How to improve your car's performance

The desire to go faster seems to be some kind of human condition. Ancient civilisations celebrated those who could run fastest at events like the ancient Olympics. Even before cars had been invented, there was an industry breeding faster and faster horses. So it shouldn’t come as any surprise to learn that people have been trying to make cars go faster from the moment the first one smoked and fumed its way around Karl Benz’s backyard way back in 1886.

These days, going faster in a car requires little more than buying the EV with the most powerful motors. Doubtless, an industry will spring up with the aim of making those EVs even faster than standard, but for now, the tinkerers of this world are still obsessed with the internal-combustion engine.

So what are the traditional ways of making an ICE-powered car go faster? Well, if we’re talking straight-line speed, then they all start with the premise of increasing engine horsepower and torque. That’s the combined forces produced by an engine as it burns fuel and air and turns it in to heat, noise and a rotational force on the engine’s crankshaft. More force on the crankshaft means more force at the car’s wheels and the more easily it will overcome gravity, rolling resistance and inertia. The faster it will go, in other words.

Read more about engine power

• What is horsepower?
• What is torque?
• What's the difference between power and torque?

Increasing horsepower can be done in a variety of ways, but traditionally, there are a handful of well-trodden paths that engineers pursue in this chase for pace. So here’s how to get more horsepower, in a broad sense, anyway:

Displacement

If you think about an engine as an air pump – which it fundamentally is – you’ll probably figure out pretty quickly that a bigger pump will move more air. Combine that air with fuel and ignite it, and you get a bigger bang and, therefore, more power produced. This is why a 5.0-litre V8 makes more power than a one litre three-cylinder. Simple physics.

So, if you make that pump’s capacity bigger by increasing the stroke of the crankshaft or the diameter of the pistons (or both), you can make a small engine into a larger one. Then, if you enlarge everything else to scale (carburettor, engine valves, exhaust diameter) to scale, you’ll be making more power.

Tuning

Production car engine are tuned to provide a good balance between smoothness, driveability, fuel economy and performance. If you don’t care about the first three in the name of the latter, then you can retune the engine to make more of its current displacement.

This can include a different camshaft profile, more compression, a larger carburettor or even multiple carburettors, different ignition timing, larger engine valves and even lighter or lower friction internal parts. On modern engines with computer control of everything, you can reprogram that computer to supply more fuel and a more aggressive ignition curve, often with just a laptop as a toolkit.

You might end up with a lumpy, grumpy engine that doesn’t like idling, uses lots of fuel, overheats in traffic and is difficult to drive, but for some (especially race-car engineers) that’s an acceptable trade-off in the name of greater power and performance.

Forced induction

This can take many forms, but essentially you’re talking about adding a supercharger (driven by a belt from the engine’s crankshaft) or a turbocharger (driven by otherwise wasted exhaust gases as they rush out of the engine). Either the supercharger or turbocharger uses the same principle: by pushing more air into the engine each time it fires, you can also add more fuel to compensate. And more fuel plus more air equals a bigger bang. And more power.

The by-product of this is heat and its heat management that is critical (as well as maintaining the correct amounts of air and fuel). Fuel consumption will also increase, but if it’s more power you want, then forced induction is a hugely successful way to get it. It’s no accident that the majority of passenger car and light commercial engines these days are turbocharged, to claw back the performance lost by the trend to downsized capacity.

It doesn’t matter whether we’re talking turbocharging or supercharging, what is boost in a car with a turbo engine is the same as boost in a supercharged unit. Boost is simply the pressure stuffing the fuel and air into the engine.

That’s consistent with the downsizing of car engines in the last decade. With forced induction in a V6, the same engine can genuinely feel like a V8. In a small engine, you can produce the power of a much larger one.

The trucking industry has known about turbocharging for decades, as it’s a great way to make a diesel engine really perform. Even modern turbo-diesels use the same basic tech and on a DD15 engine (the most modern Detroit Diesel-built truck engine), the turbocharger helps it produce up to 2500Nm of torque while maintaining fuel efficiency. We still have plenty to learn from the trucking industry in terms of engine efficiency versus output.

Nitrous-oxide

This is the stuff some dentists use to make you forget they’re currently drilling a hole somewhere in your head. When injected into an engine, nitrous-oxide can radically increase power. It does so by releasing huge amounts of extra oxygen when it’s injected into the engine. When that happens, the engine can also accept a heap more fuel and we’re back to that simple equation: More fuel plus more air equals more bang. Nitrous-oxide can also be used in boosted engines and in a normally aspirated engine.

Nitrous-oxide, however, has its problems. It needs to be stored at very high pressure inside a bottle that has to fit somewhere in the car, it doesn’t last long and it’s expensive to buy. It also only works when you’re injecting the nitrous-oxide gas. Switch it off and it the difference is like a turbocharged engine without turbo boost. Oh, and it’s pretty much illegal in road-registered cars in Australia. Best left to the drag racers out there, really.

The risks

There are other ways of convincing an engine to make more power, but those are the time-honoured methods with which most mechanics will be familiar. Speaking of which, a mechanic or specialist workshop is where you need to be to make most of this stuff a reality on your own car. Learning by your mistakes as you go might be fulfilling in a life-experience kind of way, but blowing up expensive engines when you get it wrong is definitely learning the hard way. Knowing how to increase horsepower on a car without destroying things is not something you learn overnight.

It's also worth mentioning that if you want to make the most horsepower in a car engine, then combining these methods is where the action is really at. Make the engine capacity bigger, tune it, add a turbocharger and then inject nitrous-oxide into it, and you’d have one heck of a ride. Possibly only briefly, however.

Making an engine larger internally also involves a lot of Nth-degree machining and precision tool work, while forced induction requires an expansive knowledge of tuning to make sure the end result is as explosion-resistant as possible. Even tuning can get you into trouble if you mess up the air:fuel ratio or even the ignition advance curve. And a too-big carburettor can be worse than one that’s too small in many cases, and your car will suddenly be awful to drive.

Then there’s the matter of the law. In some cases, the rules say you can’t modify a car beyond a certain point and still have it legal to use on the roads. New cars also have the question of making modifications without voiding warranty terms and conditions. In pretty much every method discussed here, your warranty would be torn up on the spot, so that’s something to consider, too.

So why not just buy a car with a bigger, more powerful engine? As in, why bother learning how to increase power in a four-cylinder car when you could buy a V8? That’s a good question, but one that is usually countered by the tinkerer’s desire to take something ordinary and make it better. What else could explain the decades-long quest to increase the horsepower and performance of the original people’s car, a car that was never designed with speed in mind, the Volkswagen Beetle.

Mechanics and backyard geniuses have managed to comfortably triple or quadruple (and then some) the power from the humble Beetle, despite the design’s 1930s roots and the limitations of the rest of the Beetle package.

Call it a hobby, but never discount the tinkerer’s appetite for such endeavours.