Over the years, Edelbrock has been known for its high-quality cylinder heads and intake manifolds, but as the company has grown older, it has diversified its lineup of go-fast components. In the past few years we have watched the Fun Team jump into the nitrous market, suspension components, and even superchargers for various applications. Its latest venture has been crate engines. This month, we poke and prod at one the company's most popular bullets, an Edelbrock Pat Musi 555ci Crate Engine that spun the dyno to 677 hp-on pump gas. Making that kind of power in naturally aspirated trim and still include a warranty would be troublesome for some companies. For Edelbrock, it was easy, and they turned to a longtime partner, and multiple Pro Street and Pro Modified champion, Pat Musi, to help design this outrageously powerful crate engine.

The two collaborated to bring forth a powerful-yet street-worthy-combination, and launched it in 2007. Edelbrock had released version 1.0 of the bullet, which made 675 hp (EFI version) and 650 hp (carburetor on top). The first public glance at the engine came during a popular weeklong cruise where Vic Edelbrock's '67 Chevelle-equipped with the Edelbrock/Musi 555-completed the entire tour without a hiccup. It proved the engine's ability to withstand the rigors of street cruising and still retain a healthy power curve. The EFI version in Vic's Chevelle knocked down 19 mpg during last year's cruise. The car was equipped with a Tremec TKO six-speed and 3.31 rear gears. The carburetor induction saw 4 mpg less, as Edelbrock observed 15 mpg in the same Chevelle during previous tours.

Since that time, the folks at Pat Musi Performance and Edelbrock continue to think of better ways to offer this popular 555ci powerplant. This year, the team decided to change the cylinder heads from the Victor 24-degree rectangular port, to the Performer RPM XT (Xtreme) heads. "The exhaust port is in the stock location with the XT heads. That means our customers won't have to rely on a custom set of headers when installing the 555," commented Smitty Smith of Edelbrock. Not only did the XT heads allow for off-the-shelf headers, but the heads also bumped the horsepower up. The CNC-ported heads swelled the big-block's rating from 675 hp to an even better 697 hp-on pump gas-with the EFI system.

Edelbrock used EFI induction for the big rating, but we saw impressive results from a carb setup on an engine at Pat Musi Performance during our photo shoot. They officially call the carbureted combo a 676hp package, and we saw one bullet produce 677 hp. It shows how dead-on the advertising numbers are in the company's literature. While we didn't do a back-to-back test with the different induction components, Edelbrock and Musi told us that the EFI was worth 20 to 25 hp more. Musi was quick to explain the power difference between the two induction systems on this engine: "The main reason the EFI makes more horsepower is that the throttle body flows more than the [800-cfm Thunder Series AVS] Edelbrock carb." He explained how the throttle body is similar in size, but doesn't have the restrictive venturis to block the air coming in. Musi equated it to adding a Dominator to the engine, which would make a lot of more power than the Thunder Series carb, but driveability would suffer. The EFI is void of that problem, thanks to it being able to control the fuel and spark delivery.

Pat Musi Performance builds all the engines, and each carries a two-year warranty with unlimited mileage during that time. The engine is based on a Dart M block with a standard 9.8-inch deck height, making it fit very well under the hood of most muscle cars. Musi then bores each cylinder hole to 4.560 inches. Mahle forged pistons have been chosen, and the flat tops contribute to the 10:1 compression ratio. Musi sourced Scat for a set of steel connecting rods and a steel crankshaft (4.250-inch stroke). A Moroso oil pump and pan keep everything lubricated.