In this installment of Project Unfair, we get down to one of the truly unfair aspects of our build, the dual-mode suspension system designed by Art Morrison Enterprises (AME). In case you missed it in one of the previous articles, the performance goal for the Project Unfair '69 Camaro is to be the fastest all-around Pro Touring car on the planet. All-around means a car that will handle with the best Pro Touring cars on the autocross and road course and cruise to the grocery store. That's the easy part. But to be "all-around fastest," we also want to be able to run 8.99 quarter-mile times and 200-plus mph in the standing mile-which has never happened in a g-machine.
To achieve our 8.99 quarter-mile times with a high-level handling g-machine suspension is difficult, if not impossible. The suspension geometry, the anti-squat, instant center, and preload of a good-handling suspension simply does not work well at the dragstrip. Sure, someone could put an outrageous amount of horsepower in a g-machine and make a Hail Mary white-knuckle pass through the traps simply overpowering the track. But we want to drag race consistently and as safely as possible. We also do not want to be in a position where we are forced to make so much crazy horsepower that we lose the streetability of the package.
So, in the planning and scheming phase of Project Unfair, the absolute most time was spent on figuring out a way to make a suspension system adjustable enough to have great handling and drag race great. One of the caveats early in the planning was that we don't mind making changes to transform the car from g-machine to drag racer, but did not want to totally dismantle and reassemble the car to do it.
There are multiple suspension designs available and one could argue for hours and hours (and they do) on which system is best. The reality is there are five suspension designs that can all work great for handling. We spent hours and hours researching all the best suspension systems available. We reviewed the anti-squat and preload capabilities of each system. We looked at adding some adjustability to currently available systems. Yes, we could add some adjustability and improve some of these systems, but no matter what we did, we found compromises in either handling or drag racing. We explored every possibility but ran into issues with each design.
Let's look at the different types of rear suspensions available and my feelings about their pros and cons for this custom application.
Leaf Springs: This was part of the original F-body suspension design. There are leaf springs made for fine handling, and there are leaf springs made for great dragstrip performance, but they are hugely different from one another. Performance handling leaf springs are multileaf design and are very firm and can handle very well. Drag race leaf springs are often a monoleaf design and are very soft and springy and do not handle well. Each spring designed to do one thing performs rather poorly at the other function.
Torque Arms: There are a few torque arm conversions for g-machines that handle very well. But the problem with a torque arm is that when set up for handling, it is not a good drag race setup (especially at our power level). Yes, there are plenty of fourth-gen Camaros that will drag the rear bumper, but you should try to turn a corner in one of those cars set up for the strip. And it is not a matter of simply changing adjustments to make it do one or the other.
Parallel Four-Link: There are two types of parallel four-link systems: one for drag racing and one for handling. The Pro Touring-style systems that are available use the factory leaf spring perches and add some upper link mounts. They are set up for handling and work well. But they do not have the antisquat adjustment or preload capabilities to be a good drag race suspension in a 1,000-plus horsepower car.
Triangle Four-Link: The Triangle four-link is the suspension design that is most capable of doing both drag racing and handling in one suspension design. They can be made to handle great, and drag race great. A- and G-bodies (Chevelle, Monte Carlo, and late-model Malibu) have triangle four-links from the factory. For a long time it was looking like it might be a triangle four-link, but we felt none of the g-machine triangle four-link systems had quite enough adjustability for an 8-second car.
Three-Link: The three-link is probably the suspension offering the most tunability. But the driveshaft limits the amount of antisquat you can dial into the system. And the three-link also limits preload adjustment, which is critical with a car where we'll need dragstrip short times in the 1.30s.
In my mind, we really needed a dual-mode suspension. Enter Art Morrison Enterprises. We bumped into Art and his son Craig Morrison at the SEMA Show last November. I told them we wanted to build a Pro Touring car that would run 8.99 quarter-mile e.t.'s. I wish I could put into words the look Art gave me! Let's just say he wondered if I had spent too much time in the bar so early in the trip! We felt we needed a true dual-mode suspension system. Not just moving a few bars around on a system, but literally have two systems in one.
Art Morrison Enterprises already builds two killer Pro Touring-style rear suspension packages. Both include form-fitting 2x4 framerails that replace the factory sheetmetal rails, and fit the stock floor perfectly. The kit comes as a jig-welded rear subframe and installs easier than one may think. These two systems were featured in the August '10 issue of Super Chevy and come in both triangle four-link version that fits under the original floor, and also in a three-link version that requires some floor modification, but still fits the factory floor. So Art Morrison made a set of their rear rails and made us what I like to call our "five-link".
All this talk about the rear suspension, what about the front suspension? That was a little easier. AME already makes a proven bolt-in front subframe for F-bodies, which uses fabricated rails, C6 Corvette arms, modified spindles, and allows for a 10-inch front wheel and 275 tires with ease. We also upgraded to a Tony Woodward steering rack. The Woodward rack is admittedly expensive, but gives incredible feel to the steering.
To make the front subframe into a drag race front suspension we will use a softer spring/shock package that will allow for more stored energy and faster weight transfer. We also will design a quick disconnect for the front sway bar for drag racing.
In a later story we will talk a bit about sways bars and the exciting new shocks and springs debuting on Project Unfair.
Anti-squat is a term describing how a car's rear suspension theoretically behaves during acceleration, and it is probably the most important thing that most modern drag racing rear suspensions are designed to exploit. Anti-squat is normally discussed in terms of percent, where 100 percent anti-squat means the vehicle's rear won't raise or lower due to acceleration effects. Less than 100 percent means the car will squat, potentially unloading the rear tires. More than 100 percent means the rear will rise, thus loading the rear tires.
For acceleration, loading the tires is good, and so more than 100 percent anti-squat is usually desirable for drag racing. As always, nothing comes free: high anti-squat will reduce rear braking ability since as the forces reverse during braking, the opposite effects occur. For road racing or street use, a better number is about 60 percent anti-squat; it's a good compromise between ultimate acceleration and ultimate braking.
Unfair's three-link setup is about 60 percent anti-squat, and the four-link is adjustable to allow changes in anti-squat and pre-load. The calculation itself is based on the lever length of the control arms divided by the lever length of the force generated by the tires, but it's a lot easier to envision if you make a line drawing of the car from a side view (see attached figure). As we've seen in our previous articles, the vehicle's center of gravity is very important when it comes to modeling its physical behavior, and figuring out anti-squat is no exception. Referring to the line drawing, first draw a horizontal line from the CG intersecting with a vertical line through the front tire's center point. From that intersection, draw a line through the rear tire's contact patch. This line is the 100 percent anti-squat line (sometimes called the "neutral line").
Now extend the virtual line for the linkage bars for the rear suspension forward until they intersect. That point is the instant center (IC) and from that IC we can calculate the anti-squat value. If the IC is below the 100 percent anti-squat line, we have less than 100 percent anti-squat. Above the line is over 100 percent anti-squat. The actual value is the quotient of the IC height divided by the 100 percent anti-squat height directly above or below the IC. If the IC were half as high, the anti-squat would be 50 percent. Twice as high would be 200 percent anti-squat.
With this understanding, we can see why drag racing four-links have so many adjustment holes. It's to change the IC to precisely dial in the right amount of anti-squat. Theoretically, it would be possible to do the same thing with the three-link since the IC calculations are the same. In practice, though, that doesn't work very well for a couple of reasons. First, the upper link runs directly over the driveshaft and is connected on top of the housing. Making that link be adjustable is difficult since space is very constrained. The second reason is that having two upper links gives the ability to preload the rear suspension. Many racers have found that pre-loading more weight on the right tire (by shortening the upper passenger side link) helps the car go straighter off the line, especially as horsepower goes up. -John Parsons