These motors are anything but stock
Dr. Edward P. Becker | TLT Automotive Tribology October 2016
The technical director for Earnhardt-Childress Racing Engines reveals what it takes to succeed at 200 mph.
Stock car engines are estimated to cost between $45,000 and $80,000.
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THE STLE ANNUAL MEETING THIS YEAR IN LAS VEGAS was a great success by any measure. One of many highlights for me was the keynote address by Dr. Andrew L. Randolph, technical director for Earnhardt-Childress Racing Engines. Titled Lubrication Challenges in an 850-hp NASCAR Sprint Cup Engine, the talk actually included discussions of the origins of NASCAR, maximizing the efficiency of engines, lubrication and materials and coatings to minimize friction. Dr. Randolph was particularly interested in the contributions of tribology to winning races, and gleefully described himself as a “closet tribologist.”
Even though the SC in NASCAR stands for stock car, the engines used could hardly be described as stock. One source (
1) estimates these engines cost between $45,000 and $80,000 each. This highlights one advantage of being a tribologist in the racing industry, namely cost is rarely a barrier. Some basic design parameters are specified (displacement, valve train arrangement, combustion chamber shape, etc.), and some parts must be purchased from approved suppliers (cylinder block and heads, for example). Apart from those, however, each team seeks to optimize the engine for maximum efficiency.
Oil for a NASCAR engine also is different from the usual passenger car oil. The NASCAR engine essentially operates continuously at high speed and high temperature, and friction control is paramount. Low and stable viscosity will allow engine bearings to have minimal shear losses, but the viscosity must be high enough to sustain a hydrodynamic film.
What a racing oil doesn’t require, however, is long life. Therefore, little or no detergent or dispersant is required. There is no catalytic converter or other emission-control devices, so common antiwear additives (such as ZDDP) can be used in any concentration. Each racing team buys its own specially blended oil, and the precise recipes are closely guarded secrets.
Another area for creative tribology is surface engineering, specifically surface textures and coatings. Dr. Randolph highlighted the piston assembly in this regard. In addition to being machined to exceptionally tight tolerances to precisely fit the bore, the piston assembly had no less than five separate coatings. The piston pin has a diamond-like carbon (DLC) coating to minimize friction and wear. The piston bore has an electroless nickel coating for compatibility with the DLC. The piston skirt features a molybdenum disulfide coating for piston to bore break-in. The top ring has a titanium nitride coating to reduce friction and wear, and the top ring groove has a plasma-sprayed aluminum oxide coating to prevent top ring pound-out.
As for reliability, Dr. Randolph says the engine simply has to last long enough to finish the race. For example, the Daytona 500 consists of 200 laps on a 2.5-mile course, so ideally the engine should fail on the 201st lap.
Of course, some margin of safety is required. After all, it would not do for the engine to fail on the 199th lap!
REFERENCE
1.
Available at
http://auto.howstuffworks.com/auto-racing/nascar/nascar-basics/nascar-race-car-cost1.htm.
Ed Becker is an STLE Fellow and past president. He is president of Friction & Wear Solutions, LLC, in Brighton, Mich., and can be reached through his website at www.frictionandwearsolutions.com.