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The Acura RSX Type-S runs the high-compression K20A2 engine (K20Z1 for 2005-2006), which needs a specific NGK or Denso plug and heat range — this is not an engine where a generic ‘2.0L 4-cylinder’ plug listing is safe to trust. The K-series also has an unusually deep tuner aftermarket, so which plug is ‘best’ really depends on whether your car is stock, built/naturally-aspirated, or running boost. These nine real, fitment-verified options are organized around that: OEM at stock heat range, then colder steps as power goes up.
| # | Product | Price | Where to buy |
|---|---|---|---|
| 1 | NGK IFR7G-11KS | $60-$87 for 4 | Amazon · eBay |
| 2 | NGK IZFR6K11 | $55-$85 for 4 | Amazon · eBay |
| 3 | NGK BKR7EIX-11 (Iridium IX, stock heat range) | $30-$45 for 4 | Amazon · eBay |
| 4 | NGK BKR8EIX (one step colder) | ~$29-$35 for 4 | Amazon · eBay |
| 5 | NGK BKR9EIX (two steps colder) | ~$30-$40 for 4 | Amazon · eBay |
| 6 | Denso SK22PR-M11S Iridium Long-Life | $28-$35 for 4 | Amazon · eBay |
| 7 | Denso Iridium Power IK22 | $8-$21/plug ($32-$84 for 4) | Amazon |
| 8 | HKS Super Fire Racing M45IL | ~$24/plug ($100-$115 for 4) | Amazon · eBay |
| 9 | Autolite Iridium XP | $5-$15/plug ($20-$60 for 4) | Amazon · eBay |
The picks, in detail
NGK IFR7G-11KS
The exact factory OEM spark plug Honda specified for the 2002-2004 RSX Type-S K20A2, sold under NGK’s own part number and as Acura part 98079-571BV. The right choice for a stock or lightly modified 02-04 car.
- OEM-specification plug for 2002-2004 K20A2
- Iridium center electrode with platinum-tipped ground electrode
- 0.044″ factory gap
- Guaranteed-correct factory heat range and gap for the 2002-2004 K20A2
- The plug used by Honda from the factory, not a generic substitute
- Higher price than the aftermarket NGK Iridium IX alternative below
NGK IZFR6K11
The correct OEM-spec plug for the later 2005-2006 RSX Type-S (K20A2/Z1/Z3), which runs a different heat range than the earlier 2002-2004 cars — do not cross-shop these two years’ plugs. Also the right choice for a stock or lightly modified 05-06 car.
- OEM-specification plug for 2005-2006 K20A2/Z1/Z3
- Different heat range than the 2002-2004 IFR7G-11KS
- Iridium-tipped design
- Correct fitment specifically for the later Type-S production years
- Same OEM reliability tier as the IFR7G-11KS
- Easy to mistakenly order the wrong-year plug — double-check your model year before buying
NGK BKR7EIX-11 (Iridium IX, stock heat range)
An aftermarket iridium plug at the correct stock heat range for the K20A2/Z1/Z3, commonly used by RSX owners as a lower-cost alternative to the OEM IFR7G-11KS on a stock or naturally-aspirated built engine.
- Same stock heat range as OEM K20A2 plugs
- Fine-wire (0.6mm) iridium center electrode
- 0.030″ gap (narrower than OEM’s 0.044″)
- Roughly half the price of the OEM NGK plug
- Widely used and recommended in K20-series owner forums
- Different electrode gap than OEM — verify gap before installing if your ignition system is sensitive to it
NGK BKR8EIX (one step colder)
One heat range colder than stock, aimed at tuned, track-driven K20A2 engines producing roughly 400-600 whp — the step up once you’ve moved past bolt-ons into real tuning.
- One heat range colder than the stock BKR7EIX
- Fine-wire iridium electrode
- Positioned for tuned/track engines
- Correct next step once a stock-heat-range plug starts showing signs of pre-ignition under load
- Widely stocked by K-series tuner shops
- Too cold for a genuinely stock engine — can cause fouling if you’re not actually making the power to justify it
NGK BKR9EIX (two steps colder)
Two heat ranges colder than stock, the step tuners reach for on heavily boosted K20A2 builds pushing past roughly 600 whp.
- Two heat ranges colder than the stock BKR7EIX
- Fine-wire iridium electrode
- Positioned for high-boost, high-power builds
- Correct choice for serious forced-induction builds where a warmer plug would pre-ignite
- Same NGK Iridium IX reliability tier as the milder steps
- Will foul quickly if installed in anything short of a genuinely high-power boosted engine
Denso SK22PR-M11S Iridium Long-Life
Denso’s OEM-equivalent iridium long-life plug for the K20A2 at stock heat range, sold under Denso’s own part number as a direct alternative to the NGK OEM plug for a stock or lightly modified car.
- 90% iridium fine-wire center electrode
- Platinum ground electrode
- Rated for sustained performance over 100,000 miles
- A genuine second OEM-tier brand option, not just an NGK-only choice
- Long service-life rating
- Less commonly discussed in RSX/K20 owner communities than the NGK options
Denso Iridium Power IK22
Denso’s Iridium Power line at IK22, the stock heat range for the K20A2 — a distinct Denso product tier from the SK22PR-M11S Long-Life plug above, aimed at drivers who want Denso’s performance-oriented line rather than its long-life line.
- Iridium Power fine-wire electrode
- IK22 = stock heat range for K20A2 (IK24/IK27 are colder steps for tuned/boosted engines)
- Performance-oriented Denso tier
- Genuinely distinct chemistry/tier from Denso’s Long-Life line, not a rebrand
- Denso also sells IK24 and IK27 in the same family for tuned or boosted cars if you want to stay in one brand as power goes up
- Price varies widely by retailer — confirm before ordering
HKS Super Fire Racing M45IL
A racing-grade iridium plug from HKS, explicitly sold as compatible with the 2002-2006 Acura RSX K20A2 — the performance-brand option for a built or track-focused car rather than a daily driver.
- Iridium racing-spec electrode
- Explicitly listed for 2002-2006 RSX K20A2
- Heat range options across the M-series line
- A genuine racing-parts brand rather than a mainstream automotive plug maker
- Popular in the K-series track/time-attack community
- The most expensive option on this list
Autolite Iridium XP
Autolite’s iridium fine-wire plug line, confirmed cheaper than the NGK OEM option — a budget iridium alternative for a stock or mildly modified car rather than a platinum downgrade.
- Iridium-enhanced 0.6mm fine-wire electrode
- Patented platinum sidewire technology
- Rated up to 100,000-mile service life
- Cheapest genuine iridium option on this list
- Real cost saving versus the NGK/HKS options at a comparable stock heat range
- Least discussed in K-series/RSX owner forums of the options here
Buying tips
- The K20A2 (2002-2004) and K20Z1 (2005-2006) Type-S engines use different spark plug heat ranges — always match the plug to your exact model year, not just ‘RSX Type-S’ generically.
- Heat range is the real decision on this engine: stay at stock heat range (IFR7G-11KS/IZFR6K11, BKR7EIX-11, SK22PR-M11S, IK22) if the car is stock or lightly bolted-on; step to BKR8EIX/IK24 for tuned or track engines around 400-600 whp; step to BKR9EIX/IK27 for serious boost past that.
- Iridium plugs come pre-gapped from the factory; the NGK BKR-series’ 0.030″ gap differs from the OEM 0.044″ gap, so don’t assume all iridium K-series plugs share the same gap.
- This engine only takes 4 plugs (inline-4), so make sure any ‘K20’ listing you buy isn’t mispackaged for a V6 application.
- Stick to iridium (not platinum) plugs under any amount of boost — platinum’s wider spark gap performance is not designed for forced-induction cylinder pressures.
As an Amazon Associate and eBay Partner, toptenpick.com earns from qualifying purchases. Prices and availability are subject to change.