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Topic: Drag springs for a VERY lightened rear (Read 1265 times) previous topic - next topic

Drag springs for a VERY lightened rear

I'm working on putting the rear of my 87 XR7 drag project back together. I'm using KYB shocks for a 'Stang and have flipped the shock mount to get some of the length back. I bolted the top of the shock in and then put the rest of the suspension in, figuring I would just jack up the rearend until it lined up with the shocks. Well, when the rear got to about 3" from the shock(fully extended), the whole car started to lift. It would appear that I have lightened the car far beyond the range of the factory springs. I weigh about 175lbs, and when I stand on the bumper, the car drops to where I could bolt it in. However, this would still leave me with no shock travel.
  So, it looks like I need to find a rear spring that has a much, much lower load rating, like around 200-300lbs less per spring. I really wish the car was mobile, so I could weigh it, but that's not at all possible right now. I stripped out everything in the car that wasn't absolutely essential. I even chiseled out all the sound deadening  on the floor boards and the trunk. Is it possible that I could have removed 500-600lbs off of the rear alone? If so, what would be a good spring to use? I think I read that my factory springs were rated at 950lbs. Is that correct? Would I be looking for something around 600?

Re: Drag springs for a VERY lightened rear

Reply #1 –
Rear springs are rated far less than 600 -950lbs/inch! Even with a torque arm the most you can get in the rear is 430lbs/inch. I have no clue what factory ratings are but SN-95 Stangs are rated at 210lbs/inch, which is the closest to the Tbird/Cougar. Aftermarket isn't kind to us so we have to use parts that are 'close enough'.

I would put the car completely on the ground before buying springs. Therefore getting the full amount of weight distributed to the rear. Even with jack stands on the front and rear suspension my car sits higher than it should. The flipped bracket works best with lowered suspensions. It may be in your best interest to buy a set of Cougar specific shocks if the suspension travel problem is not alleviated.

EDIT: I see your terms are just backwards. My bad. :sorry:
2005 Subaru WRX STi|daily driver

Re: Drag springs for a VERY lightened rear

Reply #2 –
Sounds more to me like the shock is still too short for the car...which is what happens when trying to use Mustang shocks in a Cougar, even with that bracket flipped over. A shorter spring could probably help though. What has been done so far? Fuel cell?

Re: Drag springs for a VERY lightened rear

Reply #3 –
What I meant by the 950lb springs is the amount of weight they were meant to support. What I really need to do is come up with 3 things:

1) the wieght the springs need to support(A)

2) the amount the spring should be compressed to give desired ride height(B)

3) the fully extended length I need from the spring(C)

From these three things I should be able to come up with the spring I need:
                      A/B= Spring Rate

Now I just need to figure out how much the car wieghs at each corner.
 

Re: Drag springs for a VERY lightened rear

Reply #4 –
BTW,  the shock is about 3.25 inches shorter than stock. I gained about 2 inches back by flipping the mount. Even with the stock shock, I'd still be about an inch too far away. If I were to push the car down to hook it up, I'd be driving around with the shock all the way out.