Edelbrock and Musi Racing Engines team up for a potent street-strip Chevrolet big block

By Jeff Huneycutt – Images by the Author

Pat Musi made his bones building top-flight engines for drag racing. Drivers running Musi engines have won championships in numerous classes, but the engine builder is most famous for his nitrous-huffing big-blocks.

002 Raw Dart block with machined cylinder bores ready for engine assembly — No recycled parts here. The build starts with a new standard deck height big-block iron casting that gets fully machined in the Musi Racing shops. Four-bolt mains help make for a rock-solid bottom end.

Musi has been in business since 1970, and almost exclusively building ultra-competitive competition engines the whole time. But that’s changed recently. Thanks to a partnership with Edelbrock you can now purchase a genuine Pat Musi Racing Engines big-block Chevrolet, perfect for hot street performance or even drag racing. Maybe best of all, because of the partnership, the engines can be had for a real steal. There are currently three versions, and as this went to press the lowest cost carbureted engine could be had for less than $19,000, while the most expensive EFI big-block comes in for just about $3,000 more.

003 Forged rotating assembly with crankshaft installed in Dart engine block — A forged Lunati crank is settled into the Clevite main bearings in the block. It is a stroker with a 4.250-inch sweep.

Now, that’s obviously more expensive than yanking a 5.3 out of a junkyard and throwing on an imported turbo, but we’re talking about well over 700 naturally aspirated horsepower that comes with a 24-month, unlimited mileage warranty. Plus, all the parts are aftermarket and higher quality than stock and the engines are machined and hand assembled by the same craftsmen who build Musi’s full-race engines.

004 Manley forged pistons and rods laid out for high performance engine assembly — High-end components are used throughout. The connecting rods are high-strength H-bearm forgings from Lunati while the pistons are also forged with coated skirts and a small 5cc dome to dial in the 10.0:1 compression ratio.

The origin of this program goes all the way back to a conversation between himself and the late Vic Edelbrock Jr. Musi says they wanted to come up with something unique, and Edelbrock Jr. asked about LS engines, which Musi quickly shot down.

005 Custom ground camshaft with aggressive lobes for high RPM performance builds — The cam is a hydraulic roller from Comp Cams that’s been spec’d to create both great power and plenty of vacuum for power brakes. The duration is 248/256 at 0.050 inch of tappet lift, and lift is 0.632/0.646 with the 1.7:1 ratio rocker arms.

“I’m a big-block guy,” he laughs. “When I street raced back in 1969, in my hometown all the big hitters had big-blocks. If somebody came rolling in with a small-block, we’d tell him, ‘Kid, take your mother’s car back home. You’re wasting rubber, you’re wasting gas, and you’re wasting our time. Get out of here with that!’

006 Technician installing forged piston into engine block using ring compressor — Engine builder Robert Hallberg drops the piston and rod assemblies into a new 555 short-block going together. The same exacting crew that builds Musi’s big-inch nitrous monsters for professional drag racers also build these big-blocks.

“So, I told [Edelbrock Jr.] I wanted to build a big-block. We came up with the triple nickel, a 555ci combination,” Musi tells. “[Edelbrock Jr.] wanted it to have good vacuum so you can run power brakes and he wanted all the brackets and headers to bolt right up, so if a guy already has a big-block he can just drop this one right in without having to buy a bunch of other stuff. So, we set out to do exactly that.”

007 Edelbrock AVS2 carburetor with mechanical secondary for streetstrip small block builds — If you purchase a carbureted version of the 555, you will get an 800-cfm Edelbrock AVS2 carb, which comes equipped with annular flow boosters that are proven to improve fuel atomization for a better burn.

Musi and Edelbrock’s partnership has been producing engines for a few years now and they are gaining steam in the market. Currently, there are three versions. The only difference between the three is the induction system. There is one carbureted version that utilizes an 800-cfm Edelbrock AVS2 carb with an electric choke. Then there are two more fuel-injected versions. One uses a Pro-Flo 4 EFI setup with a four-barrel throttle body and a single-plane intake manifold. This option works well if you want the convenience of EFI while still being able to run a carburetor-style air filter to maintain an old-school look. The third comes outfitted with Edelbrock’s Pro-Flo 4 XT intake with a modern front-breather intake and 90mm throttle body.

008 Edelbrock Pro Flo XT intake manifold with fuel rails for EFI conversion setups — This is the Pro-Flo 4 XT intake manifold setup. Besides the cool look, it comes equipped with a 90mm throttle body that can flow 1,100 cfm and eight 60 lb/hr injectors. This intake makes for the highest horsepower and torque output of the three options.

Because the long-blocks for all three versions are the same, Musi tries to always keep multiple long-blocks on hand. Then, when a customer places an order, they can finish it off with the intake system preferred and any other custom touches requested. For example, while we were there, engine builders were installing a really nice Billet Specialties accessory drive system to spin up the alternator and power steering pump.

009 Complete Pat Musi 555 big block crate engine with EFI and CNC ported heads — This 555 is ready to go out the door with the Pro-Flo 4 EFI setup bolted up. This setup allows you to use carbureted-style air filter up top so you can keep an old-school look with the extra power and reliability of EFI.

Edelbrock advertises these engines with peaks of 676 hp and 469 lb-ft of torque for the carbureted version, 697/643 for the four-barrel throttle body, and all the way up to 723/652 for the tunnel ram-style Pro-Flo 4 XT. But we suspect that those numbers may even be a little low. Musi showed us a recent dyno sheet where a fuel-injected 555 made 727.1 hp and a whopping 705.7 lb-ft of torque! Plus, it’s worth noting that those numbers were all made while burning pump gas.

010 Close up of 4 barrel EFI throttle body on Edelbrock intake with 555 valve covers — Although it can’t flow quite as much as the 90mm throttle body on the XT setup, the four-barrel throttle body can move 1,000 cfm of air into the single-plane intake manifold. Distributors are included in all three engine options, but only the EFI setups have a Bluetooth-capable ECU that can be tuned right from your phone.

One great tip that Musi stressed is that while you can order one of these big cubic-inch engines directly from Edelbrock with no more hassle than buying an intake manifold, there is much more support available if you need it. Musi’s brother Ralph is a one-man tech department at Musi Racing Engines and available via phone to help anyone with questions they may have when considering a triple nickel purchase—and even questions they may have after the purchase. This covers everything from choosing the ideal intake system, making sure your fuel pump can support the injectors, to dialing in the rear gear ratio that best complements your engine’s powerband.

011 CNC porting cylinder head combustion chambers using Centroid 5 axis machining center for race engine precision — Edelbrock has actually established a cylinder head performance center right in Musi’s race shop. Every 555 cylinder head that’s used gets put through an in-house porting program to significantly upgrade the power potential. Here, CNC specialist Evan LeBlanc runs another big-block head through the process, finishing up with 118cc combustion chambers and 354cc intake runners.

“They’re great engines,” Ralph Musi says. “We want people to get the most out of them and enjoy them.” With over 725 hp on tap with pump gas, there’s going to be a lot of enjoyment to be had. “Plus,” Ralph, an old-school racer himself, adds with a laugh, “There’s not a single metric bolt on the whole thing!”