Leafspring suspension handling

[hidollartoys]

I am building a 1973 duster with rear leafsprings and front torsion bars. I will be using this car for track days and crapcan road racing so i am forced to stay with the "stock" suspension. I am trying to find some info on how to get this car to handle but 99.9% of these were/are set up to drag race... not much use on a road course. Any advice or a point in the right direction would be greatly appericated.

THANKS in advance of your help.

[Skip Fix]

They did use some of the Challengers/Cudas in road race classes in the 70s, and some circle track as well. I think there was even a Mopar book that went into some chassis stuff how to's back then.

Kind of like the GM leaf spring cars. Increasing the front torsion bar rate, they can be adjusted I think for ride height. 6 cylinder or 318 torsion bars were what the drag guys always started with. Leaf springs-probably not the Mopar Super stocks drag spring, but they could work. I think most of them have a taller arch though. I would think the pinion snubber might not be the best ticket for turns as it could change how the rear handles if it hits in a turn.

[Bryce]

Look at all trams am cars from the late 60s, they all ran leaf springs. Also check out mary pozzi's 73 camaro, it runs leaf springs as well AND handle pretty good.

My suggestion would be spherical front bearings and a watts link. I would run fiberglass leafs to reduce weight and run a stiffer front half of the spring to reduce axle wrap. And get the car as low as possible. AN adjsutable sway bar may be necessary to balance the car.

[MrQuick]

As stated above leaf sprung cars are good for handling...great roll center, rear stability and durable. The only drawback is they are heavy and not very tunable.

If I remember right the leafs were raised into the body for better anti squat. Can you add a watts link or panhard bar?

I would start by lightening your car where you can, add a body connectors for torsional rigidity, then put your car on scales weigh your car, chose the proper springs and torsion bar. then add some adjustable shocks and larger sway bars.

Vince

[hidollartoys]

The car is currently set up for drag racing but is actually pretty munch junk. It is basically a shell, no motor/trans. The interior is gutted and I will have to install a cage and can employ all the chassis stiffening techniques short of building a full tube frame. By the rules the chassis components can not be "race car" components just "stock" or equivilent stock pieces. No tunable shocks or weight jacking devices. I can run a panhard bar and possibly some sort of a two bar setup as long as it "homemade". Springs can be replacements and I plan to have a set made by a local spring shop, at least the main leaf. These car were equipped with sway bars from the factory and I plan to add these. Shocks can be premium but cant be adjustable, must be "reasonable" stock equivilent units. Tires are limited to DOT street with a tread wear rating of 190 or greater so we are tire limited. I believe I can get the weight down to the 2600lb area.

I just want to be sure that I can get this thing to turn left and right.

[exwestracer]

I wonder what the rules would say about moving the height adjuster to the rear of the torsion bar (like Chevy 4WD pickups, etc.)? Then you'd HAVE front weight jackers with the "original" suspension design and stock parts...

I'd be careful with panhard bars, etc in conjunction with the leaf springs. Set the leaf springs up with minimum arch (flat, if possible), and use the widest leaves you can get on the car. That will help locate the axle better without introducing any conflicting roll geometry. If they allow a watts link, can you get away with a "homemade" Caltracs type setup? That should help with axle wrap (at least under acceleration) without locking the springs down. If not, a tapered "overload" spring from a pickup will work as well, but it'll add a lot of weight.

Definitely upgrade the front control arm bushings and see if you can get a ball setup to replace the strut rod bushing at the front.

[Bjkadron]

Dusters make great handling cars, Chrysler really did a great Job on the front suspension design and they can handle Great with just simple upgrades. The mmain problem is they are under-sprung from the factory.

From what you have said it seems like the Chrysler set-up will give you a closer to "race" setup while stock. You can have the torsion bar adjusters (because they are stock) and weight jack, Upgrade the torsion bars, Look into the mopar performance "circle track" springs(note: front section is slightly longer than stock) or the hotchkiss springs depending on how stock "stock" has to be as both control axle wrap, Also look into the pinion snubber if the caltracs are to "grey" for the rules. Spherical bearings for the front of the leafs, and a spherical strut rod(or if they won't let you use spherical try Urethane, but be prepared to cut the bushings to fix binding issues), if they will let you you can run Nylon or "del-i-lum" bushings on the front, you can get offset bushings and Moog "problem solver" cam bolts to help with alignment too.

can you use Fiberglass parts? you can get a-bodies REALLY light if you can, otherwise 25-2700# is reasonable depenging on how much aluminum you use in your engine and stuff.

If you could post the rules we can give you a lot more specific help.

Oh and Bilstien shocks are hard to beat in a non adjustable shock.

[hidollartoys]

EXWESTRACER and BJKADRON Thanks for your responses. This is getting closer to the info I need.

As for the rules (DONT LAUGH) you can google "chumpcar" and they have a pdf of the rules. But in a nutshell The suspension HAS to be "stock". We are bound by a $500.00 total car "value" less safety items, IE tires, brakes, roll cage, fuel cell, window net, master electrical, seat, harnesses. Basicly the rest of the car has to fall into the $500.00 and "race" parts will cost you lap penelity based on "value". The race directors are VERY savy racers themselves and know how to cheat. This value is EXTREMELY subjective and there is no repeal process. They do have a list of potential upgrades and associated penalities in the rules. The idea (and spirit) is to race true $500.00 cars against each other.

Most everyone uses the small imports and some x-mini stock (4 cly) cars. The races are dual 7 hour enduros or a single 25 hr event. The challenge is to build a car that is relatively easy to drive and not suffer any mech. breakdowns. Multiple driver format requires a car that will see very different driving styles and should be as neutral as possible. There are VERY few v-8 cars and I am a old chevy guy and dig the old trans am cars. Themes are worth lap bounses and since this car is available for CHEAP and I have enough sbc parts to put a motor together, I thought about a Trans am clone including paint(not counted in the $500.00 value) maybe "Donowho Race Team: AKA DiRT" ("you are as fast as dirt").

The cage can and will incorporate a slew of body stiffing techniques but i can not build a "tube frame". It will front clip hoops and all the other cage components just as a stock car would have and since some of the floor is rusty (wink wink) and I am required to use floor and backing plates for the cage i will be tying the cage to the suspension mounting points and installing "subframe" connectors. All for the sake of safety(sure). Motor will be the garden varity of 350 sbc with GM aliminum intake, 81 corvette exhaust manifolds, aluminum water pump, HEI dist, iron heads/block (would like stock alum heads but they are $700/set used and would put the engine value to high). No engine fan and only an alt. will help reduce engine weight. I will be running a T-5 trans w/ hyd clutch which is also reasonably light. We cant run any glass (except windshield) and I plan to run a lexan windshield so I believe the 2500lb target is realistic.

I plan a torsion bar change but not sure what to ask for or where to go to get them. Main leafs are easy to reproduce and with the right arch and lb/in rate. Just need to know what to aks for. If there are any "old school" tricks that were used "back in the day", these would be easier to get through tech. I just dont have any feel for this type of chassis.

[overZealous1]

hahha. i was thinking of doing the chumpcar too. i had my eye on an 89-90 rx-7 turbo 2 though. yes, they do actually count that as a bairily under $500 car. cut the springs, put a return spring on the wastegate to hold it closed longer, and you have a car that has a dam good chance of winning!
those rules are pretty tight, so you wouldn't be able to get away with much on your duster before you go over. where are ya located and which race are you hitting?

[hidollartoys]

Live in KC, will be at Iowa 4-31/5-01 and Heartland Park Topeka end of June (both in rented seat) and maybe at the Chumpionships back at Iowa. From there not sure but I plan to attend/drive in as many as possible. This is a TEAM effort requiring at least 4 drivers and maybe a pit crew. 150+ gallons of fuel, logistics and planning is paramount. SUPER FUN!!!! If you adhere to the rules with 4 drivers you will get at least 6 hours of seat time (2 hours at a time) during the event. Our team has 6 drivers, mostly old guys with alot of past racing experience in scca and vintage racing. I used to race enduro karts.

I am starting my build for the 2012 season.

[High Plains Mopars]

By valued at $500, does that mean the officials/competitors can buy your ride for $500 and you HAVE to surrender it? I'm unfamialir with this whole series, but that is what basic oval track claimer rules specify. I also figure your going to have to provide some sort of documentation along teh way to back up your claims

I'd go for a GM G or X body. Much greater selection of parts to come in on the budget target than what you will find on the mopar. Heck, half your claimer cost of $500 will be wrapped up in just upgrading the torsion bars, never mind leafs, shocks, or anything else. Compare those $200 torsion bars to budget GM coil springs you can fnd at any swap meets for $50, and the mopar isn't even close.

You might find better info on car choices, set ups, rules bending by visiting Grassroots Motorsports 20XX challenge forum.

[hidollartoys]

Buy out is $1500 (by race directors only, less safety items) but only if you get caught cheating or if the directors feel that you are not within the "spirit" of the rules. Base parts are part of the "value" and do not necessarly add to the cost since the car already has t-bars, springs,etc. If I replace the existing components with items that can be identified as "upgrade" then I could be penilized with penalty laps. The whole idea is to upgrade with items that dont look like upgrades. We are not looking at "race" race cars be mostly a bunch of junk that will last 24 hours. I have found used torsion bars from a 340 duster for $100 a set. These cars came with sway bars and I will install them on this car. I will have to duplicate the "factory" units not to draw attention to them. No hotchkis, etc pieces. Factory repops are ok but I will have to "age" them. If you visit their web site the rules are posted there. You can also check out youtube for some video of the races.

As I stated earlier the rules are VERY subjective and at the discreation of the directors. As they state... "If you want to race bring a $500.00 car and race". The entire rule book is only 42 pages. You really dont want to over think the rules. Not like other forms of racing where "if it does not say it you can do it". The directors have final word.

I realize there are better cars to race but I can get this car for change and have the drivetrain to install.

[79-TA]

See what you can do to get the car to sit as low as possible. Consider cutting the front springs, "chaining down" the suspension, and using lowering blocks. Since it's a Chump Car, you shouldn't be afraid to use a 4 lb sledge for clearancing fenders and whatnot.

[High Plains Mopars]

Then whatever your willing to risk for $1500 is up to you. That's a little better and you can get the basic chassis there for about that much.

340 t-bars are a step up from the original 318/6 bars, but not much. They are only 155# rated bar, or about 310# in GM terms. Your going to want to go 1.12 or 1.18 for race duty unless your willing to deal with the wallowing 340 bars as part of the "theme." Expect to pay $300+ for these larger, race rate bars. Same with sway bars, 1.125 front bars are easily found for around $100, but don't look like the stock .875 units. 1.25 units are available for around $300. Rear bars are available, but no A body came stock with them. These tend to be around $350. Personally, I'd spend the money elsewhere. You may find some better deals searching around on web sites, but maybe not a whole lot better so prepare now to drop some coin. I'd recommend as much t-bar and front s-bar as your willing to pay for or negotiate with the officials for, then build everything else around that.

One advantage to the mopar is you can crank down the ride height without cutting coils. Get it low enough to just avoid bottoming out with whatever T-bar you decide. Caster/camber are very intermingled on the mopar control arm and to gain one you will sacrifice the other. Use Moog problem solver bushings offset in the opposite way of the instructions to increase caster without jacking up camber as much. About $60 for a set of four.

Does it have disc or drum brakes on the front? Unless you have a late build date '73, you have the small upper control arms with a small ball joint. These won't stand up to much abuse. If you have factory disc, they are likely the small bearing, small rotor versions. You will want a 74-76 A, 66-72 B or 70-74 E body upper control arms with the bigger ball joint. This allows you to use the taller FJM body spindle and a post '73 B body 11.75 disc rotor with the big bearings. If you get real adventurous, you can go with 74-78 C body units and gain the 11.75 rotors with a 1.25 thickness and you have a huge heat sink for brakes. These can mostly be junkyard parts, so expect a covnersion to run around$125+ Good compound pads can be found at Firm Feel for around $50. (for that matter, any suspension stuff can be pickup there as well.)

For cost and simplicity, off the shelf gas shocks will suffice but are hardly optimal. Maybe if you can find a mopar guy dump his KYBs for something better you can score a high pressure gas shock for cheap. $40 to $100 here.

Leaf springs are already designed with very little arch. Adding leaves until you reach the balance you want with the front end is simple enough. A body spring are the shortest of the Mopar bunch, and they are easy to find to add extras. Use blocks if you need to level out the ride height with the front. Expect these to be free to $20.

For bracing/roll cage, tire the cage in to the uni-body structure if you think you can get away with it. Mopars twist badly in the front end, so tie the front frame horns together, diagonal brace the shock towers to the firewall, weld up bracing to the steering box mount, run a weld bead around the torsion bar mounts in the front and rear anchors.

Replace rubber bushings with poly if your up to it. $250 for a kit from PST or Just Suspension. Pay particular attention to the strut rod. Some poly bushings are too thick and create problems with the lower control arm seating. However, firming up the strut rod mount pay big dividends on reducing toe changes under braking and accelleration. You could get creative and make up an adjustable strut rod with some bar stock and a lathe. This will also help out in the caster/camber game.

Might also want to suscribe to moparchat.com There are a bunch of oval track racers there that can come up with a lot of inexpensive ideas to gain a competitive edge for low $$.

[parid]

Hey everyone. I found this thread through a google alert. I'm one of the ChumpCar staff for the West Coast and I thought I would pop in for a couple comments.

Glad to see so many people interested. If there is anything I can do to help new teams get up and running, let me know.

The best advice I have to give new teams is to be aware that this is endurance racing. A 25-50% drop out rate is common. Purely finishing the race is noteable. It's a good idea to get your car reliable before you worry too much about getting your ultimate lap time.

I will be using this car for track days and crapcan road racing so i am forced to stay with the "stock" suspension.

Technically, there aren't limits on what you can do to the suspension. The primary goal is to show up with a $500 car. The rules have a chinese menu style list for some suspension mods and what that will do to your car's "value".

We expect pretty much every car to have SOMETHING done to them. You can't just pull out 400lb of interior and expect the car to ride properly. Cut coil springs are pretty much a minimum. If you can cut it, move it, or bend it your self with common tools thats generally considered a $0 value change.

hahha. i was thinking of doing the chumpcar too. i had my eye on an 89-90 rx-7 turbo 2 though. yes, they do actually count that as a bairily under $500 car.

Sorry, but a running S5 turbo probably not a $500 car. An S4 n/a can probably make it through. An S5 n/a would be kind of iffy. If you disagree, you are free to try to make a case at the track. Read up on the AIV process (tl;dr get 10 ads showing clearly that a running car could be purchased for $500).

By valued at $500, does that mean the officials/competitors can buy your ride for $500 and you HAVE to surrender it?

Buy out is $1500 (by race directors only, less safety items) but only if you get caught cheating or if the directors feel that you are not within the "spirit" of the rules.

ChumpCar is no longer a "claim" series. There is no longer a provision for buy out of the vehicles. It has been switched (for 2011 and on) to a disqualification series. If you are cheating so badly that penalty laps don't cover it, they will just disqualify your car. Check out rule 5.6 for more detail.

Lots of ideas for cheap aftermarket parts

Most of these would affect the car's value. That's not always a problem, if you are bringing a 300-400$ car, you have some room to make it up to $500. Be careful when adding too much (or any) of this.

[Bjkadron]

Well I don't have a lot of time, but I would consider putting it together, keeping mostly stock suspension, and upgraded dampers. Fix the UCA's camber curves. swap on discs, and see how it runs. Remember that you are racing a 2500lb car, which is about 1000lb lighter than stock. so don't go overboard with spring rate. I would see how it runs almost stock at the first race and see if you are competitive, then upgrade later. also a front and rear spoiler will help a lot. otherwise all my other suggestions apply. where are you located?

[hidollartoys]

I live in KC

[redlinegw]

I would go with Hotchkis all the way! http://www.hotchkis.net/search.html?...mitForm=Search I have there TVS system on my 69 Plymouth Valiant and the car is awesome! It was only 2 tenths of a second slower then a 2010 Camaro with all the Hotchkis stuff and he had sticky Toyo tires. My car had General street tires. Best customer service as well.

[High Plains Mopars]

That approach would perhaps be great for a car in a race series with more rigidly defined rule sets. IMO, putting $2500 worth of Hotckis parts under a $500 car and spending months building it just so the inspectors can kick you off the track after teching your car as soon as you show up is counter productive.

[redlinegw]

You could always just get the Hotchkis rear springs with there mount and Bilstein RCD shocks and remove the stickers. Maybe some swap meet sway bars.