5.0 Mustang & Super FordsHow To Chassis Suspension
Grigg's Autocross/Open Track Front Suspension - Been There, Done It All
Like The Street, Strip, And Road Course? Griggs Racing Has A Chassis Plan For All Those Places, And More
Don't let Griggs Racing's dominating racetrack performance fool you. Ninety percent of the company's business is with street Mustangs. Griggs will know what to do with yours.
Credit the idea of this article to something Bruce Griggs said to us years ago. We had been discussing the huge array of suspension parts Griggs Racing offers, and how the same basic suspension system could be tailored with a few hardware changes to shine on a street car, or while the car is laying down scorching laps at a road racing track, digging in at the dragstrip, or wrapping itself around cones at an autocross.
What Bruce pointed out was that just about all his customers initially ask to have their car set up for one such specialty, be it drag racing, the street, or the road course. But, eventually, nearly every customer wants it all. That is, after sampling their car's new-found grip for their favorite specialty, they discovered they liked the way it worked everywhere else. So the autocrossers were drag racing on grudge night, the road racers were looking for street satisfaction, and so on.
What's more, with a few careful parts selections when initially installing the suspension, and sometimes a bit of hardware tweaking on track day, the Griggs Racing GR-40 system can deliver such all-around versatility.
The Holy Grail
When you think about it, what is it all these people are looking for? It's traction. The stock Mustang suspension-especially the confused four-link rear-is awfully random on traction. Get heavy on a stock Mustang's throttle and you've opened a lottery on whether the rear tires are going to stick, no matter if you're at the dragstrip, street, or road course.
And the front end? It's designed to give up early and gradually to protect inexperienced drivers. What the GR-40 system delivers is traction on demand, both in a straight line and while cor-nering. Furthermore, that traction is wonderfully linear and communicative-that gnawing fear of the car suddenly fishtailing is replaced by a calm confidence the chassis will stick faithfully until the tires finally give up. In other words, the GR-40 system always tells you how much grip is on hand and doesn't toss out pop-up surprises. That's a great thing, no matter what you're doing with your car.
So What's The Secret?
So, how does the GR-40 suspension function so well at different disciplines? The underlying fundamental is the GR-40 system separates the suspension's tire-locating function from its torque-control function. That is, the pieces on the GR-40 system that control wheel movement as the suspension compresses and extends are not the same pieces that absorb braking and engine torque forces.
As you may have guessed, the stock Mustang rear suspension has four links that try to do both jobs, and because of the compromises involved they do a poor job of both tasks. At the front end, the GR-40 system makes what are really subtle changes in the stock geometry-a pivot point moved a bit here, the strut laid back a bit there, and so on- to make it a better partner to the revised rear suspension and to optimize the Mustang's strut front suspension for today's big, fat tires.
The basic hardware pieces that do this job at the rear are the torque arm and Panhard bar, and the K-member, lower control arms, and caster/camber plates in the front. These are the guys doing the heavy lifting in sorting out the Mustang suspension geometry.
Naturally, there are many other associated parts, and while they have secondary effects, their careful selection is how the basic GR-40 suspension is tuned. As an example, there are seven different Griggs rear lower control arms. All offer the same geometry, but they differ in the type of end link or whether stock-style rear springs or coilover spring/ shocks are used. There is no one control arm style that is best, but rather one of these arms is best suited to a specific application.
Luckily, Griggs has made the job of selecting the right parts much easier by organizing several GR-40 kits to fit popular needs. These are the Drag Race, the Street Performance, the Autocross/Open Track, and the American Iron/World Challenge kits. They make selecting the major GR-40 pieces quick and easy; from there, numerous options are available for tuning the suspension any way you like it.
Because we're highlighting the all-around possibilities of the GR-40 system, we asked Griggs which of these kits is the best place to begin when the goal is a daily driver Mustang that can be used for open-tracking, autocrossing, and drag racing on the weekends. It's an unfair question, as there are so many details that could go one way or the other depending on which part of the Mustang hobby was foremost in the owner's mind, but we had to begin somewhere.
Grigg's answer to building an all-around Mustang is its Autocross/Open Track kit. Compared to other GR-40 kits, the A/OT is a little lighter, completely adjustable, and offers looser balance (it's closer to oversteer) to aid in whipping around the tight autocross corners.
The Autocross/Open Track Kit
Let's take a mental inventory of the Autocross/Open Track kit to see how it works as the best all-'rounder. There are minor variations of this kit depending on whether you have a '93-or-earlier Fox chassis or a '94-and-later SN-95. Typically, customers end up making optional changes after conferring with Griggs, but a general description will get us started.
Step one is to reinforce the Mustang chassis with the Complete Frame Kit included as part of the Autocross/Open Track kit. This step is so important we've set it aside as a sidebar (see Stiff Stuff).
When it comes to the suspension proper, changes to the rear suspension are the first step, so we'll begin there with the 8.8-inch rear axle TA cover and the Griggs Severe Duty Torque Arm designed to work with that cover. Griggs says the TA cover reinforces the differential somewhat for dragstrip use, but probably more importantly the company notes the TA cover makes a better mount for its torque arm than the stock differential cover.
The Severe Duty Torque Arm is a step up from the standard torque arm used in the Street Performance kit. It's essentially a torque arm with double beams welded together to better withstand the torque loads imposed on it by either high-powered engines (approximately 400 hp or more) or low axle gearing (ultra-low geared autocross cars are hard on torque arms and should always use a Severe Duty unit). Griggs notes that practically every one of its customers plans on making 400 or more horsepower sometime in their car's lifetime, so the sell rate of Severe Duty torque arms is high.
In reality, it's difficult to say when the standard-duty torque arm should be changed to the Severe Duty example, as driving style has much to do with it. Slicks, a freshly glued dragstrip, 400 hp, and a driver infatuated with 7,000 rpm launches are begging for the Severe Duty torque arm. On the other hand, big-time horsepower in a road racer driven with finesse won't hurt the standard-duty arm. In any case, the Autocross/Open Track kit comes with the Severe Duty torque arm. It has no downside for street use other than it costs an extra $325 for the combination of heavier torque arm and TA differential cover, compared to using the standard torque arm and stock diff cover as the Street Performance kit does.
As for the Panhard bar, Griggs opted for the same nonadjustable Heavy-Duty piece for the Autocross/Open Track kit as used in the street kit. The important concept here is the nonadjustable Panhard bar leaves room for over-the-axle tailpipes as used on street cars.
There is, however, the option of the adjustable Panhard bar on our proposed all-around car. That's because Mustangs built with some track activity in mind often use lighter, noisier, turndown tailpipes that dump immediately after the mufflers and before the rear axle. These open up the body's axle cavity so the adjustable Panhard bar can actually be adjusted up or down through its five mounting holes. With tailpipes in the way, adjusting the Panhard bar is impossible.
Any time a torque arm and Panhard bar combination is used, the rear upper control arms are not necessary and are removed. So there are some parts we don't have to worry about.
Rear lower control arms are still definitely needed. For the Street Performance kit, Griggs uses fixed-length (nonadjustable) lower arms that include a spring seat for the stock coil spring and urethane bushings at either end. Even without the upper control arms, these bushings/arms still have a bit of bind in them. Therefore, the Autocross/ Open Track kit lower control arms use a spherical bearing at one end to eliminate the bind. These arms are also adjustable in length and have no spring seat because coilover shocks are used with the A/OT kit, rendering stock-type springs and their seats unnecessary.
Speaking of coilover spring/shocks, their advantages are many. The shocks-Griggs uses Konis exclusively-are lighter, strong, and simply better shocks than stock. Griggs uses adapted single-adjustable Koni race shocks with the latest high-speed compression valving curves and some other Griggs-only valving specs, not modified street shocks. And, a huge number of high-quality springs are available in rates varying by just 25 lb/in (and they are less expensive than stock-type springs), and the ride height is infinitely adjustable. These are all concerns in an all-around car, so while the coilovers contribute greatly to the Autocross kit's extra $1,000 price tag compared to the stock-sprung Street Performance Kit, they're the way to go.
Griggs notes that while there is no lifetime guarantee on these race-derived Koni 30-series coilover shocks, they've proven more durable than street-based shocks. That, and they're only $125 a pair when just replacing the shock.
When considering the front suspension, Griggs is more relaxed in what is required and what is beneficial but not necessarily mandatory for an all-around car. The difference depends on the intended use. If occasional competition is the goal, then fewer hot rod parts are required compared to a car with the primary goal of winning an autocross or drag race, then being able to drive home as long as the cops aren't watching.
The Autocross/Open Track kit includes the tubular K-member, of course, along with tubular lower con-trol arms. The Autocross kit uses Delrin bushings in the lower arms, a step up from the Street kit's urethane. A bumpsteer adjustment kit is required to get the tie-rod ends straightened out on all cars, while competition-oriented cars should add the all-steel lower steering shaft spec'd in the Autocross/Open Track bill of materials.
A must-have are caster/camber plates, and, naturally, coilover shocks to complement the rears. Griggs recommends the significantly more expensive double-adjustable Konis for dialing in ride quality if nothing else (modern Koni Sport shocks must be collapsed to adjust). High-powered drag cars really should have the double-adjustable shocks for controlling how fast they pick up their front ends.
Additionally, SN-95 cars need an Anti-Roll Bar Relocator kit up front. This moves the sway bar forward because the Griggs control arms/K-member have moved the control arms forward. Furthermore, the actual end links should also be shorter-a $25 set of such links is also available from Griggs.
Installation of the Autocross/Open Track kit is beyond the scope of this article, but in overview, the rear-axle portion of the kit requires a fair amount of welding. Thus, that part is almost always sent out to a pro.
The front axle parts are all bolt-on pieces, however, and Griggs reports many customers do the work in their driveways. Additionally, the '93-and-earlier cars require minor front fender modifications to pull out the front lower corner of the wheel opening. Otherwise, the tire rubs continually.
Installation can also be spread out over time in order to soften what is a financial right hook to most of us. In that case, the order of operations is as follows.
1) Chassis kit (stiffening)
2) Torque arm and Panhard bar
3) Coilovers front and rear
4) K-member, front control arms, and so on
5) Additional horsepower
This order of operations results in a safe-handling vehicle throughout the build. In fact, some Griggs customers stop after adding just the torque arm and Panhard bar. They find the handling improvements from just the rear sufficient. Our guess is these are mainly straight-line-oriented people, or at least not real hard chargers on the road course. That's because a rear-only Griggs system really plants the rear tires and can result in understeer when pushing hard on the road course.
How To Use It
OK, so we've installed the Autocross/ Open Track kit-now what do we do with it? Well, really, you could leave it alone and have a ton of fun. But if a bit of fiddling will satisfy your tinkering urge, there are some tricks to explore.
For the street, relatively soft spring rates (350/200 lb/in, f/r) give a won-derful ride, as plush as stock with greatly reduced brake dive and good roll control. The car will handle like a dream and will absolutely not beat up you or your passengers in the process. These soft springs are also great at the dragstrip, where they allow fast chassis reaction at the launch, aiding rear traction.
Get on a road course with the street springs, and depending on your driving skill, you'll reach a point where more spring rate will help, but you can still go fast on the street spring rates. If you do want to swap springs on the coilover units, it's a hand-tool-and-floorjack job because they are easily unloaded, unlike stock-type springs. Griggs says open-track-oriented customers often run 425/250 lb/in spring rates for both track and street driving. In any case, by far the best advice is to call Griggs and follow the staff's ideas on spring rates, as each car/driver/track combination is a little different. Otherwise, the open-track fan can simply install stickier tires, firm up the shocks in the front, dial in some negative camber, reduce toe, and move the Panhard bar up if they have the adjustable one.
Drag racers may also want to go to a really soft front spring, turn down the rebound dampening on the struts, and definitely disconnect the front sway bar to aid weight transfer at the launch.
An adjustable Panhard bar is a big help when tuning for conditions. Moving the Panhard bar up and down raises and lowers the rear roll center, which is the best way of dialing in over- or understeer. Raising the rear roll center increases oversteer-just what the autocrosser needs on a tight course. Rain? Lower the Panhard bar to its lowest of five settings to promote stabilizing understeer.
Does It Work?
Sure, it does. We've been driving GR-40-equipped Mustangs for nearly 15 years, and they are absolutely pole-position automotive triathletes. We've seen GR-40 cars drive hundreds of miles, run 10s at the strip, drive home, and a week later hit the road course as if they were born there (which they were). John Griggs, Bruce's son, reminded us about one of his 5.0 convertibles. It ran 12.0s at 114 mph using a big nitrous hit and the suspension described here tuned with soft, 200 lb/in front springs and 175-lb/in rear springs. A great setup for drag racing, John could still humble 'em on the road course with the ragtop, albeit with some understeer. We also found it plenty entertaining on the street when we drove it. You won't be disappointed.
Early in the 5.0 days, when most Mustang tuners were thinking 160-degree thermostats and offset rack bushings were high technology, Griggs Racing did extensive testing of the Mustang unibody. What it found was the center of the chassis had the structural integrity of cooked spaghetti. The front and rear suspension attaching areas weren't exactly world class either, but the center of the car was terrible-and that was with hatchback and coupe bodies. The convertibles were downright scary, being held together strictly by the sheetmetal in the floorpan, together with whatever the overworked rocker rails along the sides could contribute.
Bruce Griggs thus began where it counted, with twin-spar subframe connectors that gain a ton of rigidity by being tall in a vertical plane. Think of floor joists in a house. You could try a zillion 2x4s under the floor, but at only 4 inches deep, such a floor would never be strong. Yet a few 2x12s make incredibly strong floors because of their deep vertical span.
Grigg's through-the-floor subframe connectors work like 2x12s. Called the Complete Frame kit, they begin at the unibody's front framerails with two tubes, one atop the other, and with the top tube slightly diverging from the bottom tube. The bottom tube ends up running under the floor to the unibody's rear framerail. The top tube runs up at an angle through the floor, protruding to its maximum height in the rear passenger footwell by several inches. Then it submerges through the floor again, to join its sister tube at the unibody's rear subframe box structure. Additionally, the two spars are joined by a vertical member about midspan. You could accurately call these things subframe connectors, but they are miles ahead of the typical undercar variety. The Griggs pieces are welded all the way along to the floor and take eight hours to install. Chassis-bending resistance increases an eye-widening 1,500 percent.
These connectors are absolutely mandatory on convertibles and highly recommended on coupes/hatches, although Griggs has its own version of undercar sub connectors if money, time, or rear footwell space are big considerations. Also, while the through-floor reinforcement is not visible in front of the driver or front passenger seats, the power-seat support on '94-and-later Mustangs must be exchanged for a manual adjuster for space reasons under the seat.
But the real bottom line is, no matter what subframe connector style you choose, step one is stiffening the Mustang's notoriously weak chassis.
While the Autocross/Open Track kit offers an adjustable Panhard bar, for more than two years Griggs has been offering a Watts link, and more and more customers are opting for it. It's a word of mouth issue, says Griggs, and the word is getting around. We have not tried the Watts link back-to-back with the Panhard bar, but those who had a Panhard bar and then swapped to a Watts link say they can feel a real difference in transitions, such as the esses on a road course.
No doubt they do, but considering the additional expense and how well the Panhard bar works, we'd be tempted to save the Watts link for cars that see some track action-but that's between you and your wallet. The Watts link is $649, the TA cover modified to work with it is $259, and there's a $59 cover plate to seal the hole in the spare tire well where the Watts link's upper horizontal bar passes through the sheetmetal. This also means the spare tire won't fit flat in its well, so there's another issue on a street car.
Still, for a fun project car, why not go for the gold? The Watts link has four height adjustments, which dial in under/oversteer just like an adjustable Panhard bar, and it works with over-the-axle exhaust tailpipes.
Speed Costs Money, and So On
Ecological pressure to close U.S. steel plants and underestimated demand for steel by China has fueled skyrocketing steel prices. Griggs says this has amounted to a 125-percent increase in its raw material costs. A "market price" thus exists on Griggs parts, similar to fresh fish in a restaurant.
Here's a quick summary of Griggs' published price-understand they're likely higher when you order. Check with Griggs for the Mahi Mahi price when you're ready.
The higher '94-'95 prices are due to more expensive camber plates and lower steering shafts on the later cars, along with the Sway Bar Relocator kit that is not needed on the earlier Mustangs.