Better Performance with Upgraded Miata Spark Plugs

How well your Mazda Miata runs has a lot to do with its spark plugs. Their main purpose is to ignite the fuel-air mixture in your engine so it keeps running.

In short, your engine won’t start or run without spark plugs. They might not look like they do much, but we can’t stress enough on how important their function is.

Spark plugs are consumable parts, which means they wear out and require timely replacement.

In this guide, we’ll show you the best spark plugs for your Miata MX-5, so you can choose the most suitable ones for your needs.

Don’t want the details, just want the products? Skip to our favorite Miata spark plugs.

Miata Spark Plug Selection: What You Need to Know

Spark plugs aren’t all the same. Every engine needs its own uniquely designed spark plugs.

If you’ve only recently taken an interest in the mechanics of your car, it may get overwhelming for you to choose the right spark plugs.

We think it’s best to stick to the owner’s manual if you want to know which spark plug type is ideal, and when to change it; unless you have a modified engine.

According to your Miata’s maintenance manual, the recommended spark plug change interval is at 30,000 miles.

As spark plugs get close to wearing out, they start affecting your car’s performance, reliability and gas mileage. Even though the mileage drop is almost negligible, it will cost you more than a set of new plugs before long.

With that said, we recommend changing them every 15,000 to 20,000 miles.

Gap Sizes

Every generation of the Mazda Miata requires a different gap size. Here are the gap sizes for a quick reference:

  • 1990 – 1998 NA: 0.040” – 0.044”
  • 1999 – 2005 NB: 0.040” – 0.044”
  • 1990 – 2005 Turbo Converted NA & NBs: 0.027” – 0.035”
  • 2006 – 2015 NC: 0.043” – 0.051”
  • 2016+ ND: 0.043” – 0.055”

Thread Size & Pitch

For your new spark plugs to fit properly, their threading needs to be of the correct size and pitch:

  • Thread Size: 14mm
  • Thread Pitch: 1.25mm

This is the same across all generations of Miata.

Construction

Spark plug technology has evolved over the years, and so has the process of selecting one. Back in the day, spark plugs would wear out a lot quicker and they needed to be dealt with very differently than what you see today.

The biggest improvement seen in spark plug design is the use of metals like platinum and iridium which have many advantages over copper plugs.

None of these materials are a bad choice. They have their pros and cons. Here’s what makes each one unique.

Copper

Copper is the most commonly used material for spark plugs because it does a great job at conducting heat and electricity. Copper spark plugs have a 2.5mm nickel electrode which is the largest electrode among all spark plug types. This electrode is paired with a copper core.

This is the reason why copper plugs give you the best spark quality but wear out much quicker than platinum or iridium plugs.

Even today, a lot of Miata enthusiasts prefer copper plugs. This makes sense because, with copper plugs, frequent replacement is the only price you pay for great performance.

If you drive an NA or NB Miata, copper plugs are your best option because they work really well with older cars.

Platinum

Platinum and copper plugs share a very similar design. The most important difference is the platinum disc thats welded under the side electrode.

Since platinum is a harder metal than zinc alloy and copper, it wears out a lot slower in comparison.

Performance-wise, platinum plugs aren’t as good as copper plugs but they last almost twice as long.

Platinum plugs are a decent choice for NC and ND Mazda Miatas but it isn’t our top recommendation.

Iridium

You can’t go wrong with iridium spark plugs. They’re the most widely accepted modern spark plugs out there.

The biggest difference between platinum and iridium plugs is that iridium plugs have a very thin firing pin and the center electrode is made of iridium.

Along with more longevity, you also get better firing efficiency with iridium spark plugs. These are best paired with newer cars.

Consider getting a pair of iridium plugs if you drive an NC or ND Miata.

Heat Range

Heat range is a unit of measurement for your spark plug’s tolerance towards heat. It is important to know that every manufacturer measures heat range on different scales.

Lower Number = Higher Heat Range (cold plug)
Higher Number = Lower Heat Range (hot plug)

A “cold plug” does a better job at managing heat and is suitable for modified engines which produce high levels of heat and horsepower.

If a cold plug is used in stock cars that produce less heat than what it is designed for, it’s electrode might get covered with carbon deposits. This will cause the plug to fail eventually.

A “hot plug” is the exact opposite. It is less tolerant of heat and is commonly found in stock cars.

If a hot plug is used in modified cars that produce more horsepower, it’s electrode might melt away because of overheating. This may lead to piston seizure which is very expensive and tedious to repair.

The Best Miata Spark Plugs

Once you know what’s required to get the right spark plug for your Miata, selecting one becomes very easy.

Here are some of the most widely purchased spark plugs for the Mazda Miata.

NGK Iridium

NGK Iridium 5464 spark plug suit NC & ND Mazda Miata MX-5

Manufacturer: NGK
Part Number: 5464 BKR5EIX-11 IX
Construction: Single Iridium
Electrode Tip: Iridium
Electrode Size: 0.6mm
Reach: 19mm
Hex: 16mm
Gap: 0.043 in
Heat Range: 5
Warranty: 1 Year
Suits: NC & ND
Buy On: Amazon

NGK needs no introduction. They make some of the best Miata spark plugs you can buy.

The best part about iridium electrodes is their high melting point. You will experience consistent performance throughout the lifespan of these plugs.

An electrode is a pin-like structure at the edge of the spark plug which generates the spark. A thin electrode will give you a sharper and more stable spark which makes the throttle feel very consistent and predictable.

The 5464 Iridium plugs by NGK come with a 0.6mm thin iridium electrode tip. This is paired with a copper core which helps redirect some heat away.

If you’re looking for NC Miata spark plugs which don’t have a high heat range but are still performance-friendly, these are the ones to go for.

Bosch Double Iridium

Bosch Double Iridium 9261 spark plug for ND Mazda Miata

Manufacturer: Bosch
Part Number: 9621
Construction: Double Iridium
Electrode Tip: Iridium
Electrode Size: 0.6mm
Reach: 26.5mm
Hex: 14mm
Gap: 0.043
Heat Range: 7
Warranty: 7 Years
Suits: ND
Buy On: Amazon

Unlike NGK, Bosch isn’t devoted to making only spark plugs. They’re one of the market leaders when it comes to automotive electronics in general. This includes vehicles of all kinds.

The double iridium spark plugs by Bosch have a laser welded Iridium inlay on the ground electrode. This is combined with the iridium firing pin, creating two sharp points for the spark to hold on to. That’s why it’s called “double iridium”.

This improves spark retention which gives you better gas mileage.

Denso Iridium Long Life

Denso Iridium Long Life 3297 SK20R11 spark plug for NC & ND Miatas

Manufacturer: Denso
Part Number: 3297 SK20R11
Construction: Iridium Pin + Platinum Tip
Electrode Tip: Iridium
Electrode Size: 0.7mm
Reach: 19mm
Hex: 16mm
Gap: 0.043in
Heat Range: 20
Warranty: 1 Year
Suits: NC & ND
Buy On: Amazon

Denso is known for making some of the highest-selling OEM and aftermarket parts.

Their 3927 spark plug is an OEM fit on many luxury cars. It works best with the NC and ND variants of the Miata.

This is the only spark plug featured here that uses a combination of iridium and platinum. Its ground electrode is platinum tipped and the firing pin is made of iridium. This combination gives you the performance of iridium and longevity of platinum in the same spark plug.

NGK Standard Copper

NGK 6593 BKR5E-11 Copper NA & NB Miata spark plug

Manufacturer: NGK
Part Number: 6593 BKR5E-11
Construction: Single Copper
Electrode Tip: Nickel
Electrode Size: 2.5mm
Reach: 19mm
Hex: 16mm
Gap: 0.043in
Heat Range: 5
Warranty: 1 Year
Suits: NA & NB
Buy On: Amazon | FR Sport

The good old NGK Standard; the most widely recommended set of spark plugs for the NA and NB Miata. Enthusiasts swear by it and claim that you don’t need to experiment with anything else.

Copper plugs are known to wear out quickly but the performance trade-off makes it a very compelling option.

They wear out quickly but are extremely cheap and so, there’s no excuse to not get them replaced frequently. Unless you’re lazy which you probably aren’t; otherwise you wouldn’t be driving an NA or NB Miata in 2019. Especially the NA.

These are the best NA Miata spark plugs you will find – you will find most other owners in the Miata community running the same in their Mk1 car.

NGK Standard (High Performance)

NGK 4644 BKR7E Copper NA & NB Miata turbo spark plug

Manufacturer: NGK
Part Number: 4644 BKR7E
Construction: Single Copper
Electrode Tip: Nickel
Electrode Size: 2.5mm
Reach: 19mm
Hex: 16mm
Gap: 0.035in
Heat Range: 7
Warranty: 1 Year
Suits: NA & NB Turbo Conversions
Buy On: Amazon

Think of these spark plugs as a high-performance variant of the NGK standard. They’re almost the same but have a much smaller gap along with a higher heat range.

Pair that with a 2.5mm nickel electrode on a copper plug and you’ll have the ideal turbo Miata spark plug setup.

These spark plugs have a higher tolerance towards heat which means they classify as cold plugs. So it’s best to avoid using these on a stock Miata because doing so may cause excessive carbon build-up.

Our Favorite Miata Spark Plugs

Switching the ignition on after installing a new set of plugs always makes us grin a little. We’d love to help you experience the same.

Here are two of the best Miata spark plugs on the market.

Best Option for NA & NB Miatas: NGK Standard Copper

NGK Standards are the best NA and NB Miata spark plugs you can get. They’re reliable and perfect for older cars. The exception to this rule is if you are running forced induction, in which case NGK’s 4644 BKR7E spark plugs are a better option.

Our Chosen NC and ND Miata Spark Plugs: NGK Iridium

Newer cars require modern spark plugs. Iridium plugs are the best option for the NC and ND Miatas because they’re easily compatible with the newer ignition systems seen on both these cars.

Which spark plugs are you running in your Miata? Let us know by leaving a comment below!

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