Indmar Marine Sparks Plug Kit – 5.7L Iridium | Catalyst Exhaust Engine | Part #491009

Upgrade your ignition system with this genuine Indmar iridium spark plug kit, specifically designed for Indmar 5.7L engines fitted with a catalyst exhaust system. Iridium plugs represent the pinnacle of spark plug technology — delivering stronger, more consistent sparks, longer service life, and measurably better performance compared to standard plugs. If you want the best ignition performance from your catalyst-equipped Indmar 5.7L — iridium is the answer.

Compatible with: Indmar 5.7L marine engines fitted with catalyst exhaust systems on Malibu, Moomba, Supra, and Tige boats. Contact us to verify fitment for your specific model year 

Catalysed or Non-Catalysed — critical to get right
Using the incorrect spark plug specification in a catalyst exhaust engine is one of the most damaging and costly mistakes you can make. The wrong plug can:

• Cause incomplete combustion that floods and permanently damages the catalytic converter
• Create combustion temperatures outside the safe operating range of the catalyst
• Void your warranty on catalyst exhaust components
• Result in failed emissions compliance checks
• Cause poor engine performance, misfires, and increased fuel consumption

Always confirm your exhaust system type before ordering spark plugs. If you are unsure whether your engine has a catalysed or non-catalysed exhaust system — contact us before ordering and we will help you identify the correct plug for your specific setup.

Looking for the non-catalysed version?
If your Indmar 5.7L is fitted with a non-catalysed exhaust system see:

• 491008 – Spark Plug 5.7L Standard Non-Catalysed

What's included in the kit?
This is a complete plug kit containing all 8 iridium spark plugs required for the Indmar 5.7L V8 engine — everything you need for a full ignition service in one part number. No need to count individual plugs or worry about ordering the wrong quantity. One kit — complete engine coverage.

Iridium vs Standard — is the upgrade worth it?
Absolutely. Here's why iridium plugs are worth the investment for a catalyst marine engine:

Longer service life
Iridium is one of the hardest metals on earth — the ultra-fine iridium electrode tip resists wear far better than standard nickel electrodes. While standard plugs should be replaced every season, iridium plugs can last significantly longer — reducing the frequency of ignition services over the life of your engine.

Stronger more consistent spark
The fine wire iridium tip requires less voltage to fire — producing a stronger, more focused spark that ignites the air/fuel mixture more completely and consistently. The result is:

• Smoother idle and throttle response
• Better cold start performance — particularly after winter storage
• More complete combustion for improved fuel efficiency
• Reduced misfires under high load on the water
• Cleaner combustion that is gentler on your catalyst exhaust system

Better catalyst protection
This is particularly important for catalyst exhaust engines — iridium plugs promote more complete combustion, meaning less unburnt fuel passes through to the catalyst. Unburnt fuel reaching the catalyst causes overheating and premature catalyst failure — one of the most expensive repairs on a catalyst exhaust equipped engine. Iridium plugs are the smart choice for protecting your catalyst investment.

Better performance under marine conditions
Marine engines face conditions that automotive engines never encounter — sustained high RPM, heavy loads, and long periods of storage followed by intensive use. Iridium plugs handle these demands better than standard plugs, maintaining consistent performance across the full range of marine operating conditions.

How often should you replace iridium plugs on a catalyst engine?
While iridium plugs last longer than standard plugs we recommend inspecting them every season and replacing at the manufacturer's recommended interval. On catalyst exhaust engines maintaining correct plug condition is even more important — a misfiring or fouled plug allows unburnt fuel to reach the catalyst, causing accelerated wear and potential catalyst damage. Never delay plug replacement on a catalyst equipped engine.

Signs your iridium plugs need replacing:

• Rough idle or misfiring under load
• Hard starting after extended storage
• Noticeable drop in fuel economy
• Visible wear or erosion on the iridium tip
• Engine hesitation or stumbling under acceleration
• Catalyst exhaust running hotter than normal — possible unburnt fuel issue
• Approaching manufacturer's recommended replacement interval

Pro tip: When fitting iridium plugs never use anti-seize compound on the threads — iridium plugs are pre-coated and anti-seize will cause overtightening due to incorrect torque readings. Always torque to the correct specification using a calibrated torque wrench. Never reuse iridium plugs once removed — the fine iridium tip is easily damaged on reinstallation and a damaged tip in a catalyst engine risks converter damage.

Pairs perfectly with:

• 491008 – Spark Plug 5.7L Standard Non-Catalysed (non-catalyst alternative)
• 556345GM – Distributor Cap High Voltage Switch
• 585018 – Exhaust Elbow Catalyst Extended Port
• 585017 – Exhaust Elbow Catalyst Extended Starboard
• 765006 – Exhaust Elbow Catalyst Gasket 5.7L
• 556202SPEC – Exhaust Gasket Catalyst Special

Features:

• Genuine Indmar OEM specification iridium spark plug kit
• Specifically designed for catalyst exhaust system applications
• Complete kit — all 8 plugs required for the 5.7L V8 engine
• Ultra-fine iridium tip for superior spark quality and consistency
• Optimised combustion protects catalyst from unburnt fuel damage
• Extended service life vs standard nickel electrode plugs
• Improved cold start performance after winter storage
• Correct heat range for Indmar 5.7L catalyst exhaust applications
• Direct replacement — no modifications needed

Part Number: 491009
In stock and shipped fast from Australia 🇦🇺