Spring Difference

This might help, though it doesn't reference 4 cyl springs - Chad's 2000 Mustang GT American Racer -- Coil Spring Tech

Yes you can change them with out a lot of modifications. A GT front spring in general is a progressive spring, the wire diameter is bigger at the bottom than at the top. A 4cyl spring has the same wire diameter from top to bottom. They are the same height, and look VERY VERY similar. You have to use caliper to tell the difference. It is very easy to confuse them.

The 4cly, GT, vert, sn95, MAch1, Bullitt, 95CobraR, springs are all interchangeable - with the exception of the rear springs with independent rear axles.

The Fox & sn95 springs are all "plug and play". Of course, changing the front springs can be a pain in some years and spring combos (i.e. Fox with correct Factory offered Stang springs - 4Cyl, GT, Mach1, Bullitt, 95CobraR, etc).

IMHO, the OTC and dropping the FCA is the best way to go! But, people have done spring changes in a number of other ways. Note that many are not safe! Like the morons that drive while drunk, not getting killed, and not killing someone does NOT make it smart or correct. Nor, does that mean that "bad stuff" won't happen to other people. A number of years ago, a professional very experienced mechanic in NH was killed when it "seems" like he may have used a pry bar to get some stubborn rear springs out of a car. The spring sprung, and very unfortunately, went right for his head.

IMHO, do it safe, or make sure you leave a HUGE insurance policy with ME as the sole beneficiary!

BTW:
Spring install on a Mustang using the OTC spring tool
Mustang 86 - Mach1 Springs


Good Luck!

gtcobra302 said:

Yes you can change them with out a lot of modifications. A GT front spring in general is a progressive spring, the wire diameter is bigger at the bottom than at the top. A 4cyl spring has the same wire diameter from top to bottom. They are the same height, and look VERY VERY similar. You have to use caliper to tell the difference. It is very easy to confuse them.

Click to expand...

The wire diameter and material stay the same. What differs is the coil spacing, and number of coils. For a progressive spring, the coils are closer in a portion of the spring. That causes those coils to bind sooner, and go into "coil bind" , which effectively increases the spring rate. In a way, all Fox/sn95 springs are "progressive". They all will go into coil bind in a specific manner.

The wire diameter absolutely is different.

gtcobra302 said:

The wire diameter absolutely is different.

Click to expand...

????

What are you basing that statement on??
The BS that you read on the InterWeb??

How about this, go measure and look at a Ford OEM progressive rate spring. Oh wait, I've done that! Also, I know about real life springs, from a Mechanical Engineering point of view.

I don't know where you read the BS about the wire diameter changing. Here's a good question, why would they do that, and how would they do that in a real world manufacturing?


Here's a page with some more info about how real world springs are made:
Spring Technical Information
RPM Net Tech Articles: Understanding Coil Springs - Powered by: AFCO
Suspension Tech: Leaf Springs and Coil Springs

More info:
Progressive Rate Coil Springs
Cutting stock 1993 5.0 springs - Corral.net : Ford Mustang Forums


Note: Engineering is typically a 5 year degree. To think that reading some 1->10 page BS on the interweb is all there is to understand a topic, doesn't make much rational sense.

BTW: Besides still having one of my *original* '86 springs (I know all of my car's history - I was there when it was ordered & picked up, and I gave my best friend rides to/from the dealer when ever it was serviced), I still have the POS ricer B springs, and a "few" sn95 GT springs. Too bad we can't do bets in the forums.

I got the many Fox GT and sn95 GT springs to PROVE to people that "unloaded length" is "pure" BS method for determining installed spring height. The dead coils on the ends are not "precisely" spaced. That's because in real life (verses interweb BS tech), it makes no difference.

I agree you can make a wide variety of springs while keeping the wire diameter constant, by changing the amount of coils per inch, diameter of those coils and altering other geometries. I also have compared rear springs from an 83 carpi rs and an 89 conv lx and it was instantly noticable the wire diameter of the 89 vert was larger, and when measured it and it was significantly larger, dont remember the specifics. Just saying that ford has used different wire dia. in their springs throughout the years which doesnt necessarily mean they did between the 4cyl and 8 cyl fronts, which is the topic of this conversation. But it stands to reason that they have used springs with different wire dia. in the past and it could possibly be a factor like gtcobra302 was postulating. As far as manufacturing goes I would have to know exactly how the springs ford uses are being made. If its extruded, the die can be changed with little effort and yield a new wire dia. with little effort, from what I hear. Not an expert in the field by any means. The reason they would change the wire dia. before anything else, is because it controls what the spring will do more than anything else. For instance, if you double wire dia. the spring rate increases by 4 times what it was before. Not a very good thing to change if you just need a tiny bit more spring. As far as engineering goes, you should use what you know to educate people when they are asking for help, not to make people feel lessor when they are not.