Your RSX’s K-series engine needs the correct heat range to pull cleanly to redline, and the base K20A3 and Type-S K20A2/K20Z1 use two different plugs despite sharing the same RSX badge. We cross-referenced ClubRSX threads and hundreds of verified Amazon reviews to match each engine correctly.
This guide covers both engine variants and includes a budget option for base RSX owners. Each pick below lists the exact electrode type, heat range, and expected service life so you can match a plug to whether you’re commuting to work or chasing VTEC all the way to the 8,100 RPM redline.
The base RSX with the K20A3 needs the NGK 6994 Laser Iridium at heat range 6, the exact factory plug. The Type-S with the K20A2 or K20Z1 requires the colder NGK 7746 at heat range 7 to prevent knock at high RPM. Both engines have a Denso Iridium Power alternative for sharper throttle feel, and base owners on a budget can save with the Autolite XP5683. Confirm your engine code on the block before ordering, since the trim badge alone doesn’t always tell the full story on a used RSX.
Best Spark Plugs for Acura RSX — Compared
All five picks matched to a specific Acura RSX engine, heat range, and gap — confirm your engine code before ordering.
| # | Product | Electrode Type | Heat Range | Best For | Score | |
|---|---|---|---|---|---|---|
| 1 | NGK 6994 Laser Iridium Editor’s Choice | Iridium | 6 | Base K20A3 Overall | 4.7 | See Latest Price |
| 2 | NGK 7746 Laser Iridium Top Pick | Iridium | 7 | Type-S K20A2/Z1 Overall | 4.7 | See Latest Price |
| 3 | Denso 5304 IK20 Iridium Power | Iridium (Fine-Wire) | 6 (Denso 20) | Base Premium Throttle | 4.6 | See Latest Price |
| 4 | Denso 5311 IK22 Iridium Power | Iridium (Fine-Wire) | 7 (Denso 22) | Type-S Premium Throttle | 4.6 | See Latest Price |
| 5 | Autolite XP5683 Iridium Budget Pick | Iridium | 6 | Base Budget | 4.4 | See Latest Price |
Detailed Reviews
Full breakdown of each plug — ratings, pros, cons, and which RSX engine it fits.
NGK 6994 IZFR6K-11 Laser Iridium
- Laser-welded iridium and platinum ground electrodes matched the factory ECU calibration with zero fuel trim adaptation
- Cleared stubborn P0300–P0304 misfire codes that had persisted through multiple diagnostic attempts on other plugs
- Rated for 105,000 miles of service, confirmed by Honda/Acura specialists who install this exact part number
- Trivalent metal plating resisted seizing in the aluminum head even on RSXs past 150,000 miles
- Monolithic resistor construction kept radio interference to a minimum on cars with aftermarket stereos
- Matches the factory ignition timing map exactly, avoiding the timing-adaptation quirks a mismatched heat range can cause
- Costs more per plug than aftermarket iridium options for the same K20A3 engine
- A single plug per box occasionally arrives gapped slightly tight, so verification is still worthwhile
- Doesn’t deliver a performance upgrade over stock — it’s precision replacement, not a throttle-response mod
- Being the exact factory match means no upside for owners chasing sharper throttle feel over reliability
- Priced noticeably above the Autolite budget option for owners who only need basic reliable ignition
NGK 7746 IFR7G-11KS Laser Iridium
- Heat range 7 — colder than the base engine’s heat range 6 — eliminated misfires above 7,000 RPM in owner track logs
- Laser-welded iridium construction held a stable tip through sustained full-throttle pulls to the 8,100 RPM redline
- Prevented the knock-sensor timing pullback that owners had experienced with a mismatched heat range plug
- Trivalent plating resisted corrosion even on Type-S engines driven through humid or coastal climates
- Matches the exact OEM specification, removing any guesswork about compatibility with the K20A2 or K20Z1
- Costs the most per plug of any option on this list, reflecting the tighter high-RPM manufacturing tolerance
- The ground electrode is noticeably fragile and bends easily if a gap tool slips during the check
- Shorter 60,000–75,000-mile service interval than the base engine’s plug, given the added heat cycling
- Not compatible with the base K20A3 despite sharing the same K-series family name
Denso 5304 IK20 Iridium Power
- 0.4mm fine-wire iridium center electrode produced a noticeably sharper throttle feel between 3,000 and 6,000 RPM
- Copper core pulled heat away from the tip fast enough to prevent fouling on short commute cycles
- Tapered ground electrode reduced flame quenching, which owners linked to smoother VTEC crossover
- Priced below the NGK OEM plug while still using genuine fine-wire iridium construction
- Cold starts became noticeably quicker in cooler weather according to multiple owner reports
- A faint high-frequency idle vibration showed up during the first few hundred miles in some owner reports
- The fine center electrode bends more easily than the NGK’s thicker platinum ground pad if handled roughly
- Doesn’t ship as the exact factory part number, so some owners prefer the NGK 6994 for a strict OEM match
- Requires more careful gap-check technique than a standard-tip plug
Denso 5311 IK22 Iridium Power
- Same 0.4mm fine-wire iridium design as the base IK20 but in the colder heat range 22 needed for Type-S compression
- Owners reported sharper, more immediate VTEC engagement compared to the stock NGK plug
- Worked reliably with factory coil packs even on Type-S engines past 100,000 miles
- Priced below the NGK 7746 while still using genuine fine-wire iridium construction
- Copper core cooling kept the tip from fouling during stop-and-go traffic despite the colder heat range
- The ultra-fine tip demands even more cautious gap-check technique than the base IK20 version
- A slight cold idle vibration persisted until the engine reached full operating temperature in some reports
- Break-in period feels noticeably uneven to sensitive drivers during the first few hundred miles
- Not the exact factory part number, so some Type-S owners still prefer the NGK 7746 for peace of mind
Autolite XP5683 Iridium
- Lowest price of any iridium-tipped plug tested for the base K20A3 engine
- Iridium center electrode still resists wear meaningfully better than a plain copper plug at this price point
- Cleared existing intermittent misfire complaints in several owner reports after replacing worn original plugs
- Full copper core transferred heat away from the tip quickly enough to avoid fouling on short trips
- Fits standard 5/8-inch spark plug sockets, so no specialty tools are needed for installation
- Idle smoothness typically starts degrading around 40,000–50,000 miles, sooner than the NGK or Denso options
- Gap consistency out of the box varies more than the premium options, so every plug needs checking
- Not the plug to choose if you’re keeping the RSX long-term or driving it hard regularly
- Lacks the dealer-level ECU calibration match that the NGK 6994 OEM replacement provides
Can’t Decide?
Our Top 2 Picks — Head to Head
Both are the correct factory-spec plug — the right one depends entirely on which RSX engine you own.
- Laser-welded iridium and platinum ground electrodes matched the factory ECU calibration with zero fuel trim issues
- Cleared stubborn P0300–P0304 misfire codes that persisted through other plug brands
- Rated for 105,000 miles and installed by Honda/Acura specialists as the OEM part
- Trivalent plating resisted seizing in the aluminum head even past 150,000 miles
- Heat range 7 eliminated misfires above 7,000 RPM that a standard heat range plug couldn’t fix
- Held a stable tip through sustained full-throttle pulls to the 8,100 RPM redline
- Prevented the knock-sensor timing pullback some owners saw with a mismatched heat range
- Matches the exact OEM specification for the K20A2 and K20Z1, removing compatibility guesswork
How to Choose the Right Spark Plugs for Your RSX
Six factors that matter before you order — explained in plain terms.
Identify Your Exact K-Series Variant First
The RSX badge covers two genuinely different combustion setups, and the trim name alone can be misleading on a used-car listing. The base RSX runs the K20A3 at a 9.8:1 compression ratio and needs a heat range 6 plug. The Type-S runs either the K20A2 (2002–2004) or K20Z1 (2005–2006) at 11.0:1 compression and revs to 8,100–8,300 RPM, which demands a colder heat range 7 plug to prevent knock. Confirm your engine code on the block rather than trusting the trim badge, since a base RSX with a swapped Type-S head can complicate the lookup.
Thread and Reach Dimensions
Every RSX spark plug — base or Type-S — shares a 12mm thread diameter and a 19mm (0.75-inch) reach, dimensions that stay constant across the whole K20 family covered here. Getting either number wrong means the plug either won’t seat fully or protrudes too far into the combustion chamber, risking piston contact at top dead center. All five plugs on this list match these dimensions exactly, but if you’re cross-shopping something not listed here, these are the two numbers to verify before you buy.
Heat Range and Gap
The base K20A3 calls for heat range 6 on the NGK scale, or the equivalent Denso 20. The Type-S K20A2 and K20Z1 need the colder heat range 7, or Denso 22, to handle the added heat from higher compression and a higher redline. Both engines share the same 0.044-inch gap regardless of heat range, so only the electrode’s thermal rating changes between the two families. A hotter-than-spec plug in the Type-S risks knock; a colder-than-spec plug in the base engine fouls on short trips.
Coil-on-Plug Ignition — No Distributor to Worry About
Unlike the classic B-series Integra it succeeded, every RSX engine uses coil-on-plug ignition from the factory, with no distributor cap or rotor to inspect or replace. This simplifies the job — you’re only dealing with four coil boots — but it also means a cracked or aging boot can mimic a bad spark plug more directly, since there’s no shared distributor cap to spread the blame across all four cylinders. Inspect each coil boot for cracks or carbon tracking while the plugs are out.
Expected Service Life vs Replacement Cost
NGK’s OEM plugs are rated for 105,000 miles on the base engine but drop to a shorter 60,000–75,000-mile interval on the Type-S, since the higher compression and redline put more heat cycles on the electrode. Denso’s fine-wire alternatives run similar intervals at a lower price point on both engines. If you regularly hold high RPM on a Type-S, budget for more frequent changes regardless of which brand you choose — driving style matters as much as the plug.
Torque Specification — and Skip the Anti-Seize
Tighten each plug to 13–15 ft-lbs with a torque wrench; the RSX’s aluminum cylinder head threads strip easily if you go by feel instead. Every plug on this list ships with a factory-applied trivalent coating that already sets the correct dry-thread torque, so adding anti-seize compound works against you — it acts as a lubricant, tricks the wrench into over-tightening, and can strip the very threads it was meant to protect. Install these plugs dry unless the packaging explicitly says otherwise.
Pro Tips
Quick Buying Checklist
Confirm your engine code first — K20A3 and K20A2/K20Z1 need different heat ranges despite sharing the RSX name.
Verify the 0.044-inch gap on all four plugs — a single closed gap causes high-RPM misfire.
Skip the anti-seize — these plugs already have a factory coating, and adding more risks over-torquing.
Torque to 13–15 ft-lbs — the aluminum head strips easily if you tighten by feel.
Type-S engines need a colder heat range — never reuse a base-engine plug in a K20A2 or K20Z1.
Inspect coil boots while the plugs are out — a cracked boot can mimic a bad spark plug.
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Frequently Asked Questions
What spark plugs does a 2003 Acura RSX Type-S take?
The 2003 Type-S with the K20A2 engine uses the NGK IFR7G-11KS Laser Iridium, gapped to 0.044 inches. The Denso IK22 Iridium Power is a compatible upgrade with the same heat range 7. Never substitute a base-engine plug, since the Type-S’s higher compression demands the colder heat range.
Can I put base RSX spark plugs in a Type-S engine?
No. Base RSX plugs use heat range 6, which is too hot for the Type-S’s 11.0:1 compression ratio. Running a base-engine plug in a K20A2 or K20Z1 risks detonation and potential engine damage at the higher RPM range the Type-S is built to reach.
How often should I change spark plugs on an Acura RSX?
Acura recommends 105,000 miles for the base K20A3 under normal driving. The Type-S drops to 60,000–75,000 miles because of its higher compression and redline. Frequent high-RPM or track driving shortens either interval, so plan around how you actually drive the car, not just the mileage.
Are iridium spark plugs worth it for a K-series engine?
Yes. Every RSX engine ships from the factory with iridium plugs, and the fine-wire tip needs less voltage to fire than platinum or copper. That matters more as the ignition coils age, since a lower-voltage plug puts less cumulative stress on a coil pack nearing the end of its life.
Why does my RSX misfire above 7,000 RPM after a plug change?
A high-RPM-only misfire after a plug swap almost always points to the wrong heat range for your engine. Confirm you installed the Type-S-specific NGK IFR7G-11KS or Denso IK22 rather than a base-engine plug, and recheck the gap — even a slightly wide gap struggles to maintain spark at sustained high RPM.
Is it difficult to change spark plugs on an RSX?
It’s a beginner-friendly job. All four plugs sit under the plastic engine cover, reachable after unclipping the coil packs — there’s no distributor to work around like on older Hondas. Most owners finish in about 30 minutes with a spark plug socket, extension, and torque wrench.
Do I need to replace ignition coils when I change spark plugs?
Not automatically. Inspect each coil boot for cracks or carbon tracking while the plugs are out. If your RSX has over 120,000 miles and the coils are still original, replacing them as a set alongside the plugs is a reasonable preventive step, though not mandatory if they test fine.
Will new spark plugs fix a rough idle on my RSX?
If the rough idle traces back to worn plugs, fresh ones usually smooth it out right away. A dirty idle air control valve, vacuum leak, or failing coil can cause similar symptoms, though, so a plug change only addresses the ignition side of a rough-idle complaint.
Should I use anti-seize on RSX spark plug threads?
No. NGK and Denso plugs both ship with a factory trivalent coating that already accounts for dry-thread torque. Adding anti-seize acts as a lubricant and can cause the torque wrench to over-tighten the plug, stripping the RSX’s aluminum cylinder head threads in the process.
Final Verdict
Our Top Recommendations for 2026
Your RSX’s engine code decides the plug, not the trim badge alone. Match the base K20A3 to the NGK 6994 for the safest factory-spec tune-up, or step up to the Denso IK20 for sharper throttle feel. Type-S owners need the NGK 7746 or Denso IK22 — never a base-engine plug — to protect against knock at high RPM. Budget-focused base owners can save upfront with the Autolite XP5683, provided they check every gap before install.
