Reverse engineering boosts NASCAR team

Manufacturing Engineering, AuG 2001

Drivers for Joe Gibbs Racing (JGR) rarely use reverse gear on the track, but engineers at the team's Huntersville, NC machine shop use reverse engineering to duplicate and machine cylinder head ports on its NASCAR Winston Cup cars.

Like all Winston Cup race teams, JGR keeps many of its engine-building secrets "under the hood." However, it's no secret that most teams, including Gibbs, use scanning equipment and CNC machinery to duplicate and machine ideal port designs with accuracies and lead times that hand porting can't touch.

When the team went shopping for its reverse engineering system five years ago, it looked at a variety of technologies, including coordinate measuring machines. But JGR chose Renishaw's Renscan 200 on-- machine scanning system for its reverse engineering.

"We were still a relatively new team, and we wanted a cost-effective yet accurate scanning system that would take minimal ramp-up to start producing finished heads," says CNC manager Mark Bringle. "At one-tenth the cost of a CMM, the Renscan 200 gave us scanning simplicity and precision, but not sticker shock."

The on-machine system allows the team to duplicate ideal port and combustion chamber designs and generate NC code necessary to machine those critical profiles into its aluminum heads. Smooth, identical head ports are essential to enable NASCAR engines to reach their maximum power potential. Team drivers Bobby Labonte (#18) and Tony Stewart (#20) certainly put that power to the pavement in 2000, as Labonte won the Winston Cup points championship and Stewart finished 6th. The two combined to win 10 of the 34 races in 2000, and both are currently in the top 10 in the 2001 Winston Cup points chase.

JGR's 145,000 ft2 (13,400 m2) facility includes separate departments for CNC machining, engine design/build, body and paint, and equipment transport. The team has access to a wide variety of computer software packages, including CAD/CAM and FEA, as well as a flow bench simulator to test CAD port designs before cutting prototypes.

Bringle's CNC department is stocked with eight machines churning out a wide variety of critical car components. But because cylinder heads have such a pronounced effect on engine efficiency and performance, they are one of the most vital components the department produces.

There is no single perfect port design-or engine combination-- suited for every race on the Winston Cup tour. For example, high torque is required on short tracks, while pure horsepower is the name of the game on superspeedways. Ports must be engineered to match the desired power curve for each race, and heads also must comply with NASCAR restrictions on maximum port volume. Duplicating ports known to be within spec ensures every port will meet regulations.

Scanning routines are performed on Gibbs' Daewoo Ace H500 HMC. A dedicated head-scanning pallet is fitted with a five-axis rotary table and special head fixture. The pallet can be quickly shuttled in for scanning duty, then shuttled out for optimal spindle usage. The Renscan unit's probe mounts in the spindle using a standard CAT-taper shank and is supplied with a special anti-rotation kit that stabilizes the spindle during scanning routines. The system captures about 125,000 data points for an intake port in just a couple of hours. Exhaust ports are scanned in a similar manner.

After scanning, the unit's Tracecut software generates wireframe models which are copied and mirrored to replicate the profiles for all eight cylinders. Tracecut then translates the data into three-axis NC code. Machining is performed with the optimal choice of tools, along the optimal toolpaths, regardless of the direction or stepover of the scanning operation. Surface finish is maintained by using a 0.025" (0.64-- mm) incremental tool stepover. After cleaning, heads are ready for assembly right off the machine tool. Circle 225.