Muscle Mustangs & Fast FordsHow To Chassis Suspension
Stiffened & Slammed Part 1
We Put the "Handle" in Project Hot Handler with parts from HP Motorsport, Koni and Eibach.
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After months of prep work we've finally put the "handling" in our Hot Handler project car. If you've been following along, you know a fresh coat of paint covers the high-mileage '87 LX hatchback body, and the interior has been renovated with new ACC carpet and new trim pieces from LRS and afterhoursracing.com. Occupants ride on a set of used FloFit seats, which came from our Pro 5.0 giveaway project car. And while our Mustang now looks pretty cool, the real intent of the project is to make this pony slice through the turns, so the time has come to rip out the underpinnings and install much-improved suspension components.
To make our LX move like a cat, we had to first think like a cat. We know that cats have nine lives (which is not bad, if you plan on purring around a road course), and there is more than one way to skin a cat (but don't tell that to your friendly feline). And, just like there are many ways to skin a cat, there are many approaches to car building. Especially if you're after one that can out-handle or out-accelerate the competition.
When it comes to suspensions, there are about a dozen manufacturers selling aftermarket kits and related handling-oriented parts. Many of these links, braces, bars and dampers may look alike, but there are quite a few different system designs, such as the three-link, four-link, five-link, torque arm, etc. Most parts work best when installed in kit form, and it is also best to stick with one system of parts. Of course, you can enhance the performance of your steed by simply lowering it, but a complete suspension system will offer the best results.
Once you begin your search, you'll find there are some exotic parts that work well but cost a fortune. There are also basic, inexpensive upgrades that work great. In my case, I wanted to stick with affordable equipment that improved handling but wouldn't break our backs (by being too stiff) or our wallet. And simply slamming the car to the ground was not going to do.
I surfed the Internet and read catalogs but finally decided to call on Paul Brown, of HP Motorsport (HPM), to help us prepare our street/track Mustang. HPM sells a variety of components, including its Touring System, designed for the street and the track, and it has an impressive on-track record. "We call this group of parts the Touring System, because it will improve handling but won't make the car unsuitable for daily driving. "But I normally like to group the parts based on the customer's needs," says Brown. This package consists of HPM's Lower Chassis Brace, Strut Tower Brace and Cross-Bar Sub-Frame Connecters, (to stiffen the chassis) along with adjustable Caster/Camber Plates, the Mega-Bite Jr. rear lower control arms, and an adjustable Panhard Bar. Brown suggested we complement the HPM parts with Koni adjustable struts and shocks and Eibach's Pro Kit that includes lowering springs and thick antiroll bars. We did just that.
Before getting started with any late-model Mustang project, it's important to understand the beast. This means realizing that the first area to be addressed is the chassis. All '79-present Mustangs feature a unibody chassis (or frame) to which all the suspension components are attached. The unibody is really a stamped steel metal box that makes up the underbody and frame of the car. It also has spot-welded brackets to serve as suspension mounting points.
Those who have raced a Mustang competitively surely realized that the body structure, or unibody, is not strong enough to handle the rigors of hard launches or high-g-force turns, and, in some cases, the actual chassis structure can flex and/or welds can crack. Since the rear suspension and front K-frame are bolted to the unibody, any flexing will result in inconsistent handling (or launches) because the suspension links will not act the same from run to run or from lap to lap. Therefore, it's important to first reinforce the unibody structure before any other modifications are made.
This is easy with the HPM kit. First we'll be installing the beefy cross-brace subframe connectors. These cross-braced units will be welded to the bottom of the car and will effectively link the front subframe to the rear subframe, where all the suspension parts are located. They also tie into the lower seat bolts to add strength to the chassis. The strut-tower brace helps to stiffen the vehicle by providing a bridge between the strut towers. This area is subject to flexing in and out during hard cornering as the top of the struts are loaded. Last on the list of HPM chassis parts is the lower chassis brace that strengthens the chassis at the point where the K-member is attached to the unibody. To further enhance the strength of the chassis (and to add driver safety), we plan on adding a roll bar at a later date. With a stiffened chassis, we're able to confidently install the HPM suspension parts.
One surefire way to turn quicker, flatter, and more accurately is to lower the center of gravity. This was accomplished with the new coil springs found in the Eibach Pro Kit. The Eibach coils are shorter than the stock springs, and they have a stiffer rate to prevent body lean in the turns. The stock springs have a variable rate (from 425-530 pounds), whereas the Eibachs are progressive and have a rating of 450-580 pounds. The rear Eibachs are also progressive (205-251 pounds), and the stock coils are variable from 200-300 pounds. However, Brown tells us that the rates are not necessarily comparable because there's no standard rating system. Controlling the jounce and rebound of the springs will be a set of adjustable "yellow" Koni Sport dampers. These shocks and struts feature race/street valving, suitable for a Mustang with lowering springs and a hot suspension. Because they are adjustable, you can run them soft on the street and tighten them up at the track. From experience, we know that sometimes using a soft setting will keep the tires compliant with the road or track, and that will produce better control and quicker lap times.
Another essential piece of any Mustang handling kit is the antiroll bar, sometimes called an antisway bar. Antiroll bars are actually torsion bars that work to keep the body of a car flat during cornering. When you enter a turn, the inside lower A-arm lifts, while the outer one drops, and since the roll bar is connected to each (and to the chassis in the center), it fights itself to keep the vehicle neutral or flat.
In addition to the rear antiroll bar, we also installed lowering springs and a HPM Panhard Bar. "The Panhard Bar kit is engineered to provide optimum handling performance by relocating the rear roll center to a lower position. It also positively locates the rear housing and prevents it from moving from side to side under cornering," explained Brown. And, when the rear housing moves, it will steer the car and you don't want that. Last on the list of rear suspension parts is the Mega-Bite Jr. control arms. Where the stock arms are formed from stamped steel and have soft rubber bushings (both prone to flexing), the HPM bars are boxed and have stiff polyurethane bushings. They are also angled upward to provide more bite at the tires.
From our experience, we can tell you that you'll end up pleased when you find a combination that suits your driving style and needs. Sure, some systems will perform better than others on a track, but you may sacrifice ride quality and end up unhappy with the way your car rides, even though it handles a turn quick and flat. In this, Part 1, we ripped apart the front end and installed the caster/camber plates, the strut tower brace, front antiroll bar, springs, and struts. In Part 2, we'll complete the job by installing the rear springs and shocks, the subframe connectors and the Panhard bar. Then we'll get the front end aligned, hit the track, and give you a full report; so stay tuned for more on the Hot Handler.