Gear and Tech : January 9, 2009
Top Speed Performance Parts! -Increasing Top Speed-
Sorry for the deceiving title, I’m not hawking parts today. This article is about increasing the Top Speed Performance of your vehicle. Sure, you can always increase acceleration, but it gets to a point where horsepower becomes a minuscule factor and you’re aerodynamically limited as opposed to horsepower or gearing limited. This is mainly for the guys that are trying to go FAST. This article is more catered to the Bonneville salt flats guys that are really going for Top Speed.
One of the most important things is vehicle choice. In order to push through the air and achieve a higher top speed, you’ll need a vehicle with a small frontal area for one. Another thing needed to be considered is the rear shape. Hatchbacks or any other car with a gentle sloping rear end will work the most efficiently. The goal here to increasing Top Speed Performance is to make your car as sleek as possible.
Since now you got shape down, now it’s time to streamline. Most people don’t realize that the bottom of the car is much “rougher” than the top of the car, as far as airflow is concerned. In this regard, a bellypan is essential as it improves airflow under the car and keeps it smooth. While doing this you should also route your exhaust through the pan so it doesn’t hang below the car. Shaving doorhandles, mirrors, trim and body joints are essential to increasing Top Speed Performance.
Regardless of what you do however, air WILL get into the car, so having trunklid louvers is a good idea so air doesn’t get trapped inside and ensures that it will flow smoothly out. Having hood louvers is a good idea as well because air can get trapped in front of your firewall and act like a giant drag bubble in front of your car.
Another thing people don’t realize is that wheel spacing is one of the most important things you can do. Having the wheels as flush as possible is key here. If you have the wheels too far in, air will get trapped inside your fender wells instead of staying slipstreamed outside of the car. While we are rolling along with wheels (No pun intended) another thing that is arguably most important is rolling resistance. Most people think weight is a big factor, but in the grand scheme of things, while it IS a factor, it’s not nearly as important as rolling resistance.
Pumping up your tires to a high pressure is a very good way of reducing rolling resistance. Along with wheels is gearing, I’m not going to devote a paragraph to this due to the fact that it all depends very much on the size tire you are using and how many horsepower you are working with. Minor inconsistencies will be wildly different, so essentially research that topic more suited for your platform or application.
Weight isn’t as big of an issue as most people think. Most people think Top Speed Performance is hindered greatly by weight, however this isn’t always true. If you drive a car with 500 HP and its 2000 pounds, and then put 2000 lb of lead weight in the car, and compensate on the wheel bearings to keep rolling resistance pretty close to the same, both cars will have the same top speed. It will just take the 4000lb car twice as long to get to the same speed. Even weight distribution is very important also for aiding stability at high speeds.
All in all, there’s a ridiculous amount of information pertaining to the subject of building a car devoted to strictly top speed performance, but this is a pretty short recap of things to keep in mind when building your salt rocket.