Getting 960 Horsepower Out Of 397 Cubic Inches With A NASCAR-Sourced Chevrolet R07 Engine

10 min read

Getting 960 Horsepower Out Of 397 Cubic Inches With A NASCAR-Sourced Chevrolet R07 Engine

10 min read

The performance expectations of the typical hot rodder begin where the automakers leave off. We'll take the biggest truck V8, add a junkyard turbo, and then cram them both into a little car - without regard for a single stock-holder. The constraints an original equipment manufacturer (OEM) has to design for can't compete with our lust for performance. But what happens in those rare moments in hot rodding history when the engineers build something without production-car constraints? You get engines like the R07.

In a sea of Turbo LS engines, Gen III Hemis, and big-blocks, who desires a small-block Chevy anymore? No one. But, if you could have a naturally aspirated 358ci SBC with over 900 horsepower, you might rethink that.

Chevrolet SB2 V8

NASCAR has used a 358ci V8 since 1974. The Chevrolet SB2, which replaced the original small-block Chevy, retired from Cup racing in 2007, but still remains active in multiple NASCAR divisions.

The 358ci Small-Block

Since 1955, the small-block Chevrolet has been a staple of NASCAR, and it's been 358 cubic inches since 1974. Cup cars have evolved from being stock-looking cars to cookie-cutter molds undisguisable without decals. The engines have taken a similar evolutionary path.

Chevrolet R07 bottom end

The PME team builds an R07 bottom end in one of their assembly rooms. The pistons feature a very narrow top land, raised piston pin, and ultra-thin oil rings. These are incredibly lightweight, efficient, and designed to handle 600 miles of high-rpm abuse.

In 1998, the Chevy SB2 replaced the original small-block Chevrolet and was the first engine designed for competitive use in NASCAR, without regard for a production vehicle. Older NASCAR-intended engines like the 426 HEMI and Ford 427 SOHC "Cammer" were explicitly built for NASCAR but were required to have a production counterpart to satisfy homologation rules. The SB2 has no connection to a production vehicle. However, per rules, it was required to "appear" like a production engine. It's still, in essence, an SBC with long pushrods, flooded water jackets, 9in deck height, and some interchangeable parts. But the SB2 featured improvements like great performing 11-degree heads, better block cooling, ideal spark-plug location, and improved oiling.

Chevrolet R07 oil squirters

Here you can see the R07’s piston oil squirters. We have to remove them for the stroker build as there isn’t enough real estate.

When Toyota entered the sport in the early 2000s, they didn't have a pushrod V8. So, they approached NASCAR with an all-new engine design that looked more like an Indy engine than a small block. While NASCAR was debating about upsetting a new multi-million-dollar OEM, Chevrolet and Ford took the opportunity to present their new machines and engine programs. All submitted engines were too extreme for the governing body, so NASCAR created a new rulebook.

The new engines could be anything, with no relation or even appearance to a production engine. Instead, NASCAR initiated what is known as "The Box," a set of over 50 engine-building parameters. It allowed no one manufacturer to build an engine with particular advantages over another.

Builders can run their own cam profiles, rocker ratios, intake porting, and can deck the blocks and heads, but they must retain the same dimensions and center lines. For instance, they can reshape the intake ports but cannot move them. For every thousandths they remove from the top, they must remove the same from the bottom, keeping the original centerline. Officials will mount inspection fixtures on the head dowels, carburetor mounting surface, and other places to check that everything lines up.

Chevrolet R07 complete bottom end

Here you can see the completed bottom-end and the huge cam roller bearings. The cam-position sensor is mounted in the front of the block for the coil-near-plug ignition to help with EFI, introduced in 2012.

The R07

Chevrolet's new R07, introduced in 2007—hence the name—features a new compacted-graphite-iron block that eliminated common SBC hot spots among other improvements. The bore spacing increased to 4.5in (11.43cm) from the SB2's 4.4in (11.18cm). The engine cannot measure over 358ci, with a maximum cylinder bore diameter of 4.185 inches (10.63cm).

The new R07 6-bolt heads have better gasket sealing and improved airflow. The valve springs are mostly submerged in oil too. Cup cars run a whopping six gallons of oil. The camshaft is higher in the block, making for shorter, stronger pushrods. There are no limitations on lift or duration of camshafts, but those are guarded secrets amongst builders. The resulting compression is around 12.5:1 depending on the rules.

Cup pistons are typically around 410 grams (the minimum rule weight is 400 grams). A Cup car's piston speed is 8,780 feet per minute at 10,000 rpm. Compare that with an F1 2.4L V8's peak piston speed of 8,349 feet per minute at 18,000 rpm. It takes serious engineering to make an engine last 600 miles with that piston speed.

Chevrolet R07 cylinder head

The R07’s 6-bolt heads alternate intake and exhaust valves like an LS, and the shallow valve angle allows for an efficient combustion chamber.

Manufacturers must have all parts available to the general public, a rule which persisted through the changes. Many parts are sold partially machined, like the engine blocks without lifter bores and cylinder heads with tiny ports. Cup cars run EFI with a Holley 4BBL 1000CFM 4150-Flange Throttle Body (PN 112-587), and your choice of either an Edelbrock Victor or Chevrolet cast aluminum intake. Other divisions, track-day cars, and the engines in this test typically run a single Holley four-barrel carb.

The R07 pricing has likely deterred its potential following. A used unit will sell north of $20,000. Plus, essentially, no parts are interchangeable with another Chevy engine. So, if you snag one on eBay that "only needs a few things," be careful of expensive, hard-to-find items you'll be forced to use. However, Chevrolet will likely replace the R07 in Cup racing in 2022. When that happens, it could flood the market with used R07s.

We caught up with Pro Motor Engines (PME) in Mooresville, North Carolina, who specialize in providing R07s to privateer teams. Pro Motor Engines can package Cup engines for street and track-day use too. With their help, the R07 will be an engine you lust for very soon.

We examine three PME engines built without the constraints of a NASCAR rule book: A stroked R07 we tested with a single and dual carb setup, and a milder variant set up for street use.

Chevrolet R07 Test: Holley 4150 and Chevrolet Performance intake

We begin the stroker test with a single Holley 4150 NASCAR legal Carburetor. This setup is very similar to what you’d find in other series and what Cup ran before the switch to EFI. The intake is a Chevrolet Performance unit ported by PME.

R07 Stroker Engine

Displacement397 cubic inches
CamshaftOver 900 lift, 280º/286º at 0.050, 110 degrees LSA
Fuel112 octane

"It has all the technology of a Cup engine," said PME owner Dennis Borem. The team starts by cleaning up the bores and stroking the engine with a 3.600-inch Bryant Racing crank. Both bore and stroke are the comfortable maximum for the R07, and due to the increased stroke there's no room for piston sprayers in the bottom of the block.

As for the heads, they're already pretty good. "We open up the ports the appropriate amount for the air you want to pump into the engine at how many RPMs and at what stroke," said Borem. "That'll determine the head design. But they're great flowing heads to begin with, so we didn't make any major changes to the ports."

Chevrolet R07 Dyno 1

The engine dynos at 924 horsepower at 8,300 rpm and 656 lb-ft at 6,500 rpm. It begins to make over 900 horsepower at 7,300 rpm all the way to 9,000 rpm.

On the first run, the engine drank from a single Holley 830 CFM NASCAR Spec carb (the former Cup carburetor) through a Cup-approved Chevrolet intake with 112 octane race fuel. The power curve grants more torque, but the power is still gathered at the top end of the range.

Next, PME adds a custom sheet metal intake; it's a specialty of theirs. This one features a pair of 750 CFM Street HP carburetors. "With more fuel, you'll usually always make more peak power," said Borem. We tested a carb version, but EFI variants are close to the same horsepower rating. When NASCAR switched to EFI, the new Holley throttle body featured smaller venturi (.375 inches each) compared to the previous carburetor's 1.591-inch-diameter venturi. This was an intentional decision made by NASCAR to keep power from jumping significantly with the switch to fuel injection.

Chevrolet R07 sheet metal intake and dual quads

With the new custom sheet metal intake and a pair of Holley 750cfm Street HP Carburetors (p/n 0-82751), the engine makes 959 horsepower at 8,800 rpm and 655 lb-ft at 6,700 rpm. Like before, it makes 900 horsepower at 7,300 rpm and maintains well over peak power.

There's power left on the table as these are out-of-the-box carbs with zero tuning. We could have pushed for 1,000 horsepower, but due to time constraints of actual Cup engines awaiting their turn on the dyno before the 2021 season, we had to move on. An R07 has the potential to make over 1,500 horsepower.

Will it handle boost? Yes, but the thin walls likely won't handle 2,000 horsepower. The ideal use for boost would be to create an even more street-able engine. One can make well over 1,000 horsepower without an extreme cam, race fuel, and RPM.

"Without a rule book, you can ad-lib some things, but it comes down to the value. Here you don't have to spend so much effort or money. You can cut a few corners, end up with a great product without constraints," said Dennis. And with that, we move on to a more street-friendly version built with other priorities in mind.

R07 Street Engine Dyno

Next up is the street engine. You can’t tell much of a visual difference from the outside of the two engines, but the power difference is there. This engine makes 750 horsepower at 7,600 RPM and 510 lb-ft of torque at 4,900 RPM on E15 NASCAR race fuel.

R07 Street Engine

Displacement358 cubic inches
Camshaft675 lift, 254/260 @ 0.050, 112 degrees LSA 

The PME team has long been building R07, FR9, and SB2 platforms for track-day cars. Now, they've begun creating similar packages targeted at the Pro Touring crowd. This particular R07 will end up in a customer’s third-gen Camaro. Therefore, peak performance takes a backseat to longevity, street manners, and the budget.

The stroke and bore are essentially the same as a Cup engine, due to the cost restraints. The compression is changed by way of a Mahle piston that drops the compression ratio from 12:1 to around 10.5:1, providing better fuel options.

Of course, cam profile is a significant factor in drivability. "We knock the lift out of it, to around 675, you don't need any more than that," said Borem. "You're taking an engine that's made to run upstairs all the time and putting it back to an rpm we can have some fun with."

Where Cup teams look for a sliver of performance, PME looks for longevity. The rod journals feature 1.850 bearings with thicker 2- or 2.017-inch main bearings, but "every R07 builder does something different with the bearings," said Borem. These bearings receive a full 180-degree oil groove.

A full race piston features a top and a second ring that has only .7 mm of thickness. That's a thin and expensive ring: "It's a delicate design that we push hard. On the street, though, if you have any kind of detonation, you'll have a problem."

"The skirt is bigger, we shorten the connecting rod, and lower the pin down into the piston which brings the ring land down, and then increase the mass by around 25 grams or more," said Borem. "The ring package will change the structure of the piston. That's one of the biggest changes. It's about making a stronger part." Cup pistons are over $4,000 for a set (pistons, rings, pins), but with more customer interest in street R07s, Borem hopes to create a piston package closer to $1,200 a set.

The Cup engine's required 6-stage oil pump uses five pumps to scavenge the oil pan and one for pressure, feeding oil back into the engine. It helps make more power, but for street use, there's little room and little need for that much scavenge. A four-stage pump is a better option.

Chevrolet R07 Intake

The twin-carb sheet metal intake used on the 959hp engine will actually live on the street engine. We simply added it to the stroker engine for testing. Now, the customer wants to add a Holley Super Sniper 2x4 4150 system (p/n 550-532).

The new street-friendly engine will also need less maintenance and will be better suited to tolerating the abuses of the street, but Borem leaves us with one thing to remember, "We sometimes ask the impossible out of these engines. We're building them with a fuse on the end. The more reliable, the longer the fuse. We want it long enough to run the cycles we intend it to."


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