Race Car Modifications for the
Datsun 240Z including information
for a Ford V-8 Conversion

Written by Terry Oxandale

Caster Changes

The factory Z car caster setting is 3 degrees. After a great deal of work in the neighborhood of trigonomics, I arrived to the conclusion that I needed more caster. The factory setting allows undesirable camber change as the wheels turn lock-to-lock. For instance, with a static, 0 degree camber setting, the wheel initially becomes more negative in camber as the wheel is turned, until just under _ of full lock (14.05 degrees of wheel turn), at which point the wheel has reached full negative camber ( about .37 degree negative) when the progression in camber stops and then reverses itself to eventually become about 1 degree positive at full lock (outside wheel only).

As the caster is increased from the original 3 degrees, the point at which the wheel starts going back to a positive setting is delayed, until eventually, a rate of progression from 0 degrees to almost 2 degrees negative camber at full lock is achieved with about 7 degrees of caster (Remember to keep in mind, these figures are for a static car, with no body lean due to dynamic sway forces). Before you say "whoa, thats way too much", remember that the progress from 0 camber to full camber at full lock is not linear, but instead follows a pattern similiar to the top portion of a sine wave, plus you probably will never drive on a course that uses full lock steering, so natually you won't be reaching the full camber point in racing. But the second benefit of this set-up is that it will allow quite a bit less static negative camber to be needed in setting up the car, which then allows for more tire to road contact in straight line braking. I currently run about 3/4 degree negative camber very successfully on my racing Z with the 7 degrees caster. The Z cars started with 3 degrees caster, which was later changed to 5 degrees in the ZX's, and I believe it ended with 7 degrees on the present day 300ZX's, which I feel vindicates my reasoning and my math.

The easiest way I found to increase the caster on my Z car was to move the cross member forward by about 1-1/4" from the original factory location. At the same time, I elongated the strut rods to allow the lower control arms, which mount to the cross member, to be moved forward the same amount as the cross member and still extend perpendicular to the fore/aft centerline of the car. To continue using the existing factory attachment points on the frame rails for the cross member, I welded an 1/8" plate that is 3" X 6" on top of the cross member on both ends where the cross member connects with the frame rails and then added a strap flange along the outside edges of the exposed portion of this plate to strengthen it against any twisting or bending loads. I then drilled two new holes, 1-1/4" rearward from the original mounting holes, in the plate/cross member ends, allowing the cross member to be attached back onto the frame rail 1-1/4" forward of original factory location and still use the existing factory threaded frame rail holes (which are reinforced inside the rail from the factory). Another very important advantage of this modification is that it allows more room behind the cross member for the engine (which in my case, is a Ford V-8, with a front sump oil pan, that has been lowered in the chassis. As it turns out, I have about of clearance between the cross member, and the oil pan).

The above crossmember modification is complete in itself, but as the design on the front suspension progressed (I had a lot more time than money), I eventually built a completely new crossmember out of 1-3/4" chromoly tubing and 1/8" steel plate. The reasoning behind this was I wanted more clearance between the crossmember and the engine oil pan. To start with I removed the original (but modified crossmember) and replaced it with the above mentioned tubing that was straight, except for the the ends were turned upward and rearward. At these slightly curved ends, a 3" x 6" x 1//8" steel plate was welded as a pad to be bolted to the chassis frame rails, creating the new crossmember that curves the middle straight portion forward and downward, giving more room for the oil pan. Now that the structural job of tying the two frame rails together is complete, I added vertical pieces of the plate steel to both ends of the crossmember to give the lower control arms a point of attachment (reinforced with steel washers at the holes drilled for the camber bushing bolt. Additional plate reinforcement for lateral forces was welded to these control arm plates, completing the suspension portion of the crossmember.

Later I decided to eliminate the camber bushings in the lower arms, by replacing them with spherical rod ends. To do this I cut the bushing end off the lower control arm and welded two NF grade 8 nuts (end on end to make one long nut) inserted into the now open end of the control arm. Normally, the cut end of the control arm would not be shaped or sized to accept these nuts, but I fabricated a hex shaped mandrel out of 1-1/2" steel bar. With this mandrel pressed into the open end of the control arm, I was able to reshape the end to match the shape of the nuts that were later welded into the new hex shaped opening in the control arm end by spot welding through holes drilled and filled over the nuts. I then screwed the spherical rod ends into the control arm, giving me infinite camber adjustment, along with an easily replacable part should wear become a problem.

O/H = Sine of angle 21" strut length (camber plate to spindle centerline) front
A/H = Cosine22" strut length rear.
O/A = Tangent
A2 +B2 = C2


Power Plant Radiator & Support T-5 Transmission Information
Ford Drive Shaft Half Shaft Modifications Differential Change
Z-to-ZX Brake Update Brake Master Cylinder Caster Changes
Steering Rack Strut Modifications Custom Sway Bars
Aluminum Differential Upright Weights Costs

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This page last updated 23 September 1997.
Problems? Suggestions? email Michael S. White at mswhite@sos.net