Autocrossing the Fox: ESP
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ESP
In Street Prepared and Prepared, cars are classified along “lines.†The 79-93 Mustang and 79-86 Capri are all listed on the same line, so parts can be updated and backdated between them. Here intake and exhaust are open, struts, springs, wheels, tires, swaybars, panhards, torque arms, suspension bushings, camber/caster (CC) plates can all be changed as well as updating/backdating between designated years. You cannot add non-stock subframe connectors, non-stock rear gears, aftermarket control arms, do much internal motor work or add forced induction. The Fox chassis hasn’t proven to be competitive due to its poor suspension geometry, flexible chassis, and low power (comparatively). The sn95s make a better choice because of their stiffer chassis, better front grip, and better power of the modular Cobra or 351 Windsor from the 95 Cobra R.
Fox vs. the Competition
Unfortunately, the Fox chassis Mustangs are a bit outclassed in ESP. The current top cars seem to be the 3rd and 4th generation F-bodies and the sn95 Mustang. All 3 of these cars have at least superior suspensions, and the 4th gen. and sn95 have superior rigidity and power to boot. The F-bodies come with torque arms, which are far superior to the Mustang’s “quadra-bind” 4-link. sn95s have the option of an IRS (factory equipment in the 99-04 Cobra), otherwise, an upgrade is needed to make the playing field level. Beyond tuning with bushings, springs and Camber/Caster (CC) plates, there isn’t much hope for improving the Fox’s front suspension. However, I don’t know that a truly competitive version of the Fox has been built and driven by a national caliber driver - at least not since John Ames.
Building a Competitive Fox?
The two advantages the Fox have are size and weight. In my opinion, maximizing the weight advantage would be the biggest key to making one competitive. Less weight is a big factor in any vehicle’s performance. There is less weight to accelerate, stop, and change direction. In autocrossing’s fast transitions, this advantage is amplified. So I would think that the Fox’s only hope at being competitive is to weigh far, far less than the competition. Additionally, every advantage that can be taken in the rulebook would have to be taken. What follows is my own personally recipe that could be used to build as competitive a Fox as possible.
First, I’d start with a coupe, as they’re lighter and stiffer. Yes, the hatchbacks have better balance on the scale, but all the weight is up high (that big piece of glass is heavy), which is not a good thing. Even better would be to start with a no-options coupe. Better yet, start with a 79-86 coupe (commonly referred to as 4-eyes), as some Foxes were equipped with very light weight aluminum bumpers, and can be fitted because of the update/backdate rule. (My favorite Fox is the 85-86 coupe, so that would be my pick.) The bumpers are sometimes hard to find, but they do turn up occasionally on eBay and a few forums. Take this light weight car and remove every bit of sound deadening to make it even lighter. Even the front inner fender liners can be removed.
Since most of these cars are now getting pretty old, one would probably benefit from some fresh suspension components. Coilover conversions, aftermarket A-arms and LCAs are not class legal, so no need to drop the extra bucks there. Good aftermarket bushings will do in the control arms. If you’re resourceful, you can get a set of early Fox LCAs with the round bushings - the later LCAs have large oval bushings. Its best not to go with too stiff a bushing in both upper arms, as it can amplify the roll-bind which will make the snap oversteer that much worse. Its better to go with a stiffer spring and lighter swaybar, and there are many different size swaybars available. I have even heard of many running NO rear swaybar as it helps get the power to the ground. I’ve heard of spring rates up front running in the 600-1000 pound range, and 175-375 out back. Just don’t pick springs that lower your car too much, as your camber curve will be ruined (not that its any good at stock height). A good set of shocks and struts are definitely worth the money, and as the spring rates go to the stiffer range, they become even more important. You can even go as far as getting them custom valved to your car’s weight and spring rates. Camber/Caster (CC) plates are pretty much a necessity, especially if you plan on lowering your car at all. And pick a good set so you don’t have to worry about them wearing out.
Fitting any kind of sizable tire under a Fox can be tricky. Anything much wider than stock and you’ll almost certainly be rolling the fender lips. Many have squeezed 16×10 inch wheels under their car, with careful attention being paid to offsets. 16 inch tires have taller sidewalls, which offer a little more forgiveness and make the car a little easier to control at the limit. 17 inch wheels are more available, however, and offer much wider tires. 17×9-10 inch wheels with 275/40s should fit with a bit of massaging. If you’re willing to flare the fenders, you can go for the big guns and some 17×11s with 315s.
Stock Fox brakes suck. But luckily, there is an answer; the 93 Cobra R. These cars came with sn95 Cobra 13″ front brakes. There is some dispute as to what the 93 Rs had for brakes out back, so the SVO Mustang makes that choice easy. Master cylinders are open, so pick your poison. Running the SVO rear brakes will cause radically different front and rear offsets - something to be aware of. Of course these are 5 lug brakes, which will require 5 lug wheels, so plan ahead. Those on a budget can use the SVO front calipers and stick with 4 lug, but they’ll still provide mediocre performance at best.
A common method of stiffening up a Fox is subframe connectors. However, as of this writing, subframe connectors are not legal (although there is a proposal to allow them for the 2008 season) in a Fox, so no luck there. The convertible cars did make use of some extra bracing, but the parts are getting hard to find and the improvement may not be worth the weight and headache. Best to just go ahead and get a good roll bar with door braces. It will add some extra weight, but it will stiffen up the chassis and will give you a place to safely mount a harness.
The best engine option is found in a 93 Cobra. If you decide to build one, the iron GT40 heads are not the same as the Cobra heads, and cannot be used, at least not legally. And if you do find a set of Cobra heads, be sure to swap the cam too, as the Cobras had unique camshafts. Basically, you have to build a numbers matching 93 Cobra motor to be legit. You can use whatever intake and exhaust you wish, so thats where you should focus. Don’t pick too big an intake that sacrifices low end power. Long tube headers are better than the shorties, so don’t even bother with them. Go straight for the big guns, and get a matching mid pipe and cat-back. You can even run dumps to save the extra weight of the tailpipes. The electronics can be upgraded as well, and probably should be, as you’ll want to squeeze every last bit of power out of the motor.
The best transmission to use is the Cobra spec T5, although any T5 will do. You can upgrade the clutch, and swap out to an aluminum flywheel, as well as replace the rear differential with something better, such as a Torsen T2R, but you can’t upgrade to an aluminum driveshaft. 3.27 gears are the quickest ever offered in an 8.8 equipped Fox, so that makes for an easy choice.
Inside, a good set of seats can help lighten the car a bit more, as well as provide much better support than found in most Foxes. The center console can be removed as many Foxes came without them. A good harness can help keep you secure, as long as you can properly mount one to a roll bar. Otherwise, a good lap belt will do in a pinch. If you have a hatchback, you can replace the rear seat with a rear seat delete that mimics the 93 Cobra R, otherwise there isn’t a lot else you can do to the interior, except maybe add some more reliable and accurate gauges.
The final step is to ditch the quadra-bind rear suspension. You can legally replace the uppers with a panhard or watts-link and a torque arm or upper links such as Steeda’s 5-link or Evolution Motorsports 3-link. I like the look of the EVM 3-link a lot, although I haven’t done enough research to know if its definitely class legal.
Could such a car be competitive on a national level? With the right driver, who knows. But if you want to have the best chance of being competitive, I think this is how to do it.
Insanity Ensues
I went through all that to say this; I’m planning on building an ESP Fox. Will it be competitive? Nope, at least not more than mildly so on a local level. However, I happen to have a Fox as well as many of the components listed above, so the build should be cheap. And I’ll still be able to have a lot of fun.
My own build will start with an AOD equipped 92 GT. It was originally purchased with the intention of resto-modding it with a mod motor swap and some other goodies and making it a clean daily driver. However, the decision to sell my race chassis has left me without a race car. Since the decision to sell the chassis was based largely on financial reasons, and I happen to have a ton of spares that just happen to be ESP legal, it makes sense (to me, at least) that I build the GT as a dual purpose daily driver and ESP autocross toy.
Autocrossing the Fox: A Primer
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At this point, my autocross experience is pretty limited and my knowledge of Mustangs is only a little better than that. What follows is basically just compiled information I’ve picked up as the internet’s biggest Mustang Bench Racer. It’s meant only as a primer, folks!
What is autocross?
Basically, its a miniature road course set up in a parking lot or maybe some blocked off roads and marked by cones. The competition is divided into classes depending on car and modifications, the course being run one vehicle at a time, with each run timed. Every cone hit adds two seconds to your time and you usually will have three or four runs, with quickest time winning. 5.0 Mustangs will find themselves in one of the following classes; F Stock (FS), E Street Prepared (ESP), Street Modified (SM), C Prepared (CP), X Prepared (XP) or E Modified (EM).
The Fox Mustang
When someone refers to the Fox platform Mustang, they’re generally referring to the 79-93 model years. The 94-04 Mustangs are commonly referred to as the sn95, but are still Fox based. People who try to autocross either of these must be either sick, or hopeless Mustang nuts (or both?), as these are poor handling cars, plain and simple. The suspension design comes from the 78 Fairmont for goodness sakes! In 2005, the Mustang got a complete redesign with the s197 chassis and is much better handling, but the s197 isn’t the focus here.
All Mustangs from 1979 to 2004 use a strut front suspension. Strut suspensions are simple designs that use only one control arm, a spindle, a strut and a spring on each side of the car. This design can be manufactured inexpensively and is light weight, but it also limits the performance potential of the suspension. Dual A-arm suspensions can be designed to perform far better than a strut style suspension, but this doesn’t mean that strut suspensions all perform poorly; both the M3 and 911 use strut designs. And just because its a dual A-arm suspension doesn’t mean it handles well - check out the Mustang II’s Pinto sourced front suspension. The problem is, the strut design in the 79-93 Mustang plain sucks. From 79-93, every few years the k-member was tweaked for a little better geometry, so basically, the newer the k-member, the better off you are. In 94 the lower control arm (LCA) length is a little longer which widens the track which makes them a little better. The 96+ (when Ford switched to the modular motors) has even better geometry.
The rear suspension in all of these cars, except the 99-04 Cobra, is a non-parallel 4-link solid axle design. Here the upper control arms (UCAs) are at dramatically different angles to the LCAs so that using only these 4 arms the rear end is held in place during both torsional/twisting forces (acceleration and braking) and lateral forces (left and right turning). The problem with this is that when cornering, the UCAs bind as the car leans over. This is because the angles of the UCAs and LCAs conflict and need bushing material for compliance. When the compliance is gone, the suspension binds and the rear end suddenly loses traction, resulting in snap-oversteer. Many think (myself included) that aftermarket UCAs or harder bushings in both ends of the stock UCAs make this problem worse as they offer even less compliance, creating even more snap-oversteer.
How do you fix these problems? The most common way is to bandage them with higher spring rates and after market control arms. The real solution is to redesign the suspension. Companies such as Griggs, Maximum Motorsports, and Evolution Motorsports are taking care of this upper-end market. Most people who are more into the autocrossing V8 pony cars than Mustang brand loyalty choose a 3rd or 4th generation GM f-body (Camaro or Firebird). These are far better handling cars with the 3rd generation cars having a strut front suspension far superior in design to the Mustang’s. The 4th generation cars get a short-long arm (SLA) dual a-arm front suspension and both 3rd and 4th have a torque arm rear suspension. For what its worth, Griggs’ and Maximum Motorsports’ popular rear suspension redesign for the Mustang also utilizes a torque-arm.
That’s as deep as I’m going to go into the specifics of the Fox Mustang’s suspension geometry. If you’re interested in more specifics on the Mustang’s suspension, Miracerros.com has a really nice write-up on Late Model Mustang Suspension Basics.
FS
Just because this is a stock class, doesn’t mean you can’t modify anything. Air filters, struts, shocks, tires, brake pads, cat-back exhaust and the front sway bar can all be changed. The Fox is completely outclassed by the sn95 cars, and the newer s197 chassis is even better.
ESP
Street Prepared and Prepared work with cars classified along “lines.” The 79-93 Mustang and 79-86 Capri are all listed on the same line, so parts can be swapped between them. Here intake and exhaust are open, struts, springs, wheels, tires, swaybars, panhards, torque arms, suspension bushings, camber/caster (CC) plates can all be changed as well as updating/backdating between designated years. You cannot add non-stock subframe connectors (currently), non-stock rear gears, aftermarket control arms, do much internal motor work or add forced induction. The Fox chassis hasn’t proven to be competitive due to its poor suspension geometry, flexible chassis, and low power (comparatively). The sn95s do far better here because of the stiffer chassis, better front grip, and better power of the modular Cobra or 351 Windsor from the 95 Cobra R.
SM
At first glance, SM sounds like a good fit for a Fox as it allows several of the common upgrades; subframe connectors, gears, cowl induction hoods and radical engine modifications. However, you can’t change any of the control arm mounting points, and you can’t replace the k-member, so you can’t fix the poor front suspension’s geometry. In SM, a rear wheel drive car has to weigh 1800 pounds, plus 200 pounds per liter. This puts a stock 5.0 Fox Mustang at 2800 pounds. Stroking the motor or adding forced induction will cause more weight to be added. However, the most the car will have to weigh is 3100 pounds. In general, SM is a faster class than CP and doesn’t allow you to truly “fix” the suspension geometry, which is far more important than horsepower in autocross. In a nutshell, you should be able to build a more competitive dual purpose street-autocross car for CP than for SM.
CP
C Prepared has to be the coolest class in Solo2, period. CP cars tend to be crude, gutted, stiff V8 sedans with loud exhausts and very fat tires. The high end prepared cars have completely redesigned front and rear suspensions that are usually adjustable, high rpm, high horsepower 310 CID V8s (cars with engines over 310 have to weigh 3000 lbs, 300 more than 310 engines) and radically flared bodies to cover the massive slicks. Having a tubular k-member adds 10% to your base weight as it causes your car to be considered “in excess” as a tube framed car. You can modify the heck out of your stock k-member though. And forced induction is a no-no.
XP
XP in an interesting class, as it’ll allow you to run any engine you want, and figure out your car’s minimum weight from a formula. You could run a LS Chevy in your Fox if you wanted. However, “in excess” cars are not allowed, so you couldn’t do a k-member swap. But you could still modify your k-member. XP will end up a hella-fast class though.
EM
So, where do you autocross your twin-turbo modular powered, tubular k-membered, IRS equipped FOX? EM, that’s where. And you’ll be uncompetitive on anything other than a local level. The typical cars here weigh half as much as a Mustang, have as much power as any Mustang out there, and are usually as, or more, purpose built than a CP car.