whrvsc
12-10-2013, 10:43 PM
My car is basically a 13 year old steel body mini-stock, using an updated the rear clip with this modified FastBoy setup, and, with a few relatively minor changes to the front clip, I got it to run competitively against a field of super stock 4’s that included 4 link tube frame cars.
The cars in this class range from updated mini-stocks to full tube frame late model style 4 cylinders. For example the track champion’s car is a Rocket chassis with a mono-leaf rear and coil-over rear suspension and another competitor has a rocket with a 4 link suspension. My car is basically the Pinto mini-stock with the new rear clip and a few relatively minor modifications to what is basically a stock Pinto front clip.
For a long time I had been think about the natural rear steer properties of a leaf spring suspension. As a leaf spring car rolls in a corner, the RR leaf flattens out getting longer as more weight is transferred to RR. At the same time the LR leaf gains more arch causing it to get shorter as weight is transferred away from LR. I was looking for a way to magnify this natural rear steer.
After seeing 4 link cars run and the rear steer they have, I realized that rear steer would have cured a problem I had in 1997. I had installed leaf spring slider boxes on my Pinto Mini Stock. The problem I was having was the rear hooked up so well it over powered the front end and just shoved it straight across the track as soon as I picked up the throttle. At the time, I fix it by increasing the front sway bar to get the balance back. I didn’t like this fix because I viewed as crippling the rear so that the front could keep up. With rear steer to the right, I could remove could remove the front sway bar and stop crippling the rear. By the time I was picking up the throttle, rear steer would loosen the car up enough that it would keep turning as the throttle was picked up. This setup does not use bird cages or floaters to obtain the rear steer and is not as setup sensitive as 4 link cars are.
This setup is similar to the FastBoy setup but it is designed to give the positive rear steer of a 4 link car as opposed to the negative rear steer of the normal FastBoy setup. It begins to produce positive rear steer which keeps the car turning from turn in through the middle and off the corner. My setup uses the leaf spring slider box on the RR and a 3 inch lowering block of the FastBoy setup. However on the LR it uses no lowering block, as opposed to the standard FastBoy setup, but it does use the 11 inch shackle of the FastBoy setup. Coil-covers are then used to reset the ride height. The Coil –overs support the car, and the leaf springs are mainly used to locate the rear-end and drive the car forward.
This results in the RR having much more arch at rest than the LR, which has almost no arch at rest. As the car turns in weight transfers away from the LR loses and weight transfers to RR. As weight transfers to the RR spring it loses arch and moves the axle on the right side back increasing the right side wheelbase. At the same time as weight is transferring away from the LR it gains arch and moves the axle on the left side forward, shortening the left side wheelbase. My car loses approximately 2 ½ inches of left side wheelbase when it is jacked up by the RR only. I believe (but haven’t measured it) the RR wheelbase picks up between 1 ½ to 2 inches in length as weight transfers to the RR. When watching the car on the track, you do not see the dramatic tucking of the LR up into the wheel well the way a 4 link car does since the wheelbase change occurs on both sides of the car. From observing the car running on track, the rear of the car steer to the right keeping the car turning like a 4 link does. However, the rear steer in my setup gradually begins as soon as the weight begins transferring, as opposed to a 4 link where there is the sudden change when the throttle is picked up in the corner. This is because my setup use chassis roll to initiate rear steer as opposed to the 4 link initiating rear steer using the torque reaction of the rear. Since part of the wheelbase change occurs due to the LR moving forward and the rest is due to the RR moving back, the motion of the transmission output yoke is reduced. This reduces the strain on the yoke caused by the forward and back motion of the rear on a 4 link.
The setup:
1. Both leaf springs are only the base spring from the multi-leaf spring pack and stock rubber bushings.
a. The LR leaf spring:
i. Is a custom made leaf spring that uses the standard large front rubber leaf spring bushing at both ends to minimize binding of the leaf spring as the car rolls due to weight transfer.
ii. Does not use the lowering block of the FastBoy setup.
iii. Drives the car forward.
iv. Locates the rear axle front to rear on the left side.
v. Provides very little support for the car.
vi. Absorbs very little of the rear axle’s torque reaction.
vii. Does use the 11 inch shackle of the FastBoy setup.
NOTE: The 11 inch shackle increases both LR wheel travel and improves the articulation of the rear axle during chassis roll.
b. The RR leaf spring:
i. Uses a 3 inch lowering block.
ii. Drives the car forward.
iii. Locates the rear axle front to rear on the right side as well centering the axle left to right.
iv. Provides very little support for the car.
v. Absorbs very little of the rear axle’s torque reaction.
vi. Uses standard rubber front and rear leaf spring bushings.
vii. Uses a Leaf Spring Slider Box, the same as the FastBoy setup.
2. Coil overs are mounted to 13.5” swing arms with 1 7/8” swing arm adjusters (the overall length of the arm is 15 3/8”).
a. The chassis end of each swing arm is mounted in a slider box to prevent binding with the leaf spring.
b. The axle end of each swing arm is mounted to pair of tabs welded to the axle directly below the centerline of the axle.
c. The swing arms are main support of the rear of the car and they also absorb a portion of the axle’s torque reaction under acceleration by directing the force through the coil-overs to the chassis.
3. A torque arm absorbs a large portion of rear’s torque reaction under acceleration and all torque reaction under braking. The torque arm is made using a heavy duty swing arm, a small rubber biscuit torque link and a third link mount:
a. The heavy duty swing arm is:
i. 16 1/2 “ swing arm made of 1 1/8 inch tubing plus an 1 7/8” adjuster for an overall length of 18 3/8,
ii. Installed 180 degrees from the normal orientation of a swing arm.
iii. The axle side of this swing arm is mounted to a pair of tabs below the centerline of the axle inline with the third link bracket.
iv. The chassis side of this swing arm is mounted in a slider box to prevent binding with the leaf spring.
b. A small rubber biscuit torque link is mounted between:
i. The top hole of a third link bracket mounted above the axle, and
ii. The hole where that the coil-over normally attach.
iii. The biscuit in the torque link softens the reaction of the torque to prevent losing traction under initial acceleration/deceleration.
4. The front end of the car has basically stock pinto front clip. I added:
a. Wedge adjusters,
b. A 2 inch dropped RF spindle, and
i. Tubular Mustang II street rod control arms. The RF upper control arm is 5/8th of an inch short than the LF control arm to make camber adjustment easier right side easier.
c. The steering geometry is stock Pinto.
d. The car does run 3 wheel brakes.
e. When I ran the cars as a mini-stock 15 years ago, it always turned in well but would pick up a push in the center of the corner. As I said before thus forced a compromised setup.
5. Shock package:
a. RF and LF shocks are Pinto Pro Shock’s Street Stocks Shocks.
b. RR Pro Shock coil-over is an equal rate shock.
c. LR Pro Shock is an easy up shock.
The cars in this class range from updated mini-stocks to full tube frame late model style 4 cylinders. For example the track champion’s car is a Rocket chassis with a mono-leaf rear and coil-over rear suspension and another competitor has a rocket with a 4 link suspension. My car is basically the Pinto mini-stock with the new rear clip and a few relatively minor modifications to what is basically a stock Pinto front clip.
For a long time I had been think about the natural rear steer properties of a leaf spring suspension. As a leaf spring car rolls in a corner, the RR leaf flattens out getting longer as more weight is transferred to RR. At the same time the LR leaf gains more arch causing it to get shorter as weight is transferred away from LR. I was looking for a way to magnify this natural rear steer.
After seeing 4 link cars run and the rear steer they have, I realized that rear steer would have cured a problem I had in 1997. I had installed leaf spring slider boxes on my Pinto Mini Stock. The problem I was having was the rear hooked up so well it over powered the front end and just shoved it straight across the track as soon as I picked up the throttle. At the time, I fix it by increasing the front sway bar to get the balance back. I didn’t like this fix because I viewed as crippling the rear so that the front could keep up. With rear steer to the right, I could remove could remove the front sway bar and stop crippling the rear. By the time I was picking up the throttle, rear steer would loosen the car up enough that it would keep turning as the throttle was picked up. This setup does not use bird cages or floaters to obtain the rear steer and is not as setup sensitive as 4 link cars are.
This setup is similar to the FastBoy setup but it is designed to give the positive rear steer of a 4 link car as opposed to the negative rear steer of the normal FastBoy setup. It begins to produce positive rear steer which keeps the car turning from turn in through the middle and off the corner. My setup uses the leaf spring slider box on the RR and a 3 inch lowering block of the FastBoy setup. However on the LR it uses no lowering block, as opposed to the standard FastBoy setup, but it does use the 11 inch shackle of the FastBoy setup. Coil-covers are then used to reset the ride height. The Coil –overs support the car, and the leaf springs are mainly used to locate the rear-end and drive the car forward.
This results in the RR having much more arch at rest than the LR, which has almost no arch at rest. As the car turns in weight transfers away from the LR loses and weight transfers to RR. As weight transfers to the RR spring it loses arch and moves the axle on the right side back increasing the right side wheelbase. At the same time as weight is transferring away from the LR it gains arch and moves the axle on the left side forward, shortening the left side wheelbase. My car loses approximately 2 ½ inches of left side wheelbase when it is jacked up by the RR only. I believe (but haven’t measured it) the RR wheelbase picks up between 1 ½ to 2 inches in length as weight transfers to the RR. When watching the car on the track, you do not see the dramatic tucking of the LR up into the wheel well the way a 4 link car does since the wheelbase change occurs on both sides of the car. From observing the car running on track, the rear of the car steer to the right keeping the car turning like a 4 link does. However, the rear steer in my setup gradually begins as soon as the weight begins transferring, as opposed to a 4 link where there is the sudden change when the throttle is picked up in the corner. This is because my setup use chassis roll to initiate rear steer as opposed to the 4 link initiating rear steer using the torque reaction of the rear. Since part of the wheelbase change occurs due to the LR moving forward and the rest is due to the RR moving back, the motion of the transmission output yoke is reduced. This reduces the strain on the yoke caused by the forward and back motion of the rear on a 4 link.
The setup:
1. Both leaf springs are only the base spring from the multi-leaf spring pack and stock rubber bushings.
a. The LR leaf spring:
i. Is a custom made leaf spring that uses the standard large front rubber leaf spring bushing at both ends to minimize binding of the leaf spring as the car rolls due to weight transfer.
ii. Does not use the lowering block of the FastBoy setup.
iii. Drives the car forward.
iv. Locates the rear axle front to rear on the left side.
v. Provides very little support for the car.
vi. Absorbs very little of the rear axle’s torque reaction.
vii. Does use the 11 inch shackle of the FastBoy setup.
NOTE: The 11 inch shackle increases both LR wheel travel and improves the articulation of the rear axle during chassis roll.
b. The RR leaf spring:
i. Uses a 3 inch lowering block.
ii. Drives the car forward.
iii. Locates the rear axle front to rear on the right side as well centering the axle left to right.
iv. Provides very little support for the car.
v. Absorbs very little of the rear axle’s torque reaction.
vi. Uses standard rubber front and rear leaf spring bushings.
vii. Uses a Leaf Spring Slider Box, the same as the FastBoy setup.
2. Coil overs are mounted to 13.5” swing arms with 1 7/8” swing arm adjusters (the overall length of the arm is 15 3/8”).
a. The chassis end of each swing arm is mounted in a slider box to prevent binding with the leaf spring.
b. The axle end of each swing arm is mounted to pair of tabs welded to the axle directly below the centerline of the axle.
c. The swing arms are main support of the rear of the car and they also absorb a portion of the axle’s torque reaction under acceleration by directing the force through the coil-overs to the chassis.
3. A torque arm absorbs a large portion of rear’s torque reaction under acceleration and all torque reaction under braking. The torque arm is made using a heavy duty swing arm, a small rubber biscuit torque link and a third link mount:
a. The heavy duty swing arm is:
i. 16 1/2 “ swing arm made of 1 1/8 inch tubing plus an 1 7/8” adjuster for an overall length of 18 3/8,
ii. Installed 180 degrees from the normal orientation of a swing arm.
iii. The axle side of this swing arm is mounted to a pair of tabs below the centerline of the axle inline with the third link bracket.
iv. The chassis side of this swing arm is mounted in a slider box to prevent binding with the leaf spring.
b. A small rubber biscuit torque link is mounted between:
i. The top hole of a third link bracket mounted above the axle, and
ii. The hole where that the coil-over normally attach.
iii. The biscuit in the torque link softens the reaction of the torque to prevent losing traction under initial acceleration/deceleration.
4. The front end of the car has basically stock pinto front clip. I added:
a. Wedge adjusters,
b. A 2 inch dropped RF spindle, and
i. Tubular Mustang II street rod control arms. The RF upper control arm is 5/8th of an inch short than the LF control arm to make camber adjustment easier right side easier.
c. The steering geometry is stock Pinto.
d. The car does run 3 wheel brakes.
e. When I ran the cars as a mini-stock 15 years ago, it always turned in well but would pick up a push in the center of the corner. As I said before thus forced a compromised setup.
5. Shock package:
a. RF and LF shocks are Pinto Pro Shock’s Street Stocks Shocks.
b. RR Pro Shock coil-over is an equal rate shock.
c. LR Pro Shock is an easy up shock.