North American Turbocoupe Organization



Factory Fox Body Spring Rates
svo_thunderchicken Offline
Senior Member
#1
Here is some of the factory specs for springs on the rear of our cars based on TRW factory replacments.... more to come...


83-88 Ford Thunderbird Turbo Coupe (Rear)

Internal Dia: 4.01” Bar Dia: .593”

Free Height: 13.33” Spring Rate: 249 lbs/in

Load Rating: 830 lbs. Load Height: 10.0”


79-95 Mustang GT Coupe/Convertible (Rear)

Internal Dia: 4.03” Bar Dia: .541”

Free Height: 13.57” Spring Rate: 174 lbs/in

Load Rating: 650 lbs. Load Height: 9.63”


78-86 LTD/Fairmont/Granada V8 (Rear)

Internal Dia: 4.01” Bar Dia: .61”

Free Height: 12.44” Spring Rate: 275 lbs/in

Load Rating: 875 lbs. Load Height: 9.25”


78-86 LTD/Fairmont/Marquis L4 (Rear)

Internal Dia: 4.02” Bar Dia: .565”

Free Height: 12.75” Spring Rate: 224 lbs/in

Load Rating: 726 lbs. Load Height: 9.5”


Here are some of the fronts....


83-88 Ford Thunderbird Turbo Coupe (Front)

Internal Dia: 3.5” Bar Dia: .64”

Free Height: 15.19” Spring Rate: 415 lbs/in

Load Rating: 1740 lbs. Load Height: 11”


79-93 Mustang L4 (Front)

Internal Dia: 3.5” Bar Dia: .625”

Free Height: 14.94” Spring Rate: 383 lbs/in

Load Rating: 1500 lbs. Load Height: 11”


79-93 Mustang GT (Front)

Internal Dia: 3.5” Bar Dia: .64”

Free Height: 15.0” Spring Rate: 415 lbs/in

Load Rating: 1660 lbs. Load Height: 11”


78-86 LTD/Fairmont/Granada V8 (Front)

Internal Dia: 3.5” Bar Dia: .625”

Free Height: 15.13” Spring Rate: 383 lbs/in

Load Rating: 1580 lbs. Load Height: 11”


78-86 LTD/Fairmont/Granada L4 (Front)

Internal Dia: 3.5” Bar Dia: .625”

Free Height: 14.94” Spring Rate: 383 lbs/in

Load Rating: 1500 lbs. Load Height: 11”


Here is a link for more information on springs.
http://www.miracerros.com/mustang/springs_calcs.htm

http://www.afcoracing.com/tech_pages/spring.shtml
84 TC Silver 5 speed - PE EEC, Big Vam, RR cam, 35lb injectors, E6 swap, T3 60 Trim, 87-88 intercooler and hood, BOV, K&N Cone Filter *under constrution*
http://www.cardomain.com/ride/2298891/1

87 TC Black 5 Speed - Stock IHI, BCS Bypassed
http://www.cardomain.com/ride/2390431
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Chuck W Offline
Posting Freak
#2
I don't have all those numbers, but the SN-95 rear springs have a load rating of between 730-780# depending on what ones are used.

I'm not 100% sure your numbers on the TC springs. Those might be the later numbers. The stock springs I pulled from my 84 XR-7 had a load rating of 940# based on the info on the tags.

Also, where are you getting these numbers?
83 TC Clone, 80 Cougar XR-7, 85 Volvo 244 Turbo, AND 88 Scorpio
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svo_thunderchicken Offline
Senior Member
#3
well these are based on facory style replacement springs. The ones i have listend for the mustang gt rears are also progressive.. so that might be why the numbers seem a little different

i corrected a typo on the 83-88 tc springs...

The xr7 calls for a different spring from what i was looking at... ill go again tomarrow and see what i can find on it...
84 TC Silver 5 speed - PE EEC, Big Vam, RR cam, 35lb injectors, E6 swap, T3 60 Trim, 87-88 intercooler and hood, BOV, K&N Cone Filter *under constrution*
http://www.cardomain.com/ride/2298891/1

87 TC Black 5 Speed - Stock IHI, BCS Bypassed
http://www.cardomain.com/ride/2390431
Reply

Chuck W Offline
Posting Freak
#4
I have a couple sets of rear springs here. I can measure them and post them up with the tag numbers and applications if I can remember them. I won't have any installed height numbers though.

For what it's worth, the factory will have several different springs which have the same spring rates, but different load ratings. I have the list including tag numbers and spring/load rates from every '97 Mustang spring (12 front and 8 rear). I'll only have free heights of one or two though.

If this info you are getting is for "generic" replacement springs, they will be just that, generic....you'll see what I mean when I post up the list tomorrow.
83 TC Clone, 80 Cougar XR-7, 85 Volvo 244 Turbo, AND 88 Scorpio
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svo_thunderchicken Offline
Senior Member
#5
most of them are trw springs

jsut trying to get some info out here so it will be easier for you.. i know your one of the few that trys to work on this subject.... im going to try and help too... maby we can solve the answer once and for all...

Me personally i have my eyes on those 4cyl ltd springs.. hehe
84 TC Silver 5 speed - PE EEC, Big Vam, RR cam, 35lb injectors, E6 swap, T3 60 Trim, 87-88 intercooler and hood, BOV, K&N Cone Filter *under constrution*
http://www.cardomain.com/ride/2298891/1

87 TC Black 5 Speed - Stock IHI, BCS Bypassed
http://www.cardomain.com/ride/2390431
Reply

Pete D Offline
Administrator
#6
If a relatively complete list could be compiled, we could put it in the FAQs as well as one of the forums
Pete Dunham


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svo_thunderchicken Offline
Senior Member
#7
well thats my goal.. i know all these spring questions are KILLING pore chuck w... he needs help

here is some usefull spring info i found on a website too.

http://www.miracerros.com/mustang/springs_calcs.htm

http://www.afcoracing.com/tech_pages/spring.shtml
84 TC Silver 5 speed - PE EEC, Big Vam, RR cam, 35lb injectors, E6 swap, T3 60 Trim, 87-88 intercooler and hood, BOV, K&N Cone Filter *under constrution*
http://www.cardomain.com/ride/2298891/1

87 TC Black 5 Speed - Stock IHI, BCS Bypassed
http://www.cardomain.com/ride/2390431
Reply

svo_thunderchicken Offline
Senior Member
#8
ok i might have a answer to the "rear c kit springs are too light" question. Yes, the rear c springs are too light... in the beginning... let me explain.

Our cars come with pacific rate springs, meaning the spring rate is the same throughout its motion. Now the rear c springs are progressive, they start out light, and progressivly stiffen up to its maximum rating as its compressed. So the c spring starts out light, but ends up right at the end.. thats why its TOO low.. but if we were to space it up to make up for the bad start, then it still should work fine, but actually a pretty stiff ride due to the amount of travel lost due to premature spring compression at the begining.

The c spring is 12" long uncompressed and rated at 200 lbs/in at the begining, whitch is too light for our cars, and ends up at 300 lbs/in which is about right for our cars at the end of its range of motion. Now considering that the factory spring is about 13.33" long uncompressed with a constant spring rate of 249 lbs/in. it just starts out too low in the first place.

When using the entire kit, front and rear, a 5/8" coil spacer would be required to help set the preload on the spring so that it sets level with the front, and allowing it to reach the maximum spring rate faster.

This just my opinion.. dont take this as fact.. this has NOT been tested yet....
84 TC Silver 5 speed - PE EEC, Big Vam, RR cam, 35lb injectors, E6 swap, T3 60 Trim, 87-88 intercooler and hood, BOV, K&N Cone Filter *under constrution*
http://www.cardomain.com/ride/2298891/1

87 TC Black 5 Speed - Stock IHI, BCS Bypassed
http://www.cardomain.com/ride/2390431
Reply

Chuck W Offline
Posting Freak
#9
Your assumption is not really valid. You can have 2 springs with the same spring rate but with different load ratings.


I found the sheet that has the load ratings for the C-kits..FINALLY

Fronts - Code "SAD", Spring Rate: 650 lb/in, Load: 1461 lb.
Rears - Code "MIB", Spring Rate: 200-200V lb/in, Load : 587 lb

Notice how light they are.....now you tell me if they're suitable for the back of a Tbird/Cougar.
83 TC Clone, 80 Cougar XR-7, 85 Volvo 244 Turbo, AND 88 Scorpio
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Chuck W Offline
Posting Freak
#10
Also, while I haven't had a chance to dig out the other springs in the garage yet...here's some numbers from some 96-98 Mustang rear springs.

3.8L -
Code: ARL, Load 742 lb, Rate, 190 lb/in
Code: BRL, Load 787 lb, Rate, 190 lb/in
Code: CRL, Load 832 lb, Rate, 190 lb/in

4.6L -
Code: OOO, Load 683 lb, Rate, 165-265V lb/in
Code: PPP, Load 731 lb, Rate, 165-265V lb/in
Code: RRR, Load 780 lb, Rate, 165-265V lb/in
Code: SHK, Load 828 lb, Rate, 165-265V lb/in

As you notice, the rates are the same, but the loads vary.

I have the "RRR" in the back of the 83 currently. I ran the PPPs for a while in the XR-7, but they were a bit light. I'm not in the mood to climb under the car and get the installed height of the RRR's just yet.

I did have one more set of springs in the garage, and they are 94-95 Mustang (I'm guessing Cobra Convert by the spring rate)

Code : KPB - F4ZC-5560 - AGA

Internal Dia: 4.05” Bar Dia: .52”

Free Height: 14.00” Spring Rate: 160-260V lbs/in

Load Rating: 848 lbs. Load Height: UNknown
83 TC Clone, 80 Cougar XR-7, 85 Volvo 244 Turbo, AND 88 Scorpio
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