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How to Increase Horsepower

Updated on September 19, 2017
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Bud Scannavino is a Certified Master Automotive Technician. When it comes to modifying cars, Bud believes in excess.

You may not be able to crank your car up to the 840 horsepower of the new Dodge Demon, but a few simple modifications can increase your horsepower.
You may not be able to crank your car up to the 840 horsepower of the new Dodge Demon, but a few simple modifications can increase your horsepower. | Source

If you want to know how to increase horsepower, you're not alone. Ever since the invention of the wheel, people have been trying new ways to make their own set of wheels go faster and faster.

Even the Roman chariot races looked like precursors to today’s NASCAR races, complete with accidents, mayhem, and pileups on the turns. Stakes were much higher in Rome, though, than just prize money, advertising and sponsorships.

Like ancient chariot owners, we want our own vehicles to go faster. How much faster? More, that’s how much. And when it comes to knowing how to increase horsepower, there is a saying: If a little is good, then too much is just right.

So, let’s look at how to increase horsepower in your car's engine. Horsepower is just one aspect of your car, there are other basic car modifications to improve performance you can make.

To illustrate the concepts of performance, we’ll compare old technology, like with restomods, to the latest computer-controlled, fuel-injected engines we have now.

Although the technology might seem radically different, the underlying basic theory of improving performance will be identical.

Your Engine Is an Air Pump

Think of an engine as an air pump. It gulps in air, takes in a little fuel as well, and then ignites that mixture with an electrical spark. The resulting combustion process greatly expands the physical volume of the air and fuel. The chemical process of rapid burning transforms cold air and very thin gasoline vapors into heat, more heat and a whole lot of hot, rapidly expanding gases.

Truly, this is "better living through chemistry." That rapid expansion of gasses drives the pistons down their cylinder bores with tremendous force, just like burning gunpowder drives a bullet rapidly out of a rifle barrel. With car engines, though, we harness that linear power to spin a crankshaft, which turns the car’s drive wheels.

To Increase Power, Advance Your Ignition Timing

If you have an older engine that uses a distributor-type ignition, you are in luck. You can simply advance the base ignition timing a little, say by 5 degrees, and notice an immediate improvement in power. The engine will seem more peppy and responsive, sometimes incredibly so. Why is that?

As the pistons near top dead center they slow down, and the spark plugs fire a brief moment before the pistons reach the tops of their travel. That "head start" gives the combustion flame a chance to start growing until the pistons swing over top dead center and begin heading back down the cylinders.

That’s when combustion, if everything was timed just right, will expand the volume of gasses in the cylinders at a faster rate, and deliver maximum force to the crankshaft. Advancing the ignition timing gives the flame more of a head start. When the pistons are still right at top dead center, and total combustion chamber volume is at its smallest, the combustion process will be further along. So, with more combustion pressure pushing against a smaller volume, more force is generated on the pistons.

The tradeoff? Knocking and pinging, because combustion pressure is greater. Knowing how to increase horsepower also means identifying engine noises that may result.

You will have to switch to a higher-octane fuel to stop the racket and prevent engine damage. Better gasoline is a small price to pay for performance, right? By comparison, NASCAR engines use extremely high octane gasoline because of their highly stressed combustion events.

High Performance Electronics

You can reprogram your car for greater performance with a variety of electronics chips and kits.
You can reprogram your car for greater performance with a variety of electronics chips and kits. | Source

If your car has modern fuel injection, it very likely does not have a distributor. Exceptions do exist, like with older Jeeps.

But even if your engine is controlled by a PCM (Powertrain Control Module), you can buy a chip or an electronic tuning box to reprogram the ignition advance curve.

The kit, really just a software package, will also command the fuel injectors to add a little more fuel as it advances the ignition timing, to forestall the knocking and pinging. It’s the same principle as advancing the distributor in your restomod.

Let in More Air

The next step in how to increase horsepower will be to make it easier for your engine to take in more air. On your restomod, with its 2-barrel carburetor, you are again in luck for some cheap horsepower.

Your most economical mod is to replace that stock 2-barrel intake manifold and carburetor with a 4-barrel carb and intake manifold. It will be a simple bolt-in process, well within the skill level of most newcomers to the world of automobile performance. Just make sure you have the right tools for a restomod.

If you are really down on money, you could even find a used factory 4-barrel cast iron intake manifold for sale. Try eBay. But purchase a brand-new carburetor.

A carb that is several decades old will have so much wear on the throttle shafts and bushings that it can’t be properly rebuilt. Besides, new carbs are not that expensive. It’s cheap horsepower, a difference you will immediately feel.

You will see advertisements for fuel injection kits that will fit the old engine in your restomod. The kits will look appealing, but the overall price of retrofitting fuel injection to an older car will be at least three times the price of simply buying a 4-barrell intake manifold and carb setup. The carb, too, will be easier to tune and adjust if you only have beginner skills in performance.

But what about your newer car with sequential fuel injection and coil-on-plug ignition? For that case, your least expensive mod, although it won’t make a dramatic difference, will be to add a cold air intake kit.

Cold Air Intakes

Have you ever noticed that your engine seems to run better in the cool night air than it does on a hot summer day? That’s because cool air is denser, so your engine is inhaling a denser, more oxygen-rich charge of air with every gulp. More oxygen means more fuel can be added to the mix, and that means more power.

Temperatures under the hood can reach 200 degrees Fahrenheit, which greatly thins out the air density in the engine compartment. Hot air blows in from the radiator, the engine radiates heat, and the blazing hot exhaust manifolds exude enough BTUs to cook food, literally.You want a way to deliver cooler air to your engine.

A CAI, cold air intake kit, will duct in air to the engine from the grill area at the very front of your car. While it is not literally cold air on a summer day, it is a lot cooler compared to the 200-degree air under the hood. More oxygen equals more power, just like when you fan the flames on your barbeque to make the fire burn hotter.

Nitrous Oxide Systems

Nitrous Oxide Systems like this are available on Amazon or other car components sites.
Nitrous Oxide Systems like this are available on Amazon or other car components sites. | Source

No, it’s not always cheap, and it’s not even legal to use on public streets in most areas, but NOS, nitrous oxide systems, do illustrate our point about extra oxygen being a good thing.

Technically not a fuel, nitrous oxide releases oxygen molecules, a tremendous amount of them, when exposed to the heat of combustion. By itself that would create an extremely lean fuel mixture that will rapidly melt aluminum alloy pistons just like a cutting torch would. No thanks.

But with all that oxygen suddenly present in the engine’s combustion chambers, it is an easy matter to supply extra fuel, gasoline, to match. That’s why bigger fuel injectors and high-volume fuel pumps come into play with the addition of a NOS kit. Like I said, not cheap.

While we are talking about fuel chemistry, consider the nitromethane fuel that top fuel dragsters run on. Technically speaking, gasoline has more potential energy than nitro does. As the nitro burns, however, it will release oxygen molecules in the process, which means you can burn more fuel.

Keep Up with Your Buddies

So, you installed the cold air intake on your late model ride, and it made a sensible, nice improvement in performance. Very well. But it was not as dramatic an increase in power as when your neighbor installed that 4-barrel carb on his restomod.

And now he’s spinning his wheels and leaving black tire-shredding streaks on the street on front of your house. Like with the Roman chariot races, our performance races can get competitive and personal really, really fast.

You will have to get a larger throttle body for your late model ride. The larger bore size of the new throttle body will allow more air into your engine, although again, it won’t be as sizeable an increase as switching to a larger carburetor on an older car.

As you can see, when it comes to performance improvements, the older technology has the advantage when it comes to fitting your budget. And with the larger throttle body you will need to have your PCM reprogrammed so it adds more fuel to match the greater volume of air.

Short Tube Headers Help the Engine Breath Better

Replace your stock exhaust manifolds with some bolt-in, short tube headers.
Replace your stock exhaust manifolds with some bolt-in, short tube headers.

For knowing how to increase horsepower, let’s go back to our air pump example. Now that we’ve advanced the ignition timing, increased the engine’s air intake, and added more fuel to match, we need to help the engine expel the spent air and fuel. Freeing up the exhaust is the next logical step.

Factory exhaust manifolds are quite restrictive. They really don’t let the engine exhale very well at all. They don’t have to, because most people drive their cars in sensible ways, and don’t feel compelled to leave black tire streaks in front of their neighbor’s house.

The next, least expensive mod is to replace your stock exhaust manifolds with some bolt-in, short tube headers. Normally they bolt in place without modifications to the rest of your exhaust system, and will work with stock catalytic convertors. They will also make your car louder, always a plus.

They will look cool under your hood, too. That should count a little toward keeping up the grudge match with your neighbor who owns the noisy, rattling, tire-burning restomod.

Even better than short tube headers would be a nice set of long tube headers. They would be more expensive, though, and usually require their own matching exhaust system to attach to. Stainless steel construction is the norm in the aftermarket industry for long tube headers. With those, we are entering the phase where knowing how to increase horsepower is no longer that economical.

Changes in Cam Timing Change the Engine’s Personality

This is where the fun in knowing how to increase horsepower begins. You can’t drive fast very often. In fact, most of our driving is creeping through city traffic, idling through parking lots, and picking up the kids from soccer practice.

But while doing all that slow driving it’s very satisfying to have a car that sounds like it’s capable of going very fast, even when it’s just idling along. Again, when it comes to fitting a low budget, the restomod car will have a great advantage over the modern tuner car.

Let’s improve our valve lift and duration profile, and get that great rumpity-rump-rump deep, loping idle we all like.

Think More Lift

So, you’ve got your engine ingesting as much air as it can possibly inhale just short of force-feeding it by installing a supercharger or turbo setup. Good. And it is exhausting free and easy through the headers and free-flowing exhaust system you installed. The next to help it breath even better is to change the camshaft profile.

For your restomod, you can buy a set of inexpensive high-lift rocker arms, install them in a few hours, and have an instant increase in horsepower. And they are cheap, bolt in parts. The job is well within the skill set of beginner tuners. Get ready to burn up a set of rear tires. You won’t, however, get that loping idle with just more valve lift. Sorry.

It is worth noting, unfortunately, that for your modern, late model car, high-lift rockers are probably not available. And if they are, they could cause interference between your valves and pistons. Very expensive damage, for sure.

Again, like we said, knowing how to increase horsepower for the least amount of money is easier with old technology than with the latest cutting-edge technology of today’s cars.

Duration Is Power, but Overlap Makes the Loping Idle

You could just skip the high-lift rockers, and buy an inexpensive high-performance cam, lifter and valve spring kit for your restomod. Dozens of camshaft profiles will be available for your engine. I recommend going milder than you really want. Your car will be more tractable, run better, and still sound good.

The longer duration profiles will increase power at higher rpm, and the ones that have the most overlap, the period that both intake and exhaust valves are open, will give you the loping, mean-sounding, intimidating idle. Expect less low end power. It’s a tradeoff.

Longer overlap also means lower intake manifold vacuum, unspent fuel swept out into the exhaust, and greatly increased emissions. So, it’s not always feasible to upgrade the camshaft (to a large degree) on a late model car that has to pass emissions testing.

Besides, your late model engine probably has roller lifters, and if your new cam requires new roller lifters, they will be expensive.

If You to Know How to Increase Horsepower, Think Incrementally

So for knowing how to increase horsepower, this is a great working order. Advance your ignition timing, provide more air for your engine, help it exhale the spent gasses better, then lastly improve your camshaft profile.

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