Stock"ish" Front Suspension for Pro Touring/Autocross Oriented Ride

[DEVIOUSDUSTER]

Hey A-Body Nation

My Nitto 555 tires came in the other day. I love these tires! I am getting ready to measure for wheels soon but want to run my intentions by you before ordering. The tires have been mocked up using the wheel simulator tool. Rears will work fine but the fronts are a little tricky. (May need to downgrade size due to interference with fender)

Fronts = 245/45-17 Nitto 555
Rears = 285/40-18 Nitto 555

I am working towards the Pro Touring look. (Reference the green G-Force Demon from Design Concepts for a close representation of what I want.)

My question is geared towards the auto cross crowd. With the Pro Touring stance the car sits much lower than stock ride height.

You guys who are running a stock style front suspension, what are you using for...

1. Torsion bars?
2. Springs?
3. Any other stock"ish" suspension upgrades to make it all work?

I'm running into the issue of the bump stop as well. How do you get around having the bump stop limit the motion of travel without killing the ride?

Additional car info:


1970 Plymouth Duster

• 1" Front Torsion bars
• Hotchkis Sway Bar (Part Number 22386F) - Weld on tabs
• '73 K-member with 11 3/4" rotors & '76 calipers
• RMS tubular upper control arms

Your help / guidance is appreciated!

 

[72bluNblu]

You'll need to get rid of the factory bump stops. I use poly button-head bump stops, Energy Suspension #9-9121G

You can get away with this because the larger torsion bars won't use the same amount of travel that the factory bars did. Higher spring rates= less travel for the same force input. With 1" bars though you'll want to make sure you still have some room, I'd give it somewhere between 1" to 1.5" from the bump to the frame. Otherwise you'll bottom more frequently than you'll want. While 1" bars are big compared to stock, they still aren't "big" in the grand scheme of things.

I run my Duster with 1.12" Firm Feel bars and 18x9's in front with 275/35/18's and 18x10's out back with 295/35/18's. No rubbing, but the rear springs are relocated 1/2" in and the rear quarter lip is cut back almost a 1/2".

I know my 18x9's didn't clear the stock UCA's at full lock and full droop so I went to tubular UCA's, but you should be fine with the RMS UCA's you have. There's lots of other things that you'll want to do if you actually want to handle well instead of just "looking" the part, but it really depends on what you want to do with your car.

More info on my car and set up here http://www.forabodiesonly.com/mopar/showthread.php?t=198098

 

[DEVIOUSDUSTER]

72bluNblu, thank you so much for this information. I'll definitely be getting a set of those button head bump stops.

I can't believe you fit a 275/35-18 in the front with a 9" wheel. That's close to an 11" section width. That has to be tight. Did you have to trim up your fenders?

What are you running for spring rate up front? I read your build but couldn't find specifics on the front shocks. (Part numbers)

I plan to do a little of everything with my car including auto cross. I do want to put on a good show!

 

[nerd racing]

My handling car build will include these parts:

PST 1.030" Torsion Bars
1-1/8" front sway bar
Polygraphite bushings kit
75 Dart BBP Brakes
17" Mustang Wheels (Haven't worked out the tire sizes yet)
Sub Frame Connectors
Torque Boxes
Front Triangulation Bars under the hood
Super Stock Rear Leaf Springs
7/8" Rear Sway Bar (I have heard this may not be needed as there will be plenty of oversteer with the super stock springs and larger T bars and 1-1/8" sway bar up front)
Bilstein Shocks all around.

 

[72bluNblu]

72bluNblu, thank you so much for this information. I'll definitely be getting a set of those button head bump stops.

I can't believe you fit a 275/35-18 in the front with a 9" wheel. That's close to an 11" section width. That has to be tight. Did you have to trim up your fenders?

What are you running for spring rate up front? I read your build but couldn't find specifics on the front shocks. (Part numbers)

I plan to do a little of everything with my car including auto cross. I do want to put on a good show!

The 275/35/18's fit great up front. No trimming on the fenders. I run an 18x9" with 35mm offset, but I also have Dr. Diff's 13" brake kit so my effective backspacing is about 6.2". I actually have the same room to the fender that I did with the 225/60/15's on the cop rims I was running before. Just 2" less to the frame . The rear fit with the 295's is much tighter than the front is, although I don't think you can go any bigger.

The FFI 1.12" bars have a 300 lb/in spring rate. Those get tamed with Hotchkis Fox shocks, part # 79020015 from Hotchkis. They're the last version, so tuned but not adjustable. I think they work better than the Bilsteins. Not that the Bilsteins aren't great shocks, they are, but I think the Fox's work better with the 1.12" bars.

My handling car build will include these parts:

PST 1.030" Torsion Bars
1-1/8" front sway bar
Polygraphite bushings kit
75 Dart BBP Brakes
17" Mustang Wheels (Haven't worked out the tire sizes yet)
Sub Frame Connectors
Torque Boxes
Front Triangulation Bars under the hood
Super Stock Rear Leaf Springs
7/8" Rear Sway Bar (I have heard this may not be needed as there will be plenty of oversteer with the super stock springs and larger T bars and 1-1/8" sway bar up front)
Bilstein Shocks all around.

That's pretty much the same set up that I have, except for the 18's with Dr. Diff's 13" brake kit and the super stock leafs.

On that note, I would not use super stock springs for a handling car. They raise the back of the car too much, and they're not the same spring rate side to side. Neither of those are good things for a handling car.

I'm running Afco 20231M springs on my Duster. 121 lb/in rate, and they're pretty much zero arch. They have a reinforced front section like the super stocks to limit spring wrap, and with stock spring hangers they move the wheels back just a smidge to center the wheels in the wheel well. The only thing that you need to do to run them on an A body is run Energy suspension 2-2117G bushings in the back because they have a 1" eye. If you have a 111" wheelbase car you might consider the 20230's, they have a 142 lb rate. That might be too much though.

If you stay with the super stocks, you may not need a rear sway bar at all, they're very stiff springs. Especially with the 1.03" bars up front, balance is the key to setting up a car. Keep in mind that XHD springs are only like a 110 lb/in spring rate. The old Mopar oval track springs were 120 lb/in. Super Stocks start at 140 lb/in and go up from there. Ideally, I think the leaf springs for these cars should be between 120 - 130 lb/in, depending on the overall weight of the car and torsion bar size up front. But if you run that with an adjustable rear sway bar you should be close enough to dial in what you need.

 

[DEVIOUSDUSTER]

72bluNblu thanks again for detailing your build. You sound very knowledgable about auto cross and suspension tuning. Do you compete often and have you had good results with your set up?

My car won't be pure Auto cross but I do want to compete at shows like the Car Craft summer nationals in St. Paul MN and various SCCA events around the region. I'm having difficulty findng information about about Mopar A-Body's in this division of motorsports. Any recommendations for good Mopar pro touring/auto x forums?

Thanks

 

[2 Darts]

Add positive caster, a little more negative camber, and slightly decrease toe-in. This will sharpen steering turn-in response with a little less self-centering action than stock. It will raise steering effort a little. See chart. I went with something close to the Max Performance Street settings for my street cars.

 

[1970Duster]

Might wanna get in touch with autoxcuda

 

[67Dart273]

On that note, I would not use super stock springs for a handling car. They raise the back of the car too much, and they're not the same spring rate side to side. Neither of those are good things for a handling car. .

I keep trynna say this and nobody wants to listen. SS springs were designed for one thing only.......drag racing, period.

 

[ntsqd]

I keep trynna say this and nobody wants to listen. SS springs were designed for one thing only.......drag racing, period.

Hence their name?

I'm seriously considering the AFCO spring linked above. Thanks for that!