CGI: Not What You Think It Is

01 R07 Engine

The Chevrolet R07 NASCAR Racing Engine (Illustration courtesy Chevrolet)


When NASCAR allowed Toyota to design and fabricate a two-valve pushrod V8 specifically for Sprint Cup competition, it marked the first time that it had allowed a purpose-built racing engine to compete in any of its three top touring series. Prior to this, all engines competing in NASCAR had to be based on a production-based design. The change in rules also opened the door for Chevrolet to design its own NASCAR-specific engine, the R07, which employed CGI.


02 SB Comparo

The Original SBC and the R07 (Illustration courtesy Chevrolet)


Toyota’s move put Chrysler, Ford and Chevy at a big disadvantage. Chevy was still using an architecture that debuted with the 1955 265 Small Block. The fact that this basic design lasted until 2006 speaks to the basic excellence of the SBC concept and execution. The new R07 includes a number of enhancements not found on the SBC: higher cam placement, shorter and stiffer pushrods, and integral piston oil spray, to name a few. For comparison, the R07 has a peak piston speed of 8780 feet per minute at 10,000 rpm; a 2.4 liter F1 V8 develops a peak piston speed of 8349 fpm at 18,000 rpm. Think NASCAR motors ain’t tough? Try running 600 miles in your F1 machine.

But probably the most interesting aspect of the R07 is that the block is cast from Compacted Graphite Iron, or CGI. CGI is still cast iron, but it consists of a sophisticated alloy combining the qualities of gray iron and ductile iron. It was discovered by mistake in 1947, but due to the extremely precise nature required in adding magnesium to the alloy, CGI didn’t find commercial application until the early 1990s when it was used to cast the brake discs for high speed trains in Europe.


03 R07 Block

R07 Short Block (Courtesy Chevrolet)


So given a clean sheet of paper, why did Chevy choose CGI? The reasons are compelling. CGI has 75% higher tensile, 45% higher stiffness, and double the fatigue strength of gray iron. But more importantly, it outperforms aluminum permitting a smaller package size (due to thinner wall sections, fewer stiffening ribs), higher specific performance (more hp per kg), reduced cylinder bore distortion especially at elevated temperatures, no need for cylinder liners, and lower complete engine weight of up to 9%. CGI is particularly applicable in Vee engine configurations where its fatigue resistance can come into play. Audi’s 4.2 liter Diesel CGI V8 block outperforms Mercedes Benz’s aluminum 4.0 liter Diesel on the metrics mentioned above. And the larger Audi engine weighs 19.8 pounds less.


04MX-13 Engine

PACCAR’s MX-13 Engine (Courtesy PACCAR)


CGI blocks and heads may be relatively recent additions to the automotive scene, but CGI has been used in large truck and prime mover engines for some time now.

PACCAR’s (Kenworth, Peterbuilt) wholly-owned subsidiary, DAF, of the Netherlands, began producing engines with CGI blocks and heads in 2001. Today MX series engines are produced in the US as well as the Netherlands with the top of the line MX-13 producing 500 hp and 1850 lb-ft of torque at 1100 rpm from its 12.9 liters.

PACCAR is not alone in the US producing large capacity Diesels using CGI. Deere, Cummins, International, Caterpillar and General Electric are also players.

Interesting that a material that first found application in the rail and trucking industry has finally trickled down to NASCAR. Will Formula 1 be next?