What’s bigger than a breadbox and has more power than steaming locomotive? Answer: The not so mild mannered Edelbrock/Pat Musi five-fifty-five (555 cubic inch) crate engine. We needed a bad ass big block Chevy crate engine that could make 800+ reliable horsepower for our 1978 Chevrolet Malibu code named Project Grandma.

Since Edelbrock and Pat Musi have joined forces to build this 555ci crate, which makes 675+ hp on pump gas and is just itching for a dose of Edelbrock Nitrous, we decided to work together with these two industry legends on this multi-part project. Here’s our story on the Edelbrock/Musi 555 Engine, Part I.

In this article, the first in a series of three articles on the Edelbrock 555ci, we will be doing two things. First, giving you a quick overview of the Edelbrock/Musi 555. Second, we’ll be taking a closer look at the short block assembly and the components that make up the muscle of this pavement punisher. We are also producing a series of videos on the short-block, long-block, and dyno testing.

The 555ci Edelbrock/Musi Crate is described as “street friendly” by the engineers at Edelbrock. At the same time, no matter how drivable it may be, 675 hp is never friendly. It’s angry, rip-roaring power, just wrapped in a civilized package. Just like we like it.

In fact, Edelbrock took their Chevelle on the road on the entire Hot Rod Power Tour with this very engine in it. And it was described as being a “docile street car that hauled ass” by everyone that drove it.

The only thing missing from this robust power plant is red tights and a cape. When we wanted a powerful engine to go into our sleeper project car, a 1978 Chevy Malibu that we call Project Grandma, we sought out a superior crate engine with high horsepower capability. As we refined our search to GM big blocks, the roads kept pointing to Edelbrock and Pat Musi. We wanted a Crate Engine that could handle nitrous, but also run on pump gas with good manners.

One of the jewels in the Edelbrock line was the Big Block Five-Fifty-Five (555 cubic inch). The clincher for us was the collaboration of Edelbrock and Pat Musi in the development of this motor.

Why a Big Block?

The common wisdom is that pump gas small block Chevy’ crate engines make 500 reliable horsepower and up to 750 with the right components, but sacrificing some longevity. Large cubic inch Big block Chevrolet engines are more likely to make 650+ plus dependable horsepower for a longer period of time. Regardless of what you’ve been told, bigger is better.

The Edelbrock/Musi 555ci crate engine was developed for anyone that wants big cubes and tire-shredding horses on pump gas. The brainchild of the Edelbrock design team, this big block motor provides excelent power for the pump swill crowd by relying heavily on quality components. Early on in the development process, Edelbrock enlisted the experience of Pat Musi to collaborate in the engine design. Musi is a very accomplished big block engine builder bringing with him 38 years of performance engine building experience and 8 world championships in street legal drag racing.

Pat Musi knows big block Chevy engines at well as anyone in the industry, and his higher-end drag racing oriented motors have been winning championships around the world for many years now. Some things just go together, and putting Edelbrock and Musi together in the GM Big Block arena is akin to Hollywood Hulk Hogan and Macho Man Randy Savage joining together as a tag team. The “beast from the east” engine builder and the “best of the west” parts maker. Let’s get ready to rrruummmbbble……

Edelbrock/Musi 555ci Overview: The Choices

Edebrock and Pat Musi offers two different 555ci crates: a carb version (650 hp) and an EFI version (675 hp). They are similar in terms of their short-block and long-block, but they have slightly different camshafts, and naturally, the induction system is specific to your fueling preference. Both engines provide big time power that ingests 91 octane pump gas, include the Edelbrock Power Package include the Victor/Musi 24-degree cylinder heads, and Edelbrock Victor intake.

Here’s an page from the Edelbrock Catalog with all of the specs of the 675 hp EFI version:

Many times when an engine builder like Musi gets involved with a big time manufacturer like Edelbrock, it’s often a simple licensing arrangement where the engine builder just sells his name to Edelbrock. That could not be further from the truth here. Musi is a developmental partner for Edelbrock, and helps them develop and R&D products across the entire spectrum of products.

His shop, Pat Musi Performance, has also been tapped to hand-assemble each and every Edelbrock/Musi 555 crate engine. So you are starting to see, Musi has his fingerprints on more than just the parts list. His shop literally puts the touches on each engine with the same level of attention to detail they do a 2,000 hp racing engine. That, you cannot buy.

Both 555ci engines are great choices. We chose the EFI version for three reasons.

  1. Greater horsepower – 675 hp vs 650 hp
  2. Greater drivability
  3. Better hood clearance for our sleeper Malibu

Here’s some of the highlights of the 675 hp 555ci Musi Engine:

Even though it doesn’t apply in our situation because we are going to be hosing our 555 down with copious amounts of Edelbrock nitrous, we’d be remiss without mentioning that these engines come with a 24-month/unlimited mileage warranty. Yes. 24-months for a 675 hp. Cool, isn’t it!

In this article, we’re going to give you an overview of the components that comprise the short-block that serves as the foundation of the Edelbrock 555ci, and cover the buildup of our Malibu’s short-block at Pat Musi Performance in New Jersey.

The Dart Big-M Block: 9.800-inch Deck

The foundation for this engine starts with the Dart Big-M block. Dart’s Big-M is based off of the Generation VI GM blocks with some upgrades that make it one of the strongest cast iron blocks around. It’s a great choice for the 555 because it is capable of supporting well over 1,000 hp and will allow an enthusiast to add nitrous to the Edelbrock crate engine without fear of hurting the block. Musi machines the bore to 4.560-inches which works with the SCAT 4.25-inch crank to make 555 ci.

Specs for the Dart Big-M block:

  • Extra thick decks. Deck height 9.800 (stock height).
  • Bore sizes available in 4.250”.
  • Priority main oil system that oils all of the main bearings before the lifters for extra reliability.
  • Stepped main oil gallery, 9/16” to 1/2” to 7/16”, increasing the flow of oil the crankshaft at high RPM and preventing oil pressure drop at the top end.
  • Splayed 4 bolt main caps for the ultimate bottom end strength.
  • All precision CNC machining to eliminate the need for expensive blueprinting.

Musi does all of the machining of the Edelbrock 555ci engine in house. In addition to the specs listed above, the Dart Big-M block also boasts of a stout 0.325 inch thick cylinder wall for better wear and less wall deflection.

The four bolt splayed main caps are absolutely the strongest arrangement available. Because the outside bolts on these caps are splayed at an angle, they are machined into the strongest part of the web area. 4 bolt main caps that are machined straight into the web tend to weaken the web area and eventually cracks begin to develop.

Even though Musi does the machining of the Dart Big M in house, the Musi engine builders check every single block before assembly. Double and triple checking is nothing new to this crew.

We’ve got a great relationship with Dart, and we think the Big-M was a great choice by Edelbrock to build a solid foundation. Musi Performance does the machine work on the Dart-M block right in-house, as you can see by all of the pictures below.

SCAT 4.25-inch Forged Steel Crankshaft

Buried in the depth of this sturdy Dart block is a forged steel 4.25-inch stroke SCAT crankshaft. SCAT has been manufacturing racing crankshafts for over forty years, and their forged crankshafts are well respected by many racers. The 4.25-inch stroke is what produces what Musi calls the “Triple Nickel” displacement of 555 cubic inches along with the 4.56-inch bore.

SCAT makes a nice crankshaft which features a number of high-end features in a very reasonable price for a fully forged steel crank. With the Edelbrock/Musi 555 you’ll get a precision machined crank which is heat treated and nitrided, has profiled and pendulum cut counterweights, a straight shot oiling system, lightening holes, and gun drilling. And yes, it’s made of top flight E4340 Steel.

While most crankshafts claim to be precision ground, SCAT crankshafts are desirable because the company exercises strict quality control measures. Every crankshaft produced must fall within very tightly controlled specifications. The crankshaft chosen for the 555 engine is heat treated and nitrided for strength. The nitriding process effectively hardens the surface of the metal without excessive heating. By using the Nitriding heat treatment process, there is less chance of distortion and can be accomplished with excellent dimensional control.

The primary reasons for Nitriding metal is:

  • To increase surface hardness and wear resistance
  • Improves fatigue life
  • Corrosion resistance

The counterweights on the SCAT cranks are profiled, where many crankshafts have a blunt edges on the counterweights. By rounding the counterweight edges, the crankshaft slices through the air and oil in the sump rather than slap against the lubricant. Needless to say, this reduces the amount of energy it takes to turn the crankshaft, and by slicing through the air there is less windage in the sump. Lighting holes in the rod journals and gun drilling the main line decreases the amount of rotating mass. This all translates to more horsepower to the drive train. “We feel we make a great crankshaft, said Tom Lieb, President of SCAT, “what separates SCAT cranks is preparation of the metal and heat treating the metal. Prep and treatment are the key. The bitterness of poor quality remains after the sweetness of low price is forgotten.” We think that’s a very clever way of saying; you get what you pay for…

Here is a picture of our Edelbrock/555 Dart Big M block with the SCAT 4.25-inch crankshaft installed.

SCAT H-Beam Connecting Rods

Throwing a rod. No fun at all. Nothing we’re planning on doing with our 555 ci even with 200+ hp of nitrous spraying down it’s throat.

Connecting rod selection is extremely important in higher horsepower engines. The rods must be able to withstand high temperatures and the constant pounding of the pistons reacting to the explosions taking place in the combustion camber.

Transmitting the power from the piston movement to the crankshaft, the rod has to be strong enough to repeat this action thousands of time each minute, yet be light enough not to contribute too much weight to the rotating assembly. One high horsepower solution to the power vs. weight question in connecting rods is the SCAT H-beam connecting rods.

The SCAT rods in the 555ci engine are manufactured out of the same high tensile strength steel as the crankshaft. This aircraft grade 4340 steel combined with an “H beam” engineering design makes for a very dependable strong and lightweight connecting rod. The rods are enhanced by utilizing ARP capscrew style bolts with alignment sleeves to ensure a perfect fit. They are matched sets, all within one gram of each other for better balance of the rotating assembly. These rods are a very good choice for the higher horsepower engines. No more need to worry about throwing a rod because of metal fatigue.

Musi inspects and measures every SCAT rod that comes through the shop during 555ci assembly.

Specs on the Edelbrock 555ci SCAT-spec rods:

  • 6.135 Length
  • Weight: 775 grams
  • Rated to 1,200 Horsepower (that should do us!)
  • 4340 Aircraft grade material
  • ARP extreme duty bolts

JE/SRP Pistons – part number 211760

Selecting pistons to drive the SCAT crank, the Edelbrock/Musi team selected a forged piston design from SRP Pistons. Located in Huntington Beach, SRP Pistons are a brand of JE Pistons, renowned for their high performance forged piston work. The same engineers that design NASCAR pistons in the same facility, also design and manufacturer SRP Pistons. For the five-fifty-five crate engine, the SRP piston is a slightly dome’d, 4032 high silicon-low expansion aluminum alloy.

It was designed by SRP and JE as an off-the shelf piston, but it can easily take the horsepower and nitrous we are going to hit the 555ci with. It’s designed to fit the Edelbrock 24-degree Musi Victor heads, has a strong wrist-pin, CNC ring groves, and a tight-clearance fit.

Musi’s team carefully assembles the pistons and rods before dropping them into the Dart Big M block that is the foundation of the Edelbrock 555.

Setting the torque on the rod bolts is one of the last steps of 555ci assembly.

Moroso Oil Pan – part number 20413

Quietly efficient, the contribution of the oil pan is often overlooked as just being a sump for lubricant. When put under the microscope however, huge efficiencies can be gained in selecting a quality oil pan. Not only must the oil pan have a design that fits with clearance for crossmembers and steering linkages, but also it has to be fabricated for a precise leak free fit. Situated only inches from the pavement, the oil pan also must be fabricated for strength.

The Moroso oil pans are designed with internal reinforced rails for additional strength. With a 6 quart capacity, horsepower gains and lubrication advantages can be gained with a sump design that minimizes oil sloshing, windage and less aeration (foaming) of the lubricant. Moroso adds a sump tray in this design to prevent oil sloshing and reduce windage. The sump tray is removable for inspection and cleaning. The pan also incorporates dual anti-slosh plates at the rear to direct oil into the sump during hard acceleration. Baffling by means of trap doors are constructed in the sump area to contain oil near the pickup during deceleration.

The design and features of the Moroso oil pan help keep excessive oil off of the rotating assembly thereby lessening the rotating mass, and keeps the oil near the pickup so that it can be pumped through the lubrication system. Strong, big capacity and quietly efficient best describe this part.

Edelbrock Hydraulic Roller Camshaft – part number 2264

One of the coolest features of the Edelbrock/Musi 555 crate is the use of the hydraulic roller camshaft. It’s streetable and capable of making big power.

If the other components of the rotating assembly can be described as the muscles of this beast, the camshaft can be called the brains. Utilizing a hydraulic roller camshaft in this application has distinct advantages. A more aggressive cam profile without excessive valve overlaps can be used because unlike conventional cam profiles, roller cams have steeper ramp up surfaces.

The use of roller lifters allow the steeper profile where the edges on non-roller lifters would grind the steeper ramp. Plus, using a hydraulic roller cams on an engine like the 555ci Musi motor eliminate all camshaft break-in problems.

Here is the specs on the Edelbrock/Musi Hydraulic roller:

Lift: .632 Intake / .648 Exhaust
Duration @ .050” lift: 248 degrees Intake / 256 degrees Exhaust.
Lobe separation: 112 degrees
Intake centerline: 109 degrees

We’re finished…

That wrapped up our 555ci Edelbrock/Musi Short-Block, but we’ve got LOTS more for you. Three videos and two more stories, all on your new favorite crate engine. The thing is, you can afford this one, and you’ll be buying quality parts that will last for years.

Mild mannered Clark Kent? Absolutely not! A big block chevy engine that is built with parts that are made with aircraft grade steel make this the superman of engines. Like bullets bouncing off the man of steel’s chest, this motor is bulletproof and has the tensile strength of superman’s forehead. The added bonus of having genius engine builder Pat Musi custom assemble this engine puts it in the horsepower League of Superheroes.

We’ll show you how much power we can make in Part III, when we get out the Edelbrock nitrous and start spraying down the house. Until then, enjoy the pictures of the complete Edelbrock crate 555 short-block below:

For more information, visit www.Edelbrock.com