I'm considering driving my 2013 Mustang V-6 Performance Package car in some autocross events. I also plan on lowering it. However, all of the local clubs go by SCCA rules, which means if I install adjustable LCAs or LCA relocation brackets, I am immediately stuck in C Prepared or the equivalent. If I forgo those and install a Panhard bar in place of my Fays2 Watt's Link I can be placed in STX.
I read up on MotoIQ (great article BTW, Sky_Render) about how LCA angles can affect roll understeer. I was wondering, how bad can the understeer be without LCA angle correction? I'm guessing pinion angle will also be changed, so is there any other way to correct that besides LCA angle adjustment? I know UCAs can be changed out and still be legal for STX.
Do you care about being competitive?
If not, which you won't be in STX anyway, I'd just build the car how you want and go have fun.
You have to keep in mind that any class in the SCCA your car will be in, the 5.0 version will as well. Since you'll never out-do that, I'd suggest finding another club/classing system (what does MCA have?), or better yet, just build it however you want. You'll end up finding somebody with similar times to benchmark off of overall.
I've run my 08 V6 in some events and it is definitely fun, but it would probably take a lot of work to be competitive in STX. Thats what I run in because of a few modifications my car has. Although, your 13 would be a better starting point without the massive weight i have in the front only making 220ish hp. I guess it all comes down to driver in the end though. At one local event I was quicker than a GTI and a WRX, which surprised me a lot.
Does anyone know where the toyoburu twins fit in the ST classes?
The LCA brackets are a kinda nice thing to have, but far from required. Also - you can run the Fays2 in STX.
I don't usually run in SCCA events. So take what I say with a grain of salt.
I lack the talent, resources, and time to be competitive in the SCCA at any sort of level, let alone the national level. Therefore, I flat out do not care what class my car is in. I'm going to build it to perform the way I want it to. I autocross to tinker with suspension tuning, test out new parts, and--most of all--to have fun.
Last time I was at an SCCA event, I don't even know what class I was put in. Everyone else was on slicks, and I was on 300-treadwear street tires. Whatever, I still had fun. 
So if you're just going to autocross it occasionally, my advice is to bolt whatever you want onto your car. And Dave is (obviously) right; you can keep that Fays2 unit on. You simply can't use a differential-mounted one.
Also, never ever ever correct pinion angle using lower control arms. In fact, you probably shouldn't ever adjust their length at all unless you're just making them the stock lengths. Changing the LCA lengths alters the wheelbase of the car and can cause a lot of problems. Correct pinion angle with an adjustable upper control arm.
One of the only reasons to adjust a lower control arm is to preload one side of the suspension, which is useful in extremely high-power drag race cars that can twist coming off the line.
Will
Dork
2/1/13 7:57 p.m.
Call Sam Strano.
He'll make your Mustang fast, and save you money on parts you don't need.
real men drive on a track
Teggsan wrote:
real men drive on a track
Like.
But I expect a bunch of comments about risk tolerance, etc
Teggsan wrote:
real men drive on a rally stage
Fixed that for you. 
Now that the troll comment is taken care of, have fun autocrossing!
Real trolls drive under bridges.
I am an SCCA member and do plan on attending some events. I think my pride is just getting in the way WTR classing and I need to overcome it. I'd like to stay in a Street tire PAX in the local clubs (i.e. New Hampshire SCC) and being classed in CSP in SCCA punts me into the Race PAX whether or not I'm on race tires.
Good to know about the Watt's link being STX legal. I'd like to keep the Fays2- the rod ends are a bit noisy over low speed bumps and it's not light, but the rear axle feels far more planted than with the stock toothpick Panhard bar. Also good to know about not using LCAs to correct pinion angle. The Whiteline UCA is adjustable, right? (EDIT: It is)
In reply to Javelin: IF I can get my AWD Eclipse to stop leaking and have a skidplate made up I plan to rally(cross) it. Big IF there, considering how rusty it is...
In reply to Teggsan: Do you know of any 3.7L V-6 drivers who do track days, specifically those still running the stock driveshaft and 118mph speed limiter? How much of a limitation are those? I am interested in doing at least one track day at NHMS or Lime Rock in the Mustang. However, the infamous exploding driveshaft concerns me, and an aluminum driveshaft and ECU tune to raise the limiter aren't in my immediate plans.
Will wrote:
Call Sam Strano.
He'll make your Mustang fast, and save you money on parts you don't need.
In reply to Will:
^^^ This, just be prepared to have a 60min+ phone conversation with him (he likes to talk, but in a good way)...
...for great justice! And road course advice.
