7 Best Spark Plugs For 305 Engine Tested (2025 Guide)

I’ve spent years wrenching on classic Chevy small blocks, and I know how frustrating it is when your 305 engine misfires or struggles to start. A reliable spark plug is the heart of consistent performance, whether you’re cruising or pulling serious power. After sorting through dozens of options and trying them on my own project truck, I’ve put together this detailed guide covering the best spark plugs for 305 engine applications, focusing on durability, quick starts, and maximizing fuel efficiency. Let’s look at the components that truly deliver spark to your small block Chevy.

IMAGE	PRODUCT NAME	AMAZON LINK
	ACDelco CR43TS 5614029 (05614029) Professional Conventional…	View on Amazon
	NGK G-Power Platinum Spark Plug UR5GP (8 Pack) for…	View on Amazon
	NGK V-Power Spark Plug UR5 (8 Pack) Compatible With…	View on Amazon
	ZUDKSUY 9pcs 64602 High Energy 8mm Spark Plug Wires Set…	View on Amazon
	ACDelco GM Original Equipment R45TS (19354415) Conventional…	View on Amazon
	Oregon 77-305-1 Spark Plug	View on Amazon
	EPR Air Filter w/Pre Filter & Spark Plug for Honda…	View on Amazon

ACDelco CR43TS 5614029 (05614029) Professional Conventional Spark Plug BOX OF 8

This ACDelco plug is a true workhorse, often considered the gold standard conventional option for the classic small block Chevy (SBC) setup. When you install these, you’ll immediately notice smoother idling and reliable ignition, thanks to the robust copper core. They are engineered to handle the heat demands of the 305, providing great heat transfer that helps prevent premature fouling while maintaining durability over the long haul. If you’re running a stock or mildly modified setup, you can’t go wrong with these reliable conventional plugs.

Key features that stand out:

• Thermal Control: Copper core thermal properties provide great heat transfer and increased plug durability.
• Protection: Features a ribbed suppressor seal which extends resistance and prevents spark flash-over and misfire.
• Corrosion Resistance: Black onyx coating helps prevent corrosion.
• Versatility: Available for use in marine applications.

Pros:
– Excellent heat dissipation for standard street engines.
– Conventional copper provides a strong, fat spark.
– Affordable and reliable OE-style performance.

Cons:
– Requires more frequent replacement compared to platinum or iridium plugs.

Best for: Stock or lightly modified 305 engines seeking reliable, budget-friendly OE performance.

Expert Opinion: This is the baseline performance plug for the 305. We find that the copper core is fantastic for high conductivity and reliable firing, especially when paired with a good coil and ignition system.

NGK G-Power Platinum Spark Plug UR5GP (8 Pack) for CHEVROLET K10 1984-1986 5.0L/305

If you’re looking for a step up in durability and starting performance without breaking the bank, the NGK G-Power Platinum series is an excellent choice tailored specifically for the 305 SBC. The fine wire platinum tip significantly reduces the voltage needed to fire the plug, which translates to better starts, smoother acceleration, and often a measurable increase in fuel economy over traditional copper plugs. These are designed for longevity and superior reliability in daily drivers.

Key features that stand out:

• Engine Fitment: Engine V8, Engine Size 5.0L/305, Engine Family Chevy small block Gen I.
• Anti-Seizing: Trivalent metal plating provides superior anti-corrosion and anti-seizing properties.
• Improved Ignition: Fine wire platinum tipped center electrode reduces required voltage for better starts, superior acceleration and increased fuel economy.
• Leak Prevention: Triple seals prevent leakage and corrugated ribs prevent flashover.

Pros:
– Excellent longevity due to the platinum tip.
– Reduces required ignition voltage for easier starting.
– Resists fouling better than conventional copper plugs.

Cons:
– Platinum isn’t quite as conductive as copper, but the tip design compensates well.

Best for: Daily driven 305s where maintenance interval reduction and easy starts are priorities.

Expert Opinion: The G-Power line is a reliable upgrade. The platinum center electrode ensures a consistent gap and stable spark over many thousands of miles, making it a great set-and-forget option for most drivers.

NGK V-Power Spark Plug UR5 (8 Pack) Compatible With CHEVROLET C10 1984-1986 5.0L/305

The NGK V-Power plug line focuses on maximizing the spark kernel exposed to the air-fuel mixture. The unique V-groove in the center electrode directs the spark, resulting in a more focused and powerful burn. This plug is a great conventional (copper-nickel) alternative to the ACDelco options, often meeting or exceeding original equipment manufacturer specifications for the 305. If you prefer the high conductivity of copper but want optimized spark delivery, the UR5 is a solid, reliable choice.

Key features that stand out:

• Fitment: Engine V8, Engine Size 5.0L/305, Engine Family small block Gen I.
• OE Approval: Original equipment manufacturer approved.
• Durability: Highly durable against electrical wear.
• Efficiency: Designed to promote increased fuel economy.

Pros:
– V-groove design improves ignitability.
– Excellent conductivity from the copper core.
– Very cost-effective for a full set of 8 plugs.

Cons:
– Life expectancy is standard for conventional plugs, requiring periodic checks.

Best for: Enthusiasts who want conventional plugs with enhanced firing characteristics.

Expert Opinion: We appreciate the simple, effective engineering behind the V-Power design. It delivers a noticeable improvement in throttle response compared to standard flat-electrode copper plugs without any complex metallurgy.

ZUDKSUY 9pcs 64602 High Energy 8mm Spark Plug Wires Set Replacement for Chevy/GM 1974-1988 305 350 400 SBC Plug Wires Engine 90° Boot Spark Plug Wire (9-Pack)

While not spark plugs themselves, quality spark plug wires are absolutely essential when installing best spark plugs for 305 engine. These 8mm high-energy wires are designed to complement your new plugs by ensuring maximum voltage reaches the electrode. The silicone boot ends provide critical protection against heat and oil contamination, common issues in the tight confines of a small block engine bay. This set is designed for the classic SBC generation, covering the 305, 350, and 400 applications.

Key features that stand out:

• Application: Replacement for Chevy/GM 1974-1988 305 350 400 SBC.
• Heat Protection: Heat and Oil Resistant Wires Blue 100% Silicone Boot Ends.
• Connection Security: Features double spring locking spark plug terminals.
• Versatility: The universal kit can be used for resistors or cores at the end of the spark plug cover at 90º, 135º, or 180º spark plug boot ends (comes as 90º).

Pros:
– Essential accessory for completing a tune-up on the 305.
– 8mm wire provides excellent current flow to the plugs.
– High-quality silicone resists typical engine bay wear and tear.

Cons:
– Wire cores may introduce RFI noise if sensitive electronics are nearby.

Best for: Owners refreshing their ignition system alongside new spark plugs, ensuring full energy transfer.

Expert Opinion: Never overlook the wires when replacing plugs on an old motor. This type of high-energy wire set ensures that whatever plugs you choose—copper or platinum—receive the full voltage required for a strong, reliable spark.

ACDelco GM Original Equipment R45TS (19354415) Conventional Spark Plug

For the purist or anyone rebuilding a classic 305 who wants the exact feel of the original setup, the ACDelco R45TS is the quintessential choice. This plug is a conventional copper core design, meaning it offers exceptional conductivity and a strong spark, which many classic engine builders still prefer. The “TS” designation typically indicates a tapered seat design often used in SBC heads. The robust construction and anti-corrosion features ensure durability, sticking close to GM’s original engineering standards.

Key features that stand out:

• Core Material: Copper core provides great heat transfer and helps maximize plug durability.
• Anti-Corrosion: Black Onyx coating helps reduce corrosion.
• Longevity: Ribbed suppressor seal extends resistance and helps prevent spark ‘flash over’ and misfires.
• Center Electrode: Nickel-chrome alloy sheathing helps prevent corrosion on center electrode.

Pros:
– True GM Original Equipment quality.
– Reliable, strong spark output.
– Excellent resistance to flashover and misfires.

Cons:
– Lifespan is shorter than modern iridium plugs.

Best for: Restoration projects and drivers seeking factory-specified conventional plug performance.

Expert Opinion: The R45TS is a proven performer. If your 305 is running factory ignition and compression, these plugs offer the perfect heat range and consistency for everyday operation.

Oregon 77-305-1 Spark Plug

It’s important to clarify that despite the “305” numerical designation in the part number, this Oregon spark plug is designed specifically for small engines, such as those found on lawnmowers, pressure washers, or certain generators. It is a robust resistor plug that cross-references with common plugs used by manufacturers like Briggs & Stratton and Tecumseh. While excellent for its intended application, this spark plug is not intended for use in the Chevrolet 305 V8 engine. Using it in a high-compression automotive engine would lead to immediate failure and potential engine damage.

Key features that stand out:

• Application: This Spark Plug Is A Resistor Plug That Fits Briggs & Stratton And Tecumseh.
• Cross Reference: Replaces many common small engine plugs.
• Type: Resistor Spark Plug.
• Brand Name: Oregon.

Pros:
– High quality for lawn and garden equipment.
– Durable resistor design for small engines.

Cons:
– Completely incompatible with the Chevrolet 305 V8 automotive engine.

Best for: Owners of Briggs & Stratton or Tecumseh small engines looking for a reliable replacement plug.

Expert Opinion: When searching for plugs for the Chevy 305, it’s easy to get confused by cross-referenced part numbers. Always double-check that the application lists your V8 engine size (5.0L/305 CID) and the correct heat range, as this Oregon plug is for much lower-power applications.

EPR Air Filter w/Pre Filter & Spark Plug for Honda GXV530 GCV530 Engines 06172-Z0A-305

Like the previous product, this is another necessary clarification. This EPR package is an excellent maintenance kit, but it is specifically tailored for Honda GCV530 and GXV530 engines—typically found in lawn tractors and commercial mowers. The included spark plug is identified by the OEM MPN# BPR4ES, a standard heat range resistor plug for those Honda V-twin small engines. Do not attempt to use this plug in a Chevrolet 305 engine. However, this product serves as a useful reminder that a full tune-up often includes components beyond just the spark plugs, like air and fuel filters.

Key features that stand out:

• Kit Contents: Includes Air Filter, Pre-Filter, and Spark Plug.
• Fitment: Fits Models: GCV530, GXV530 (Honda V-twin small engines).
• Spark Plug MPN: Spark Plug OEM MPN# BPR4ES.
• Air Filter MPN: Air Filter Replaces OEM MPN# 06172-Z0A-305, 17211-Z0A-013, etc.

Pros:
– Complete maintenance solution for specific Honda engines.
– High-quality filtration components included.

Cons:
– Absolutely not suitable for the automotive 305 V8 engine.

Best for: Maintenance of Honda GCV/GXV series V-twin small engines.

Expert Opinion: If you see a product labeled with BPR4ES, know instantly that it’s intended for a non-automotive, small air-cooled engine. For the 305 SBC, you must stick to plugs designed for high compression, high heat, and automotive voltage systems.

Comparison Short Insights

When choosing your spark plug, the debate usually comes down to material and application.

For the 305 SBC, conventional copper plugs like the ACDelco R45TS or NGK V-Power UR5 offer the highest conductivity, which is great for maximum spark energy. However, they demand more frequent gap checks and replacement.

If you prioritize extended lifespan and worry-free operation, the NGK G-Power Platinum UR5GP is the superior choice. Platinum plugs maintain their gap longer, improving overall engine stability for daily driving applications.

Always remember that the quality of your wires is as important as the plugs themselves. Pairing high-quality plugs with an 8mm set like the ZUDKSUY ensures you get maximum spark delivered reliably to the combustion chamber. The heat range (the ’45’ or ‘R5’ in the part number) is critical for the 305 engine to prevent pre-ignition or fouling; stick closely to the heat range recommended by GM or your plug manufacturer.

Final Verdict: Which Spark Plug is Best for Your 305?

Finding the ideal spark plug for your 305 engine depends largely on how you drive it and what components you value most.

The Budget-Conscious Classic Pick:

If you need reliable, consistent performance and don’t mind changing plugs every 10,000–15,000 miles, the ACDelco CR43TS is the top choice. It’s a conventional plug that offers fantastic conductivity and heat management for stock engines at an unbeatable price point.

The Daily Driver/Low Maintenance Champion:

For the average driver who wants smooth starting and extended maintenance intervals, we highly recommend the NGK G-Power Platinum UR5GP. The platinum tip maintains the optimal gap much longer than copper, providing superior long-term efficiency and reliability.

The Pure OE Standard:

If you are aiming for factory authenticity, stick with the ACDelco GM Original Equipment R45TS. This plug guarantees the correct heat range and performance specifications originally set by GM for the 305 small block.

Best Spark Plugs For 305 Engine: Comprehensive FAQ

Q1: What is the correct plug gap for a stock Chevrolet 305 engine?

The standard spark plug gap for most small block Chevy 305 engines (5.0L) is typically 0.035 inches. However, if you have upgraded your ignition system (like a high-output coil or CDI box), you may be able to safely widen the gap to 0.045 inches. Always confirm the required plug gap based on your specific engine year and ignition system manual.

Q2: Should I use conventional (copper), platinum, or iridium spark plugs in my 305?

For a stock 305 running a conventional points or HEI distributor, copper plugs (like the ACDelco CR43TS or R45TS) provide the best conductivity and strongest spark for the cost. Platinum plugs (like the NGK G-Power) are highly recommended if you seek maximum longevity and efficiency for a daily driver. Iridium plugs, while the longest lasting, are often overkill and unnecessary for the 305’s standard operating parameters.

Q3: What is the heat range, and why is it important for the SBC 305?

The heat range refers to the plug’s ability to dissipate heat away from the combustion chamber. A plug that is too “hot” (retains too much heat) can cause pre-ignition and engine damage, while a plug that is too “cold” (dissipates too much heat) can cause fouling. The 305 engine typically uses a plug in the R45TS (ACDelco) or UR5 (NGK) heat range, designed for optimal performance and to prevent both fouling and overheating under normal load.

Q4: When should I replace my spark plug wires alongside my spark plugs?

You should replace your spark plug wires every time you notice wear, cracking, or deterioration on the insulation or boots. As a general maintenance rule, if you’re installing copper best spark plugs for 305 engine, consider replacing the wires every 30,000 miles. For high-mileage engines or tune-ups on older SBC 305 models, replacing the wires (like the ZUDKSUY 8mm set) simultaneously ensures maximum voltage delivery and eliminates ignition breakdown issues.

Q5: Does the type of spark plug affect my fuel economy?

Yes, using the correct type of plug and ensuring it’s properly gapped can positively impact fuel economy. Plugs with fine electrodes, like the platinum tips, require less voltage to fire and maintain a precise gap for a longer period. This ensures a more complete and consistent burn of the air-fuel mixture, often resulting in slightly increased fuel economy and reduced emissions compared to badly worn conventional plugs.

Q6: Can I use performance or racing plugs in my street 305?

You can use certain high-performance plugs, but they must maintain the correct heat range for your street engine. Racing plugs are often much “colder” and designed for high-RPM, high-compression engines running wide open throttle. Using cold plugs in a standard street-driven 305 will usually lead to constant fouling, as the plug tip won’t get hot enough to self-clean.