How to build a fast motor

NASCAR style
With a maximum cylinder bore of 4.185 inches, the 358ci displacement limit is achieved with a stroke of 3.25 inches. (However, builders may juggle those dimensions a bit so they can perform multiple rebuilds without exceeding the bore limit.) Connecting-rod lengths are typically in the 6.00- to 6.200-inch range, constrained by the 9.00-inch deck height rule. NASCAR limits engine speed by specifying the allowable transmission and final drive ratios for each track. The approach is not as hard and fast as, say, an electronic rev limiter, but it does keep engine speeds in the 9,300- to 9,600-rpm range.

That's pretty fast for a pushrod V-8, especially given the 800-mile service life that must be designed into the R07 to make it through practice, qualifying, and race day at a typical NASCAR Sprint Cup event. And it's pretty darned impressive when you think about it. Consider this: when you run the numbers, at 9,500 rpm, mean piston speed is 5,145 feet per minute with a maximum velocity of 8,380 ft/min at a crank angle of 76 degrees. Maximum positive piston acceleration is approximately 3,100 g, while the negative acceleration is nearly minus 5,300 g. How on earth can a big old 358ci pushrod V-8 live under such tremendous and sustained abuse, handling forces heretofore seen mainly in F1 engines? There's one part of the program that is no secret at all: extremely good parts and very careful assembly.





The cam is raised in the block to the legal maximum, which permits shorter, stiffer pushrods, while the 60mm cam journals allow a greater base circle for the NASCAR-mandated flat-tappet camshaft. The raised cam also makes room for two rows of integral oil galleys on either side, which supply the piston squirters. (Two more galleys are positioned on the outboard sides of the block.) The oil squirters keep wristpin and piston-crown temperatures under control. The squirters and plumbing were installed by the team engine shops on the SB2 engine, which required considerable machining and fabrication. So did the elaborate lifter-valley shields installed to prevent return oil from showering the camshaft, increasing windage losses. However, the R07 block features a cast-in-place cam tunnel. A minimum of 50 hours of hand labor was required to prepare the old SB2 block for competition. With all these features designed into the R07 block from the start, the teams are treated to a significant savings in time and cost.

The new block also includes several safety advances. By incorporating the coolant and oil passages into the block casting, there are fewer external lines and fittings, reducing the possibility of fluid spills and fires in a crash. Also, the NASCAR-required mechanical fuel pump can be driven either from the left side of the engine or remotely via a cable from the rear of the camshaft to a rotary pump mounted near the fuel cell. The old small-block V-8's fuel pump is on the right, and thus more vulnerable to wall impacts.



There are three basic intake... read full caption
There are three basic intake manifold configurations for the R07: speedway, short track, and restrictor plate-this is the speedway version. They differ mainly in runner and plenum volume. The intake manifold runs totally "dry," with no coolant passing through the casting or lubricant splashing it from underneath.

This view of a partial long- block shows a wealth of detail. Note the timing belt, shaft-mounted steel roller rockers, head stud bosses extending down into the crankcase, and oil galley boss just above the oil pan rail that feeds the outboard bank of piston squirters.

Unlike all other Chevrolet V-8 engines to date, the R07 has its distributor at the front. The Holley 830-cfm carburetor is required under NASCAR Sprint Cup rules. NASCAR also limits the carb flange height to just over 18 inches above the crankshaft centerline.The R07's cylinder heads are a brand new day as well. The small-block's "mirrored" or "book-fold" head layout was compact and efficient back in 1955, but it had several drawbacks for performance use. For one, the valve layout places two exhaust valves adjacent to each other on the center cylinders of each bank, creating two large hot spots that are difficult to cool. On the R07, the valves are deployed in intake/exhaust order across the cylinder head, eliminating these hot spots. Additionally, each cylinder is fed coolant individually via the manifold passage cast into the central valley cover. (On the original small-block the outside cylinders were cooled first.)

We would love to be able to show you the intake and exhaust ports of the R07, but those details are rather sensitive, and they vary among teams as well. GM Racing furnishes the head castings in raw, semi-finished form with the intake and exhaust passages left in their as-cast state, so teams can perform their own porting. In this and other aspects the R07 is unique, as the engine is not so much a product of GM Racing but a close technical collaboration between the factory and what GM calls its "key partner teams." GM Racing provides the foundation and framework of the engine, while the Chevy teams develop the engine into a winning package. When the R07 program was launched, these teams included Hendrick Motorsports, Richard Childress Racing, Dale Earnhardt Inc., and Joe Gibbs Racing. (Since then, RCR and DEI have merged their engine shops while Gibbs has moved on to Toyota.) The key partner teams meet with GM Racing's engineers once a month, and it was their input that produced many of the improvements found in the R07, including the design changes in the cylinder block and heads.





In the last decade or so there's been a revolution in how NASCAR teams operate their engine shops. Now each one is a competent engine development company in its own right, with the ability to handle nearly any part of engine R&D. If NASCAR let them, many would be capable of building their own engines from scratch. As the sport has exploded, technical resources and personnel have flooded into NASCAR from every corner of the globe. For example, the manager of the engine department at Childress is Nick Hayes, formerly the technical director at Cosworth Engines. So these engine shops (which are really more like factories; Hendrick alone builds more than 300 engines per year) are more than capable of handling their own cylinder-head and manifold development using CFD (computational fluid dynamics) and other advanced tools.

And while the NASCAR teams once relied upon outside companies like Crane or Competition Cams to perform their camshaft and valvetrain development, that work is now brought in-house as well. So we can't really talk about valve lift, duration, or other valvetrain specs either. That is proprietary information, as they say, and also varies with application. Different venues-speedways, short tracks, and restrictor-plate events-call for different combinations. Precise valve locations and included angles are also closely held secrets. However, here is one interesting and revealing data point: According to our sources, all the builders are currently using rocker-arm ratios of 2:1 or greater.



GM Racing's R07 team, from left: Block engineer Ondrej Tomek, cylinder head and intake engineer Ed Keating, Chevrolet Sprint Cup Program Manager Alba Colon, cylinder head and intake engineer Ron Sperry, Director of GM Racing Mark Kent, and NASCAR Engine Technical Manager Jim Covey.

The R07 cylinder head is shown at the top, with the old SB2.2 head beneath it. Like the small-block Chevy on which it was based, the SB2 had its valves arranged with two adjacent exhausts in the center of the head....


...That troublesome old hot spot was corrected with the R07. Also note the copper-beryllium valve seats, which are compatible with titanium valves.With a maximum cylinder bore of 4.185 inches, the 358ci displacement limit is achieved with a stroke of 3.25 inches. (However, builders may juggle those dimensions a bit so they can perform multiple rebuilds without exceeding the bore limit.) Connecting-rod lengths are typically in the 6.00- to 6.200-inch range, constrained by the 9.00-inch deck height rule. NASCAR limits engine speed by specifying the allowable transmission and final drive ratios for each track. The approach is not as hard and fast as, say, an electronic rev limiter, but it does keep engine speeds in the 9,300- to 9,600-rpm range.

That's pretty fast for a pushrod V-8, especially given the 800-mile service life that must be designed into the R07 to make it through practice, qualifying, and race day at a typical NASCAR Sprint Cup event. And it's pretty darned impressive when you think about it. Consider this: when you run the numbers, at 9,500 rpm, mean piston speed is 5,145 feet per minute with a maximum velocity of 8,380 ft/min at a crank angle of 76 degrees. Maximum positive piston acceleration is approximately 3,100 g, while the negative acceleration is nearly minus 5,300 g. How on earth can a big old 358ci pushrod V-8 live under such tremendous and sustained abuse, handling forces heretofore seen mainly in F1 engines? There's one part of the program that is no secret at all: extremely good parts and very careful assembly.

mmmmmmmm, 9600rpm, i want one