BMW 3-series around their own track by about a full second. They even used their pro driver.

 

[NC Engine Builder]

You just cant ever convince some people how good of a design the mopar suspension is. They call you a "hater" or "purist" ironically, people by these coilover kits for the WOW factor, and in my experience 99% of the average public isn't even capable of using all the handling potential in the mopar chassis. I have yet to see anyone actually outrun a leaf spring/torsion bar car, that is properly set up, with ANY of these "suspension conversions" I raced these cars for years, and STILL hold the track record at the fastest paved trioval short track in the US. On leafs and torsion bars. Hell, buddy baker was able to go 200 MPH in 1970 in a 4K pound B body with 15" bias ply tires.......torsion bars/leaf springs.....

 

[67autocross]

Sure, driver skill is always a factor. But here's the thing. A torsion bar suspended, leaf spring equipped, 4 door B body came in 2nd place. That car has a 116" wheelbase. Think about that. It averaged over a second faster a lap than a coilover equipped, 4 linked A-body with a 108" wheelbase. A full second. On an autoX course. We aren't talking a mile long course. 1 second in a course that's being run in 48 to 54 seconds.

And really, read that article. Take a look at the suspension set ups on some of those other cars. Look at those cars! These aren't grocery getters, most of them are purpose built track day machines. And we aren't pulling drivers off the street, most of those drivers frequent track events. All those cars have a minimum of several thousand dollars into suspension set up. Heck most of them probably have $10k in suspension work. Maybe more. And they were slower than torsion bar/leaf spring car.

Yeah, the driver is always part of it. But so is physics, and a 4 door 116" wheelbase car has some serious disadvantages in the physics department. And yet it still managed to be faster than a whole handful of cars with some really fancy suspension. I mean, fully subframed Camaro's vs a '70 Satellite 4 door? I'm not saying that coilover set ups can't be fast. They can. But you don't need them. And it doesn't have to be just the Hot Rod article. Look at what Tomswheels did with his Valiant in the CAM class. I mean, 2nd only to Mary Pozzi at SCCA San Diego? Not bad considering Tom's '67 Valiant was probably giving up 250+ horsepower to Mary's '73 Camaro.

The point is torsion bar cars can be fast too. Faster, in fact, in the right hands.

In the test you posted by Hot Rod the guys who I would suspect to go the fastest ( Danny Popp and Kevin Wesley) finished the autocross 1 and 2. I would speculate that you could let them drive any of the cars in this test and the results would be the same.

Now as far as the suspension debate that never ends on every mopar site about stock vs coil over, until somebody gets 2 cars and builds them with matching power, weight, tires,brakes, ect as well as driver and tests them side by side no one can truly say which system is better or faster. I would again speculate that there would not be a whole lot of difference between them...but who really knows, until then it's just bench racing.

 

[Woods74]

^I can sure as hell tell you which one is more inexpensive to build! :happy1:

 

[ssba]

The best way to approach any type of competitive build is to understand
the design of what you have and why it is built the way it is. And why it reacts as it does to driver input. Then you can determine how and what to modify to make an improvement.
Contact patch is #1. It is the only thing holding all applied force.
#2- How much your car weighs at each wheel should then be used to get your spring rates to oppose this force.
#3- Controlling deflection on everything that is not a spring so that inputs are transfered more direct and precise. This needs to be done without adding a lot of weight.
Budget can definetly determine how this acomplished.

 

[HemiDenny]

^^^^^^^^^^^
ssba. I like your thinking .....(IMHO) both of your recent posts are some of the best guidelines one could follow if considering a competitive build.

 

[72bluNblu]

Some of the things I would pay attention to:
You need to know what your car weighs how it is distributed and
the center of gravity. The lower and closer to center
the weight is in your car the faster and flater your car can go thru a turn.
You may not end up with 50/50 frt to rear but you can get real close if you keep this in mind
while choosing and placing parts in your car. Shoot for a center of gravity close to12".
Solid greasable bushings frt and rear. Delrin is a good choice for most as aluminum would hammer out and need replaced more often. Steel in the front leaf spring eyes. They can be drilled to lighten them some.
300 lb/in. front torsion bar rate. 125 lb/in. rear leafs. 450 lb./in. front sway bar. No rear bar.
8" &10" width wheels. 4.10 - 4.88:1 gear.
11.75 front disk 11" drums rear brakes.
16:1 manual steering box.
Lower front roll center to 3 or 4 in. 5°+caster 1°-camber 3/32" toe out.
Control fluid weight. Oil pan and fuel tank baffles.
This would be stiffer than you would want on the street. You would need to glue all your
dash screws in place. And check the car often for loose fasteners and stressed sheet metal.
Run over a dime and you could tell if it was heads or tails.

This is almost identical to the set up currently on my Duster, most of it has been on it for the last year and a half.

-1.12" Firm Feel torsion bars (300 lb/in)
-Afco leaf springs, 120 lb/in with Afco leaf spring sliders
-Hellwig 1 1/8" tubular front sway bar
-Hellwig 7/8" rear sway bar (e-body application)
-Hotchkis non adjustable Fox shocks
-13" Dr. Diff cobra style front disks, 11x2.5" rear drums
-16:1 flaming river manual steering box
-18x9 front rims with 275/35/18 BFG KDW2's, 18x10 rears with 295/35/18's same tires
-lowered to ~1" clearance from frame to .375" thick LCA bumpstops, ~5" from ground to K-frame, 4" to the Dougs header flanges
-Milodon road race oil pan (baffled, trap doors, 6qts)
-3.55 rear gears with 833, 68-70 B rear with 1/2" spring offset
-frame stiffening: subframe connectors, tubular radiator support brace, torque boxes, "J" bars tying firewall to front frame rails above radiator support brace, shock towers tied in and reinforced to J's. Stock LCA's boxed

-currently running non adjustable tubular UCA's and stock LCA's, soon to be replaced with Bergman double adjustable UCA's and gusseted QA1 tubular lowers for easier alignments and additional frame to LCA clearance for further lowering.

A couple of notes on the car- it's not too stiff for the street. The key is good shocks, and the Hotchkis Foxs are the best I've tried so far. They work better for the really large bars than the RCD Bilsteins I had before, at least in my opinion. The car is my daily driver, and I haven't had any issues like my dash screws being rattled out. Also, the rear bar doesn't seem to make the car too tail happy. I'm on the lowest of three settings though. The 1/2" spring offset and 295's play a part in that though. I suspect like autoxcuda found some courses will be faster with the rear bar while on others it may need to be disconnected. The 3.55 gears aren't ideal for my cam or short courses, but they keep me from getting run over on the freeway until I can go T56.

 

[67autocross]

^I can sure as hell tell you which one is more inexpensive to build! :happy1:

As someone who was done both suspensions in the same garage paying for all the parts with my own money , I really can't find a big savings when you buy all the really good parts for the stock front end.

 

[67autocross]

This is almost identical to the set up currently on my Duster, most of it has been on it for the last year and a half.

-1.12" Firm Feel torsion bars (300 lb/in)
-Afco leaf springs, 120 lb/in with Afco leaf spring sliders
-Hellwig 1 1/8" tubular front sway bar
-Hellwig 7/8" rear sway bar (e-body application)
-Hotchkis non adjustable Fox shocks
-13" Dr. Diff cobra style front disks, 11x2.5" rear drums
-16:1 flaming river manual steering box
-18x9 front rims with 275/35/18 BFG KDW2's, 18x10 rears with 295/35/18's same tires
-lowered to ~1" clearance from frame to .375" thick LCA bumpstops, ~5" from ground to K-frame, 4" to the Dougs header flanges
-Milodon road race oil pan (baffled, trap doors, 6qts)
-3.55 rear gears with 833, 68-70 B rear with 1/2" spring offset
-frame stiffening: subframe connectors, tubular radiator support brace, torque boxes, "J" bars tying firewall to front frame rails above radiator support brace, shock towers tied in and reinforced to J's. Stock LCA's boxed

-currently running non adjustable tubular UCA's and stock LCA's, soon to be replaced with Bergman double adjustable UCA's and gusseted QA1 tubular lowers for easier alignments and additional frame to LCA clearance for further lowering.

A couple of notes on the car- it's not too stiff for the street. The key is good shocks, and the Hotchkis Foxs are the best I've tried so far. They work better for the really large bars than the RCD Bilsteins I had before, at least in my opinion. The car is my daily driver, and I haven't had any issues like my dash screws being rattled out. Also, the rear bar doesn't seem to make the car too tail happy. I'm on the lowest of three settings though. The 1/2" spring offset and 295's play a part in that though. I suspect like autoxcuda found some courses will be faster with the rear bar while on others it may need to be disconnected. The 3.55 gears aren't ideal for my cam or short courses, but they keep me from getting run over on the freeway until I can go T56.

Thats in the same vane as my 69 Valiant, I run 1.14 torsion bars and Viking double adjustable shocks and the ride is good. I have 19" wheels for the car but I most run 15" cop wheels with 225/60 coopers because the streets are so bad around here (plus the car looks better on black steels). Not to stiff the way it is but I think I will drop the torsion bar size down to 1.03 this summer and bump up the compression damping on the shocks a bit.
I was going to run a rear bar but with the adjustable shocks I don't think it is necessary at this point. My springs are home made jobs as I don't feel you can just buy some off the shelf kit springs and have them work on just any car, A bodies that I have owned have had close to a 600lb weight spread from the lightest one to the heaviest.

 

[Woods74]

As someone who was done both suspensions in the same garage paying for all the parts with my own money , I really can't find a big savings when you buy all the really good parts for the stock front end.

So your telling me having to use an after market K member for coil overs because there isn't enough support in the fender wells is the same price as a set of torsion bars? lolz..

 

[ssba]

Most cars won't need all this as they won't be pushed like this was built for.