This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your Porsche Boxster. The book contains 312 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 950+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Boxster owner's collection. The book is currently available and in stock now. See The Official Book Website for more details.
The Porsche Boxsters are well known for their agility and superb performance in handling. However, because of the design of the chassis, there exists a weakness in the handling of the cars. The front shock towers are not well supported in the Boxster chassis: they are somewhat isolated and unsupported. As a result, the towers can bend and flex under heavy cornering. This flexing can cause detrimental changes in the handling of your car, because in general, the stiffer the chassis, the better the handling of the car. Camber strut braces are designed to maintain the distance between the shocks under heavy cornering. A bar linking the top of the shock towers insures that the towers do not bend when the chassis is flexing.
Well, that's what the marketers say when selling these bars. The strut bars are yet another controversial product that many people feel the need to install on their cars. On some cars, the early Porsche 911s for example, the installation of the strut bar is an important chassis stiffening device. Because of their rear engine design, the front chassis can be decidedly weak, particularly when rust has started to affect the chassis stiffness. But the Boxster mid-engined chassis is different: it's supported by a much more rigid frame, which includes a very strong sheet metal structure that runs the width of the car. Included in this are two welded strut braces that can be seen in Figure 1.
Which strut bars are most effective? First of all, I have little faith in the strut bars that are manufactured out of aluminum. Aluminum is not a very strong metal: you can often bend aluminum pipes with your hands. Add to that the fact that most of the strut bars must have some type of angle in them in order to fit neatly around the engine and under the hood: there's no straight shot across the engine bay. This combination creates a very weak support when you think of the forces you're trying to counteract. In my opinion, the aluminum strut braces are merely window dressing for the engine compartment.
I'm also not fond of bars with hinges built-in to the strut mounts. If they move at all, the shock towers are likely to see movement that would place the strut brace in both compression and tension. This means that a stiff connection between the strut towers is vital to proper operation of any strut bar. Any time you place a fastener in the assembly, you will introduce backlash and slop in at least one direction (compression or tension). This results in the bar becoming ineffective in at least one direction (compression or tension).
The best strut tower braces are the one-piece units manufactured out of thick steel pipe welded together. These will offer the best protection against any chassis flex when installed between the two strut towers. Unfortunately, I can't say that I've seen one installed in a Boxster that I actually thought would provide additional stiffness.
I also find it surprising that if you ask die hard racers who drive their Boxster cars on the track, most of them don't run with a strut brace, and can't even feel the difference even when pulling some significant side loads (1.4G) out of the corners. For dedicated track cars, the strut towers are often reinforced with steel pipe that is welded diagonally across the front trunk compartment. Another problem I see is that the Boxster already has reinforcement bars bolted from the shock towers to the chassis. These already provide a tremendous amount of structural support for the towers.
The bottom line? If you believe that a strut bar will do you some benefit, or you are looking to spruce up your engine compartment, then adding one to your car is a relatively simply task: simply bolt it on top of your strut towers. If your goal is increased performance, then I would probably spend your money elsewhere.
Shown here is a great-looking carbon-fiber strut bar that extends across the rear of the battery. This bar in particular is only really good for show, in my opinion. The aluminum brackets that these bars are manufactured out of are relatively weak, are designed with multiple fasteners, and also have their strength weakened by the angled bracket design. Ironically, the entire strut brace is hidden by the side plastic covers, thus diminishing its visual appeal as well.
I included this photo of an E30 BMW M3 to illustrate what I feel a good strut brace should look like. Although not as attractive, the brace shown in this photo is probably one of the most effective I've seen. It's a thick, large diameter steel pipe that directly reinforces the shock towers, and requires significant forces to deflect and bend. Despite the fact that there are two rather large angles in the brace, the strength of the steel pipe should more than compensate for the reduced rigidity. These are the types of bars that I recommend if you're going to be installing one in your car. Unfortunately, the lack of room in the Boxster's front trunk make the installation of this style somewhat prohibitive.