Ford 331 Cubic Inch Stroker Engine - Going For 400/400

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.

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

Iron Heads And A Hot Roller Cam
You might be lulled into believing aftermarket aluminum heads are necessary to achieve 400/400, but Marvin proves otherwise. Make 400 honest horsepower and 400 lbs-ft of torque with ported Ford 289/302 cylinder-head iron castings. PowerHeads performs a CNC-port job, along with a five-angle valve job that includes hardened exhaust valve seats, new guides, and new stainless steel 1.94/1.60-inch valves. Comp Cams has provided Marvin with 100 percent of the valvetrain system, which includes dual springs with dampers, steel retainers and keepers, and a hydraulic roller camshaft long on torque. Marvin chose a Milodon dual-roller timing set. Comp Cams 1.7:1-ratio roller rockers were also inspected and blueprinted by Marvin. ARP screw-in rocker-arm studs with guide plates get everything square on top.

Marvin has opted for an aggressive hydraulic roller camshaft that gives him a lot of lift (.544) and enough duration (212 intake, 218 exhaust at .050 lift), with a lobe separation of 112 degrees that provides ample low-speed vacuum for power brakes, and other accessories we need on the street.

Heads Up!

Bumpstick Be-Bop

Induction
Marvin goes back to basic high-school physics. Engines are air pumps, he tells us. The power made is directly affected by how much air and fuel we can huff and ignite in the combustion chambers. Induction is the all-important beginning of this process. Marvin opted for the new Edelbrock Performer RPM Air Gap intake manifold, which offers all of the same features as the Performer RPM, as well as getting the manifold runners off the engine for a cooler intake charge. Marvin has also chosen a 750-cfm Holley carburetor with vacuum secondaries fed by a Holley 110-gph fuel pump.

MCE Builds The Stealth 331
We've already addressed many of the important elements of power: the recipe that is the 331 Stealth small-block from Summit Racing and MCE. We've shown you the block, the reciprocating internals, the cam and valvetrain, the iron Ford heads, the induction package, and the oiling system. Now, we're going to address the many fundamentals of a spot-on engine build.

Engine Building 101

These pesky details may seem like overkill, but when reviewing the remains of a failed engine, it's no comfort to realize you should have sweated the details. Detail is of utmost importance in any engine build.

Next month, we'll continue our Summit Racing/MCE Engines 331 Stealth build in Part 2 with more details important to engine integrity, reliability, and power. Then we'll put this engine on Westech's dyno for a polygraphic look at how power is made, and how we can sometimes come up short for reasons not immediately apparent.

Who Is Marvin McAfee?
If you're familiar with the racing world around Los Angeles, you know Marvin McAfee. Marvin is outspoken and extraordinarily-talented with a mindset for engine science. Marvin's Competition Engines has been around since the '60s and has been building engines for a fortunate few ever since. When Boss 302 Mustangs and Z-28 Camaros were tearing up the SCCA Trans Am circuit in 1969-1970, Marvin was there building the powerful engines that made these cars and their drivers legendary. When the jet age was unfolding during the '50s and '60s, Marvin was building, installing, and testing jet engines and the aircraft they powered. His disciplined psyche was born of knowing when to forego the short cut. Marvin has never given in to a clock or a budget in his engine building philosophy. It's logic rooted in his aerospace and racing background. If he can't build it right, he doesn't build it.

Marvin maintains his shop in a quiet Los Angeles neighborhood where he's been building engines since the dawn of the baby boom. There, he passionately burns the midnight oil, learning and practicing everything he can toward engine building excellence. This may sound like a puff job, but Marvin has touched our knowledge of engines like no one else has in 20 years of automotive journalism. He has taught us much in the short time we've known him. Our experiences with him have been extraordinary, and he's become an extraordinary friend. Marvin is the teacher and we are the students. Let class begin. -Jim Smart