Can you start a V8 with a four cylinder car? It’s all about the amps – Jalopnik

Okay, we’ll admit from the start that this is kind of a trick question. Technically speaking, you can indeed give a V8 a flying start with a four-cylinder, but the ability to do so actually has nothing to do with the number of cylinders. Remember, you don’t need a moving car (or its engine) to get off to a flying start. You can also start a car without cables. What you do need are plenty of amps – and maybe a quick refresher on what actually happens when you start a car this way.

Normally, you turn the key in your ignition (or press the starter button), which allows your car’s starter motor to draw electricity from the battery to get the engine parts moving. When you jump into a car, whether you rely on jumper cables or portable jump starters, it’s that external source that provides the electricity instead. Once the engine of the second car starts and runs for a few minutes, it will be enough to charge its own battery and you can disconnect it from the jumper source. So the key here is that you need enough electrical power (measured in amps) to run the engine of the car you’re jumping into.

This does mean that larger engines with more cylinders will likely require more electrical power to start than smaller engines. But that’s because of their weight, not necessarily the number of cylinders. And it still means you need to know how many amps your jumper provides compared to how many the target motor requires.

Ampère, usually shortened to amplifiers, are named after André-Marie Ampère, a French mathematician/physicist who worked in the early 19th century – although the current definition of an amplifier was only formalized in 2019. We’re not going to wade too deeply into those waters, but you can think of an amplifier as a measure of how fast the current of electricity flows. However, in the automotive world this is usually refined into cranking boosters (CA) and cold starting boosters (CCA). Both measure how many traditional amps the battery can deliver over a 30-second period without the voltage dropping below 7.2 volts; CA takes the measurement at 32 degrees Fahrenheit and CCA takes it at 0 degrees Fahrenheit.

It takes about 400-600 CCA to get a typical gas car going. But as mentioned, the larger the motor (in terms of the weight of the rotating components), the more amplifiers you need. For example, a truck with a heavy diesel engine may require 1,000 CCA. Cold weather and older batteries can also increase CCA requirements. Of course, the best way to know how many amps you need for a specific vehicle’s battery is to consult its owner’s manual. (Here’s a bonus tip if you’re shopping: The best car batteries aren’t always the most expensive, according to Consumer Reports.)

While an electrical source with the correct number of amps is essential to jump-starting a car, you can rest easy knowing that using the wrong number of amps generally won’t damage your car. But if you use too few amps, your vehicle will obviously not start either.

Thanks to the workings of Ohm’s law, an electrical device – such as a car with a dead battery – is limited to the number of amperes it directly draws, based on voltage and resistance. We’ll have to do a bit of math on readers here, but the relevant formula is essentially current (amps) = voltage/resistance (ohms). In other words, as long as the good and bad batteries have the same voltage and resistance, current flows at the same rate. (Ohms, by the way, are named after one of Ampère’s contemporaries, the German scientist Georg Ohm.)

With all this talk about traditional 12-volt car batteries, you may be wondering about the growing number of non-traditional cars with 48-volt architecture, also known as mild hybrids. The good news is that these vehicles still use 12-volt batteries to start, so jumping should be as easy as jumping any other gas-powered car. The bad news? If the 48-volt system fails, a new mild hybrid battery can cost an average of $1,500.