Let’s be honest for a moment. You may be a diehard car enthusiast with fully-synthetic 10W-30 pumping through your veins, but there are probably at least a few aspects of the automobile that you are still a bit hazy about, even basic concepts – we’ll be the first to admit this. So let’s take an opportunity to discuss and clarify some automotive terms and concepts that are commonly thrown around in conversation. Want to learn more? Make sure to check out our Building Blocks article series for an in-depth look at automotive systems.
10. Brake Horsepower vs. Wheel Horsepower
The amount of horsepower a car makes at its drive wheels versus how much its engine actually produces are two very different things. Brake horsepower (bhp) refers to the amount of power available at the crankshaft, before any of it has been lost through the drivetrain. OEM power ratings are usually based on brake horsepower, while dyno numbers refer to wheel horsepower (whp), which is the true measurement of a vehicle’s performance.
Torque is simply a measurement of the rotational force on an object, such as a car’s flywheel. More so than horsepower, torque is what makes your car feel fast; it’s what gets you off the line and pins you back in your seat under acceleration. Since horsepower is a function of torque, an engine’s torque curve will always intersect its power curve at 5,252 rpm, regardless of the application. Imagine you are lifting weights at the gym: the amount of weight you lift is the torque and the reps are the horsepower.
8. Naturally Aspirated vs. Forced Induction
With the recent rise in popularity of turbocharging, it’s important to make a distinction between a naturally aspirated motor versus one that relies on forced induction, which means either a turbocharger or a supercharger is employed. Naturally or normally aspirated engines can be thought of as a vacuum, sucking in air under their own power. Conversely, forced induction applications actually force air into the cylinders, allowing for the same volume to have a much denser intake charge. Turbochargers and superchargers are basically just air pumps - if you add more air, you can also add more fuel, resulting in a more powerful explosion. Volumetric efficiencies over 100% can be easily achieved in forced induction applications.
7. Carburation vs. Fuel injection
Younger generations may not be familiar with carburation, as it was phased out in the late 1980s and early 1990s. A carburetor is a device which mixes air and fuel together in the exact right proportions before it enters the cylinders under the engine’s own vacuum. Carbs are simple, inexpensive and can be tuned, but cannot match the efficiency of modern fuel injection systems. These days, carburetors are most commonly found on older muscle cars and hot rods. Since the early 1990s, almost all gasoline-powered passenger vehicles sold in first world markets have been equipped with electronic fuel injection (EFI). Advances in technology and the computer age made fuel injection possible, as an ECU now controls virtually every function of an engine. With fuel injection, individual injectors spray fuel into each cylinder as a pulse, usually at a point somewhere on the intake manifold, before the intake ports. A fuel pump and fuel pressure regulator (FPR) supply and maintain a constant fuel supply and optimal pressure. The benefits of EFI are a more fuel efficient engine, cleaner emissions, better throttle response, easier starting and less maintenance.
6. Pushrods, OHV & OHC
Almost all modern car engines use an overhead cam (OHC) design instead of the outmoded overhead valve (OHV) layout. In an OHC motor, the camshafts are located in the cylinder head(s), above the combustion chambers, and more efficiently drive the valvetrain. With less reciprocating mass, OHC engines can rev higher and are vastly more efficient than OHV engines. Also referred to as a pushrod engine, an OHV motor has the camshaft and lifters in the cylinder block and uses long pushrods to actuate the rocker arms above the head to open and close the valves. While less complex and smaller overall, an OHV engine has a heavy rotational mass which ultimately limits its ability to rev high.
5. Direct Injection
In modern vehicles, direct injection has begun to replace traditional multi-point fuel injection due to stricter emissions regulations and fuel economy requirements. Instead of spraying fuel into the intake manifold, direct injection relies on a special pump and injectors to highly pressurize the fuel before it is injected directly into the combustion chamber. Improved fuel atomization and leaner air/fuel ratios are possible with direct injection, resulting in more power and better fuel efficiency.
4. Distributor vs. Coil-on-Plug Ignition
In order to ignite the air/fuel mixture in each cylinder, a distributor routes high voltage from the ignition coil(s) to each individual spark plug in the correct firing order. In most cases, the distributor is geared off of the camshaft and is synchronized to send spark to each cylinder at precisely the right moment for optimal power. Direct or distributor-less ignition systems utilize a separate ignition coil for each cylinder, or one coil for two cylinders. In addition to being more reliable due to simplicity, direct ignitions can be more precisely controlled by the ECU, resulting in more power, better fuel economy and cleaner emissions.
Every time you fill up at gas station, you choose a fuel with a particular octane rating. But what do these numbers actually mean? Everyone knows that high-performance cars require premium fuel, such as 91 or 93 octane instead of 85 or 87. The octane value denotes how likely the fuel is to self-ignite; as you probably guessed, the higher the number, the less likely this is to occur. The goal of using a higher octane fuel is to prevent detonation that can occur at high cylinder pressures and increased temperatures.
2. Alternate Fuels
Rising oil prices during the last decade have necessitated the use of alternate fuels and vehicles designed accordingly. True flex-fuel vehicles can run standard gasoline or alternate fuels in any proportion and the ECU will automatically adjust for the mixture. Ethanol, or E85, is the most commonly used alternate fuel; although it is about 33% less efficient than gasoline, it is usually much cheaper. By mass, the stoichiometric ratio of ethanol is 9:1 (9 parts air to 1 part fuel), as opposed to 14.7:1 for gasoline. E85 is a blend of roughly 85% denatured ethanol and 15% gasoline or other hydrocarbon by volume. The real benefit of using ethanol is its higher octane rating compared to hydrocarbon fuels – around 105 for E85. This equates to a cooler intake charge, making it ideal for performance applications, particularly forced induction motors, where heat and high cylinder pressures can trigger detonation. In many cases, the ignition timing can be significantly advanced when using ethanol. Cars not equipped to run E85 can be converted by replacing certain fuel system components, such as the injectors and pump, and then re-tuning the ECU to accommodate for the changes.
1. Longitudinal and Transverse Engine Layouts
We’ll save the simplest for last – what’s the difference between a longitudinal and transverse engine? Longitudinal, like the name suggests, describes an engine in which the crankshaft is parallel to the long axis of the vehicle, from front to back. Most rear-wheel drive vehicles have a longitudinal engine layout, which favors a V8 or inline-6 motor. Transverse, on the other hand, is all about packaging. Popular in front-wheel drive applications, a transverse engine’s crankshaft is perpendicular to the long axis of the car. By utilizing a transverse layout, a larger engine (such as a V6) can be squeezed into a small engine bay, although the inline-4 configuration is the most common in passenger vehicles.