The Chevy based TD’s are Chevy Chevette, Pontiac T-1000 vehicles. Luckily, the front suspension used in the these cars were used in the Pontiac Fiero.
ALL of the TD replica producers were interested in using as much of the donor car as possible and were not really interested in handling and ride as long as it looked right. Hence we have lame directions to cut and rotate VW front beams, cut Pinto and Chevette springs, etc.
As you know, a coil spring is nothing more than a torsion bar that is wound into coils. The shorter you make it, no matter what the diameter of the wire, it gets stiffer. So, you are correct in the assuming the ride height will drop, but the spring will increase rate and the car will ride stiffer.
Luckily, there are many different rate front springs available in different heights for the Fiero. There used to be a place called Held Motorsports that marketed an entire tubular control arm/adjustable height coil over front suspension for Fiero’s. Not sure if they are still around. I was going to use one in my Chevette based TD. There are literally hundreds of different size and rate springs for coil over shocks, plus the ride height is adjustable.
Because the Chevette/T-1000 were front engine, the springs are little longer in height (better ride) and a little stiffer (nose heavier) than the mid engine Fiero’s. There may be a Fiero spring that will be a “bolt-in” swap? If there is, Eaton-Detroit would know.
If you can, remove one of your front springs. Measure the static height, # of coils, the outer and inner diameter of the coil and wire diameter. Then call Eaton-Detroit spring and tell them what you are doing and what it’s for. They may have that diameter/style spring that will do exactly what you want.
I have two sets of NOS, uncut Chevette front springs and one set of NOS rears. My car is a British Coach Works TD and is considerably heavier than the CMC car. I may get away without cutting coils. I can measure these if you like?
The correct way to spring a car is on scales. Short of that, the correct rate is a crap shoot, completed by trial and error. Let the Tech’s at Eaton-Detroit Spring help you out. They were very accomodating when I ordered from them.
I built a rolling chassis on a Ford (Pinto) based CMC TD kit. It used quarter elliptical rear springs that were made by cutting the stock rear leaf springs in half. The car was so stiff that my 6’3″/250 lbs could not make it squat 1″. Eaton-Detroit made me a set of new Pinto leaf springs, cut them in half and told me what leaves to remove to dial the spring in.
Also, DON’T Cut Coil Springs With a Torch …use a cut-off wheel.
Hope this helps. http://www.eatonsprings.com/