The late Marvin McAfee of MCE Engines in Los Angeles was the architect and builder for this effort using a new 5.0L roller block stuffed full of Probe Industries rotating mass consisting of JP forged and coated pistons, 5140 forged I-beam rods, Fluidampr harmonic dampener, Comp Cams roller hydraulic technology and more.
Although some of what we’re about to impart doesn’t make much sense in an environment with dozens of great aftermarket aluminum heads out there, we want to show you what can be done with factory iron castings if you want to maintain a stealthy stock appearance on the outside.
This engine build was performed using what was available back in the day, and much of it remains available now. PowerHeads, no longer in business, took a pair of 1969 Ford 302 truck heads with 64cc wedge chambers and performed nice port work via CNC technology and hand porting. You can achieve the same results via a good head porting shop today. PowerHeads turned a 331ci 300 horsepower stroker into a 400 horse powerhouse. MCE’s own blueprint work helped enhance the rest of the build by reducing internal friction and doing further port clean-up work on the heads and intake.
Although we used the 1969 truck heads, they were not the best Ford casting to use. Earlier 1963-67 289 heads with the 54-57cc chambers were the most optimum choice because we would have gotten greater compression and quench from these chambers. Although extremely rare these days, 1968 302-4V heads are the best option thanks to petite 53cc chambers. Because Ford made so few 302-4V engines in 1968, the odds of finding a pair is a long shot.
If you think factory iron castings won’t make real flow on a flow bench, take a close look at these PowerHead numbers. There’s a dramatic improvement in airflow with porting. You can save money by doing this job yourself, however, it’s good to know what you’re doing before taking a die grinder to your heads. It makes more sense to allow a head shop to do the port work and install solid bronze valve guides, hardened exhaust valve seats, and a complete set of 1.94/1.60 inch stainless steel valves.
Cylinder Head Flow Numbers for the 331 Ford
Stock 289/302 Ford Heads
Lift/Inch
0.100
0.200
0.300
0.400
0.500
0.550
Intake CFM
51.8
94.7
131.7
139.2
140.9
150.9
Exhaust CFM
39.2
73.7
95.7
100.4
103.6
105.1
Ported 289/302 Ford Heads
Lift/Inch
0.100
0.200
0.300
0.400
0.500
0.550
Intake CFM
63.6
122.3
174.1
189.8
203.4
212.0
Exhaust CFM
62.4
109.1
150.2
161.8
168.6
171.9
How Power Is Made
MCE’s 331 Street Stealth sports a broad torque curve that comes on strong at 2,500 rpm, a whopping 350 lbs.-ft. of torque down low where it counts on the street. It starts making torque around 1,200 rpm, which is exactly where you want it. Torque never falls below 350 lbs.-ft. of torque, topping out at 396 lbs.-ft. at 4,000 rpm.
This was Marvin’s trademark as an engine builder. Nearly 400 lbs.-ft. of torque from 331ci. This means real street power at the traffic light and at the drag strip for bracket racing.
When we took this 331 to the Westech dyno, it was a hot day with ambient temperatures above 100 degrees F—a disadvantage on dyno day because it hurts power. We needed a cooler day. With better conditions, our 331 Stealth would have blasted through 400 lb.-ft. of torque and delivered a solid 400 horsepower at 6,000 rpm. Add a hotter roller cam, single-plane intake manifold, and increased carburetion, you can count on 450 hp and 450 lbs.-ft. of torque from this package.
This was not a Cinderella story. We didn’t meet our goal of 400 horsepower. Our 331 topped out at 367 horsepower at 5,500 rpm. This teaches us to honor this engine’s advantage—street torque. A solid 400 lbs.-ft. of torque at four grand. To achieve 400 horsepower, we needed a hotter roller cam, a variety of carburetors to play with, and a cooler day.
Marvin always tended to err on the side of caution and ended our dyno session prematurely—particularly frustrating because we understand this engine was capable of making more power given additional tuning time. Marvin’s intent was to perform a cam swap and return to Westech for another dyno session.
Failing health and other priorities prohibited him from returning to the dyno.
Getting Real Power
There are two ways you can build a 400 horse 331ci small block. Marvin opted for the more expensive approach with a 4340 steel crank, heavy-duty I-beam rods, forged pistons, and a lot of special attention to detail by MCE Engines to get durability. If you want to save money on an engine like this, do a lot of the labor yourself, pass on the 4340 steel crank, heavy-duty I-beam rods, and forged pistons. The factory cast crank with aftermarket heavy duty I-beam rods and hypereutectic pistons will endure 400 horsepower.
We’re working with 1969 Ford 302 truck heads with 64cc chambers CNC-ported and hand-ported by PowerHeads, which is no longer in business. These chambers are conservative in terms of compression ratio. (Image/Jim Smart)The most optimum heads for an engine like this are the earlier 289/302 heads prior to 1968, which have 57cc chambers and better quench with good anti-knock qualities. (Image/Jim Smart) Marvin points out the quench qualities these chambers have—which give these heads better “squish” around the chamber. The early 289/302 heads with 54-57cc chambers deliver even better quench and greater compression. (Image/Jim Smart)If you can find them, 1968 302-4V heads with 53cc chambers remain the best early Ford small-block heads going. Because Ford did so few 302-4V engines, these heads remain hard to find. (Image/Jim Smart)Marvin applied his blueprinting efforts to the PowerHeads castings by checking valve steam to guide clearances and ease of valve movement. He knurled the guides as necessary to reduce internal friction and improve oil control. (Image/Jim Smart)Marvin refined valve seat contact depending upon the performance desired. Marvin believed a wider valve seat improves valve cooling. By the same token, too much contact takes away from airflow. The best approach is a five-angle valve job. (Image/Jim Smart)PowerHeads always opted for larger 1.940/1.700 inch Chevrolet valves for its small-block Ford heads. This is an easy upgrade for your stock Ford casting. You may also opt for hardened exhaust valve seats or stainless valves. (Image/Jim Smart)Marvin always used his own special low friction coating cocktail for valve springs and other moving parts. These are Comp Cams valvesprings and dampers. (Image/Jim Smart)The best valve seal to use is a Viton seal (not shown here, but similar to this Teflon seal), which has an incredible track record for valve stem oil control. Valve guides had to be cut down for seal fitment. (Image/Jim Smart)Valve spring pressure is controlled with shims placed here at the spring seat. Shims are added to increase spring pressure or subtracted to reduce pressure. Shim also controls installed spring height. Springs are chosen based upon cam profile. (Image/Jim Smart)Marvin opted for Comp 1.7:1 roller rockers to increase valve lift. This approach also reduces valve shrouding by extending the valve head deeper into the chamber. This can be accomplished with a split ratio with two different rocker ratios—typically with a 1.7:1 intake and 1.6:1 exhaust. You can even experiment by trying different rocker ratios to see what the end result is on the dyno. Check valve-to-piston clearances in any case. (Image/Jim Smart)We’ve opted for the spider style hydraulic roller tappets, which are less common today than they were two decades ago. The message here is low friction. Although roller tappet cams are more expensive, they pay long term dividends in terms of efficiency and power. When you reduce internal friction, you free up power. (Image/Jim Smart)Whether you’re building a stocker or an aggressive street/strip mill, it is strongly suggested you opt for one-piece 0.080 inch wall Comp pushrods for unlimited durability. Marvin waited on ordering pushrods until he successfully worked out valvetrain geometry. The roller tip should be centered on the valve stem. (Image/Jim Smart)Marvin was always quite fond of Fluidampr harmonic dampers for his builds. He always degreed both the cam and the damper to ensure accuracy. A 36 degree mark was applied to the damper to help determine total timing at 3,000 to 3,500 rpm. (Image/Jim Smart)Marvin was always obsessed with smooth fluid and oil flow. He would massage oil galleys and coolant passages to reduce fluid turbulence. (Image/Jim Smart)The Edelbrock Performer RPM Air Gap manifold goes nearly every dual-plane manifold one better with improved runner cooling and a cooler air/fuel charge. Marvin port-matched both the intake runners and cylinder head ports for reduced turbulence. He liked trying different carb spacers to see what would happen to torque primarily. (Image/Jim Smart)We like the conventional Holley 750cfm double pumper carburetor. It sports all the elements Holley carburetors are known for, plus nice refinements that make it the most tunable carburetor ever made. We tried a number of different carburetors on the 331. In the end, the 750 gave us the best numbers. (Image/Jim Smart)When you opt for Holley carburetion, equip your shop with a variety of Holley kits. We’re talking jet and gasket kits, accelerator pump diaphragms, float needle valves, and more. Few things are more frustrating than going to a race or weekend getaway and discovering you have a fuel leak or inoperative accelerator pump. (Image/Jim Smart)There are a couple of approaches to intake manifold sealing. We like running a solid bead of Permatex’s The Right Stuff along the rail ends. Marvin would “dimple” the manifold and block rails to keep the end gaskets in place. This, coupled with a thin film of The Right Stuff works quite well too. (Image/Jim Smart)Unless you live in a cold weather environment where manifold heat is a necessity, it is suggested you block off the manifold heat passages to reduce manifold heat. This keeps the intake charge cooler—which translates into more power. (Image/Jim Smart)One of the most oft-seen mistakes we come across is improper fuel line sizing for the power that enthusiasts expect to make. If you have a stock 5/16 inch fuel line into the fuel pump, but have a 3/8 or 7/16 inch fuel line between the pump and carburetor, you still have a 5/16 inch fuel supply. The fuel line between the tank and carburetor should be 3/8 inch minimum for 400/400 horsepower and torque. Looks like Marvin opted for 7/16 inch lines with this Holley pump. (Image/Jim Smart)MCE Engines’ in-house tuner was Benton Jackson who employed a wealth of engine tuning knowledge. Here he’s tuning the Pertronix billet distributor with vacuum advance for the 331 Street Stealth. Both advance units must be tuned to achieve the proper rate of advance. The vacuum advance control advance rate as you start out. It hands off to centrifugal advance as rpm increases. Consider the vacuum advance “throttled” advance as you get underway. (Image/Jim Smart)Because we’re running a steel roller camshaft, the distributor gear must be either brass (shown) or a steel gear. An iron gear is soft and will never stand up to the hardness of a steel cam. If you’re running a flat tappet camshaft, run the iron distributor gear. (Image/Jim Smart)Unless you’re going drag racing, it’s a good idea to run a road-race oil pan, which keeps the sump full of oil when you’re cornering. The stock front sump pan with a windage tray and baffles is suitable for cruisers. (Image/Jim Smart)Marvin always took blueprinting to serious degrees, treating every engine build to race caliber levels to ensure durability. Here everything is polished for improved oil drainback, plus safety-wired for security. Red GE Glyptal coats iron surfaces to improve drainback and seal the rough iron. Screens keep debris out of the pan. (Image/Jim Smart)Westech Performance throttled our 331 employing a number of tuning approaches including ignition timing, jet and carb swaps, and more. The 331 Street Stealth, as its name implies, exhibits excellent street manners at 396 lbs.-ft. of peak torque. This means terrific 60-foot times at the drag strip and faster launch times at the traffic light. (Image/Jim Smart)Marvin liked checking spark plug heat ranges to see what was going on in the chambers. He would perform a jet check by going full throttle under load for 30 seconds, then, check spark plug condition. This is a perfect jet check color wise. If it is snow white, you are too lean and potentially have too much timing. Too lean will kill an engine in nanoseconds. (Image/Jim Smart)
Jim Smart is a veteran automotive journalist, technical editor, and historian with hundreds of how-to and feature articles to his credit. Jim's also an enthusiast, and has owned and restored many classic vehicles, including an impressive mix of vintage Ford Mustangs.
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