When the PPG Indy Car World Series heads to the Mid-Ohio Sports Car Course for the Miller 200 Aug. 11, a key element to unlocking the horsepower necessary for getting to the checkered flag first will come from the eight powerful laptop computers used by the engineers in charge of the Mercedes-Benz IC108C race engines that power eight of the top drivers in the series.

However, the work of a Mercedes-Benz trackside support engineer is not limited to precision exercises performed with carefully calibrated micrometers and the latest laptop computers. There is also an element of educated guesswork. The nightly ritual of engine inspection requires the engineer to draw upon his experience and intuition to decide whether an engine should be bolted into a car for competition or packed up and whipped out as the rebuilder's next project.

"As an engine manufacturer, we have three priorities: performance, durability and cost," explained Mark McArdle, a senior trackside support engineer for Ilmor Engineering, the race engine-building arm of Mercedes-Benz. "We have to make intelligent decisions, on behalf of our teams and Mercedes-Benz, based on those parameters. Ideally, we would tear down and rebuild every engine after every session and eliminate just about all of the risk, but obviously, from a cost and logistics standpoint, that's not feasible. Instead, we do and engine inspection, which, while it only lets us look at a very small portion of the internal workings of the engine, can often give us enough information to make those though decisions and avoid failures."

Borescope Analysis

The first step of engine inspection involves removing the spark plugs and, using a special tool known as a borescope, visually inspecting the inside of the cylinders for signs of wear or damage from debris which can enter the inlet track through the turbocharger. The engineers look for shiny spots on the crown of the piston, which are an indication of contact between the piston and cylinder head fire face. Circular indentations or shadows on the dome of the piston usually mean valve-to-piston contact, and burning or charring around the edges indicates the piston may be damaged due to overheating. Other imperfections such as scuffing on the cylinder liner walls, cracks in the piston crown or the presence of debris are also grounds for pulling an engine from active duty.

Leak-down Testing

The second half of the nightly engine inspection involves plugging up each of the spark plug holes and pressurizing the cylinders one at a time. The engineer monitors the pressure in the cylinder, watching for any sudden drop off, which would indicate a faulty seal between the valves and valve seats or piston, rings and cylinder liner. These leaks can inhibit the compression that occurs when the piston rises towards the cylinder head, squeezing the fuel-air mixture in preparation for combustion.

"If you get a leak that's more than eight percent, then the next step is to try and determine where the leak is occurring," said McArdle. "Nine times out of ten, it's the cylinder head or inlet valves. You pressurize the cylinder, open the throttle, and you'll hear the air escaping into the plenum on top of the engine. If you hear the air escaping at the exhaust, then the problem is in the exhaust valve. Otherwise, the problem is most likely in the bottom half of the engine."

While a small leak may seem incidental, each cylinder must endure more than 14,000 rpm at race speeds. At that rate, each cylinder is put through its paces more than 230 times each second, creating an amazing combination of heat and friction. If an engineer misses a tiny crack or leak during inspection, it can lead to an engine failure or explosion.

The Mercedes-Benz IC108C race engine is among the most recent additions to a tradition of engine excellence that dates back more than 100 years. German automotive pioneer Gottlieb Daimler built the first motorcycle (1886), the first motorboat (1886) and the first powered aircraft, a hot air balloon with twin propellers (1888).

His company, Daimler-Motoren-Gesellschaft, adopted a three-pointed star as its trademark, symbolizing power "on land, on the sea, and in the air." Later, a circle was placed around the star, standing for the world, according to company historians. In the more than 90 years it has been use on Daimler, Mercedes and Mercedes-Benz cars, trucks and engines, it has become one of the most widely recognized trademarks in the world.

Source: IndyCar News Service