Muscle Mustangs & Fast FordsHow To Chassis Suspension
1997 Ford Mustang GT Suspension - Beginner's Luck
Our little filly gets a full chassis overhaul courtesy of Griggs Racing.
We ALL want to go fast. Horse-power is king in our myopic world of best e.t.'s, but when building a vehicle to do double duty between daily driver and open track racer, speed in other areas is just as important. Fast around a corner is as important, if not more so, than speed in the straights, and if your plan is to add considerable horsepower and torque down the road, it's a good idea to tighten up the chassis as much as possible because stiff is fast and flex is, well, second place.
Stopping fast is also important, but we'll get to that soon enough. For now, we're going under the car to clear out the old and import an entirely new GR40 suspension system from Griggs Racing, including its Short/Long Arm (SLA) front suspension, a Watts link rear suspension, and subframe connectors for stiffening. But first, a little pregame analysis.
The stock suspension on the '97 is a little squishy, a little boaty, but gets the job done pretty well for a daily driver. The ride is smooth on the open highway, but still has some strength in the turns. It's not until you put the car under duress that the flaws start coming out. On an open track, at higher speeds, the body roll is considerable, and prevents a driver from really pushing the car. Also noticeable is the dramatic understeer. This will vindicate drag racers, but the car feels like it wants to go straight.
For those who read Part 1 of this project in the May issue, you know that this is my first attempt at building a project car. The goal here is not just to tell you what I did, but also to explain from a novice's point of view the reasoning and results behind the buildup. Most readers probably know a lot of this information already, but for the quick starts like myself, consider this a crash course in physics.
To start, the tighter you can make the suspension, the faster it'll make it around the track, but I also want to drive the California freeway system without needing a kidney belt. On top of that, the stock profile of the GT resembles something closer to a 4x4 truck, with huge gaps between the tires and the wheelwells-and we all know that a lowered car is much cooler.
Without needing any further motivation, the folks at Domestic Performance and Restoration in San Diego put the car on the lift and immediately began tearing apart the front end, basically removing anything that wasn't part of the powertrain. With two guys working on the car, the entire front suspension was removed or pushed aside to make room for the new equipment.
At first glance, the Griggs parts are slimmer, sleeker, and a lot more colorful, mostly dressed in Griggs' standard blue anodize. Once you pick up the parts, though, you notice the heft and durability of the equipment-not heavy but strong. The last piece removed is the stock K-member replaced by the new tubular one. The first question that comes to mind is why does Ford use so much metal on a part that can easily be a lot more sparse? Without the use of a Ford engineer, the first thought has to be with cost. It's much easier to stamp out a big piece of tack-welded metal than mandrel-bend tubing and weld it together.
We didn't have access to a scale, but just by comparing the two parts side by side, it's apparent that we lost a reasonable amount of weight in the front end just by replacing the stock K-member. Then came the SLA Mini Towers, the lower A-arms, and the coilover shocks. Once the coilovers were installed, I noticed their positioning in relation to the stock struts. The new setup puts the coilovers in a more upright position over the wheel, which makes a lot of sense in regard to carrying the load of the front end. I also noticed the gaping holes in the engine bay that used to be the upper mounts for the struts. Aesthetically, the holes look a little funky, but I just used them as peepholes to my new suspension. I did joke with Griggs saying they should send along aluminum plates to go over the strut mounting hole-a piece of aluminum with the words "Griggs inside" etched into the top.
DPR's Greg Smith and Shawn Fowler finished up the front by replacing the stock spindles, adding a new steering shaft and tie rod ends, and putting the brakes back together. We're just about finished with the front except for the antiroll bar. Everything so far has mounted into stock positions, but the bar needs to be repositioned a bit, so we'll drill a couple of holes and weld up a mounting point along the front framerails. The antiroll bar will start here and connect to the SLA setup. The ride height and alignment adjustments will be handled once the entire car is together.
Shawn puts the wheels back on the car to make sure the fitment is still good, and then places the car on a drive-up-style lift in preparation for welding on the subframe connectors. You want the suspension fully loaded when welding up the connectors because if you use a frame-mounted lift, there is a chance that once you have the connectors on the car, the chassis could be slightly crooked, making the doors not close correctly or the stance of the car would be off a bit. Using a drive-up lift prevents this from happening.
Greg welds up a crossmember that will hold one end of the torque arm. One thing we noticed was how close this crossmember came to the "H" in the stock midpipe. The torque arm gets mounted with large rubber bushings that will most likely melt down after a while from the heat of the exhaust. Griggs' recommends moving the crossover pipe forward, or installing a good x pipe system, for all the benefits they give.
Finally, before tackling the rear suspension, Greg removes the tailpipes (with all the subtlety of an axe murderer) to make room for the Watts link. He then saws the pipes just past the muffler. Again, this is more out of function than aesthetics, but you do get a nice, deep tone to your exhaust note. Being from California, I already see one possible downside, though. Smog testing facilities usually put tubes over the exhaust pipes when running their test to vent the exhaust outside. The tester is going to have a hard time finding mine now, but I'll deal with that problem later.
When it comes to the rear suspension, the word of the day is "modify." There are few parts to the Watts link setup, but there is definitely more work involved, mostly in massaging parts into place. From the get-go, Griggs suggests cutting part of the plastic gas tank cover and also cutting into the spare tire housing to make room for the Watts link frame, which is a well-engineered piece in itself, but it becomes quickly evident that it fits in one spot and one spot only. I didn't really want to cut into my spare tire housing, so we "modified" it with hammers. We removed the differential cover and replaced it with the new cover. One end of the torque arm mounts here, and when we mounted the other end, the rubber bushing I mentioned before was a tad thick, so Greg "modified" them with a knife. From everything I've experienced so far with this car, the one constant is that there are never any guarantees. Bruce Griggs has spent a good portion of his life engineering suspensions to work with different vehicles, but no matter how many Mustangs you work on, the next one will probably be a little different. I asked him about the bushing issue, and he could only speculate that my driveshaft clearance was off probably due to the upgraded transmission not being shimmed in the stock location.
Earlier, while Greg was "modifying," Shawn removed the rear lower control arms and rear shocks, making room for the new control arms and rear coilovers. Once those were mounted, Greg attached the links from the frame to the bell crank mounted on the diff cover. The bell crank came mounted to the cover at the second-from-the-top spot. Typically, this is the position where Griggs recommends starting on any track-driven car. Later, when I get to the track, if I need to I should be able to move up the Watts link to loosen the car during corner exit (increase oversteer), or down to tighten the car (increase understeer).
The guys buttoned up the last few nuts and bolts on the rear, set the coilovers to a lowered yet reasonable ride height, and adjusted the tie rods to allow for a small bit of toe-in, where the wheels are pointed slightly inward toward each other. This setting is for street use; hard tight cornering like autocross may require toe-out settings. Then they lowered the car off the racks and let me take it for a spin.
The difference was immediate. When I steered the car, it turned without hesitation. It also felt like the entire car was moving together rather than forces of gravity and inertia pulling it different directions. Those are the pluses. I also noticed it's much louder in the cabin than before. The exhaust is louder because of the cut tailpipes, but I also hear more of the road. It's almost deafening at first. Shawn says it's the torque arm that is transmitting all that noise down the center of the car. The torque arm is also helping put what was once displaced power back to the wheels where it belongs, so a little more noise is worthwhile.
I rolled the car back into the shop and without even letting it cool down at all, the guys started ripping apart the interior, pulling out the seats and carpet, and started cutting into the floor to make room for the in-floor subframe connectors. I was apprehensive about installing them at first because I thought the car would be too stiff, but after they put the bars in, welded them up, and replaced the interior, I took it for another drive. I was right about the car being stiffer, but not in the uncomfortable way I expected. Instead the car felt tighter, as if for the first time all pieces were tied together. It felt snug like a machine tied to my slightest movement. On top of that, it was quieter in the cabin. The road noise diminished a bit, and all the creaks and groans of a traditional Mustang were all but gone.
I brought the car back one last time for some fine-tuning. You may not have this available to you, but if you do, I recommend it. The guys at DPR called a friend who brought over a set of scales to corner balance the car. Since the Griggs system provides for infinite ride height and corner weight adjustments-just like any good race car-they said you should do this to obtain maximum benefit from your investment.
I could tell what was going on because they balanced the car with me in it, adding and subtracting adjustments to the coilovers and tie-rod ends to get the perfect balance from front to back and side to side. Although not as extreme, I felt even more change to the ride and handling of the car. On the long drive home from San Diego to L.A., I kept the radio off and instead listened and felt the road all the way home.
When I put the car through the paces at SVTOA's Howling at Buttonwillow (see June '06, "In Case You're Not Going to SEMA"), chasing down cars with far more horsepower, the improved handling became abundantly clear and the car was, well, faster. That being said, it is my goal to get my hands on a set of R-compound tires.
This Mustang stuff is fun.
|Street Use:||Camber: -0.75 deg |
Caster: 6 deg
Toe: 1/16 in
|R-Compound Tires:|| |
Camber -2.0 deg