Jim Smart
August 10, 2007

Step By Step

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Mufp_0603_01z Ford_stroker_engine TuneMufp_0603_02z Ford_stroker_engine Pressure
Most engine builders check only crankshaft endplay, but Marvin also checks camshaft endplay to ensure its 0.004-0.008 inch...
Mufp_0603_03z Ford_stroker_engine Camshaft
...with camshaft endplay of around 0.0010-0.0055 inch.
Mufp_0603_04z Ford_stroker_engine Connecting_rod
Marvin works the large end of the connecting rod with a proper radius. He does the same thing at the crankshaft journal to reduce stress.
Mufp_0603_05z Ford_stroker_engine Rocker_arm_stud
All engine parts should be carefully inspected and dressed for smooth operation. Rocker-arm stud threads should be chased and the shanks dressed with a fine stone for smooth assembly. For smooth operation, Marvin suggests removing any nicks or rises in mating surfaces. Nicks create high spots on machined surfaces that can cause problems later. Marvin uses only ARP rocker-arm studs due to the extraordinary 190,000-psi tensile strength.

Last month, we began our two-part series on how to get 400 hp and 400 lb-ft of torque from a 331ci stroker small-block fitted with factory Ford iron cylinder heads, and we learned something remarkable during the attempt. You can achieve 400 hp and 400 lb-ft of torque from 331ci and iron cylinder heads without selling the farm.

This month, we wrap up our Summit Racing/MCE Engines 331 Stealth build and show you why we fell a pinch short of 400/400. What's more, we're going to show you how to hit pay dirt and make 500 hp and 500 lb-ft of torque with a few easy modifications and these same iron Ford heads. Think we're just bench racing? Read on ...

Let's begin with the events of a steamy, hot Southern California summer day. We arrived early at Westech Performance to get our 331 Stealth small-block engine on the dyno. Right away, two things necessary to make the projected power weren't available at Westech on the day of our test. Without a velocity stack for the carburetor and the appropriate-sized 1-3/4-inch Hooker Super Comp headers, our numbers fell below 400/400. Despite these shortcomings, we did remarkably well on the dyno, turning in the broadest torque curve we've ever seen from a low-cube small-block Ford.

When Marvin McAfee of MCE Engines was planning our 331 Stealth small-block, he predicted numbers between 350-400 hp and 350-400 lb-ft of torque through the mufflers, which we essentially made. Marvin's goal was a streetable small-block powerhouse that would:

  • Have a single four-barrel carburetor;
  • Have a cam profile that would provide enough intake-manifold vacuum to operate power brakes and run other accessories;
  • Operate on pump gas;
  • Be able to run an automatic or manual transmission in a matter of hours, swapping a flexplate for a flywheel;
  • Have the minimal upgrades required to make at least 100 more horsepower from the same short-block and iron heads.
  • Under ideal circumstances, we should have achieved 410 hp and 404 lb-ft of torque with our engine package. Ideal conditions include:

  • A velocity stack on the carburetor with cold-air induction;
  • Ambient temperatures in the 60s with humidity in the 40-60-percent range;
  • A match-balanced flywheel. Westech didn't have a dyno-coupling package that would work with our match-balanced Milodon flexplate;
  • Hooker Super Competition headers with 1-3/4-inch primary tubes;
  • Open headers or a verifiable set of low-restriction mufflers.
  • Step By Step

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    Mufp_0603_06z Ford_stroker_engine Fit
    Marvin insists on a smooth fit, what he calls zero clearance fitment. If you have to use any force, it's too tight. If the fit is loose and sloppy, find out why and correct it. Dress the parts as necessary to achieve a perfect slide-on fit.
    Mufp_0603_07z Ford_stroker_engine Friction
    Examine the friction factor of every part. Did you know there's friction in valve-spring operation? Marvin minimizes it by smoothing out the rough edges and coating the springs with a graphite lubricant. The springs to the left are out of the box. On the right are springs that have been friction treated.

    Dyno tests rarely occur under ideal conditions, especially in the middle of a hot Southern California summer with coastal desert temperatures pushing the 90-degree mark. Temperatures in our dyno cell were hugging 100 degrees with very low humidity, which adversely affected our performance numbers. This means our Summit Racing/MCE Engines 331 Stealth was ingesting hot air warmed even more by engine-radiated heat. Without the velocity stack and cold-air ducting we needed, our 331 took on stifling hot dyno-cell air instead of the cool air charge temperature necessary for maximum power.

    Marvin notes how important inlet temperature is to power. The cooler the temperature, the more power an engine will make. The hotter the temperature, the less power it's going to make. According to Marvin, every 10 degrees up or down equals 1 percent of power up or down. Cool the intake charge by 10 degrees and gain 1 percent in horsepower and torque. Cool it by 20 degrees and you gain 2 percent. Do the math: That's a significant change.

    A cool intake charge helps the engine make more power because we're dealing with denser air. Molecules are condensed and ready for rapid expansion when they roar into the combustion chamber. When we add humidity to the mix, we're feeding the engine more oxygen and more air density via microscopic water droplets. Let there be power.

    Again, that glide-fit factor is important. Marvin dressed the surfaces and coated these pieces with colloidal synthetic graphite. Note the smooth fit.

    Check All New Parts
    Just because it's brand-new doesn't mean it's ready for service. Marvin cautions that every part, including the block, must be checked and corrected as necessary.

    Our brand-new Ford Racing Sportsman-block needed machine work to be ready for service. The decks were .017 inch out of true, which means they ran downhill on both sides by .017 inch, unacceptable by anyone's standards. The decks were milled and brought into specification. Cylinder bores were bored .025 inch, and then honed using a torque plate to 4.030 inches, making allowances for proper piston-to-cylinder-wall clearance.

    Intake-manifold gaskets are port matched for smooth air flow. Sealer is used super-thin to keep it out of the coolant and only at the coolant passages.

    Marvin also checked the line-bore and had it honed to specification.

    Piston weight out of the box should be within 0.5 gram before dynamic balancing. Ours were as much as 1.8 grams apart. This was corrected with outstanding balance work by The Balance Shop.

    Piston valve reliefs were advertised at 4cc per piston. They were actually as much as 5.4cc. This is why you should always cc both the combustion chambers and piston crowns during the mock-up stage of engine building.

    These are just a few examples of why you should inspect and correct every part before engine assembly. If a part can't be brought to within specification, it should be discarded and replaced with a suitable part. If this seems excessive and unnecessary, remember that it's always less trouble and expense to correct the problem now rather than deal with engine failure later.

    Think Factory Iron Heads Won't Flow?
    Just look at what CNC port work and some careful massaging by PowerHeads and MCE Engines can accomplish. If you think factory iron-castings won't cut the mustard on a flow bench, take a close look at these numbers. There's quite a dramatic improvement in airflow with a weekend's worth of porting. You can save money by doing this job yourself, but you better know what you're doing before taking a die grinder to your cylinder heads. It's easier to allow PowerHeads to CNC port these guys and ship them to you ready for assembly with solid-bronze valve guides, hardened exhaust-valve seats, and a complete set of 1.94/1.60-inch stainless steel valves. PowerHeads supplies the appropriate valve springs and seals. For our project, the company provided valve springs designed for a .550-inch lift camshaft.

    Intake Port
    LIFT .{{{100}}} .{{{200}}} .{{{300}}} .350 .400 .450 .500 .550
    In/cfm 51.8 94.7 131.7 139.2 140.9 150.9 153.9 153.9
    Ported 289/302
    In/cfm 63.6 122.3 174.1 189.8 203.4 212.0 215.1 215.7
    Ported 351W
    In/cfm 69.5 128.0 182.0 196.8 205.7 219.5 224.9 229.0
    Exhaust Port
    LIFT .100 .200 .300 .350 .400 .450 .500 .550
    In/cfm 39.2 73.7 95.7 100.4 103.6 105.1 106.7 107.0
    Ported 289/302
    In/cfm {{{62}}}.4 109.1 150.2 161.8 168.6 171.9 173.8 174.9
    Ported 351W
    In/cfm 62.4 109.1 150.2 161.8 168.6 171.9 173.8 174.9

    Throwing You a Curve
    Power comes not only from a hot cam, compression ratio, and cylinder-head porting, but also from knowing how to program the distributor's advance curve. Marvin curves the MSD distributor, which operates at half the crankshaft's speed, for a total mechanical advance of 10 degrees at 2,800-rpm engine speed. Initial advance is 16-18 degrees BTDC at 500-rpm engine speed. Marvin curves the timing by starting out at 16-18 degrees BTDC at 500 rpm and advancing to 36-38 degrees at 2,800-rpm engine speed.

    The following chart illustrates how Marvin curved the MSD distributor. Double these numbers for pinpoint accuracy. They are in distributor degrees, half the number of crankshaft degrees. By 2,800 rpm, we should have an aggressive program to maximize low-end torque.

    Engine RPM 500 1,000 1,500 2,000 2,800 3,000 4,000 5,000 6,000 6,500
    Degrees BTDC 16-18 +2 +4 +7 +10 10 10 10 10 10

    The Polygraph Room
    As you can see from the following chart, the 331 Stealth has a broad torque curve that comes on strong at 2,500 rpm, a whopping 350 lb-ft of torque down low, where it counts on the street. It actually starts making torque around 1,200 rpm. It never falls below 350 lb-ft of torque, peaking at 396 lb-ft at 4,000 rpm. Understand that this is big-block power in an iron-head, carbureted small-block. This approach to engine packaging will make your Mustang a rocket ship in traffic-light to traffic-light challenges. For a Saturday night dragstrip, it promises excellent 60-foot times as long as your Ford can hook up, and you know something about drag racing. In real-world bracket racing, a properly-packaged classic Mustang can clock 11-12-second quarter-mile times at 110-115 mph with an educated drag racer at the wheel, leaving the traffic light faster than the next guy.

    With the improved conditions our 331 Stealth needed to reach its maximum potential, it would have blasted through 400 lb-ft of torque and delivered a solid 400 hp. With a hotter cam, single-plane intake manifold, and increased carburetion, you can count on 500 hp and 500 lb-ft of torque from this power package. You need a solid foundation to produce 500/500: the 4340 steel crank and 4340 I-beam rods, forged Probe pistons, and main-cap girdled Sportsman-block that Marvin specifies for doing it safely. With a stock block, nodular-iron crank, shot-peened heavy-duty rods, and hypereutectic pistons, your limit is 400/400.

    The following dyno numbers were achieved with a streetable hydraulic-roller camshaft from Comp Cams (grind number XE-264HR-12) through Edelbrock mufflers. Just imagine what we could have done under ideal conditions-and just imagine what you can do following this recipe.

    RPM HP Torque Fuel lb/hr Oil Pressure BSFC Air/Fuel
    2,500 167.0 350.0 75.8 78.0 0.497 12.5
    3,000 214.0 375.4 86.5 {{{80}}}.4 0.440 12.8
    3,500 260.0 389.5 113.1 83.5 0.475 11.7
    4,000 302.0 396.8 143.2 86.0 0.517 11.9
    4,500 337.0 393.6 151.1 88.7 0.490 12.1
    5,000 364.0 382.3 165.2 91.7 0.497 12.3
    5,500 367.0 350.7 172.3 95.2 0.515 12.3

    What's All This Power Cost?
    There are two ways you can build a 400/400 331ci small-block. Marvin opted for the more expensive way with a 4340 steel crank, heavy-duty I-beam rods, forged pistons, and a lot of special attention to detail by MCE Engines. The cost is $12,500 as built by MCE Engines.

    If you want to save money on an engine like this, do a lot of the labor yourself. If you're happy with 400/400 and aren't planning any more power, you can pass on the 4340 steel crank, heavy-duty rods, and forged pistons. This knocks the price down to $9,400. If you do most of it yourself, you can save even more.

    Marvin will be the first to tell you a high-revving, bulletproof, small-block powerhouse doesn't come cheap. Making 400/400 on a modest budget isn't easy. Even doing most of it yourself, the least you can expect to spend is around nine grand for an engine of this design. When it comes to engines, those that perform and last can't be built cheaply. There are all kinds of angles for horsepower on a budget, but very few of them are realistic. Building a healthy engine involves time and money or it falls apart quickly.

    Marvin McAfee is the founder of Marvin's Competition Engines (MCE) and heads up this team of professionals. At 72, he's been an avid and methodical engine builder and aviation technician for most of his life.

    Team MCE
    Engine-building excellence doesn't always come from one person's abilities, talent, and experience, but from a team of close friends working together on a passion they've shared for a lifetime. Marvin McAfee, Benton Jackson, Ken Van Fleet, and Fred Christian have been a well-oiled machine for more than three decades. Each practices an area of expertise that makes them all-but-unbeatable engine builders and tuners.