An example of a traditional aluminum body roller- tipped rocker. Jim Mcfarland
DLC run against a lubricant and a properly prepared mating surface has an extremely low coefficient of friction. DLC-coated tappets run successfully because the low friction at the cam/tappet interface prevents wear.
Some teams run DLC on the cam as well. Running DLC against DLC may reduce friction, but this system is harder to run successfully. The DLC tappet running against the steel cam is very sensitive to the type and quantity of lubrication. Qualifying is a worst case scenario for engines as the oil is heated above 250 degrees and the water is chilled down near freezing. Qualifying oils approach a zero weight. This combination of hot, low viscosity oil with a cold engine is a recipe for failure if conditions are not perfect. The failures that occurred in some of the engines were directly related to the wear that occurred on the time trial laps, even though the engine failure occurred later during the 150 races. The lesson that may be taken from this is as follows: Always inspect critical components prior to the race, and if there is any doubt that damage has occurred, change the part or engine.
During Speedweeks, some teams did not provide a sufficient safety margin and problems occurred at the cam tappet interface. This caused good time trial efforts to be wasted. Many engines needed to be changed and thus cars had to go to the back of the grid for the 150s. The lesson to be learned here is that the last horsepower is not worth obtaining, if the risk of failure is significant. All the teams who had problems were able to recover for the 500, and only one unrelated engine failure occurred during the race.
Other engine news form Daytona: TRD engines were seen with a DLC-coated roller-less rocker. Why would a roller-less rocker be used? Roller-tipped rockers were first used to reduce friction as the rocker tip scrubbed across the top of the valve or lash cap. Removing the roller would seem to be a backward step. The low friction of the DLC coating has made it possible to run without the roller and have only a small friction penalty. The benefits of not having a roller on the tip are:
An example of a roller-less steel rocker. Jim Mcfarland
*A massive reduction in moment of inertia (less nose weight)
*An improvement in system stiffness
*Increase in accuracy
*Possible improvement in rocker-to-lash-cap contact
*A part with less complexity (no needle bearings to fail in the nose wheel)
In these examples shown, the roller-less rocker has a moment of inertia (MOI) reduction of 90 percent and stiffness increase of 60 percent. As mentioned in a previous segment of the CT Series on Cup engine technology, reducing the moment of inertia has a similar effect to reducing valve mass. This change may either allow a reduction in spring force or more aggressive valve motion. Without changing thevalvetrain to take advantage of the mass, no perform-ance gain would be obtained.
What may be learned from this example is that performance gains in either the vehicle or the engine rarely come from simply bolting on a part. A change to the system must be made to take advantage of the new component. All that is usually learned from bolting on a new part is determination of the system's sensitivity.
Here's an example. If the roller-less rocker (from the above case) was bolted on in place of the aluminum rocker with no other changes, a power decrease may occur. This result shows only that the engine was sensitive to the rocker change, not that the new part was inferior. To understand if the rocker itself was a positive change, other elements of the valvetrain may have to be made. The worst possible outcome of a bolt-on test is to observe no change. This means that the area you are working in has little sensitivity and may not be worth investigating.
Around the world, participants in motorsports are facing financial challenges that have not previously occurred. From the streets of Monte Carlo to your local dirt track, there are universal truths. If you work more efficiently than your competitors, you will have better results. You must spend your resources on those things which will improve lap times. You must continually ask yourself if the project you are working on is going to produce results. If the answer is you are not sure, then stop working on it! Only spend time and resources on projects which will make you faster.
Remember, no matter what type of racing you do, the driver is the key performance element. Mechanical changes which make the driver perform better are a plus!