When it comes to making horsepower, the thought that bigger is better has driven the motorsports hobby for years. In the late 1950s, the first 348 ci big-block Chevrolet spawned an infamous family of engines ranging from the 409 in 1961, and then the 427 Mystery Motor two years later. With a 4.840-inch bore center and 9.800- to 10.200-inch deck height, the next generation of big-blocks opened the door for engines with displacements of 396, 454, 472 and 572 ci, which is at the top of the food chain for GM big-block crate engines.
Even so, the demand for greater horsepower continued to grow as stock Rat motors gave way to strokers, which in turn, stepped aside for a rash of mountain motors.
Starting at around 632 ci, cubic inch inflation began to push the limits of conventional thinking. Engine builders responded with aftermarket blocks with spread pan rails, revised cam locations and raised deck heights, but they began to hit a brick wall when it came to getting much more than 700 ci out of an engine block. Sonny's Automotive Racing (SAR) helped break that barrier years ago by developing stretched engine blocks with 4.900-, 5.000- and then 5.300-inch bore centers.
By stretching the block to provide a bigger combustion chamber, larger bore and broader power band while still maintaining optimal valvetrain geometry, a larger engine with a higher base power level would provide builders much more flexibility, no matter what kind of power adders they used. Spraying less nitrous would lead to blowing less gas past the exhaust valve, smaller turbos would give quicker spool up and smaller blowers would lead to less engine wear. With the greater range of choices that a bigger engine provides, crew chiefs in Pro Mod, Outlaw 10.5 and Top Sportsman suddenly had more options and flexibility in putting an engine combination together.
Today, the evolution of this engine species continues to evolve as SAR has released a new 940 ci monster motor that represents the top of the food chain in naturally aspirated engine technology (and price). Representing the top of the mountain in the 5.300 engine family, this new 940 engine, even in this pump gas configuration, provides a number of advantages over the smaller, but better known IHRA Pro Stock engines that have produced the quickest and fastest N/A quarter-mile doorslammers in the world.
"No matter whether it's F1, NASCAR or drag racing, the trend over the past few years have been to go with a larger bore and less stroke in order to move the power band up," said Sonny Leonard. "An 825 ci engine will typically use a 4.800-inch bore with a 5.700 stroke. Here, we're using what cleans up to a 5.080 bore with a 5.800 stroke. As a result, the engine is much easier on the rods, makes more power and actually costs less, too."
Of course, brute power is what any of the 5.300 family of monster motors is all about. Dyno tests on this particular engine showed a whopping 1,702 peak horsepower at 7,200 rpm with 1,357 lb-ft of torque at 6,000 rpm on 93 octane pump gas. By comparison, this is nearly 2.5 times the peak power of a 720hp ZZ572/720R crate engine. Figure to spend just under a hundred grand for the 940 in this article.
Bigger is proving to be better in this instance, but that doesn't mean there isn't a point of diminishing returns. The upper limits of current block technology have been reached for a race engine that's going to last.
"I could build an engine with 1,000 ci, but the durability would be suspect because of the long stroke that you would need," Sonny said when asked about how big an engine could go reliably. "The block would have to be really tall and you'd have a lot of issues with rod flex, side load, bad angularity and ratios.
"For an engine this big to perform, you also have to have anywhere from an inch up to 1.300 inches of valve lift," Sonny continued. "You really have to do your homework to get the valvetrain geometry right in order for the roller tip to stay on the middle of the valve stem for as long as possible. You've also got to have a valve lash cap that will accommodate it."
Besides sheer size, another attractive feature of SAR's 5.300 engine family comes in the choice of cylinder heads. When originally introduced in late 2007, these engines came with SAR's semi-hemispherical heads, which utilize a bathtub shaped combustion chamber rather than a true 360-degree cup. This arrangement not only gives the burnt exhaust gases a straighter path to the exhaust valve, but it also allows relocation of the spark plug to a much more desirable location for better flame propagation, which in turn leads to more power and less opportunity for detonation. Most recently, SAR also introduced a new wedge head, which is ideal for use in nitrous applications. In addition, the smaller sized wedge will also make head removal much easier trackside.
Racers, crew chiefs and street enthusiasts also like the flexibility afforded through Sonny's engine kit program, which makes heads and short blocks readily available for do-it-yourselfers and other engine builders. Sonny's also keeps a deep inventory of rods and pistons from a variety of manufacturers so parts availability won't be an issue.
Besides the accomplishment of being able to engineer and build an engine of this magnitude is that fact that it made over 1,700 peak horsepower on 93 octane pump gas. That, in itself, has raised the eyebrows not only of a number of muscle car enthusiasts, but also boaters as well.
"When people ask how long an engine will last, you really have to answer that in terms of operating hours," Sonny said about some of the more common questions he gets. "We recommend approximately 500 hours of run time under normal driving conditions before having it serviced for lifters and springs. You can find cheaper ways to make power on pump gas, but it's a little harder to get away with it on a big, naturally-aspirated engine. In the long run, that's why it pays to go with the best quality parts you can find."
Block: CN billet aluminum water
Deck Height: 12.225-inch
Bore Dia: 5.082-inch
Bore Spacing: 5.300-inch
Oil Pump: Dailey 6 stage
Oil Pan: Moroso 12-quart
Crankshaft: Sonny Bryant billet steel
Main Journal: 2.748-inch
Main Bearing Clearance: 0.0038- to 0.0041-inch
Rod Journal: 2.1982
Rod Bearing Clearance: 0.0035- to 0.0038-inch
Bearings: Clevite H-series
Rods: Carrillo Steel
Rod Length: 7.995-inch
Pistons: 12.0:1 BME gas ported dish
Top Ring Gap: 0.040
Second Ring Gap: 0.045-inch
Oil Ring Gap: 0.030-inch
Cylinder Heads: SAR semi-hemispherical
Gasket: Copper 0.051-inch thickness
Intake Valve: Manley 2.750-inch
Exhaust Valve: Manley 2.060-inch
Pushrods: Manton 9/16-inch dia.
Intake Length: 11.400-inch
Exhaust Length: 12.750-inch
Springs: PSI brand, installed height 2.430 intake/2.460 exhaust
Rocker Arms: Jesel 1.75 intake, T&D 1.80 exhaust
Camshaft: SAR 70mm custom grind
Cam Lifters: Cam FX
Intake Manifold: SAR sheetmetal
Throttle Bodies: SAR 4x2 2.500-inch bore
Nitrous System: Speedtech 2-stage Fogger
Fuel Injectors: Precision Turbo 96 lb/hr
Engine Management: Big Stuff 3