Racing Bolt Technology

An area that deserves some real attention is the exhaust system, specifically header flange hardware. The exhaust on race cars goes through extreme variations in temperature. These changes can cause sealing issues as the gaskets expand and contract. This leads to exhaust leaks, and the hardware gets the blame. The last place where any problem should occur is in the exhaust system, especially if the problem is completely preventable.

Exhaust leaks may not be an issue with the hardware loosening up. It may be more traceable to gaskets being unable to seal after multiple expansion and contraction cycles. This is especially an issue with aluminum heads. The biggest problem here could be the inability to adequately tighten the bolts to the correct torque levels due to header tube interference. This problem may be resolved by using different hardware with smaller heads to help provide adequate tool clearances.

Still another area that we need to look at as the power levels increase is the interface between the engine, transmission, and drivetrain. The bolts and/or studs that secure the engine to the bellhousing and the bellhousing to the transmission need to be the best fasteners we can locate. The OE hardware is more than adequate when power levels never exceed several hundred horsepower, but the modern race engine, even at the weekend warrior level, can surpass 650 hp.

That level of output places a large amount of stress on the hardware, which can be compounded by the level of grip developed by the tires and the chassis. This can transfer very high loads to the hardware responsible for keeping the drivetrain together. The thought of using OE hardware is scary, to say the least.

We should be using the best hardware possible in these critical areas. The superficial cost savings of using substandard hardware is not worth the economic risk. From a risk mitigation perspective, using quality hardware in these high-stress areas saves money and keeps you safe in the short term and the long term.

We have already established that bolts are basically springs, and the tension they apply to an interface is a function of the amount of force they can apply (i.e., clamping force). Racers joke about tightening a bolt until just before it gets loose again in order to get the most force out of it. While this may be good for some comedic relief, it is not even close to the truth.

Bolts have very specific torque requirements, and the ways to measure them are varied and a good subject for another article. If possible, consult the manufacturer of the bolt first. The SAE has developed some torque values based on the size and grade of the bolt. The intended application has a great deal to do with final torque values.

We measure torque to establish preload on the bolt or stud. Any excess friction between the bolt and the joining threads can skew the torque reading. The torque reading could be artificially high compared to the amount of actual bolt stretch. To minimize this condition, the threads need to be lubed. This lubrication can be accomplished in a variety of ways with a variety of products.

Some specialty bolt manufacturers have very specific recommendations for the lubricant. Consult with the manufacturer regarding its specific recommendations. If that is not possible, there are a number of products on the market for this specific application. Just make sure all of the threads are clean and free from any damage. In some applications, the threads may need to be assembled dry, which is why it is important to consult the manufacturer of the product you are dealing with to secure the company's recommendations.

The manufacturer of the product you are using has put a great deal of engineering into the product, so consult the manufacturer if there are any questions regarding torque values. Connecting rods are a good example. There is a good deal of information on how to generate sufficient clamping loads. The most popular method is to use a torque wrench to measure the force on the bolt or nut. While this may be the most popular method, there are better ways that eliminate any guesswork.

Measuring the amount of bolt stretch is really the best way to determine the correct load placed on the bolt. This requires special tooling (such as a stretch gauge), which is available to the racer for a reasonable price. However, you won't always be able to apply this method due to the limited clearances and accessibility to both ends of the bolt. That means the only other option left to the racer is a torque wrench.

While the bolt is a seemingly mundane and simple part of the modern race car, it is a complex and incredibly important component. The cost of bolts, nuts, and quality washers is a fraction of the cost of the complete car. If they are poorly matched to a specific task, they can cause catastrophic damage that can make the cost of the highest quality hardware seem insignificant in comparison. Knowing the risks, it just does not make sense to scrimp on hardware. Use the best and feel more confident at the racetrack.