Prepping a Unique for Track Day Events.

[NRP/MN]

OK guys here goes- approached by a customer to upgrade the shock and spring package on an older Unique. He wants to do some track day events with the car. Previous discussions lead me to believe it has a 460 based engine. The plan is to put double adjustable shocks on the car. My question is what spring rates are you using with the Jag rear end? What has been recommended to me seems kinda stiff considering there are 4 shocks and springs in the rear (350#).
Thanks in advance, Mike

[t walgamuth]

It sounds a bit stiff to me too.

I will say this too, back in the day the cobras leaned a lot in the curves.

[EM-0785]

Originally Posted by NRP/MN

OK guys here goes- approached by a customer to upgrade the shock and spring package on an older Unique. He wants to do some track day events with the car. Previous discussions lead me to believe it has a 460 based engine. The plan is to put double adjustable shocks on the car. My question is what spring rates are you using with the Jag rear end? What has been recommended to me seems kinda stiff considering there are 4 shocks and springs in the rear (350#).
Thanks in advance, Mike

Hi Mike,

For my older EM replica with 460 and Jag rear, here’s what I did. I weighted my car at CAT scales and obtained the weight info of about 2,950 lbs with like 52% to the rear.

I used the QA1 tech Spring Rate Chart info, which addresses lengths, angles, axle weights, etc. I came up with 250 lb springs, based on the Jag IRS row in the chart. Then I spoke with two separate QA1 techs and ran through everything to get their recommendations, given angles, intended use, etc., and they both came up with 250 lb springs. So, I considered that verified in my specific application for my desired setup after those discussions.

That was a pretty basic approach, I found many more detailed/complex methods online, which didn’t seem to change things much from the basic approach above (at least the ones I appeared to understand).

At that time I was told that Unique still used Jag IRS in their cars, so you may want to check with them, as well as any shock/spring manufacturers you have under consideration.

Best of luck! Brent

[Unique427]

Unique factory currently uses #350 in front for big block and #325 rear.
Info is direct from the Weavers

[csx4995]

I have a early model Unique that has 428 BB in front. It has a Jaguar IRS which had the original Boge Shocks and springs. I replaced the (4) rear springs and shock with Protech Shocks Ltd.

Protech recommended #275, Unique recommended #350. I went with #350, my thinking was Unique knew best... its too stiff. I wish I had gone with #275.

FYI, This is for a street only car, I have no intentions of track driving.

[patrickt]

If you go with the Jaguar rear, ERA will use 350 lbs/in springs at 10" or 8" depending on whether your dampers have height adjustment.

[strictlypersonl]

We (ERA) have been using 350's for many years. Because we shorten XJ lower control arms between the inner pivot and the shock mount, the the spring's equivalent rate is a little lower than on an unmodified control arm. The only comment that I've ever heard is "Wow! This thing rides pretty well."

[Unique427]

Originally Posted by strictlypersonl

We (ERA) have been using 350's for many years. Because we shorten XJ lower control arms between the inner pivot and the shock mount, the the spring's equivalent rate is a little lower than on an unmodified control arm. The only comment that I've ever heard is "Wow! This thing rides pretty well."

Is it reasonable to assume that ERA and OP's Unique would share some
similar DNA regarding Jag rearend mods and thus similar selected spring rates (#350)?

[RUFdriver]

For track use, it’s going to be MCS or Penske, everything else is modded street stuff.

[strictlypersonl]

Originally Posted by Unique427

Is it reasonable to assume that ERA and OP's Unique would share some
similar DNA regarding Jag rearend mods and thus similar selected spring rates (#350)?

A little, but ERA doesn't solidly mount the differential directly to the chassis. We use a tubular sub-frame and trailing arms.