Best Spark Plugs for 604 Crate Motor

When I was setting up my 604 Crate Motor for track day, I quickly realized that cheap spark plugs just wouldn’t cut it. A consistent, powerful spark is absolutely crucial for optimizing horsepower and maintaining reliability under the high-stress demands of short-track racing. We need plugs that can handle the specific heat range requirements of a sealed engine like the Chevy 604 Crate Engine without fouling or causing pre-ignition. I’ve gathered the best options available today to help serious racers find the quality 604 crate motor spark plug upgrades they need.

IMAGE	PRODUCT NAME	AMAZON LINK
	8 Pcs Spark Plug Wires Set & 41-110 Iridium Spark…	View on Amazon
	NGK # 3186 G-Power Platinum Spark Plugs TR5GP – 8…	View on Amazon
	ACDelco GM Original Equipment 41-109 (12681660) Iridium…	View on Amazon
	Iridium Platinum Spark Plugs 6509 Compatible with Buick…	View on Amazon
	ACDelco 41-962 Professional Platinum Spark Plug, (8)	View on Amazon

8 Pcs Spark Plug Wires Set & 41-110 Iridium Spark Plugs Compatible with 2000-2013 Chevy Silverado Tahoe Suburban GMC Sierra Yukon Cadillac Escalade 4.8 5.3 6.0 6.2 L, Replace for 41-162 9748HH 9748UU

This package is a fantastic value proposition, bundling high-quality Iridium plugs with a fresh set of wires—perfect if your current ignition system components are showing wear. The 41-110 Iridium plugs are known for their strong corrosion resistance and reliable performance in high-compression GM V8 applications, making them a solid choice for the 604 platform. Having the wires included means you’re addressing the two most common components that lead to misfires and power loss at once, ensuring a complete tune-up for peak performance.

Key features that stand out:

• Comprehensive Kit: Includes eight Iridium spark plugs and a full set of eight wires.
• Iridium Durability: Features a fine Iridium tip for long life and stable spark performance.
• Pre-Gapped: Plugs arrive with a 0.04″ (1mm) pre-gap, offering immediate installation ease (though always confirm the gap for your specific engine tune).
• Wide Compatibility: Designed to replace many common GM/LS engine OEM numbers (41-110, 41-162, etc.).

Pros:
– Excellent value by including both plugs and wires.
– Iridium construction delivers superb ignition consistency.
– Highly reliable under typical track conditions.

Cons:
– The included wires, while functional, might not be as heavy-duty as specialized racing wires.

Best for: Racers looking for a comprehensive, budget-friendly ignition system refresh.

Expert Opinion: This set provides dependable performance right out of the box. For the 604, the Iridium core helps maintain a steady spark even when the temperature starts climbing in longer runs.

NGK # 3186 G-Power Platinum Spark Plugs TR5GP – 8 PCSNEW

NGK is a trusted name in high-performance motorsports, and the TR5GP G-Power Platinum plugs are designed specifically to handle tough conditions. These plugs are engineered to operate effectively across a wider thermal range than conventional plugs, which is exactly what a sealed engine like the 604 needs when transitioning from idle to high-RPM track speed. Their patented triple gasket sealing process prevents combustion gas leakage, ensuring every ounce of compression is utilized.

Key features that stand out:

• Platinum Construction: Utilizes high-quality platinum for superior service life and consistent voltage demands.
• Triple Gasket Seal: Patented design ensures maximum sealing integrity, crucial for maintaining compression in race engines.
• Wide Heat Range: Specifically designed to resist both carbon fouling at low speeds and pre-ignition at high load.
• Reliable Performance: Known as a reliable OEM replacement and mild performance upgrade for many GM V8s.

Pros:
– Exceptional resistance to carbon buildup.
– Superior sealing process guarantees reliable compression.
– Handles temperature swings exceptionally well.

Cons:
– Platinum isn’t quite as durable under extreme, prolonged heat as modern Iridium.

Best for: Drivers who need a highly reliable plug known for resisting fouling during warm-ups and caution laps.

Expert Opinion: These NGK Plugs are a tried-and-true option for durability. Their ability to minimize carbon buildup makes them excellent for engines that spend time idling or running at low RPMs before high-load sprints.

ACDelco GM Original Equipment 41-109 (12681660) Iridium Spark Plug

When you’re running a GM-based crate motor, sometimes sticking with GM Original Equipment (OE) is the smartest move. The ACDelco 41-109 Iridium plug is a high-quality OE component that offers fantastic engine idle stability and smooth overall performance, which translates directly to more predictable power delivery on the track. This plug features an innovative fine-wire design that helps burn away carbon deposits as they form, maintaining plug efficiency over time.

Key features that stand out:

• OE Quality: Guarantees compatibility and reliability expected from a General Motors part.
• Fine-Wire Iridium Tip: Small, efficient electrode design ensures reliable cold starting and quick acceleration.
• Suppressor Seal: Features a one-piece suppressor seal to block radio frequencies (RFI) that could interfere with sensitive vehicle electronics.
• Carbon Resistance: Iridium electrode actively helps maintain a clean tip, resisting fouling.

Pros:
– Unmatched consistency and quality control of a GM OE part.
– Excellent for smooth idle and quick throttle response.
– Suppressor seal protects sensitive ignition components from interference.

Cons:
– They are typically priced slightly higher than equivalent aftermarket Iridium options.

Best for: Racers who prioritize OEM precision and absolute reliability in their ignition system.

Expert Opinion: The 41-109 is often the baseline recommendation for high-performance GM engines. Its ability to maintain a clean burn means less maintenance throughout the racing season, which is a huge benefit for sealed crate motors.

Iridium Platinum Spark Plugs 6509 Compatible with Buick Lacrosse Cadillac SRX Chevy Impala Equinox Ford Edge F-150 GMC Lincoln MKX Mazda CX-9 V6 3.0L-3.8L Replacement for LTR6IX-11 Pack of 6

While sold as a pack of six (designed primarily for V6 applications), the performance technology packed into these dual-material 6509 plugs makes them worthy of consideration for the 604 Crate Motor. These plugs combine an Iridium center electrode with a Platinum ground electrode. This dual construction maximizes conductivity while simultaneously ensuring outstanding durability and wear resistance, leading to extended engine life and reduced maintenance intervals.

Key features that stand out:

• Dual Metal Construction: Utilizes Iridium (center) and Platinum (ground) for superior wear resistance.
• Efficiency Focused: Fine tip design provides excellent conductivity to generate strong, stable sparks, maximizing fuel combustion.
• High-Quality Shell: Features a nickel-plated shell for enhanced resistance to oxidation and corrosion.
• Prevents Cross-Threading: Cold-rolled threads help prevent damage during installation.

Pros:
– Combines the best features of Iridium and Platinum for long life.
– Highly efficient spark ensures complete fuel burn and reduces carbon buildup.
– Extremely resistant to oxidation and corrosion.

Cons:
– You will need to purchase multiple packs since they only come in sets of six.

Best for: Drivers looking for maximum electrode durability and high efficiency fuel combustion.

Expert Opinion: The dual-material approach is great for longevity. While buying two packs adds cost, the reduced risk of fouling and the improved spark stability under pressure are worthwhile performance benefits.

ACDelco 41-962 Professional Platinum Spark Plug, (8)

If you prefer the stable, consistent voltage requirements of platinum over iridium, the ACDelco 41-962 Professional series is an excellent alternative. These plugs feature double platinum point pads on both the center and ground electrodes, which helps reduce the wear on your ignition coils and provides very consistent voltage demands over time. Crucially, they include a pure copper core, which is highly effective at drawing heat away from the tip, maximizing durability and resistance to thermal fouling—a critical factor in high-compression engines.

Key features that stand out:

• Double Platinum: Point pad on both electrodes for maximum durability and reduced ignition system wear.
• Pure Copper Core: Results in a cooler electrode temperature, boosting durability and fouling resistance.
• Fired-In Seal: Uses a sophisticated glass blend seal to ensure a gas-tight seal and reduce radio frequency interference.
• Consistent Voltage: Designed to maintain steady voltage demands throughout their lifespan.

Pros:
– Copper core provides superior heat dissipation and thermal stability.
– Double platinum extends plug life and maintains reliable voltage requirements.
– Excellent fouling resistance for extended use.

Cons:
– Platinum tips wear slightly faster than Iridium under extremely high heat and lean conditions.

Best for: Engines prioritizing maximum heat resistance and those using older-style ignition systems that benefit from stable voltage demands.

Expert Opinion: Many mechanics prefer copper core plugs in demanding environments because of their thermal properties. The 41-962 is a workhorse that guarantees a long service life and exceptional consistency in the 604.

Helpful Comparison Short Insights

When choosing the Best Spark Plugs For 604 Crate Motor, material matters immensely. While Iridium plugs (like the 41-110 and 41-109) offer the longest life and smallest tips for the most focused spark, Platinum plugs (NGK TR5GP and ACDelco 41-962) often provide better thermal stability and resist pre-ignition more reliably in certain high-compression setups.

If longevity is your biggest concern, the dual Iridium/Platinum 6509 offers the maximum wear resistance. However, if you are focusing purely on high-RPM track reliability, the NGK TR5GP’s wide heat range capability makes it a difficult option to beat.

For drivers looking for the most hassle-free installation and known quality control, the ACDelco GM Original Equipment 41-109 is a foolproof choice. Meanwhile, the ACDelco 41-962 with its copper core is the champion when battling tip overheating and thermal fouling. Remember, consistency is king in sealed racing engines, so choose a plug whose material matches your specific running conditions and tune.

Final Verdict

Choosing the right plugs for the 604 Crate Motor isn’t about finding the most expensive option; it’s about finding the one that best handles the thermal demands of your specific racing environment.

The Overall Winner for Reliability:
The ACDelco GM Original Equipment 41-109 Iridium Spark Plug earns the top spot. Its OE reliability, excellent carbon burn-off capabilities, and superb cold-start performance make it the most balanced choice for high-stress race use.

The Best for Thermal Management:
If your 604 Crate Motor tends to run hot or you frequently experience fouling, the ACDelco 41-962 Professional Platinum Spark Plug is the clear winner. Its pure copper core handles heat dissipation better than pure Iridium options.

The Best Value Upgrade Kit:
For drivers who need to replace their wires simultaneously, the 8 Pcs Spark Plug Wires Set & 41-110 Iridium Spark Plugs provides an unbeatable combination of quality parts and convenience at a solid price point.

FAQs About Best Spark Plugs for 604 Crate Motor

Q: What is the recommended spark plug gap for a 604 Crate Motor?

A: While plugs often come pre-gapped, you should always consult your specific engine builder’s instructions, especially for sealed racing motors. Generally, for a standard HEI ignition system on a 604 Crate Motor, a gap between 0.035″ and 0.045″ is common. Always double-check the exact required spark plug gap for your specific setup to maximize performance.

Q: Should I use colder or hotter plugs in my 604 Crate Engine?

A: The 604 is a high-compression racing engine that generates significant heat, especially under sustained high RPMs. Generally, you should stick to the recommended heat range or perhaps run a slightly colder heat range spark plug to prevent pre-ignition (detonation), which is catastrophic in racing motors. Colder plugs transfer heat away from the tip more quickly.

Q: Are Iridium plugs really necessary for a 604 Crate Motor, or is Platinum sufficient?

A: Iridium is preferred for high-performance engines because its fine wire allows for a more intense, focused spark and generally offers the longest lifespan. While Platinum plugs are more than sufficient and often offer better heat stability, Iridium is usually chosen for its superior consistency and reduced maintenance in sealed racing environments.

Q: How often should I replace the spark plugs in a 604 Crate Motor?

A: Unlike street cars, racing engines require much more frequent inspection and replacement. Even if the plug looks fine, the intense heat cycles degrade performance. Many competitive racers inspect and potentially replace plugs every few race weekends or after specific heat cycles to maintain peak horsepower and ensure reliable ignition performance.

Q: What happens if my spark plugs start fouling?

A: Fouling means deposits (usually carbon or oil) are building up on the electrode tip, preventing a clean, strong spark. In a 604, fouling leads to misfires, a noticeable loss of power, and poor idle quality. If you see consistent fouling, you may need a hotter spark plug heat range or an adjustment to your air/fuel mixture, although excessive rich mixture is the most common cause.

Q: Does the spark plug wire quality matter when using premium plugs?

A: Absolutely. Even the best spark plug is useless if the wire can’t efficiently deliver the high voltage from the ignition system (often a magneto or HEI distributor). For the 604, always use high-quality, low-resistance spark plug wires that are properly routed to minimize RFI and ensure maximum voltage reaches the plug.