Inspired by the Mustang II suspension thread I spent the last couple of days testing the torsional rigidity of my 67 coupe. Since I am installing a MII front end from Rod & Custom this gave me the opportunity to compare stock to MII. I also tested various additions like front torque box and subframe connectors.
The car: 67 Coupe, rust free and solid. 67s are odd in that they have a single torque box on the driver's side. Earlier cars have none and will be more flexible. Later cars have boths sides and should be stiffer.
The setup: support the car at three corners and use a ten foot bar with weight (me, 210lbs) to twist the frame and measure deflection with a dial indicator.
I placed the rear jackstands where the shackles attach to the leaf spring. I placed the single front jackstand under the frame just behind the radiator support. I attached the 10 foot bar across the lower part of the radiator support. Although this setup does not accurately reflect how the frame is loaded by the suspension it gave me a way to test both suspensions as well as any future modifications, front or rear, with the same twisting force.
Opposite corner must be securely lashed to the ground.
Torque bar attachment.
Dial indicator to measure deflection.
This test does not address beam strength as I couldn’t come up with a good way to load the chassis other than getting about 10 volunteers to get in and out of the car after every change and measure the deflection under the center of the car.
To begin I removed all factory bracing. The doors are not latched and the trunk is open. All glass removed. This limits the strength to the unibody alone.
The results:
Baseline 0.66"
Factory crossmember 0.64" I'm surprised this added anything
Export brace 0.48" The biggest single improvement
Monte Carlo bar 0.48" Not surprised with this.
Passenger side torque box 0.48" Very surprised. I guess this is more for beam.
Subframe Connectors 0.48" I thought I would see a little improvement.
Subframe X brace 0.475" Very dissapointed. Did I make a mistake?
Remove export brace/MC 0.65 Nearly back to baseline.
Remove all parts 0.67" More flex than baseline? Torque box still there.
Cut out shock towers 0.69" Lost some but not much.
MII X member 0.63" Slightly better than stock crossmember.
Subframe connectors 0.63" Still nothing here.
Subframe X brace 0.61" Slight improvement.
Notes: I didn't have the factory shock tower braces so I couldn't compare to the export brace. Subframe connectors were bolted in. I will retest after welding them. I haven't added the repair panels to replace the shock towers yet. I also haven't removed the strut rod brackets yet.
I plan addition bracing for the front end and will retest as I go.
Conclusions:
At least in torsional rigidity, the MII setup is slightly stiffer than a stock chassis without an export brace. However, it is no match for the stock chassis with an export brace. We'll see what happens when I add additional bracing.
When bolted in, subframe connectors (at least the Heidt's model) offer little torsional resistance even with the cross brace. Hopefully this will change when welded. The Heidt's subrame setup is similar to the TCP setup except Heidt's uses smaller diameter tubing.
The car: 67 Coupe, rust free and solid. 67s are odd in that they have a single torque box on the driver's side. Earlier cars have none and will be more flexible. Later cars have boths sides and should be stiffer.
The setup: support the car at three corners and use a ten foot bar with weight (me, 210lbs) to twist the frame and measure deflection with a dial indicator.
I placed the rear jackstands where the shackles attach to the leaf spring. I placed the single front jackstand under the frame just behind the radiator support. I attached the 10 foot bar across the lower part of the radiator support. Although this setup does not accurately reflect how the frame is loaded by the suspension it gave me a way to test both suspensions as well as any future modifications, front or rear, with the same twisting force.
Opposite corner must be securely lashed to the ground.
Torque bar attachment.
Dial indicator to measure deflection.
This test does not address beam strength as I couldn’t come up with a good way to load the chassis other than getting about 10 volunteers to get in and out of the car after every change and measure the deflection under the center of the car.
To begin I removed all factory bracing. The doors are not latched and the trunk is open. All glass removed. This limits the strength to the unibody alone.
The results:
Baseline 0.66"
Factory crossmember 0.64" I'm surprised this added anything
Export brace 0.48" The biggest single improvement
Monte Carlo bar 0.48" Not surprised with this.
Passenger side torque box 0.48" Very surprised. I guess this is more for beam.
Subframe Connectors 0.48" I thought I would see a little improvement.
Subframe X brace 0.475" Very dissapointed. Did I make a mistake?
Remove export brace/MC 0.65 Nearly back to baseline.
Remove all parts 0.67" More flex than baseline? Torque box still there.
Cut out shock towers 0.69" Lost some but not much.
MII X member 0.63" Slightly better than stock crossmember.
Subframe connectors 0.63" Still nothing here.
Subframe X brace 0.61" Slight improvement.
Notes: I didn't have the factory shock tower braces so I couldn't compare to the export brace. Subframe connectors were bolted in. I will retest after welding them. I haven't added the repair panels to replace the shock towers yet. I also haven't removed the strut rod brackets yet.
I plan addition bracing for the front end and will retest as I go.
Conclusions:
At least in torsional rigidity, the MII setup is slightly stiffer than a stock chassis without an export brace. However, it is no match for the stock chassis with an export brace. We'll see what happens when I add additional bracing.
When bolted in, subframe connectors (at least the Heidt's model) offer little torsional resistance even with the cross brace. Hopefully this will change when welded. The Heidt's subrame setup is similar to the TCP setup except Heidt's uses smaller diameter tubing.
