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 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.
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.
Lifter bores are chamfered for smooth installation and operation. They have also been honed for improved oil control.
Heads Up! Vintage '70 302 two-barrel car castings (D0AE or D0OE castings) 1.94/1.60-inch valves Bronze guides Hardened exhaust valve seats CNC-ported for improvements in airflow MCE advanced port and bowl work by hand GE Glyptal 1201 coating inside Comp Cams 1.7:1 roller rocker arms and guide plates ARP rocker-arm studs Comp Cams one-piece push rods
Bumpstick Be-Bop Comp Cams (PN 35-320-8) grind number FW XE264HR-12 Designed for '82-'95 5.0L with 351W firing order Gross valve lift: 0.544 intake, 0.544-inch exhaust Duration at 0.006-inch: 264 intake, 270 exhaust Valve timing at 0.006-inch: 24 BTDC intake (open), 60 ABDC (closed); 71 BBDC exhaust (open), 19 ATDC (closed) 108-degree intake center angle Duration at 0.050-inch: 212 intake, 218 exhaust Lobe lift: 0.32-inch intake, .032-inch exhaust 112-degree lobe separation with a 43-degree valve overlap Recommended Comp Cams valve springs (PN 986-16)
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.
This is a blueprinted Milodon water pump from MCE. Marvin has worked all of the passages for smooth coolant flow. He took this one out of the box and completely disassembled it for inspection and blueprinting.
You won't find an Edelbrock Performer RPM Air Gap manifold like this one on the shelf. Marvin pulls these rascals out of the box from Summit Racing and massages them to MCE standards. He works the passages and does a port match, then he works the plenum area to improve airflow and reduce turbulence. A 1/2-inch phenolic carburetor spacer improves torque and keeps the heat farther away from the carburetor. Note the absence of rough edges in the plenum, which results in less turbulence and air disruption.
Marvin pulls the 750-cfm Holley out of the box and knocks it down for inspection and detail work by his associate Benton Jackson. Marvin likes this 750 Holley with removable air bleeds. He has installed sight glasses for float adjustment purposes. Everything inside has been massaged, adjusted, and tuned for optimum performance. Jet changes will be made on the dyno after a spark plug reading.
We will call this one-hour Marvinizing: Ford Racing valve covers tall enough to clear the rocker arms and stud girdles. Marvin did the Ford Racing graphics in red to accent the satin black finish.
Engine Building 101 Chase, clean, and inspect all of the bolts and bolt-hole threads Bolt threads should be clean enough that you can screw and fully seat the bolt dry. If it hangs up, inspect and chase the threads, or replace the bolt Lubricate bolt threads before torquing. Never torque bolts dry Check all the dimensions three times Check all the torque specs three times-seriously Apply assembly lube lightly, as opposed to dripping wet Do not use Teflon tape on bolt threads; It can leak. Use a thread sealer Use high-temp RTV sealer on brass freeze plugs in the block and heads. Do this sparingly on bolt threads where necessary (e.g., wet decks, cylinder heads, screw-in rocker-arm studs, and intake manifolds) When using RTV silicone sealer on gaskets, use a thin layer that will not squeeze out. Excess sealer can break free and clog water jackets and radiators All engine parts should fit together with a comfortable fit (i.e., a nice, smooth fit with minimal effort). Marvin calls this a zero fit. A timing gear should slide right on the crankshaft or camshaft without effort-not loose and sloppy, just a smooth fit. If you need a hammer, it's too tight; if it can fall off, it's too loose. One exception is the harmonic balancer which has to be a press fit Piston-ring width controls engine friction and temperature. The wider the ring, the greater the friction and heat transfer. Run 5/64-inch width on the street because of long-term wear requirements, and 1/16-inch for racing because there is less long-term wear and friction concerns. Watch ring tensions also Cylinder bores shrink with heat; pistons grow with heat. Aluminum pistons grow at a rate of 3:1 compared with iron or steel. Keep this in mind when boring and honing for proper piston-to-cylinder wall clearances Forged pistons grow more with heat; cast and hypereutectic pistons grow less with heat Be attentive to crankshaft and camshaft clearances and endplay. If it's too tight, it will run hot, and it it's too loose, you risk instability Did you know you don't have to use gasket sealer on the oil pan gasket? Use sealer only to retain gaskets during oil-pan installation. Use sealer sparingly at gasket joints at the front and rear main seals Use engine oil on the cylinder walls during the final assembly. Never use synthetic oil during assembly, and absolutely no cam break-in lube Use engine assembly lube on main, rod, and cam bearings between the journal and bearing only. Dry between the bearings and block saddles Make sure all bearing-oil holes line up. Bearings don't always arrive from the factory properly machined Machining mistakes do happen. Inspect and cross-check everything Do a mock-up before assembly. Preassemble the long-block without the piston rings, and check compression and deck heights as well as piston-to-valve clearances. Check side clearances and end play also. Follow basic engine math and check compression ratio twice. While this takes time, it is necessary for engine-building integrity Be sure to degree the camshaft and check valve-timing events Blueprint the oil pump, checking rotor side clearances and relief valve for proper operation. Never trust an oil pump out of the box Always examine valvetrain geometry. Rocker arms don't always line up with valve stems. The rocker-arm tip needs to be dead center on the valve-stem tip at 50 percent of valve lift Blueprint the valve springs. File ragged edges smooth at both ends and spray them with graphite lubricant for reduced friction Did you remember to inspect all of the rocker arms? Rocker arms can arrive with flaws no matter how expensive they are. Pay close attention to snap rings, needle bearings, and rollers Inspect and dress all rocker-arm studs Apply GE's Glyptal 1201 to all unmachined iron surfaces for better oil drainback and to keep stray iron particles out of the oil Use main bearing cap screw-in studs instead of bolts for added strength Safety wire bolts where possible for added security With no exceptions, always use Grade 8 bolts in the build Ascertain proper head-gasket installation. Gasket end cooling passages always go at the rear of the block. Don't use sealer Dimple the intake gasket end rails for gasket security Do a five-angle valve job for improved airflow; never anything less than three-angle. Valve seat width affects valve temperature. Narrow seats (contact) makes the valve run hotter and wide seats run cooler. A good rule of thumb is .040-inch intake and .060-inch exhaust for racing, and .070-inch intake and .100-inch exhaust for street. A good compromise when doing both is .060-inch intake and .090-inch exhaust Lap the valves with a fine compound in 90-degree turns. Count the exact number of turns (e.g., 10 spins). This ensures a perfect 360-degree contact with the valve seat and a perfect seal Clean all assembly parts with mineral spirits. Identify them and put them in a plastic bag Use a magnetic oil-drain plug to pick up any stray iron or steel particles If using a cast-aluminum oil pan such as a Cobra T-pan, use GE's Glyptal 1201 on the inside surfaces to prevent leaks from porous aluminum and to keep stray aluminum particles out of the oil RTV or screw the rear-cam plug to ensure it doesn't leak
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