Why this topic? I'm beginning to shop for a 05-06 Mustang to realize a long desired dream after playing with Euro cars for years. As I do with every car purchase, I like to research the hell out of things far in advance of buying. That I'm buying a S197 GT is a foregone conclusion. The part I'm wanting to piece together now is what it will take to make it a track car on par with the E46 M3 BMW. Why this as the target? Two reasons: 1) I think the goal is easily achievable without spending a fortune, and 2) my brother-in-law has one.
I'm not worried about the horsepower; I'm more interested in what suspension and chassis bits would be needed to achieve a comparable on track dynamic. Springs, shocks, bars, tire/wheel combos, etc. Please no speculation; only real corner-carvers need apply. I'm looking for a predictable package and not something that will be knife-edge scary even if it is faster.
My background: I have a racing license and instruct HPDE's at some east coast tracks. I have been racing a E30 BMW but for a few reasons want to give that up and go in a different direction away from W2W. And if anyone is interested in doing a trade...
In order of what I personally think the car is lacking in:
-Wheels/Tires - Obvious to anyone with track experience, the stock 235's are ice skates relative to the car's weight...
-Dampers - The stock shocks/struts are AWFUL for basically everything.
-Rear Axle Location - Yes, it's a live axle and it will still "hop" over bumps, but the solution to the majority of that problem is quite simple, albeit slightly expensive. Basically the way the a PHB behaves forces the rear suspension to move in an arc laterally. The axle itself is about 250-300lbs of weight. I don't think I need to tell you what that weight moving laterally is going to do for rear grip and driver confidence!
The solution is a watts link. Plenty of options out there from street car to race car in varying price ranges. The least expensive (Fays2) happens to have the most adjustment for rear roll center height and uses rod ends instead of bushings. When set up correctly it does not make any additional noise, at least mine hasn't. Barring a watts link, I would do everything in your power to remove any lateral deflection you can. IE: Rod ended PHB at least.
-Springs - More like lack thereof. For a 3500lb car the springs are ridiculously soft. Lots of brake dive, lots of squat, lots of body roll. Plenty of options here to fix this. Since dampers are coming off anyway and camber plates are recommended, coilovers are the easy ticket.
I ran, and for the most part still do run, that same basic setup. Here is what is on my car now:
-Ground Control Coilovers w/ 440lbs/in front springs, 200lbs/in rear springs
-Alignment: -3.0º camber, +7.0º Caster, -0.10º Toe (out))
-Strano 35mm front bar
-Strano 25mm rear bar
-Fays2 Watts Link
-Enkei PF01's in 18x9 at all four corners (class limited)
-Hankook RS3 in 265/40/18 (class limited)
-Cortex Racing Torque Arm
-Poly bushings in rear lower control arms
Frankly, the last two are fixes done because of class rules preventing me from doing them an easier way and you can basically ignore them for the "what I would do at a minimum". I would definitely recommend going wider for tires. These cars will fit some pretty good rubber under all four corners with relative ease. You'd be wise to take advantage of that. I'd suggest at a minimum 285's on an 18x10 wheel or wider.
Once that is done, the rest of the mods are more or less geometry restoration. You'll lose some forward bite from lowering the car, LCA relocation brackets will restore some of that. With that restoration you'll probably see wheel hop return, so a new upper control arm out back and both lower control arms. I don't really consider these "necessary" in the sense as it's a major issue that I'd fix ASAP, but it certainly is something to keep in mind. The rear upper control arm takes care of all the wheel hop and pinion angle changes. With big drops like with coilovers, the pinion angle change is a big deal... too low and you'll put a lot of wear on the pinion bearings... Front roll center also takes a dive thanks to the strut geometry but that is a lesser issue than the forward bite drop.
That is all suspension wise. Seats, harness and harness bar or roll bar would be a great start to improve driver confidence and take some weight out of the car.
If you have any questions, this is the place to ask them. Lots of folks with experience here!
Someone, a familiar face, would be the Vorshlag crew, Terry and Jason are both on here (Fair and modernbeat respectively) who have obviously got experience with both the E46 and S197 chassis!
They might be able to tell you where they'd improve more specifically.