In addition to vehicle power, the overall weight of the vehicle and how it is distributed are very important to overall acceleration. In general terms, a weight reduction of 100 pounds will lower the ET by .1 second. Furthermore, the more weight that rests over the drive wheels, the better the traction and thus the quicker the time. Adjusting the weight for a street car is easy. For front wheel drive cars, be sure to remove as much stuff out of the trunk such as the spare tire, jack, etc. And don’t forget to race with about a 1/4 of a tank of fuel. Extra gasoline adds weight over the rear wheels! For rear wheel drive cars, you can either follow the above advice, or actually leave everything in the trunk and run with a full tank of gas. The extra weight over the rear wheels will increase traction. For more serious race cars, consider permanent weight loss actions such as removing non-essential parts. One place to start is the interior. Serious track cars remove a lot of interior trim such as carpeting, passenger seats and sound deadening material. Serious weight can be removed from under the hood. Start by replacing heavy cast iron engine components and accessories, such as the intake manifold, exhaust manifold, and even the heads with lighter cast alloy or aluminum after-market units. A lighter intake manifold can save up to 40 pounds alone. You can also remove non-essential components such as the air conditioner compressor. You will often see an increase in performance along with a significant weight savings. Next, look at the body. Entire panels can be replaced with either aluminum panels (like the Super Duty Pontiacs of old), plastic inner fenders (used by some Oldsmobiles), drilled body panels (another Super Duty trick) or Carbon Fiber panels (as seen on many imports). The biggest gains are to be made with replacement of panels on the front of the car such as the front fenders and hood, and near the top of the car, such as the hood, roof, or trunk, which will reduce the center of gravity of the car, improving handling. True race cars even replace the heavy glass in the windows with a clear plexiglass to save a lot of weight up high. Just be aware that this is extremely dangerous for a street car as the plexi glass is harder to see out of and is probably illegal for use on public streets.
An important concept is “unsprung weight.” This is weight that is not supported by the suspension of the car. This usually includes the the weight of the wheels and tires as well as a percentage of the weight of the suspension itself, including control arms, anti-roll bars, shocks, and struts. Reducing unsprung weight is the key to improving handling. The lower the unsprung weight, the less work the shocks and springs have to do to keep the tires in contact with the road over bumpy surfaces. An easy way to reduce unsprung weight and improve traction is to replace stock wheels and tires with special lightweight wheels. Note that as the wheel diameter or width increases, the weight of the overall wheel and tire package increases, thereby increasing unsprung weight