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June 17, 1998
Making Your Mustang Hook, Part III
Suspension Considerations
Now-a-days, it's not uncommon to see a street-driven 5.0 Mustang that has 400 and even 500 hp. With the availability of quality cylinder heads and 10 psi from an S-Trim Vortech, power is relatively easy to come by.
Once a person has spent the money to build an engine capable of these power numbers, one of the first things they do is take it to the drag strip for a quantifiable result, an ET slip. Unfortunately, many people are disappointed their first time out and come home with a 1/4 mile ET that is one full second slower than they thought it should be.
One of the most over-looked and taken for granted aspects of a good ET is traction. Consideration has to be given to tire choice, traction bars and other suspension tuning. This Water Box is part 3 in a 3 part series and will discuss suspension considerations. Part I - Tires and Drag Racing and Part II - Traction Devices can be found in the Water Box Archives.
This installment of the "Making Your Mustang Hook" series focuses on suspension considerations. By considerations, we mean all the things we haven't yet addressed that can make a substantial difference.
Polyurethane Bushings
Many people already know that the soft factory control arm bushings are not conducive to efficient suspension travel. In other words the soft rubber factory bushings flex a lot during launch or cornering and allow the suspension to move further than it should, harming handling and traction. By installing a quality set of polyurethane bushings in the 8 pivot points of the rear control arms handling and traction are greatly improved. Polyurethane is much more dense than the factory rubber bushings and therefore much stiffer. They increase traction by preventing the factory suspension from traveling too far. The only down side is that they are also better at transferring noise and vibration into the cockpit. With polyurethane bushings you'll also experience a rougher ride. But it's worth it.
All good aftermarket traction devices come standard with polyurethane bushings. But don't feel the need to run out and buy a set of traction bars just yet. The stock rear lower and upper control arms on a Fox chassis work extremely well with just the additional stiffness offered by polyurethane bushings. We have had very good results with polyurethane bushings and just a few other chassis mods. One of our customers, Mario Crocenzi has run as quick as 10.04 with nothing more in the rear suspension than polyurethane bushings in the factory control arms and an air-bag.
Polyurethane bushings installed in the front control arms can also provide a substantial improvement, especially for road racers. But to put it bluntly, they suck on a street car. Every little bump and vibration is transferred and seemingly amplified in the cockpit and steering wheel. So if you have a track only car or don't mind major sacrifices in ride comfort, polyurethane bushings in the front control arms are an asset. But if you drive your car everyday on the street we wouldn't recommend it.
Chassis Stiffening
Providing your rear suspension with a rigid chassis is important and aids in effective weight transfer to the rear wheels and eliminating chassis roll. Chassis roll is the natural tendanancy of the body to "twist" during hard acceleration.
Subframe connectors make a very substantial improvement in rigidity and are fairly inexpensive. They should be your first step in providing your rear suspension with a solid chassis. Don't waste money on any bolt-in subframe connector. Bolts simply don't provide a strong enough mounting point. For a subframe connector to provide optimal strength in MUST be welded-in. It's also important that they be beefy enough to prevent flexing. Many of the available subframe connector kits available are too flimsy to provide quality stiffening. Use a heavy-duty weld-in connector like the ones we offer.
We've seen many cars that hooked hard without subframe connectors. And several of them are easily distinguished by the tell-tale wrinkles in the rear fenders and cracking A-Pillars around the front windshield. A uni-body suspension flexes more than most people realize.
A roll bar or roll cage also provides a great deal of chassis stiffening along with driver protection. Again, weld-in is much stronger than a bolt-in roll bar, though when done properly, a bolt-in roll bar is NHRA legal in unibody cars like the Fox chassis. Relatively few street cars actually need more than subframe connectors and even fewer drivers are willing to make the sacrifice.
Weight Reduction
Any weight that you can remove from your car will help it run quicker. And any weight that you can either take off the front end or transfer to the rear will make the car's front end unload more quickly thus transferring weight to the rear end.
These are a few very effective ways of removing a lot of weight off the front end:
- Fiberglass hood
- Tubular cradle
- Tubular control arms
- Coil-over conversion
- Remove front sway bar
- Relocate battery to rear of car
- Light weight front wheels and tires
- Remove front bumper and 5 mph shocks (track only cars)
- Lightweight Front Runners
Weight Transfer, Front Suspension
Physically removing weight from the car or relocating it to the rear is important. But is is also very important to have a front suspension that reacts quickly upon launch and applies leverage to the rear suspension for added traction.
Removing the factory front sway bar is one quick, easy and completely free way to help your car hook harder. The factory front sway bar is intended to keep the suspension tight while cornering and eliminate body roll. The problem in drag racing is that it prevents the front end from easily rising into the air during a launch. By removing it, the front suspension can more easily raise during acceleration/launch and apply leverage to the rear tires. Not to mention you're shedding over 15 pounds of weight.
The front sway bar is not the only consideration when making your front suspension more efficient for drag racing. The front struts are also very important. The factory struts are designed for a comfortable ride and balanced handling. But in drag racing it's important to get the front end up in the air. A quality pair of Drag Struts like those from Koni or Lakewood are designed to extend much easier and then compress gradually for a more controlled wheelie/launch. It's not uncommon to see the front end of many hard hooking cars with cheap front struts bouncing as they leave the line making the car more difficult to drive. A good drag strut will help eliminate this problem.
Koni drag struts are adjustable and can be made firmer when driving on the street. They are an excellent choice and are just as at home on the drag strip as they are on the highway when adjusted properly. Lakewood drag struts are a more economical choice but do not offer the adjustability or engineering of Konis. The Lakewood 70/30 struts are perfectly acceptable on the street and also work very well at the track. Lakewood 90/10 struts are tolerable on the street for limited use and are preferable over the 70/30s at the track.
Springs
The Mustang has coil springs at all 4 corners. And as with most other factory components the stock springs are designed to provide a comfortable ride and acceptable handling. But with a drag suspension, it's important for the front end to unload quickly and smoothly and the rear suspension to resist severe squatting which can result in a springing (unloading) that kills traction.
There are several quality drag race oriented spring kits on the market. By far the nicest for the front end is offered by Griggs. It is actually a coil over conversion kit. The Coil over feature is much more compact and lightweight than the factory set-up and provides a wide range of spring choices and ride height tuning options.
Eibach also offers a high quality drag race spring kit. The front springs are designed to help the front suspension raise up quickly and transfer weight to the rear. The rear springs feature unique and different spring rates for the left and right.
RV air bags are also an effective means of increasing rear suspension effectiveness. A bag placed inside the right rear coil spring keeps the suspension from squatting down too far and then unloading. They're economical, very tunable through different air pressures and can be very effective if your rear suspension squats too much during launch. An air bag in each rear coil spring offers the ultimate in tunability.
We discussed front struts but haven't yet mentioned the importance of rear shocks. Many cars do just fine with the factory rear shocks. But with higher power levels and an efficient suspension they may not provide enough stiffness. Lakewood makes an affordable 50/50 rear drag shock that works very well in making the rear suspension firmer. And they're tolerable on the street for all but the pickiest drivers.
This 3 part series has given the average drag racer many of the basic ideas and necessary mods behind making a Mustang pull sub 1.40 60 ft times. But the most important thing to remember is that without a quality set of slicks or very sticky tires, all the other money spent on suspension mods will do little more than help your high horsepower Mustang peel out in a straight line.
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