In competition on dirt, more so than in any other form of motorsports, the battle is not just against other drivers. Dirt racers also have to battle the track by keeping it out of the various mechanical systems on the car. Dirt can ruin a very expensive engine, transmission, rearend, brakes, and the cooling system. And dirt seems to find its way into the various systems of the car no matter how hard you try to keep it out.
The EngineThe most recognizable and fundamental dirt blocker is the engine air filter. The intent is to supply the engine with a constant stream of clean air. Nothing will ruin your day at the races quicker than getting a stone or large clump of dirt past the carburetor and having it go through the engine. The damage does not have to be instant to be detrimental.
A poorly maintained filter, or one that is ill suited to the task at hand, can do just as much damage as not running a filter at all. Drawing in a constant stream of dusty air can destroy the rings, cylinders, and valves. This same dirt can then get passed to the oil and the damage just keeps accelerating. This kind of damage can be progressive or sudden. Passing a small stone into the engine will do some serious damage, ending your day at the races and providing a weight loss scenario for your wallet. But a filter that continually allows dirt to pass is just as damaging as a stone or any other hard object that might go through the engine. It is just that the damage will be seen in a much shorter useful life as opposed to an instant catastrophic failure.
Most circle track engines will also have at least one crankcase breather installed in the valve covers. They may even have two. The pressure changes internal to the engine on the bottom side of the pistons can be volatile. The act of the pistons traveling up and down at high speed can, and does, create some rather large swings in the crankcase pressure. Engines that are fitted with a dry sump pump can actually develop a vacuum in the crankcase. This can make the sealing of the engine crankcase a difficult proposition. For the majority of the Saturday night racers who are not running a dry sump oil system the standard solution is to vent the crankcase to ambient air. This has to be done carefully. It is just as easy to draw dirt or foreign objects through a breather as you can through the air cleaner and the potential for damage is just as great. The breather should be routed through a filter that will prevent any dirt or other objects from entering the engine.
Many of the engines used in classes run by the Saturday night racers have a breather system that was designed by the OEM (Original Equipment Manufacturer). The volume of air these systems were designed to handle is not sufficient for the higher rpm application that will be seen by the racer. I am speaking of engines in the Street Stock classes and even some of the more advanced classes. As the rpm increases and is sustained, the stock breather systems will not be able to cope with the amount of air that will be moving through the breather. This elevated rpm results in pressure building in the crankcase and that can cause oil leaks and a path for dirt to enter the engine.
The simple fix is to remove the stock breathers if your local rules allow this and replace the stock breather(s) with a system more suitable for a racing application. There are many systems available that will bolt to your engine and solve this problem without too much cost or real effort to install. It is an easy fix to a potentially damaging problem.