How Many Spark Plugs Do I Need?

I’ve been asked so many questions about the number and types of spark plugs a specific car needs that I’ve decided to sum it all up in one article, and explain all you need to know about spark plugs. But first, I’ll answer the question of how many sparks plugs you need.

You need as many spark plugs as there are cylinders in the engine of your car. For an inline-four, you need 4 spark plugs, for an inline-six or a V6, you need 6 spark plugs, and for a V8 you need 8 spark plugs. There are some exceptions that use 2 spark plugs per cylinder, like HEMI V8, Alfa Romeo Twin Spark, and some Mercedes Benz engines, as well as those of high-end motorcycles like the Honda VT500 and Ducati Multistrada.

How Spark Plugs Work

The spark plug is an ingenious electrical device designed to ignite the compressed gasoline by firing off a spark. The average lifespan of a spark plug is 80,000 miles, during which it can fire up to 110 million sparks!

Spark plugs sit at the top of the engine block, away from the crankshaft. The rotating movement of the crankshaft translates into the vertical rise of the piston that forces the air and gasoline mix to compress. When the aerosol gasoline reaches the ideal mixture and pressure, the ignition coil sends a signal to activate the spark plug. The resulting ignition pushes the piston down, and the cycle is repeated.

What Spark Plugs Do I Need?

The best rule for choosing spark plugs is to consult the owner’s manual or the manufacturer’s website and find the official spark plug specification for your engine. You can choose the brand type yourself, and you always upgrade to a higher-class spark plug if you want the added safety.

Spark plugs have to tackle two problems: heat generation and horsepower. Generally, these factors come in a pair, with a more powerful engine naturally generating more heat. If you’ve tuned or upgraded your engine parts to get more power, upgrading the spark plugs is the necessary next step.

What types of spark plugs exist?

There are four main types of spark plugs that have been developed over the years. Even though the early technology has been surpassed, the older types of spark plugs find their use in classic cars and small low-power engines.

Copper Spark Plugs

Copper spark plugs have a copper core with a nickel alloy coating on the part where the spark is generated. The drawbacks of the copper spark plugs are the low melting point of both copper and nickel, which means they cannot endure high-power engines. They also require the highest voltage out of all spark plugs and have the shortest lifespan.

However, copper spark plugs still have a wide range of uses, especially on older cars without direct fuel injection, where they won’t affect fuel economy. Copper spark plugs are also the cheapest, so there’s no need to upgrade if your engine uses them.

Platinum Spark Plugs

Platinum spark plugs replace the copper alloy tip with platinum, which significantly increases their lifespan. They also generate more heat which helps reduce carbon buildup, another factor that contributes to their longevity.

Double Platinum Spark Plugs

Double platinum spark plugs have a better platinum coating to make the plugs even more durable and long-lasting. They’re recommended for wasted spark systems, where spark plugs may see more wear.

A wasted spark system has been used on older vehicles to simplify design and eliminate the high-tension distributor. Rather than a single spark plug, each coil is connected to two spark plugs, which fire off at the same time. The name stems from how the system works – while one spark plug will ignite the air-fuel mixture in one cylinder, the other will spark when the cylinder is at the bottom of its travel, igniting nothing. This means that every other ignition of the spark plug is wasted and that the spark plugs fire off twice as often.

Iridium Spark Plugs

Iridium spark plugs are the most durable and have the highest tolerances to heat and power. Most modern vehicles are using iridium spark plugs as they require less voltage and lead to more complete combustion in comparison to other options. The only drawback of the iridium spark plugs is the higher price, which is somewhat balanced through the longer lifespan.

Silver Spark Plugs

Silver spark plugs cannot be considered one of the main types of spark plugs, but they’re still worth mentioning. Their lifespan is equal or slightly better than the copper spark plugs, and they were meant to be used on older performance cars. Nowadays these plugs are widely replaced by platinum alternatives.

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Signs of a Failing Spark Plug

When spark plugs start to fail, you’ll experience a number of problems with the engine. The first symptom is a rough and jittery idle, followed by problems with starting the engine.

Surging is another common problem, where the engine RPM becomes higher than normal to compensate for a faulty spark plug. Other symptoms include increased fuel consumption, poor acceleration, and characteristic engine misfire. If you’re experiencing any of these problems, it’s likely that one or more spark plugs have failed.

How to Change Spark Plugs

Changing spark plugs is not a complicated task that requires some precision and care. The only tool you’ll need is a spark plug wrench.

These are the steps of changing the spark plugs:

  1. Carefully remove the ignition coils off the spark plugs.
  2. Use the wrench to unscrew the old spark plugs.
  3. Place the new spark plugs in position, and screw them in without overtightening.
  4. Put the ignition coils back on.

And that’s all you need to do! It takes a few minutes per spark plug and doesn’t require any special skills to complete. Even if only one spark plug has failed, it’s still recommended to change the whole set to keep them in the same condition.

FAQs

What kind of spark plug is the best?

Iridium spark plugs are the most modern design that has superior reliability and firing efficiency than platinum or copper spark plugs.

Who makes the best spark plugs?

There are a number of great spark plug manufacturers: NGK, ACDelco, Champion, Denso, and Bosch.

How many spark plugs are in a V6?

A V6 engine has six spark plugs, one per cylinder, unless it’s a twin-spark system, in which case it uses 12 spark plugs.

How many spark plugs are in a V8?

Generally, V8 engines have eight spark plugs, but if it’s a Hemi or other high-performance V8, it uses 2 spark plugs per cylinder, so the total number of spark plugs is doubled to 16.

Do all spark plugs fit the same?

Not all spark plugs are made universal, and even if they fit, it doesn’t mean they’re rated for the engine of your car. When in doubt, always consult with the owner’s manual or the manufacturer to know exactly what type and rating of spark plug you need.

How much does it cost to replace spark plugs?

A mechanic will charge you between $40 and $150 depending on where you live, and the number of spark plugs your car uses. If you want to save some money, check out the how-to-replace spark plugs section to see what steps and tools are involved in a DIY job.

How many spark plugs does a 4-cylinder engine have?

Standard 4-cylinder engines have 4 spark plugs, one per cylinder, but some variants, like the Alfa Romeo twin-spark, have two spark plugs per cylinder, for a total of 8.

Summary

In most cases, the number of spark plugs you need matches the number of cylinders your car has. When you have to replace spark plugs, you shouldn’t change only the failed one, and instead, replace the whole set to keep it running consistently. If you’ve learned something by reading this guide, I’ll suggest checking out some of the other articles to learn more about car maintenance, repairs, and modifications!