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Truck Engine Parts To Increase Horsepower - Horse Power 101

Posted in How To: Engine on December 1, 2002
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To a lot of us, engines are a bit like women. We can usually figure out when something is wrong, but we don't know for sure what makes them tick. That's because engines, like the fairer sex, are complicated.

An engine is basically an air pump. The standard gasoline-powered internal-combustion engine, the sort of contraption that most likely is under the hood of your rig, uses a four-stroke combustion cycle to convert air and fuel, which is mixed at a ratio of about 14 to 1, into energy. The four-stroke cycle used by our engines sometimes is referred to as the Otto cycle, after Nikolaus Otto, who invented it in 1867. In the first stroke, known as the intake stroke, the piston starts at the top of the cylinder. As the piston moves downward, the intake valve opens and the resulting vacuum fills the cylinder with a fuel/air mixture. Next comes the compression stroke, where the piston moves back up the cylinder to compress the fuel/air mixture, which it can do because on this stroke, the intake and exhaust valves are closed. When the piston reaches the top of its stoke, the ignition system sends an electrical charge to the spark plug, which does its job and emits a spark, igniting the mixture. The resulting explosion drives the piston downward, thus turning the crank through the connecting rods and sending power to the transmission. This part of the cycle is referred to as the combustion stroke. The final part of the cycle is the exhaust stroke, in which the exhaust valve opens and the piston makes another upward stroke, as always driven in part by the rotational forces of the flywheel, to push the remnants of the ignited mixture out of the cylinder.

If you're like us, you're wondering how your engine works within the context of looking for more power from it. And this is where things start to get complicated. Besides just understanding the basics of how an engine works, you must also understand what horsepower and torque are. Horsepower is defined as a unit of power numerically equal to a rate of 33,000 lb-ft of work per minute. Torque, meanwhile, is the twisting motion that tends to produce torsion or rotational motion. Well, fine, but these definitions really don't apply to the real world, do they? So what are torque and horsepower when it comes to the real world? To put it simplistically, horsepower is the ability to move weight a given distance, while torque provides the ability to get that weight moving.

So is it better to have torque, or is it better to have horsepower? For the most part, the more you can have of both, the better. Lots of horsepower is great, but without low-end torque, horsepower, especially at the top of your engine's rpm range, is fairly useless-unless you are a professional mud racer or spend a lot of time in the dunes at high rpm. A ton of torque is also a good thing, but without appropriate horsepower, it's also of little use. For the most part, a healthy balance of both, with as much of the torque as possible in the low end of the rpm range, is the best setup for an all-purpose trail rig.

Now that you have a little clearer picture of how an engine works, and of what horsepower and torque are, the quest for more power can begin. Because an engine is an air pump, the majority of modifications you can make to improve its power output involve making the engine inhale and exhale more effectively and more efficiently. As more fuel and air enter the engine, and spent gases exit the engine more quickly, horsepower is unleashed. Let's take a look at the basics of what is inside of your engine and how those parts can produce more power.

The Air Filter
What Does It Do?
The air filter plays a vital role, especially for those of us who like to play in the dirt. It filters out dust, dirt and debris while still allowing air into the engine. Without a filter, the life of your engine would be a short one. Dirt and other foreign objects are your engine's enemies because they rapidly accelerate wear.

How To Get More Power:
Getting more power from an air filter is simple. Like the majority of factory parts, most stock air filters are manufactured with cost being the overriding concern-and they tend to be fairly restrictive in nature-which means that they don't flow as much air as we might like them to. Luckily for us, the aftermarket has come to our rescue with high-performance filters for pretty much every vehicle you can think of. These are much less restrictive than the standard items, and they still do a great job of filtering. Even a bone-stock engine can benefit from a better-breathing filter, and they are mandatory for a modified engine.

Tips For The Trail
When you get a new filter, make sure to get one that is washable and reusable. This makes a big difference because air filters get dirty rather quickly on the trail. Once they're dirty, they lose their efficiency and rob the engine of horsepower. A washable and reusable air filter can always be kept clean and it beats running out and buying new air filters all the time.

Fuel Delivery
What Does It Do?
The fuel delivery system's job is self-explanatory: It delivers fuel to the engine and mixes it with air. On late-model vehicles, fuel injection is used, and on earlier vehicles, a carburetor is used. Whole books have been written on fuel-injection systems and carbs, so we won't go into much detail here. To keep things simple, you can just think of their main job as supplying the right amount of fuel, at the right mixture of fuel and air, into the engine.

How To Get More Power:
Getting more power from a fuel system is where things start to get tricky. This is because if your engine is stock, your factory carburetor or fuel-injection system already does a pretty good job of metering the air and fuel mixture-those systems already are more or less optimized to your engine by the factory. But when you modify your engine, it requires more air and fuel. So simply slapping on a bigger carb-"bigger" means that it flows more CFM, or cubic feet of air per minute-or a set of larger injectors onto an otherwise stock engine does not increase power output. To the contrary, doing so would hurt performance by sending too much mixture to the engine. What you do want to do, however, especially with carbureted engines, is to make sure that your intake system is properly adjusted to send the right mixture of air and fuel down to those combustion chambers. Remember that 14 to 1 ratio-said to be the stoichimetric ratio. Too much fuel, and you waste gas and lose power because your mixture is too rich. Too little fuel, and you also lose power, and your engine might run hotter than it should because your mixture is too lean.

Tips For The Trail:
Carbs can be pretty picky animals. Just by the nature of their design, they are not the best setup for hillclimbs or off-camber terrain. That's because they like a constant, consistent level of fuel in their float bowls, which is where raw gas is stored immediately before it is mixed with air and shot into the engine's combustion chambers. Fuel sloshing around in the float bowls of the carb when your rig achieves weird angles tends to produce stalling. If you have been on the trail in a carbureted rig, you probably already have noticed this. So what is the solution? For most carbs, you will want to run the float level as low as possible to avoid stalling. We have also found Quadrajets to work well on the trail, and the new Holley Truck Avenger carb also does a good job. The ultimate, but more expensive solution, is fuel injection. By the nature of its design it eliminates float bowls and injects the fuel either directly into the cylinder or into a throttle body, giving your engine the ability to run at any angle.

Intake Maniifold
What Does It Do?
On a carbureted engine, the job of the intake manifold is to channel the fuel/air mixture from the carb to the engine's combustion chambers. With fuel-injection systems using a throttle body, the job of the intake manifold is the same. For later and more modern fuel-injection systems, however, the job of the intake manifold is to deliver just air, as the injectors squirt fuel directly into the cylinder, or into its intake port. While the intake manifold performs a basic duty, it is not a part that should be overlooked in the quest for more power because it has a direct influence upon how much air flows into the combustion chambers, and upon how quickly and smoothly it flows there.

How To Get More Power:
Most factory manifolds are built with cost and emissions, not performance, as primary considerations. Therefore it is fairly easy to improve upon their performance. The main difference between a stock manifold and an aftermarket unit is that an aftermarket manifold features smoother, and sometimes larger, passages-or runners, as they are called-and is designed to improve the flow of air and fuel. Using runners of differing lengths and diameters, an aftermarket manifold can also deliver the majority of its power in different areas of the engine's rpm band.

Tips For The Trail:
Probably the most important thing to consider when making a decision on purchasing an intake manifold involves determining where you want your power: Do you want high-rpm horsepower, do you want a strong midrange, or do you want low-rpm torque? Manifolds can be chosen to deliver the majority of their power in certain areas of the rpm band, so choose wisely and match it to the type of off-roading you do.

Cylinder Heads
What Do They Do?
The primary functions of the cylinder heads are simple. They top off the cylinders, sealing them so that the pistons under them can build compression, and they house the valves and their associated parts-on overhead-valve engines, these would include the valve springs and rocker arms-that enable each cylinder to breathe. They also compose the very top of each combustion chamber, and instead of being perfectly flat, often incorporate shapes to aid efficient combustion. Modifications to cylinder heads or adding a new set of aftermarket heads can unleash horsepower.

How To Get More Power:
Modifications to cylinder heads mostly deal with getting more flow of the fuel/air mixture through them. One way to do this is to "port" the heads. This means that the passages in the heads are enlarged and reshaped to provide improved flow. Most aftermarket heads come with bigger ports and passages. It's important to match these with the ports on your intake manifold. The result is a big increase in the ability to flow more air and fuel into, and spent gases out of, the engine. This makes for big horsepower gains. One thing to be careful of here, though, is that larger ports and runners tend to slow down the speed at which the mixture travels through them. This can detract from throttle response. For the kind of good, crisp throttle response needed by most trail rigs, you don't want runners and ports that are too large.

Tips For The Trail:
The major consideration when modifying a set of heads, or getting a new set of aftermarket heads, is to determine the rpm range in which they make their power. That way, you can select a set of heads, or figure out modifications to your stockers, based on where you want your power. A 40hp gain might sound great, but if it comes at 5,000 rpm, it's fairly useless on the trail.

What Do They Do?
For the overhead-valve systems typically found in our rigs, lobes on the camshaft push on the pushrods, and through them, the rocker arms, to open and close the valves located in a cylinder head. In overhead-cam engines, the cam lobes can still push against rocker arms, or they can directly actuate the valves.

How To Get More Power:
The proper camshaft choice is critical. A camshaft can also add more horsepower, and it can determine where in the rpm range that horsepower appears. The basic way it does this is through altered shapes of the cam lobes. Those altered lobes can hold the valves open a little longer-this is referred to as duration. With the valves held open a little longer, more fuel and air can make their way into and out of the cylinder. Also, the lobes can provide more lift, so more air and fuel can enter and exit the cylinder. As always, increased flow equals more power.

Tips For The Trail:
While a cam with a lot of lift and duration might sound great, these detract from idle quality. This might not be a concern if you run at a dragstrip, but if you are trying to creep along trails in low range, having an engine that barely idles is not the way to go. Another concern is that if you have a radical cam and a brake booster that relies on vacuum, braking performance can suffer because radical cams tend to produce less vacuum than milder cams do, thanks to all that lift and overlap. So when you choose an aftermarket cam for your engine, it's critically important that you select one that will place the horsepower and torque in the rpm range where you most need it.

Pistons And Rings
What Do They Do?
Pistons and rings have torturous jobs. The piston slides upward in the cylinder, compressing air and fuel as it progresses toward the apex of its stroke. Just before it reaches that apex, the spark fires and explodes the mixture at temperatures between 400 and 600 degrees Fahrenheit, driving the piston downward with great force. The ring gets the fun job of constantly being dragged along the cylinder wall. Its purpose is to seal the piston against the cylinder wall so that the combustion force can't leak past it into the engine's bottom end, while being lubricated by just a thin film of oil.

How To Get More Power:
The main way to get more power from a piston and ring is to install pistons that boost the compression ratio. Pistons with slightly different-shaped tops can produce higher compression ratios. This is desirable because the more you compress the fuel/air mixture, the more powerful the explosion is when it is ignited.

Tips For The Trail:
A higher compression ratio might sound like the hot ticket, but higher compression can also make an engine run slightly hotter; so care will have to be taken to properly cool the engine. Also, higher-compression engines can also require high-octane gas, which can suck the money right out of your wallet if you put lots of highway miles on your rig.

Connecting Rods And Crank
What Do They Do?
The connecting rods are the link between the piston and the crankshaft. The top of the rod, known as the small end, is attached to the piston, and the bottom, known as the big end, is attached to a lever arm, or throw, on the crankshaft. The size of that throw determines the crankshaft's stroke, which is one of the factors involved in measuring a cylinder's capacity (the other is the diameter of the cylinder bore). The crankshaft spins around in its bearings at the bottom of the block as the pistons transfer the force from combustion to it through the connecting rods. The crank's rotation then channels power and torque to the transmission. Obviously, a great deal of load and force is put on the crank.

How To Get More Power:
Crankshafts and connecting rods really don't provide more power. What they do provide is strength. The strongest crank and connecting rods you can afford should always be used in an engine that is going to see hard use. And here's another crankshaft-related item: A term that you might have heard is four-bolt main or two-bolt main. This is a characteristic of the lower end of the engine block. An engine with four-bolt mains has four bolts holding down each main-bearing cap on the crankshaft, compared to two-bolt mains, where just two bolts-one on each side-hold down each bearing cap. The four-bolt setup is much stronger than the two-bolt setup.

Tips For The Trail:
If you are going to be putting your engine under lots of load and high rpm, such as you'd see when dune running and mud running, you'll want to think in terms of a forged crank and rods, instead of cast items. Also, set them up in a block that uses four-bolt main bearings.

What Do They Do?
The header, or exhaust manifold, helps to evacuate the spent gases from the cylinder and then sends those gases out through the rest of the exhaust system. While a manifold's job is basic in function, big gains of power can be realized when tossing the stock cast manifolds and switching to an aftermarket set of good tubular headers.

How To Get More Power:
As we've seen with other parts we've considered, factory exhaust manifolds are built with cost being the primary concern. Other factors, such as noise, are also taken into consideration. Luckily, the aftermarket doesn't really have to abide by the same rules, and can make headers where the primary concern is to increase performance. So how does a set of headers make more power? Through their design, which is a science in itself, they do a better job of evacuating the gases out of the cylinder and getting rid of them more quickly. This increase in flow boosts horsepower.

Tips For The Trail:
Life on the trail is rough on a set of headers. Most of us have all overheated our engines at one time or the other. That heat can take its toll on a set of headers. That is why it is important to get a quality set of headers with a thick mounting flange to avoid warpage. Also look at the thickness of the material used to build the tubes as a thin-wall header can crack more easily.

Another consideration when selecting a set of headers involves, again, asking where you want your power. A Tri-Y style of header tends to increase torque at the bottom of the rpm band while a standard equal-length 4-into-1 header puts the power up a little higher. Also remember that smaller tubes tend to produce increases in torque, while larger ones favor increases in horsepower.

Finally, remember that an engine needs to be thought of as a system. So be sure, when you're building yours, that you select components that are aimed at achieving similar goals. You wouldn't, for instance, match a high-rpm cam with headers designed to produce low-rpm horsepower and torque. Now if women were only that easy to understand!

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