The Horsepower FAQ

So you want more power, eh? Well, any engine can be modified to make radical horsepower, but it depends on the application...is this car going to be driven daily, or driven only on the track? Is smog an issue? Before we get into that, lets look at the basics of gaining ponies.

The engine is just a pump, plain and simple. It sucks air and fuel in, and expels exhaust. So anything that you can do to allow more air and fuel to enter, and more exhaust to exit will increase power. Easy enough, right?

Smog legal methods

Turbos and Superchargers
The easiest and most expensive method, these will increase your power output without making any other modifications. They basically enhance the pumping action of the engine by ramming compressed air into it. This, in turn, increases the power of every combustion stroke (more air & fuel = more power). Although the two both compress the air / fuel mixture, the way that they do it is different.

Turbochargers
Turbochargers are exhaust-driven compressors. They turn the lost energy in the hot exhaust into boost. The turbo is simple in construction; a turbine is connected in the path of the exhaust, when this spins, it turns a compressor via a lubricated shaft. A valve called a wastegate controls the amount of boost; when the limit is reached an actuator pushes the wastegate open, allowing exhaust to bypass the turbine. By adjusting the actuator, you can adjust the boost made.

Turbos run at extremes: the turbine & compressor can spin at speeds up to 100,000 RPM and the turbine can reach temperatures of 2,000 degrees F. They must be fed fresh oil to keep the bearings from melting, and some turbos have a water jacket around the bearings as well.

There are problems with turbos. The first is heat. The other is lag, which we will not get into here...check the Turbocharger FAQ for that one. Anyway, turbos generate a LOT of heat. It's not uncommon for the exhaust portion of a turbo to glow bright red after high-speed driving. And remember, this red-hot housing is in direct contact with the intake compressor, and that leads us to another problem: Intake air heat.  After a certain boost level (5.5 PSI), the compressed intake air will be so hot that detonation is bound to occur, which would destroy an engine quickly. Two forces cause this: compression generates heat, as well as the oven of a turbine which is just inches away. Fortunately there is a solution.

Intercooling
The answer is an air-to-air heat exchanger, called an intercooler. The intercooler is basically a radiator that cools the air flowing through it to an acceptable level. Hook this up to the intake tract of a turbocharged car, and the air will be cooled sufficiently to prevent detonation.  This means more power (the colder air is, the more dense it is, which equates to more power) and the ability to run higher boost.

Superchargers
I'm sure you seen it...the old muscle car with the big shiny thing sticking out of the hood with the round valves that rotate every time the throttle is tapped. That is a supercharger. A supercharger is a crankshaft-driven compressor. The design of the supercharger varies greatly, and I won't go into detail about every single type. All that matters is that some types need RPMs to generate boost (negative displacement), and some generate boost at idle (positive displacement).

There are two types of superchargers: positive displacement, and negative displacement. Positive displacement superchargers can make boost at idle, and are more of a "pump" than a true compressor. Due to their nature, they tend to super-heat the air above a certain boost threshold. But for applications below 9 psi, the heat is tolerable by the engine.

Negative displacement superchargers are nothing more than the compressor section of a turbo, set up to run off of an engine-driven belt. These superchargers share the same efficiency as a turbocharger, with minimal heat. They do not make boost at idle however, and there is some lag experienced.

A supercharger is roughly equivalent to an a/c compressor in terms of load, and the more boost, the more load. This is offset by the power it makes, but that constant stress has to go somewhere...a belt, a pulley, etc. And you can't adjust boost like you can with a turbo. Boost is dependant upon pulley size, and there are limits.

If your car has either of these, then the easiest way to make more power is to up the boost, if the engine can handle it. Another way is to add an intercooler (yes, even to a supercharged engine).

Nitrous - Fun In a Bottle
Aside from its medicinal uses, nitrous oxide (or just nitrous) has huge benefits in an engine. The nitrous molecule, NO2, is one part nitrogen and two parts oxygen. Just what an engine needs.

You should already know this, but I'll reiterate just in case. Fire = Fuel + Oxygen + Heat. In the internal combustion engine, this is Combustion = Gasoline + Oxygen + Spark. We know where all three come from, and only one is what we are concerned with: oxygen.This is, after all, what we are looking to squeeze more of into the engine. And thats where nitrous comes into play.

Many people make the mistake of thinking nitrous is a fuel. It is not, I can assure you. Nitrous is an oxidizer, that is, it helps provide oxygen for combustion. It does not take the place of gasoline.

When nitrous is introduced into an engine, it immediately turns into a gaseous mist - nitrous is stored as a liquid - and this mist, upon combustion, is changed. The bonds that hold the nitrogen and oxygen are broken, and suddenly we have all of this new power-making oxygen. Hopefully, this engine compensated for the nitrous and added enough fuel, otherwise the surplus oxygen would lean out the mixture and explode instead of combust...very bad. So lets say that there's enough fuel. Now even though we have enough, the mixture would still explode - without one crucial ingredient. Nitrogen. That nitrogen that seperated from the O2 acts as a cushion for the combustion, and no damage is done. Added with the natural tendency of the nitrous to cool the intake air stream, makes the beauty of nitrous.

The bad thing about nitrous is its tendency to kill an engine if its leans out.The fuel controls on the engine must take the nitrous into account, and NOT LEAN OUT the mixture. This is the main cause of a nitrous-equipped engine's failure, other than structural failure. If done properly nitrous can be a cheap, safe way to increase horsepower. And its even smog-legal for certain applications.

Tunnels and cold air
Another popular way to increase power, and save a couple bucks, is to add a "snorkel" or cold air induction. The snorkel is usually a long metal tube which acts to "time" the incoming air mixture to ram itself into the cylinder. This happens at a specific band of RPMs, so make sure you get one designed for your engine. Cold air induction can be used seperately, or in conjunction. It takes cold outside air, as opposed to hot engine bay air, and funnels it into the engine.

Electronica
Today's vehicles are a marvel of engineering. They use computers and sensors and actuators to give the internal combustion engine more efficiency. This means more power, better gas mileage, and less pollution. The latter is the real reason today's cars are so complicated. If not for smog laws, cars would probably still be carbuerated with ignition points.

The computer in your car has been programmed to provide reliability, economy, and not pollute. This means less power. Most of this has to do with ignition timing and fuel delivery, and sometimes shift points in auto transmissions.

Timing is everything
If your car has a distributor or external cam/crank sensor, then there's a good chance you can adjust your timing. And this is a good thing; most new cars do this with sensors and the computer, so the only way you can change timing is by swapping chips. More on that later.

The ignition timing in an interal combustion engine is crucial. It's all based around TDC, or Top Dead Center. TDC occurs when the number 1 piston is at the absolute top of its travel. Timing will most likely be a couple degrees before TDC, or BTDC. A degree is used to measure crankshaft rotation. So if your car says to set timing at say, 10 degrees BTDC, then the spark is going to occur 10 degrees before the piston hits the top of its travel.

By changing when the spark occurs, you can alter the power of your engine. Advancing your timing makes power. Advancing means making the spark happen sooner, or farther away from TDC. How does this make power, you wonder? Well, when the mixture is ignited before the piston is done compressing it, the combustion process can be amplified somewhat. The piston will continue to squeeze the ignited mixture, causing compression pressures to rise, and this makes more power (remember more compression = more power).

However, there is a problem. At a certain point, which is different for every engine setup, a phenomenon known as detonation, or "knock",will occur. This is based upon gas octane, air temperature, and so on. And its very destructive. What happens is that several different combustions take place instead of one uniform combustion, and when the different combustion waves hit one another, it causes the familiar "knock".

There are ways to combat knock. Most newer cars have knock sensors which will retard the timing until the knock is eliminated. This will ensure that you don't kill your engine, but it will not allow you to use the set timing. The only practical way to fix this is to run a high-octane fuel.This will eliminate the knock, and your computer will bring your timing closer and closer to the set value.

Chips
For those of you who can't change their timing, the only practical way to get around this is to buy a new ROM chip. The ROM chip tells the computer what parameters to use, like what RPM to shift if the throttle is at halfway, and etc. Usually the chip will change your fuel timings as well. And depending on the chip, you might have to run premium gas too, but hey, you wanted more power, right?

Racing only methods

Aftermarket Engine Management Systems
Almost a requirement when modifing boosted engines. An aftermarket EMS allows the change of fuel & ignition timing on the fly. Programmable via PC and with the ability to save maps (ECU programs) to disk, many different configurations can be made available. Switching between a map for 91 octane pump gas, to 108 octane VP C12 is as simple as loading the map from disk.

Internal Engine Modifications
For those of you where pollution isn't a problem, then you can focus on the internals of the engine for your power gains. We'll start with the top-end.

Heads, ports, and valves
The very thing that delivers air and fuel to the combustion chambers, contains the combustion itself, and expels exhaust might be what's choking your power potential. Its called the cylinder head, and its come a long way since its introduction a century ago.

Back in the day, all the cylinder head did was provide a threaded hole for a spark plug, and contain the combustion. That was the stone age of engine design. Nowadays, cylinder heads are precision components, sometimes made from aluminum, that are designed around reliability and restricting pollution. As usual, this means retricting power as well. Lets look at how the air / fuel mixture travels through the head.

Lets imagine for a second that you are an air molecule (and no, we aren't trippin' on any mind-altering substances). You get sucked up by the air intake of, for example, a typical carbureted engine. The first thing you meet is the air filter, then the carb, where you mingle with gasoline, and begin the end of your journey: the combustion chamber. Before you get there, you have to wait your turn getting through the tiny port,  slowing by the valleys and peaks of machined metal that make up the intake port walls. To our eyes, this port would look slightly rough, but to an air molecule, these are obstacles that cause turbulence, which slows the velocity of the mixture. And finally, you have to push your way through the valve, which doesn't drop very far.

The easiest thing to start with is to polish the ports. By removing the rough metal, you'll provide a smooth almost-turbulence-free surface to increase airflow. You should do this down to the valve seat (without bogarting the seat, of course) and if you're tedious enough, do it to the intake manifold as well.

Next is port size. Like I said earlier, anything you can do to increase the flow of air will increase power. So a bigger intake & exhaust port (and valve) is the place to start. By enlarging the port, you let the air hit the valve faster. That's the next change.

In order to allow all of that new air & fuel to hit the chamber, the valve will need to open farther and longer, This brings us to the mechanical "brain" of the engine, the camshaft.

Camshafts
The camshaft is an odd-looking rod that resides in the engine block, or on top of the cylinder head. For every valve, there is a cam lobe that actuates it (variable valve timing engines, like those found in Toyotas and Hondas are different, and I'm not covering that here). The difference between a cam in the block and in the head is important. Depending on who you talk to, either have their advantages.

A camshaft in the engine block, known as cam-in-block, drives the valves through a series of lifters, pushrods, and rocker arms. The lifters "ride" on the cam lobes, and when the lobe extends, the lifter rises, pushing the pushrod upward, which lifts the rocker arm. The rocker arm pivots, pushing the valve open. While this works great, it has trouble with high RPMs and robs power. This doesn't necessarily mean this setup is crap...the 2006 Corvette makes 400 HP from a 6.0 lliter V8 using cam-in-block, and the Dodge Viper has it in its 500-horse V10.

Overhead camshafts, known as SOHC or DOHC (for single or double cam, respectively) sit in the cylinder head and actuate the valves through lifters or rocker arms. By eliminating the pushrods and pushing on the valves directly, the engine can rev higher, and four valves per cylinder can be employed. That's what DOHC is for. Instead of a single intake and exhaust port, there are two, and this increases the ability of the engine to pump. Some engines have four valves per cylinder, but just one cam, and they use rocker arms to actuate the valves. This is true of 12-valve engines as well. In comparison with the examples above, the late 90s Ford Mustang Cobra uses DOHC in its 4.6 liter V8...and made 320 HP!

Anyway, the camshaft(s), wherever they are, control the duration, lift, and overlap of the valves. Duration is the length of time the valve is held open. Lift is how far the valve is opened, and overlap is how soon the intake valve will open while the exhaust valve is closing, but not closed completely, during the exhaust stroke.

Changing these three can allow you to make large gains of horsepower, but smog is out of the question. There is also greater wear rates associated with greater valve duration and lift, as well as the chance of "crashing" the valves if a timing chain or belt snaps, but its worth it, right?

Pistons, rods, bearings, oh my
Finally, we've arrived at the pieces that do the work. And this is another opportunity for power.

The piston is yet another marvel of engineering. They are demanded to go up and down (or side to side for those VW & Subaru folks) for hundreds of thousands of miles, subjected to thousands of degrees of heat, exposed to acids and gases formed in the crankcase, and so on. They also directly control compresson. The shape and height of the piston will determine the compression ratio. By raising compression, you will definately gain horsepower.

And you'll want to lighten those pistons, too. Usually high power goes hand in hand with higher revs, even in big 8-cylinders. Heavy pistons and rods will put huge stresses on themselves and other parts once their weight becomes amplified by centrifugal forces. So they must be lighter and stronger.

This brings us to forged aluminum. Extremely strong and light, this alloy is ideal for internal engine parts. With these parts, you can run higher RPMs and extreme forms of turbo/supercharging or nitrous.

The final part of this section is the bearing and crankshaft. The bearings, main and connecting rod, absorb a great deal of stresses. If the engine is disassembled to make internal modifications, heavy-duty bearings are a must. And the crankshaft should be forged steel for maximum stress resistance.