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
Ported 289/302 Ford Heads
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.
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.