by Robert Kozak
For the past 25 years, doorslammer rear suspensions have been dominated by the four-link design.
The four-link is as common knowledge in chassis building as adding bread to butter. If you went to a chassis builder a few years ago and told him you wanted to run a fast door car, he didn't suggest a rear suspension option-- because there wasn't one that could match performance capabilities with the four-link. That is how reliable and trusted the four-link is, it's just a given to work as prescribed.
The benefits of this design have been many; they include but are not limited to accessibility, technical help and ease of adjustment. The accessibility and ease of getting technical help the four-link has remained unparalleled. It is readily accessible to the do-it-yourselfer; there are an endless number of manufacturers at the other end of your phone line willing to sell you one in kit form and back it with technical help. Nearly any chassis builder in the world could build you a four-link car backed by his working knowledge of the design. There have been several articles and even complete books written on the topic of four-link set up and design.
Track surfaces and weather conditions vary from place to place and time to time, so being able to adjust the chassis accordingly is a necessity with a four-link car. Four-links have a variety of possible locating points making it possible to compensate for different conditions in the track and/or the engine set up depending on the weather conditions.
For all of the benefits of the design, it has a few drawbacks, which include torque steer, the chassis unloading at gear changes, and repeatability, not to mention the racers themselves.
In recent years four-links have been put into some of the most violent launching cars on the planet and withstood the abuse-to a point. Having to withstand the intense abuse to which four-links have been subjected to, the fundamental design has not changed as much as it has evolved. In recent years, both builders and racers have attempted to harness the enormous power made by the engine combinations of today (1200 to 2000 + hp), by using various types of track locators, anti-roll bars, stiffer shocks and the double frame rail design. All of these advancements are designed to try to get the power evenly distributed to both tires, which would take care of the twisting that a chassis undergoes on launch and between gear changes. This twisting at launch causes torque steer. Torque steer is caused by the rotation of the motor pulling the car to the left. (To get an idea of this try punching the throttle from a dead stop in a front wheel drive car on a wet surface.)
When a car shifts from first to second gear it tends to unload the power from the rear tires then get on it again or lose traction altogether. This can cause tire shake and traction problems. This is where a driver must pedal the car down the track or get out of the throttle altogether.
The next problem is getting the setup to repeat each time. We all know that no two runs are the same due to a number of variables (weather, track, etc.). So trying to get a setup to repeat isn't always the easiest thing to do. This is where the racer becomes a factor, being able to adjust a four-link for different conditions is a plus but over thinking your self by having several adjustments is like shooting yourself in the foot. (HOW MANY HOLES DO YOU HAVE IN THAT RIGHT FOOT?)
Enter the challenger. The swing arm rear suspension may not just be an alternative; it could be the answer. Yet for all of the positive and negative aspects that the four-link has the swing-arm seems to have equal and opposite attributes. The positives are easily seen by anyone who witnessed Scotty Cannon's 1953
Now all is well and good at the start but how about shifting? Since the swing arm is a single unit and not four individual bars there is no flex when shifting, which takes care of the problem of unloading at shift points.
Let's create a scenario. Suppose you are a Pro Modified driver and you just made a good pass, but later in the event the track changed: What do you do to compensate? Nothing.
According to veteran chassis builder Murray Anderson, who has proven to be a wizard with the swing-arm, "Once the swing arm is built -- it is set and this takes away a variable which racers tend to hurt them selves with. By having no adjustment, the repeatability of a swing arm is 95% opposed to the four-link's 60%."
It seems that a swing arm has taken care of all of the problems inherent to a four-link. Not so, since this design is relatively new, not many people know how to run with it and even less people know how to build it correctly. This is evident in a few of the cars built and campaigned on this side of the Atlantic. Some builders have taken the design and incorporated it into cars not having total knowledge of how it actually works. Herein lies the main problem: the four-link has 25 years of testing, by some of the greatest (and not so great) minds in the sport behind it. The swing-arm is so new that only a handful (a handful may be a stretch) of people have an understanding of it.
Anderson adds, "Just about all of the racers running the swing arm in IHRA Pro Mod have been tapping us for information, even though their cars were built elsewhere."
While our text may be portraying the swing-arm as the only way to go Pro Modified racing with, according to chassis builder Tommy Mauney says the four-link is far from reaching its performance barrier.
"The four-link is not dead by any means," explains Mauney, whose race cars have won numerous world champions."There are variables on the four-link such as hole location, not just where you put it from one run to the other or from one track to the other, hole locations from in front of…over or in front of the center of the rearend housing…heights on the frame..it is nowhere close to being dead…much less being done."
He continues, "The four-link is a complicated piece. That's why so many screw it up. You make changes not knowing what direction it is going to take you in and that's where everyone gets in trouble at. To take care of body rolls, you simply include the anti-roll bars or the sway bars or whatever you want to call them. You have an endless array of possibilities. Some might think that one has to change the four-link with every outing, I have had customers that have never changed their set-up at all. Blown cars and nitrous cars react totally different and they call for different applications. Mike Castellana is running a swing-arm car with nitrous and it doesn't run any faster than his four-link car did."
In the early to mid-Nineties, Cannon, Bill Kuhlman and most recently Joey Moore ran phenomenal times with four-link cars that bettered the current national record for Pro Modifieds. This certainly lends credibility to Mauney's statement.
Technical help falls far short on the swing-arm side of the fence as opposed to the four-link which is why several of the more prominent cars of this type were chasing a pesky shock problem at the first part of the season. With more testing and a better understanding of it by racers and chassis builders, it may someday overtake the four- link, as the design of choice-but for now the four-link is still the reigning champion.