David Vizard's How to Build Horsepower

By David Vizard

Proven methods for increasing horsepower in any engine. Explains the latest and most effective engine building techniques and strategies. Vizard's unique and entertaining style of writing clearly explains the key principles and provides extreme detail.

• Language: English
• Publisher: S-A Design
• Release date: Jul 1, 1990
• ISBN: 9781613252567

Book preview

INTRODUCTION

As I type this I am approaching my 52nd year modifying engines—the last 45 doing so in a professional capacity. I would like to say they have all been smooth but that is far from the reality. It was in England, my home country, and in 1966 that I had my first taste of building/modifying a V-8 engine. It was a Ford Flathead, the principal components of which I lucked into as an unfinished project. The gentleman I bought these cut-rate parts from was to be the guest of Her Majesty’s Government and so had no need of them for 10 years or so.

A thick-wall block with a big overbore and a billet stroker crank resulted in a massive displacement, for a Ford Flathead of 301 cubes. A lot of porting work and the use of high compression, a race cam, triple Strombergs, and a whole lot of other high-performance moves resulted in 224 hp and 300 ft-lbs as measured on a dyno of unknown accuracy. Up to this point I had used only chassis dynos to prove the validity of my work. This was my first go around on an engine dyno and, as it has subsequently proved to be, the first of more than 250,000 dyno pulls over the next 42 years.

At the time I was disappointed with the results from that Flathead, but 30 years later I was to find that this output was a relatively creditable result for a side-valve engine. But the disappointment of that engine was to be offset a couple of years later. Over the winter of 1968–1969, I was asked to port some small-block heads for a 302 small-block Chevy powering a Lola T70 sports racer. It seemed the heads used on the popular Bartz or Traco USA-built engines of the day had a propensity for cracking, and a new set of heads at a couple thousand dollars each (remember this is 1969 and a grand is more like $2,500 as of 2010) were needed for every race. I started with castings that I thought might do the job but were different from those used by engine builders in the United States.

Here I am about...

Here I am about to time-in the cam on a low-buck 5.0 Ford Mustang engine. What is being passed on to you in these pages is 50-plus years of experience building high-performance engines.

After a few weeks of experimentation, on my very simple flow bench, I had some promising working heads. The dyno subsequently demonstrated this very much to be so. That, in conjunction with a few other moves, proved to be the formula for killer results. With what I learned helping out on that engine, I reasoned (with good cause) that I had a working handle on what it takes to build an international-level race-winning small-block Chevy. Over the next few years I was to amass hundreds of wins, lap records, and pole positions, plus a half-dozen or so championship wins—two at international level—all with European engines.

What you see here...

What you see here is my 145-mph supercharged GMC truck. This is what I use to tow my racers, two of which you see here. The point I am trying to press home is that I actually live what I write.

Fast forward to 1976–1977 in Tucson, Arizona, where I was industriously working on a Chevy rebuild book. As a side project, I built a hopped-up street 350 and looked forward to a similar degree of success as I had with the 302 in 1969. I had read and absorbed a huge amount of info from the big-circulation performance magazines and the product tests they published. I knew how to build a high-dollar race engine so I assumed that building a relatively high-output street engine on a more mundane budget would present little in the way of a challenge. Back then I was naive enough to assume that everything in black and white was a printed version of reality. With the parts I bolted together, I expected to have an engine of at least 375 hp and around 400 ft-lbs of torque. What I got was a pitiful 281 hp and something less than 340 ft-lbs of torque; and it had cost what was, for my budget, a sizable amount of cash for a non-event engine. A few phone calls to some engine builders who made their living building and dyno testing successful small-block Chevys caused me to re-evaluate much of the component choices I had made. It seemed my piston selection was far from optimal as was, among other things, the cam, carb, and intake manifold.

With the input of sound advice, a return to the drawing board, and some more work on the flow bench, a new 9.5:1 pump-gas-burning street 350 was born. It was with a great deal of trepidation that I hit the dyno with this one. However, I need not have worried; the dyno delivered a respectable 402 hp and 404 ft-lbs of torque. All this came with a smooth 650-rpm idle and more than enough vacuum to run power brakes.

Making 402 hp on...

Making 402 hp on pump gas was good in 1976 but things have moved on. Here is a 10.5:1 pump-gas 355-ci (5.8-liter) small-block Chevy street driver. Built on a reasonable budget with 2008 know-how and parts, it made 584 hp (more than 100 hp/liter) and turned 8,000+ rpm.

This 340-hp 5.0...

This 340-hp 5.0 Mustang engine was built on a very tight budget. The only new parts used were the intake manifold, MSD distributor, and the exhaust manifold (or headers).

At the end of the day, the final analysis shows conclusively that knowledge is a key ingredient to building successful performance engines. That knowledge is best acquired from people who have hands-on experience developing successful engines. Acquiring such knowledge means the cash element in a successful build is vastly reduced. Here I have to say that, given the knowledge, you can cut the cost of a high-performance engine in half with ease, and sometimes cut it as much as 65 to 70 percent.

The dyno validates or...

The dyno validates or disproves theory. Time spent here is worthwhile, but only if what is going on is largely understood. If results are misinterpreted, then much of what might be gained is forfeited.

Unlike many performance books, this is not written by a journalist reporting on what others might think or have you believe they do to produce power. Think about this: Why would any successful builder/development engineer want to give away any real info that could well have cost them time and money to accrue? This book is a firsthand rendering of experience from 50-plus years of hands-on building for speed.

Information Transfer Logic

Life has shown me that it’s one thing to have the knowledge to do something well, but an entirely different thing to pass on that knowledge in a simple and clearly understandable manner. Teaching is a science in itself and, since the subject we are dealing with has many interacting complexities, it becomes very important to convey information in as logical a fashion as possible. My first thoughts here were to start at the point of the biggest impediment to power a high-performance engine has—the intake valves. But once I had covered that, which way should I go—up through the intake tract to the air filter or down through the exhaust? Adopting this approach, it seems that any organized logic failed at the second step so I re-thought what might work best.

The first move, within the pages of this introduction, is to make sure that you fully understand that the intake valves’ flow capability is by far the greatest impediment to the production of horsepower. With that understood, I tackle the production of power by starting at what seems to be the most logical point—where air enters the engine—and carry right through the system to the point where it exits. Somewhere about the middle of the book I deal with the short-block and considerations within it that affect power. Hopefully, by presenting the information this way, you can quickly look up anything relevant in a speedy and effective manner.

A straight pipe, or venturi...

A straight pipe, or venturi, such as used in a carb, is an efficient means of transferring air from one place to another. On the other hand, a valve (even when fully open) is not good because the route the air has to take to navigate around it is tortuous. In addition to this, it spends most of the time closed. When it is called upon to open, it takes time to reach sufficient lift to be able to deliver relatively high flow rates. The percentages here show typical flow efficiencies for each section of a typical production V-8 cylinder head intake port.

CHAPTER 1

THE BASICS OF EVERY KNOWN SPEED SECRET

A bold chapter title to be sure but, before going into the fundamental principles of what makes horsepower, let us look at the definition of horsepower. This seems a necessary step because, too often, novice enthusiasts are unaware of how horsepower is defined and derived.

The definition of 1 hp was determined by British engineer James Watt of steam engine fame. After suitable tests, he set the value of 1 hp to be 33,000 ft-lbs per minute. That means either lifting 1 pound through 33,000 feet vertically in one minute, or 33,000 pounds through 1 foot in one minute, or any combination that multiplies out to 33,000. From this, we can say:

where work done is the force involved (in pounds) and the distance (the number of feet) that it acts over in one minute. This is expressed as foot-pounds of work done per minute (not to be confused with ft-lbs of torque).

For a professional...

For a professional engine builder, a dynamometer is an essential tool to have. For the serious enthusiast, it is an essential tool to rent.

But an engine does work rotationally so we need to translate the work done in a circle to the equivalent of a straight line. To do that, we multiply the crank radius (R) in feet by PI (3.142), then 2, and then multiply that by the force (F) in pounds as generated by the mean cylinder pressure and the revolutions per minute (RPM) involved.

But R × F equals Torque, so we can simplify this equation to:

In other words, we can divide the 2 × 3.142 × Torque × RPM on the top line by the 33,000 on the bottom line. This gives us (assuming English units) the universal formula for horsepower, which equals:

The Dynamometer

So now that we know how horsepower is derived, let’s look at how we actually measure it. For this we use a device known as a dynamometer. A dyno, which applies a braking force to the engine (hence, the term brake horsepower), does not directly measure horsepower but derives it by measuring the torque the engine can make at a particular test RPM and then calculating the power from these two known values. Power (as opposed to horsepower) is simply torque × RPM. To express the result in units of horsepower, it has to be divided by a constant. From the previous formulas, you can see the constant involved is 5,252. For example, a power calculation looks like this, if an engine produces 200 ft-lbs at 3,500 rpm. The formula is:

Here is how an...

Here is how an engine develops torque. As the piston goes down, the bore pressure drops and the torque follows suit. Multiple cylinders, the mass of the engine’s internals, and a flywheel tend to damp-out torque fluctuations.

Double the torque at that RPM, and the power doubles. Doubling the RPM, but without changing the torque, also doubles the power. Therefore, you can see that any change in torque at a given RPM also changes the horsepower at that RPM.

1-1. Here, you see the...

1-1. Here, you see the basics of every speed secret known to humankind, and plenty that are not. It covers all the basic elements we need to improve to build more power. In the following chapters, we tackle each of the elements shown in more detail, starting with the factors at the top of this chart and finishing at the bottom.

Engine torque is exactly the same as the torque produced with a torque wrench (Force × Radius). In the case of an engine, the radius is half the stroke and the force is the average produced by the gas pressure pushing down on the piston. The gas pressure is the result of filling the cylinder with air and then heating it by burning fuel in it. Here it is worth taking a mental note of the fact that we only have atmospheric pressure (14.7 psi at sea level) to work with to fill a cylinder. This factor puts a limit on how much torque an engine can develop unless forced induction (a supercharger) is used. For an ultra-high-compression, normally aspirated engine (no means of mechanically boosting the intake charge), something a little over 1.65 ft-lbs per cube (101 ft-lbs per liter) is about the best that is currently being achieved. With the aid of some type of efficient supercharger, the torque per cube can be doubled, tripled, or even quadrupled, but there are consequences, which I deal with in Chapter 5.

Now we know what torque and horsepower are, so let us look at what it takes to make as much as possible of both these factors. Chart 1-1 shows all the elements that affect the engine’s final output. But everything has its limits, and before we go on to discuss how best to increase engine output, it serves us well to understand what limitations we may be faced with.

When Isn’t Bigger Better?

You may have heard it said that an engine is nothing more than a simple air pump. Reduced to basics, it can be looked upon as an air pump, but the reality of producing horsepower means that it is hardly simple. A much better description is that it is a complex thermodynamic air pump. If high output is sought, the first aspect we need to pursue is the production of torque, closely followed by all the means possible to raise the RPM to where that torque occurs. Just how much torque an engine makes is governed by the weight of charge inhaled in one working cycle. We can increase that charge weight by making the engine bigger, by supercharging it, or both. At first thought, making the engine bigger by virtue of a bigger bore and stroke seem like a process that can be carried on without limits other than the sheer size of the final engine. Therefore, if you doubled the displacement of an engine, you may think that the output would double. Unfortunately, things don’t work out that way.

I stretched this Ford...

I stretched this Ford Windsor engine from its original 351 to 425 ci by means of a 0.6-inch stroke increase and a 0.060-inch overbore. To make the most of this capacity increase, it was necessary to change valve events and lift to more appropriate values.

I tried to dig...

I tried to dig up a big 5-inch aero-engine piston for this shot, but all I had at hand was a 4.185 small-block Chevy piston to compare with the 1.250-inch-diameter piston from a gas-powered lawn trimmer. Big pistons may look good, but you need to remember that the cylinders they reside in are far harder to fill than small cylinders.

As the engine’s cylinder proportions are increased, it becomes harder to extract a proportional increase in power. Just after World War II, it was considered that, in normally aspirated form, 125 hp per cylinder was about the limit with the materials, oils, fuels, and technology then available. These days, better materials, modern fuels and oils, flow benches, and valvetrain dynamics have allowed the 125-hp figure to be exceeded by a big margin. Currently, a good V-8 Pro Stock mountain motor in the 825-or-so cubic-inch (13.5 liters) range can put out about 200 hp per cylinder. But it hasn’t, nor will it ever, come easily. The reason for this is largely a question of proportions and geometry. It is better, if designing a given size engine from scratch, to have a lot of smaller cylinders rather than a few large ones. At first this seems less than logical, so let’s go through some clarification logic.

Here is the intake...

Here is the intake valve from a 1,050-cc-per-cylinder Pro Stock engine compared to the valve from a 23-cc-per-cylinder engine. Given all the same proportions, the small cylinder with its small valve breathes easier than the big one.

Even if all the engine’s proportions remain unchanged, it is more difficult to fill a large cylinder than a proportionately identical but smaller cylinder. Here is an example to illustrate the situation: Assume we have a 180-ci (3-liter) one-cylinder engine as a starting point.

Let us also assume that this engine has what is a fairly typical bore/stroke ratio of 1.2:1 (bore is 1.2 times the stroke) and the intake valve is 50 percent of the diameter of the bore. If this 180-inch engine has just one cylinder, the intake valve would be 3.252 inches in diameter, the valve’s area would be 8.306 square inches, and its circumference would be 10.22 inches. For a cylinder head equipped with this valve to breathe effectively at the cylinder’s limiting RPM, it would need a minimum lift of about 0.980 inch (25 mm).

If our 180-ci engine obtained its displacement from eight proportionally similar cylinders, the intake-valve diameter would be 1.626 inches. In this instance, the combined area of all eight intake valves is 16.612 square inches and the circumference is 40.88 inches. The lift needed to get near-maximum flow is only about 0.487 inch. This means the eight small cylinders of 180 ci have approximately twice the breathing power of one big cylinder of 180 ci, even though the valve and bore proportions remain unchanged. Also, if we assume 5,000 feet per minute maximum piston speed, the maximum RPM of the one cylinder engine is 5,500, where it is 11,000 for the eight-cylinder engine. There are other factors involved, but from this you can see the reason it is harder to extract power from big cylinders rather than a greater number of small ones. You can also get an idea of how, ultimately, these and other limitations call a halt to the amount of power that can be had per cylinder.

The bigger the engine...

The bigger the engine, the more important heads become. This CNC-ported head has the biggest valves possible. It also has thermal barrier coatings to keep the heat out of the intake charge in the port, and in the burning charge in the chamber.

Since most of us build an engine using an existing block, rather than designing from scratch, understanding these limitations allows moves that help optimize what can be done within the constraints of a set number of cylinders. It is often said, and rightly so, that a successful engine is the sum of a parts collection that is the right combination. What often defeats many engine builds is the fact they are not an orchestrated combination.

This Jon Kasse...

This Jon Kasse big-block Ford displaces a massive 900 ci (15.1 liters). The output from this 6-inch-stroke gas-burning behemoth is around the 1,700-hp mark, with torque just short of 1,600 ft-lbs.

CHAPTER 2

PRIMARY POINT INDUCTION

In this chapter we...

In this chapter we deal with atmospheric conditions and composition, and how to maximize the power that can be made from those prevailing atmospheric conditions.

We are dealing with an air breathing heat engine here, so let’s start off with the air our engine has to work with. At what we call Standard Temperature and Pressure (STP) conditions, atmospheric pressure at sea level is 14.696 psi (1,013 millibars or, as measured with a mercury barometer, 29.9213 inches of mercury). At 70 degrees F the density of air at 14.696 psi is 0.074887 pound per cubic foot. Assuming the air is dry, we find that, by volume, 21 percent of it is oxygen and 78 percent is nitrogen. The remaining 1 percent is composed of trace gases. But in most parts of the world, the air is far from dry; it has a water vapor content. Since water vapor does not support combustion, an even lesser amount of the whole is oxygen available for combustion.

Assuming we are not racing under less-than-normal conditions, the atmospheric conditions just described are about the best we are likely to be able to see.