What's the secret to hidden horsepower? Who cares? This engine-building effort is all about torque-street torque-and how to get a lot of it from your small-block Ford V-8 without spending a fortune. It's called making the most of low displacement using the right parts, building technique, and factory iron heads.
Would you like to know more?
The Summit Racing/MCE Engines 331 Stealth small-block is the brainchild of our good friend Marvin McAfee of Marvin's Competition Engines (MCE) in Los Angeles, California. Marvin conceived this engine with his closest associates using a lifetime of experience as an engine builder and craftsman. This vision was to build a rock-solid small-block that would make 350-400 hp, with potential for approximately 100 more, using factory iron cylinder heads. He envisioned the perfect Mustang power package with plenty of power for a 3,200-pound automobile that could, with the right chassis, driveline, and driving technique, crack the quarter-mile in 11-12 seconds at 110-120 mph, yet be docile enough for the street on pump gas. Yes: pump gas, and yes: iron Ford heads.
"We don't like the research and development approach to engine building," he tells us, "We don't like guesswork either. However, we do like going with what we know works from proven experience." Marvin has built a number of 347ci stroker engines in his time. He's also built an untold number of 289 and 302ci small-blocks in this engine's 44-year history. But he is quick to tell us he prefers the underdog: the 331ci stroker package in a 289/302 block.
Marvin used his cache of aftermarket catalogs and visited the Web for inspiration. He focused on Summit Racing Equipment, Comp Cams, Probe Industries, Mustangs Plus, PowerHeads, Edelbrock, MSD Ignition, and Holley. From this list of aftermarket companies and help from a lot of local talent, Marvin became the architect for torque. He came up with the name Stealth to describe his 331ci engine-building effort because it is invisible: that right-cross black eye we weren't expecting from an iron-head small-block. Stealthy performance because it is the unexpected: a small-block with modest displacement that makes big-inch horsepower and torque.
There are two approaches with the 331 Stealth small-block stroker. For 400 hp now and another 100-200 hp later, build a brute platform that can stand up to the pounding of more ponies. This is a Probe Industries 4340 large-radius steel crank that has been micro-polished for smoothness and reduced friction... | 
...Oil holes have been chamfered to improve oil flow to the bearings. We like the Probe 4340 I-beam lightweight rods. Probe forged 4.030-inch pistons are whittled from 2618-T6 aluminum. Marvin has worked all of these pieces to exacting MCE standards. | 
Summit Racing provided Marvin with a Fluidampr harmonic balancer which dampens vibration better than a factory balancer, especially if spinning above 6,000 rpm. |
So how does a 331ci mill make 400 hp and 400 lbs-ft of torque? To Marvin's way of thinking, it's simple high school physics. "Our recipe leans toward more go and less show, which is a MCE hallmark. We want to build a kick-ass 331ci street engine with a healthy dose of durability without having to take out a second mortgage on the house and sell one of the kids." He adds that if you are building an engine with the intent of making more power, invest in a strong bottom end to grow with. It costs money but is well-spent if there are big plans for more power later.
If the beer and pretzel budget won't allow a bulletproof bottom end that can take 500-plus horsepower, you can still achieve 400/400 with a nodular iron crank, forged I-beam rods, and hypereutectic pistons for street and Saturday night strip fun. Just remember that 400/400 is the maximum power you can throw at these pieces in a stock block. Anything more is courting catastrophic failure.
Stealthy Formula For Success
"Everybody loves horsepower-the more the better," Marvin tells us. "Producing horsepower isn't a secret. Take torque and rpm, multiply these numbers together, and then divide it by 5,252. If you're going to perform on the racetrack, more horsepower is mandatory. On the street it's unnecessary. You need torque on the street to get respect." So how to get torque from a 331-inch small-block? And how to get even more horsepower and torque later if you decide to go racing? Marvin and the MCE performance team show us how.
Marvin admits there are two approaches to making 400 hp: liberal budget and conservative budget. You can make 400 hp and 400 lbs-ft of torque from a 289/302-based block with a low-buck 331-inch stroker kit and nodular iron crank, I-beam rods, and hypereutectic pistons. However, this is the package's service ceiling. For 100-200 more horsepower and an equal amount of torque, you're going to need a stronger block, steel crank, bulletproof rods, and forged pistons. This is what Marvin has specified to achieve a platform with potential for growth. He is building a powerful 400/400 small-block with a plan for 100/100 more using iron heads. He doesn't want it to break on the dyno because he chose to do it on the cheap. He invested wisely in a strong bottom end he could build on.
Block Party
Remove all the freeze and oil galley plugs Remove the cam bearings Hot-tank and jet-clean the block Check for core shift by looking at the lifter bores. If you see an offset, don't use the block for performance use Magnaflux the block to check for cracks and casting flaws Deburr all the sharp edges in the block casting, both inside and outside Remove all the internal sand cavities (i.e., craters in the casting surface) Tap all the front oil galleys for screw-in galley plugs Radius the lifter-valley oil drain holes for improved drain back Install oil drain-back screens to catch any debris Chamfer the oil filter-station passages for improved flow Chase all the bolt-hole threads using bottom taps. Then chamfer and radius all holes for smooth bolt installation Tap the crankshaft-to-camshaft oil galley passages for oil restrictors in main journals 2 through 5 only. Do not install a lifter galley restrictor if running a hydraulic camshaft Mill the block-decks to true (i.e., parallel to each other and flat within .002-inch in any 6-inch direction, and an equal distance to the crankshaft centerline) Install the main caps and torque to specifications for a snug fit Bore the cylinders to 4.025 inches, then finish-hone them to micro-smooth at 4.030-inches. Always use torque plates during the honing process: Never any greater than 4.030-inches if racing, and never any higher than 4.040-inches for street use Line-hone the main bearing saddles Clean all the passages by hand using mineral spirits, bore brushes, and compressed air. Visually inspect all of them Jet-clean the block and check all passages for cleanliness again Install the cam bearings, solid-steel shell type only Prefit the camshaft and check for smooth rotation. Any binding or resistance to rotation is unacceptable and indicates bearing misalignment Install the restrictor kit to camshaft bearings using high-temp Loctite Install all of the oil-galley plugs Drill the passenger-side oil-galley plug .020-inch for timing-chain lubrication, then install the plug in the block. Clean the plug before installation Install the camshaft rear-bearing plug at the back of the block Coat all the nonmachined, rough, internal surfaces with an oil/acid-resistant paint, such as GE's Glyptal 1201, available from The Eastwood Company Mask all the machined surfaces and paint the block exterior with a high-temperature engine paint of your choice. VHT is recommended Dimple the intake-manifold endrails with a center punch, both manifold and block, to help retain the end gaskets Install the oil-filter adaptor fitting, and torque it to 70-80 lb-ft.