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I am building a 66 fairlane with a mustang II front supension.It will be a drag car with an aluimium head 460 that must wiegh 3450.What rate coil over spring will I need and any ideals on shock valving.
 

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There are formulas to find spring rate. But you need the cars actual weight, plus the front/rear weight ratio.

Also the spring rate will partly depend on HOW the coil over shocks are mounted. On a coil over/A-arm front suspension, how close to the front spindle the shock is installed/mounted on the bottom control arm effects spring rate. Closer to the spindle will reduce (some) the needed spring rate. Farther away needs more spring rate.

Same thing goes for the rear suspension. The farther away from the rear suspension's pivot point (I.C.) the coil over shock is mounted, (in front, over the top, or behind the housing) the less the required spring rate will be.

If you are looking for Koni's on epay, racejunk (etc) and want a "drag racing" valved Koni, be sure to ask if the shock has "SPA-1" on them. Road racing or dirt car valved shocks don't work well on a drag car.
 

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Measure the angle of the spring relative the the ground. Alternatively, provide the horizontal and vertical measurements of the top and bottom spring purchases.

Measure the how far the distance from the center of the tire that a strightline through the center of the spring would be when it intersected the ground.

Determine how much sprung weight will be on each corner (weight minus the weight of the unsprung portions, such as brakes, wheels and tires). Email all this data to me and I will give you my answer. While my answer might be better for road aracing than for drag racing, I think it should be in the ball park.

Best,
 
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