Transmission Technology in NASCAR Racing Series

It is hard to believe that a modern racing car, breaking records in one of the most entertaining race series, owes its transmission design to a unit that was installed in the road car back in the '50s.

But don’t be surprised because we are talking about NASCAR, where the only allowed transmission solutions still have to look like a legendary BW ST10, firstly used by GM more than six decades ago. Despite the external similarity with the classic transmission, the internal components of current NASCAR transmissions have several peculiarities, which we will consider this article.

Some insights into NASCAR philosophy

NASCAR is a popular racing competition in America that attracts tens of thousands of spectators to its events each year. Currently, NASCAR racing cars use 4-speed transmissions, which have not changed significantly since the time of a 1950's Ford. The reason of such a strange adherence to the classic designs (not only in transmission, but also in other components) in the time of fast-developing automobile technologies lies in strict technical regulations of NASCAR, which make this competition so special.

NASCAR differs from other well-known racing series – here driving skills and experience of racers and their teams play a greater role than talents of engineers who design and develop the cars. In contrast to Formula 1, where without sophisticated technologies you can forget about the victory, the NASCAR racing series can to some extent be considered as more just competition, where all racers are in equal conditions. Therefore, NASCAR officials still stick to strict rules that restrict implementation of new tech solutions on the cars and therefore placing utmost importance on the human factor.

To achieve good results in NASCAR, engineers have to use their ingenuity to the fullest – in order to gain even the slightest competitive advantage for their teams without braking technical regulations. The basic technical rules for NASCAR cars can stay unchanged for decades. Therefore, all engineers of NASCAR teams always face the same task: how to outperform their opponents having the same set of components and technologies at your disposal. NASCAR engineers cling to each change in the regulations in the hope of finding a competitive strength.

Inside the NASCAR car

This is why NASCAR races are so fascinating and unpredictable. In NASCAR, a tenth of a second can be a serious advantage over other racers. In F1 this same advantage would be about 1-1.5 seconds. Therefore, in an effort to keep its high audience appeal, NASCAR leaves small room for new technologies. The necessity to use the 4-speed manuals during these wild rides significantly increases the probability of the driver’s error, thereby stressing the importance of driving skills. Unlike the F1 paddle shifters that use a computer to do the shifting.

According to the regulations, each car can have 3 transmissions for every event, and the service life of each unit commonly reaches up to 4,500-5,000 miles. Due to their mechanical reliability, simplicity, and well-organized supply chain, NASCAR-type transmissions have become widely used in other types of motorsports.

What is so special about NASCAR manuals?

NASCAR transmissions are not manufactured by auto giants such as Ford or GM, by they are actually from specific race car transmission companies (for example, G-Force, Andrews, Xtrac ).

Andrews A431

G-Force 101A

These 4-speed manuals are unbelievably simple and efficient. But how exactly do they operate? What enables them to cope with up to 800-plus hp during long races when, for example, a 5-speed Subaru WRX transmission has to do its best to deal with 300 hp?

Instead of the usual silent-operating helical (spiral) gears, the NASCAR transmission has robust straight-tooth gears to decrease case thrust and successfully deal with additional torque loads. There are only four gears in a NASCAR car, but the main peculiarity of these transmissions is that they do not have synchronizers. Instead of synchronizers, there are dog rings, ensuring rapid and accurate gear shifting. Since NASCAR racers do not have to use a clutch, they shift gears when they have the road speed matched. That means that the drivers perform the gear shifting operation relying on the sound and feel of the car. And in general, all NASCAR components are more robust and durable than in conventional manual transmissions and thye are designed for ease of service.

A short video on NASCAR transmissions design peculiarity

Principle of operation

To get into gear in the NASCAR car, the transmission mechanism uses a so-called dog clutch – durable claws on the side of 1 gear interact with slots in the side of the neighboring gear to drive the gear. The same principle is applied in motorcycle gearboxes. Simply reduce the load on the transmission and shift to the next gear.

Disassembly and explanation of G-Force transmission

The NASCAR transmission (using the example of G-Force transmission) operates as follows: firstly, the power is transmitted to the input shaft of the transmission, which is not connected to the output shaft. Then the power goes to the countershaft via the drop gear, which is responsible for the overall change of gear ratios. After that, the power is transmitted to the gear which has to be engaged. When the 4-th gear gets engaged, the input and the output shafts get linked together and they rotate with the same speed, i.e. the 4-th gear in NASCAR transmissions is always 1:1 to get as much efficiency as possible. The reverse gear set in this transmission is positioned at the output shaft.

Ways to improve the efficiency of NASCAR transmissions

Even the slightest changes in the NASCAR transmission design are strictly controlled by the rules, and not a single detail can be replaced or upgraded without the knowledge of the decision-making body. But, it does not mean that transmission makers for NASCAR competitions become complacent and give up new ideas for the transmission design. Engineers are constantly working on some small refinements to enhance the efficiency and durability of the whole unit. Despite the fact that these modifications may seem inconspicuous at first sight, these small steps play a great role in optimization of the transmission performance, without compromising the importance of driving skills.

One of the promising directions considered by NASCAR engineers in the quest to improve the efficiency is the weight reduction of the powertrain components. Despite the prohibition of the use of the exotic light materials, significant achievements in CAD (computer-aided drafting) and simulation technologies have enabled manufacturers to further modify the design of existing car elements.

Fig. 1

Fig. 2

The image of the selector fork modification provided above is a vivid example of NASCAR engineers efforts to enhance the efficiency of racing cars. Fig. 1 shows the initial version of the fork, while Fig. 2 is a modified version. Thanks to the detailed analysis of the fork structure, the engineer managed to remove redundant material while also optimizing the geometry of the element to enhance its rigidity, improving the precision of gear shifting.

Some producers of racing transmissions also focus their attention on decreasing friction (drag) losses. During NASCAR racing competitions, even a slight decrease in power loss can play a crucial role, especially on tracks where restrictor plates are required. Surface finishing methods have proved to be an efficient solution in these frictional reductions. All producers of transmission solutions for racing transmissions resort to either a media or chemical-based finish on transmission elements such as gears and shafts.

Chemical-based approach to improvement of the surface finish parameters has become especially popular, thanks to the ability to enhance the material characteristics of a component as opposed to simply smoothing its surface. This solution not only reduces friction between the gears, it also increases their robustness.