Modified Mustangs & Fords
Ford 331 Cubic Inch Stroker Engine - Going For 400/400 Part 2
We Wrap Up Our Summit Racing/MCE Engines 331 Stealth Stroker, Then Put It On The Dyno For A Little Truth-Telling
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:
Under ideal circumstances, we should have achieved 410 hp and 404 lb-ft of torque with our engine package. Ideal conditions include:
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.
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.
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.
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.
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|
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.
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.