Chassis Design Details

Chassis Structure
Description:
The chassis is a semi-Monocoque structure fabricated from thin wall (.109 and .060) square steel (1018) tube and stress bearing panels of mild steel (1018) .050 in thickness.

In Figure 1, the tubular structure is shown without the installation of the stress bearing panels.

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Figure 1

As can be seen, this structure alone would be considered a fairly substantial structure when compared to the standard "ladder" type frames as are currently in predominant usage as COBRA chassis. This tubular structure is in reality a space frame, which alone would have a torsional stiffness of only 1800-1900 lbs per degree. This is due to inadequate triangulation of the various box sections.
The total weight of these tubes is 288.41 lbs.

In Figure 2. below, the various .050 mild steel (1015) panels are shown before installation on the tubing in their relative positions. These panels also serve as the footbox, firewall, and tunnel skins.

The total weight of these panels is 129.59 lbs.

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Figure 2

All of the panels shown above are welded to the tubular subframe. (Please note: a bottom tunnel panel is recommended for competition usage. This is attached with .250 bolts directly into the inserts in the lower 2X2 tubes after engine and gearbox installation.)

In figure 3, the tubular structure is shown with the installation of the stress bearing panels in place. The stress bearing panels are welded to the underlying tubular structure to make up the complete chassis. The application of these panels completes the semi-Monocoque structure.

The total weight of the chassis structure is 418 lbs.

Finished car weight with 351 alloy head motor is 2350 lbs.


Figure 3

The resulting chassis structure has an torsional stiffness of over 4800 lbs per degree. In its racing configuration (Engine and Gearbox stressed) the torsional stiffness will exceed 5500 lbs per degree. This compares quite favorably to current WINSTON cup and TransAm race vehicles. The inclusion of a full roll cage would further raise the rigidity to the area of 7500 lbs per degree. The importance of chassis torsional rigidity is very simply the ability to maintain a stable platform for the suspension to operate from and relate to the road surface.


Suspension Type And Geometry Description
This chassis utilizes fully independent suspension on all four corners.

Front:
Rocker arm type, unequal length, non parallel, with inboard coil-over dampers and inboard attachment of anti-roll bar. Adjustable for caster, camber, and toe.

Description of various components:

  1. Upper Rocker Arm. CNC 6061-t6 alloy with Aurora PTFE lined rod ends and center pivot Garlock composite bearings. Also includes camber adjustment on outboard pickup point.
  2. Lower Control Arm. Fabricated tubular steel with Aurora PTFE lined rodends at inboard chassis and outboard pickup points.
  3. Upright (spindle) CNC machined 6061-t6 billet with ford cartridge bearing, with 12 inch by 1.38 inch thick vented rotor. The caliper is a Wilwood NASCAR Ultralight 4 pot unit.
  4. Anti-Roll Bar & Dampers. The anti-roll bar is a dual rotary blade adjustable unit, the rate is adjustable from 85-1200 lbs per inch. Damper and springs are conventional alloy coil-over type with spherical ball joint ends.


Figure 4 Upper Rocker Arms


 

Figure 5 Front Suspension - General Layout

  1. Rocker Arm - Aluminum, 2. Coil-Over Dampers, 3. Filament Wound Composite Bearing,
    4. Lower A-Arm, 5. Anti-Roll Bar, Rotary Blade Type, Adjustable

Rear:
Conventional unequal length, non-parallel, A-arms with outboard brakes and pull rod actuated coil over dampers and anti roll bar. Adjustable for caster, camber, and toe.

Description of various components:

  1. Upper Control Arm. Fabricated tubular steel with urethane outboard pivot and FK PTFE lined rodends at the inboard pickup points. Attachment of the anti-roll bar is on the upper surface.
  2. Lower Control Arm. Fabricated tubular steel with urethane outboard pivots and FK PTFE lined rodends at the inboard pickup points and toe adjustment location. Attachment of the damper and spring is to the pullrod actuated inboard rocker.
  3. Upright (hub carrier) And Halfshaft. Ford Alloy unit with 12 inch by 1.25 inch vented rotor and Wilwood 4 piston caliper.  Halfshaft is standard Ford large diameter unit with CV joint and inner tripod joints.
  4. Anti-Roll Bar & Dampers. The anti-roll bar is a dual rotary blade adjustable unit, the rate is adjustable from 85-650 lbs per inch. Damper and springs are conventional alloy coil-over type with spherical ball joint ends.
  5. Differential. Standard Ford 8.8 Alloy center section unit with Traction-Lok limited slip. Ratios are customer selectable.


Figure 6 Rear Suspension

Figure 7. shows the general layout of the rear suspension components.

Figure 7

  1. Upper A-Arm, 2. Anti-Roll Bar, Rotary Blade Type, Adjustable, 3. Coil-Over Dampers,
    4. Lower A-Arm W/Toe adjustment, 5. Half Shaft, 6. Constant Velocity Joints

Geometry Front: Rear:
1. static camber .5 deg neg. .2 deg. neg.
2. castor 1.5 -3 deg. -5 deg. to + 5 deg.
3. scrub radius 3.408 in. 0
4. king pin angle 9.27 deg. 15.84 deg
5. roll center altitude 0 in. .635 in. positive
6. ride height 5.00 in. 5.00 in.

Index Cont'd.