What you want to do with your car & what you plan on using your car for is
how you're going to determine what to do. I'm sure other more knowledgeable
people will add to this, but here is my .02 cents...

Suspension upgrades are the "always there" mods. They are there whether
you're going full throttle or dead stop. They will make the car handle
better and feel more solid. I would suggest some good subframe connectors
for starters. Also, I don't know how prone 97 GT rear sway bars are to
breaking, but my 98 GT sway bar broke TWICE. I lucked out at the salvage
yard and found a rear swya bar from a 95 GT and picked it up for $25. Me & a
buddy installed it in about an hour. There are MANY other suspension
upgrades.. another popular choice is springs. When you're dealing with
suspension though, you'll want to get components that work well together.
This isn't my area of expertise, so I'll leave this alone. Somebody else can
help you out w/ this.

If you're driving a manual 5-speed, you'll want to get a short-throw
shifter. I chose Steeda Tri-Ax because of SVTKate's recommendation a while
back. I do not regret it one bit. It is one of the best bang-for-buck mods,
IMHO. If you're driving an automatic 97 GT.. I'm sorry. Those are slow =).
J/k.. anyway...

Another mod you should consider is rear differential gears, aka "rear-end
gears". I chose 3.73 gears because I have a 5-speed manual transmission & do
drive occassionally on the interstate and I didn't want that bad of gas
mileage. If you have an automatic or don't drive on the interstate, I'd go
with 4.10 gears.

The above mods are the best bang-for-buck that I can think of right now
without getting into the more expensive power-adders... like turbochargers,
superchargers, and nitrous.

Avoid crap like cold air kits (yes, I have one, and no.. it didn't add any
HP). It's all marketing hype. That is, of course, unless you are dealing
with a F/I motor (forced induction). Then, cold air kits aren't so
ridiculous. I've seen some pretty impressive power gains on 03/04 Cobra's
when they've used BBK cold air kits.

Give us a little more information on your car & what you're wanting to do
with it so we can further guide you. Good luck w/ the 'stang & have fun!

-Mike

--
A happy kid behind the wheel of a 98 Mustang GT
Cold air intake
FRPP 3.73 gears
Steeda Tri-Ax Shifter
Full Boar turbo mufflers
Hi-speed fan switch
255/60R-15 rear tires

How much money do you want to spend?

Mike has made some good suggestions and others will add more. I just felt
the need to offer up a little advice borne of age and experience.

Aside from the usual 'no place to use radical amounts of power other than
the track' cautions, it is all to easy to get something so radical that it
is downright unpleasant to drive in traffic situations. That brief adrenalin
rush we get as we try to turn ourselves into another statistic pales in
comparison to the frustration of negotiating heavy traffic or coaxing a
beast through the parking lot of the KwikkeeMart.

A few well thought out modifications can give you what you're looking for
while keeping your car fun to drive.

Steeda tri-ax, shorter springs and a set of tokico struts/shocks will
make the car handle much better.

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