Best Spark Plugs for 3.5 Ecoboost: OEM and Replacement Plugs Reviewed

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Ford's 3.5 EcoBoost provides outstanding performance per liter and fits modern ecology requirements at the same time. To make it happen, engineers used the best technology available right now, including an ignition system and spark plugs themself. In this article, we'll review OEM plugs and see what are the best replacements for them.
Ford’s 3.5 EcoBoost engine is a modern twin-turbocharged V6 engine. It is capable of producing from 310 HP in Ford Transit up to 660 HP in Ford GT, but the majority of those engines output 365 or 375 horsepowers and 420-470 lb-ft of torque. This engine has the same power and torque numbers as older big V8s. Actually, it was specifically designed to replace bigger displacement engines while providing better efficiency. Ford disproves saying “there’s no replacement for displacement” with modern components and systems: ECU, turbochargers, injection, and ignition. With all technologies implemented, conditions inside the cylinder became way tougher: more pressure, hotter temperatures, bigger loads. To operate in those conditions, 3.5 EcoBoost spark plugs must correspond to the engine’s performance. Let’s see what spark plugs can fit the 3.5 EcoBoost engine and what of them are the best.

3.5 EcoBoost Engine Specs

Bore x Stroke 3.92 in x 3.58 in (99.49 mm x 90.88 mm)
Displacement 345 cu in (5.654 cc)
Power 310-660 hp
Torque 400-550 lb-ft
Layout V6
Spark plugs 6
Valves 24
Production years 2003-present
Applications Ford: F150, Flex, Explorer, Expedition, Taurus, Transit
Lincoln: MKS, MKT, Navigator

💡Consider the following: gen 1 and gen 2 3.5 EcoBoost spark plugs are the same - no matter what engine year you have, all reviewed plugs will fit.

How We Find the Best Spark Plugs for 3.5 EcoBoost?

We have no secrets. Finding the best plugs for a 3.5 EcoBoost is a fairly easy yet time-consuming process. You can do it on your own, but we’ve done it for you to save your time. Here are the steps of the research.

1. Find the OEM plug

It all starts from recommended plugs. For 3.5 EcoBoost is Motorcraft SP-534.

Screenshot from 2015 Ford F150 owner’s manual

From it, we see that the OEM plug is Motorcraft SP-534, so we are able to know its dimensions and specifications to find replacement plugs.

OEM Spark Plugs Specifications

Reach25 mm
Thread14 mm x 1.25 mm
Gap.031″ (0.8 mm)
Seat typeTapered
Heat range6

All spark plugs must have the same characteristics to make a perfect fit with 3.5 EcoBoost.

2. Find cross reference spark plugs

We’ve collected a comprehensive spark plugs database, part of which was released to the public access as a spark plug cross reference tool. We filter the database by OEM characteristics to get the complete list of plugs that will fit.

3. We evaluate their features

The important parameters, besides must-have specifications, are:

  • Electrode materials (longevity)
    Spark plug reliability and longevity depend on them. The best materials are platinum, iridium, and ruthenium (by reliability ascending)
  • Ground electrode design (performance)
    It impacts performance and efficiency by how well ignited A/F mixture will spread. There is a great article from NGK on this topic.
  • Price (value)
    Everything is relative, right? We evaluate how the spark plug’s price correlates with its features in comparing with other plugs.
    Another parameter we consider is miles per cent (longevity/price ratio).

Using this methodology, we’ve compiled a list of best spark plugs for 3.5 EcoBoost engines for any needs, check it out!

Motorcraft SP-534 - OEM Spark Plugs for 3.5 Ecoboost

MaterialsCopper + Iridium
Appr. price$7.5
Electrode designStandart
up to 60 000 mi

Featuring copper center electrode and iridium ground one, their reliability is greater than copper+copper combo but lesser than double platinum or iridium ones.

3 out of 5

Motorcraft iridium spark plugs for 3.5 EcoBoost aren’t made for performance. Their ground electrode has a standard square shape, which works fine but is not the most effective design in terms of performance.

4 out of 5

Considering its price of around 7 bucks per plug and decent mileage, they are a good cost-effective solution for the 3.5 Ecoboost.

If you need an OEM spark plugs, those are exactly what you are looking for

Bosch HR7NII332W - Best Spark Plug for 3.5 Ecoboost

Brand Bosch
Code 9697
Materials Double Iridium
Appr. price $8
Gap .031″
Electrode design Taper cut
up to 100 000 mi

This plug has both center and ground electrodes made of iridium. This makes the plug much more durable, resulting in an almost x2 mileage increase compared to OEM.

4 out of 5

Instead of the square-shaped ground electrode, it features a taper cut design, meaning the 2 corners are cut creating fewer obstacles for fire to grow, improving the ignition, performance and efficiency.

Overall value
5 out of 5

It has better materials and improved efficiency in comparison to OEM. The good news is those upgrades don’t affect much a price: it costs only 50 cents more.

Those plugs are all-around better than OEM, but costs about the same - a great deal!

NGK LTR6BHX - Best Performance Spark Plug for 3.5 EcoBoost

MaterialsPlatinum + Ruthenium
Appr. price$12+
Electrode designProjected square
up to 120 000 mi

This plug features new material – ruthenium. It’s more durable than iridium, thus it increases the plug’s lifespan beyond 100k miles and decreases misfires. This is the best durability out there.

5 out of 5

The projected square platinum electrode provides even better ignitability than the tapered cut electrode. NGK patented this design and recommends it for turbo and supercharged engines – a perfect fit for the EcoBoost engine. Those are the best 3.5 EcoBoost spark plug upgrade currently available on a market.

Overall value
4.5 out of 5

It’s the most expensive plug out there with almost twice the price of an OEM plug. Instead, it provides twice a lifespan and better performance, so the price difference is not a big thing, especially considering innovative electrode design and materials. However, it’s a newer plug and prices vary a lot since there aren’t many of them on a market yet.

If you need uncompromising performance this one is for you

☝️ Note: If you've boosted up your engine, it's recommended to choose one grade colder spark plugs to compensate for extra heat to keep the plug running in the optimal temperatures. NGK LTR7BHX are the same as other NGK spark plugs for 3.5 EcoBoost from the article, but one step colder (you can tell it from its code) - we recommend them because best-in-class performance is a must for tuned engines.

Those are 3 spark plugs worth your attention. There are more plugs that fit the engine but don’t bring anything on a table and loose in terms of value. Those worth mentioning plugs are:

  • Champion 7004, 9016
  • NGK LTR6CI-8
  • Autolite XP5363, XP5683, XP5863
  • Pulstar IEF1H
  • E3 E3.74

FAQ on 3.5 EcoBoost Spark Plugs

How many spark plugs does 3.5 EcoBoost have?

The 3.5 EcoBoost is a V6 engine with one spark plug per cylinder, totaling 6 spark plugs for the engine.

When to change plugs on 3.5 EcoBoost?

It depends on the plugs you are using. OEM Motorsport 3.5 EcoBoost spark plug change interval is 60k miles. If you install the same plugs, the next change will be also after 60k miles. If you decide to change spark plugs, the 3.5 EcoBoost spark plug replacement interval will correspond to the plugs’ lifespan from the manufacturer.

What is the 3.5 EcoBoost spark plug socket size?

The socket size for 3.5 EcoBoost plugs is 5/8 inches or 16 millimeters.

What is the 3.5 EcoBoost spark plug torque spec?

Considering its block is made of aluminum alloy, the torque spec for plugs is 15 Nm or 11 lb-ft.

What is the spark plug gap for 3.5 EcoBoost?

The optimal gap for 3.5 EcoBoost spark plugs is .30″-.33″ or 0.75-0.85 mm. The OEM gap is .31″ or 0.8 mm.

What are the best spark plugs for 3.5 EcoBoost?

In terms of value, it’s Bosch HR7NII332W; in terms of performance, it’s NGK LTR6BHX.