Full weight street car with AC and sub in the back, currently running Koni 4/3 SA, paired with 500lb springs up front and stock cut springs in the rear. Car makes 525rwhp, build S60 rear with 28" ET Street radial in the back, struggling to get traction under 40mph.

Also running Ground Control coil over conversion up front, so my 500 lb spring is only 10" long. Wanting to get the car to transfer weight better, so would going to a 325lb spring up front allow me to do this? My only issue is that the GC conversion kit uses shorter springs, so would a 10" 325lb spring act identically to the common 14" 325lb spring most people use with coil over kits?

The QA1 high travel springs are sold in a 10" 325lb if this will suit my needs.

Any help is greatly appreciated, haven't seen much info for this type of situation.

 

For an application like yours, assuming it is an aluminum block, I would say a 325 or 350 rate in the front would be good, and something in the 150-175 range in the rear.

As for length, you are correct. A longer spring will allow more travel and have more stored energy. However, once the car does start to transfer, that extra travel may actually hurt as it will allow the front to come up too much (read as: drag bumper and come back down violently) and higher power cars end up needing to limit travel and strap the front end down. It ends up being a sliding scale with power versus desired extension to get a car to launch, so it ends up being a slightly slippery slope.

The shocks you have are not going to help you unfortunately. The Koni's are better valved for handling as even on their softest setting, the rebound is fairly stiff in comparison to the drag shocks (Viking, Strange, Qa1 etc).

Honestly, my suggestion would be to sell the setup you currently have to someone who is needing a more handling oriented setup and look into a Viking Coilover setup. It will give the ultimate in adjustability, choice in spring rate, and even save weight in the process