Text by Marshall Pruett
Photo Credits:

ApeWorks
Robert Glass Jr.
Darin John
NDRA File Photos
 Subaru N.A.
Robert Glass Jr.
Darin John
NDRA File Photos

The Street and Strip

There's a way to regain lost horsepower from your ride, but you can't find it in you favorite Import magazine. Big name tuners don't offer it. It's arguably the most important "secret" aspect of speed on the street, strip, or track, but you can't buy aero improvements and efficiency from a catalog.

With so much of the average enthusiast's time dedicated to finding and buying power, we decided to step back and explore some tips and tricks to saving horsepower that gets wasted while pushing your car through the air.

We aren't just thinking about the local drag strip or road course; most of the cars that show up at the strip or track also serve as a daily driver. There's no reason for a car to not only look good from 9-5, but to also outperform the other cars with a smart blend of power and aero modifications.

Before we get lost in a bunch of overly complex terms, learning to visualize air and its effects on your car is vital. Air, like water, is nothing more than a fl uid--since we can't see air, it's easier to envision it as water fl owing over your car; think about how water fl owing down a stream wraps around every obstacle in its way.

The main concepts we'll be dealing with are downforce and drag. In the world of aerodynamics, downforce is a pretty simple one: the force of the air passing over or under a car (pushing or pulling down on the body) is called downforce.

That aerodynamic (down)force on your car is like a pair of big invisible hands pressing your tires into the road and making them bite harder. Beyond trick shocks, tires, or sway bars, finding improved traction and cornering from downforce is incredibly important.

Just like everything that's good for you, there's always some sort of negative that comes along with something positive. In this case, downforce's arch enemy is called "drag." Where downforce is like a pair of hands pushing down on your car, drag is like a big parachute trying to pull your car backwards. In the game of straight line acceleration, anything that holds you back is robbing horsepower, time, and peak performance.

Just as you'd never think to deploy a 'chute when the starting light goes green, improving anything on your car that acts like a parachute under acceleration should be the highest priority.

Wings naturally produce both downforce and drag-the best wing designs maximize the most downforce with the least amount of drag penalty. Not only do you suffer some degree of drag with a wing, but any surface that impedes, upsets, or traps air will produce drag.

True, you can add more power to overcome a car that looks or acts like a brick, but if you did nothing else under the hood and concentrated only on improving the shape of that brick, you'd free up a ton of power being robbed every time that brick cut through the air.

Wings and things

Looking at a Top Fuel dragster, you'll fi nd tiny front wings and a massive rear wing. Why? It makes so much power it will light up the tires at 300mph; all the available downforce to keep the rear tires glued to the ground is a necessity. Without the rear wing, it would likely never get off the starting line for all the wheel spin. The small front wings help to keep the front and rear of the car balanced, and to help the front wheels stay on the ground!

Next

Dragging with Drag

To start assessing your car, we'll assume that the body kit or stock body package lives on your car permanently. This means that whatever we'll look to do to improve your car, you can do in your garage at home easily, and with minimal time or money invested. Secondly, we won't get caught up with expensive parts and pieces; a trip to your local giant hardware store will provide you with everything needed to improve your car, or a few minutes browsing eBay for good used body pieces.

One BIG note before we get started: because this is a feature about basic aerodynamic principles and improvements, please read over the rules and legalities for modifying your car prior to employing any of suggestions. I'd hate for anybody to invest hours and money on improvements that aren't legal for the road or your particular class of competition.

With any vehicle, air flows over and under its surfaces, filling every gap, hole, and opening. Getting your car through the air with as few disturbances as possible is our first goal. To think about what we can first address, it's important to review the qualities of your car. How much power does your ride make? Do you need to make downforce to get better traction, or would downforce actually slow you down? This might sound like an extra simple question, but there are improvements to be gained by the answer you give.


The enemy down below

Focusing on the topside of a car is massively important, but concentrating on the underside for aerodynamic improvements is also a necessity. Limiting the amount of air that travels beneath a car headed to the strip will bring much bigger returns than you might expect. Granted, we're not talking about dropping 2 seconds from your E.T., but every fraction of time that can be saved is worth the effort.

As we aren't trying to make downforce and also want to eliminate drag, selecting a body kit that has a deep and effective front bumper is mandatory. Front bumpers that either extend close to the ground or forward slightly are commonly called "splitters"-they serve to *split* the air up and over (or around) a car rather than letting the air travel directly beneath the bumper.

This is an important move to make because the more air that hits the front of your car and travels under it, the more unneeded downforce and drag you'll get. For the air that does manage to get under the bumper, it travels the length of the underside hitting all the odd and rough shapes possible before exiting out the back. The turbulence caused along that trip from the bumper to bumper is a big source of drag; most rear bumpers stick down into the path of the exiting air, and due to the curved form of that rear bumper, end up acting like a air huge trap. Depending on how far down the bottom lip of your rear bumper extends, it does more than act like a parachute: it is a parachute.

This rear bumper parachute problem is the easiest to solve, and the best excuse to head to make some homemade improvements. With your car on a lift, and using a large piece of cardboard to make a template, evaluate the best shape to fi ll the void from the bottom lip of the rear bumper to the bottom of the fuel tank.

With that pattern cut out in cardboard, buying a thin, light, but sturdy piece of plywood or plastic sheet to shape to your cardboard pattern is next. Cut and ready to put into place, rest the rear of your panel on top of the bottom bumper lip-it will help to support the rear of the panel and allow you to swing the front of the panel up and fl at against the bottom of the gas tank. Held in place, use generous amounts of aluminum tape (a big personal favorite-it looks just like a roll of duct tape, can be found at most hardware stores, and is incredibly strong).

Provided all the mating surfaces were cleaned, using aluminum tape around all 4 corners of your plate will hold it in place nicely. This is meant to be a DIY solution, and not something you'd need to drill a bunch of holes in your car to use. With the beefy aluminum tape, you can secure the plate in a matter of minutes, and take it off in 30 seconds.


© 2008 TPR / Tuner Performance Reports Magazine.