With cast-iron heads stacked...
With cast-iron heads stacked up in the background, we gathered enough proof that aluminum heads don't make more power, but they will help acceleration, due to the obvious weight savings.
It seems as though we're surrounded by myths in our everyday lives. "An apple a day keeps the doctor away," and "The check is in the mail," are just two examples. Building high-performance engines has its fair share of fallacies also. Most everyone has an opinion about something. Unfortunately, not everyone's opinion is as right as it should be.
We recently sat down with Bill Mitchell, of Bill Mitchell Products and World Castings fame, and discussed several myths that always seem to be floating around in our industry. Bill brought up some very simple and basic truths that most of us never seem to think about, because we've been "brainwashed" to just accept them. But, when you sit down and really think about these, they have a lot of truth.
A dilemma Mitchell lives with everyday is, "Do you make a part the right way, or do you just sell a customer what he wants." While Mitchell will sell you what you want, he commented, "I want to make sure a customer gets what he or she really needs, and sometimes that takes educating the consumer a little. Yes, that sometimes takes a little more effort than just giving somebody what he wants, but it's important that we at least lay down the facts and then let them make the choice."
What follows here are the facts. Some of these ideas might seem to contradict today's style of thinking. However, if you think about them using everyday common sense, you'll realize that they all have merit.
Myth #1 - Aluminum Heads Make More PowerBuilding power requires one important ingredient: heat. You've all probably heard the term, "Heat equals horsepower," and it's true. When the spark plug fires in each cylinder, it creates an explosion of the fuel and air mixture. The containment of that explosion creates pressure on the piston and forces it back down the cylinder. The faster it is forced back down, the more power it ultimately transfers to the crankshaft and, eventually, out to the tires. So far, that's relatively simple to understand, but where does heat come into play?
The explosion obviously creates heat. The amount of heat is then divided up, and most goes towards the creation of pressure on the piston, but some is transferred into the block and head casting and, eventually, finds its way into the water jackets (and is cooled). There's no way you could contain all the heat without transferring some of it out, but theoretically, if we could, well, that's just dreaming.
Let's get back to heat. Aluminum is great at dissipating heat. Heat up two equal-size blocks of aluminum and iron, and you'll quickly understand that theory. The heat is transferred very quickly out of the aluminum, while the iron will take longer to cool. That's why you're seeing more aluminum radiators around lately. Now the question remains, "If we want to keep heat in a combustion chamber, why do we use an aluminum head?" A cast-iron head will undoubtedly hold the heat in more and will make more power than an equally modified aluminum piece. But, unfortunately, there are drawbacks.
To start with, a cast-iron, big-block Chevy cylinder head just about requires the use of a small crane to lift on and off a motor. There's another term that's floating around, and it's, "Weight equals horsepower." Using the general statement (which is close to being true), "100 pounds equals a 10th of a second," it then stands to reason that the 75-85-pound savings from using aluminum heads on a big-block is worth close to a 10th in e.t.
Acceleration is also an important factor. In the 1600s, the Greek astronomer, Galileo, reasoned that both light and heavy objects fall at the same rate of speed. However, we're not sure if his testing involved big-block Chevrolet dragsters, with and without aluminum heads. The plain fact is that, while they both might fall at the same speed if dropped from a tree, the lighter car will accelerate faster. Can losing a 10th of second due to using cast-iron heads be picked up in the extra power made by them? Probably not.