Performance Parts & Procedures - Is It Fact Or Fallacy?

Let's Address Some Common Horsepower Parts And Procedures Myths

John Dibartolomeo Apr 1, 2003 0 Comment(s)
Sucp_0304_06_z Performance_parts_procedures Iron_main_caps 2/7

Both Merlin and Motown blocks from World utilize four-bolt, nodular iron main caps that are located to the block by the use of dowel pins.

However, a problem occured simply because of the placement of the outer two bolts. To just add two bolts right next to the stock ones, and drill them in the same plane, meant that the block had very little meat (or metal) for those bolts to tie into. The only solution was to drill them at an angle, splaying them outward, because there was enough metal there for them to bite into. Henceforth, from that time forward, "Splayed caps are essential." Another myth exploded.

Mitchell says, "We cast all our Merlin big-block and Motown small-block cast-iron blocks with enough reinforcement in the main bearing web area to alleviate that problem. All our blocks have four-bolt caps that have all the bolts drilled in the same plane."

Another problem with splayed caps is that they tend to distort the bottom of the cylinder bore. It's the same reason that we hone blocks with a torque plate in place of the cylinder head. Because of the close proximity of the head bolts to the cylinder bore, they distort the top of the block. Splayed bolts within close proximity to the bottom of the bore will do the same thing.

While we're on the subject of main caps, let's talk about steel caps. Again, another myth that harkens back to the "dark ages," where we didn't know any better. When somebody got the idea to install four-bolt caps, they didn't just run out to the hardware store and buy them. They had to be made. What easier and available material was there besides steel? So steel caps were made, and along with them came another myth.

The nodular iron caps used on the World Products blocks have the same rate of expansion as the cast-iron block, something steel caps don't have. This translates into the top and bottom bearing halves' keeping the same clearances. Steel caps will elongate more, allowing the bearing half in the cap to loosen up more than that of the block half.

Sucp_0304_07_z Performance_parts_procedures Big_intake_ports 3/7

Big intake ports might look good on the flow bench, but they won't work all that well when it comes time to drive the car. The same theory applies for big-port intake manifolds, as well.

"If you look at a Caterpillar diesel engine," says Mitchell, "it's got 22:1 compression, and it runs simply by detonation. There's no spark plug to fire it. Every one of those motors has nodular iron caps that are located by the use of dowel pins. Like I said earlier about Chevrolet's using cast-iron guides, if nodular iron caps live in a Cat engine, there's no reason to reinvent the wheel and think we can do it any better."

Myth #4 - Big Manifolds And Big Ports Make Power
Bigger is not always better. Making power requires not only making heat, like we alluded to earlier, but it's also a combination of the camshaft, cylinder head flow, bore, and stroke. After all, you can't make a fire if you get fuel in the cylinder.

Big ports, though, will flow air but lack air velocity that gives a good, clean signal to the carburetor. The lack of air velocity means that not enough air/fuel mixture will reach the cylinder before the spark is ignited. And we know that the more air/fuel mixture you can pack into the cylinder, the greater the explosion and the greater the power.

An example of this is a water hose. Turn the spigot on and watch how much water flows out of a typical 5/8-inch water hose. Now install a 1-inch hose, and while you'll see more water flow out, you'll notice that it flows with less pressure. Liken that pressure drop to the signal seen by the carburetor. With less signal, the carburetor will feed less fuel to the cylinders. Less fuel, less explosion. Simple.

There are some engines that will work with big ports, but it's generally a trade-off. Big ports also reduce the driveability of a combination. High winding, stick-shift cars that maintain rpm in a short band could benefit by big ports. But, a 468ci engine (that tops out at 7,000 rpm), put in front of a tight converter and an automatic transmission, will not like 350cc intake ports. A combination like that would go faster with a set of 250-280cc ports. It's all a matter of velocity.

Bigger isn't always better, and it's best to have a matched combination with smaller ports than to brag to your buddies that you've got cylinder heads that flow like sewer pipes.


World Castings
Sterling Heights, MI 48312
(810) 939-9628
Bill Mitchell Products
Ronkonkoma, NY 11779


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