Choosing the Right Spark Plugs for Your 1956-1965 Chrysler Imperial
Get the correct spark and avoid common issues with the right plugs for your classic Imperial's V8 engine.
- Stick with standard copper core spark plugs from brands like Autolite (85) or NGK (V-Power XR4/XR5) for the best performance and value.
- Ensure you are buying plugs with a 3/8-inch thread reach, not the longer 3/4-inch reach used on some industrial engines.
- Set the spark plug gap to 0.035 inches using a wire-style gapping tool before installation.
- Replacing spark plugs is a simple, low-cost tune-up item you can do yourself in about an hour.
Signs of Failing Spark Plugs in Your Imperial
The ignition system on your 1956-1965 Imperial is simple and robust, but spark plugs are a wear item that need regular replacement. If your plugs are old or fouled, you'll likely notice it in the way your car drives. Look out for these common symptoms:
- Rough Idle: The engine may shake or run unevenly when stopped. 🎬 Watch: How to diagnose and fix a rough engine idle
- Engine Misfires: You might feel a stumble or hesitation during acceleration.
- Hard Starting: The engine cranks for a long time before it finally starts, or it may not start at all.
- Reduced Power: The car feels sluggish and doesn't accelerate like it used to.
- Poor Fuel Economy: You're stopping for gas more often than usual.
Choosing the Right Aftermarket Spark Plug
For a classic vehicle like the 1956-1965 Imperial, you don't need fancy or expensive spark plugs. The original points-style ignition system was designed to work with simple, effective copper core plugs. While modern platinum or iridium plugs will fit, they offer no real benefit and are not necessary. Sticking with proven copper plugs is the most reliable and cost-effective choice.
Brand Recommendations
Based on owner feedback and performance in classic Mopar engines, here’s how the available brands stack up:
- Top Recommendations (Autolite & NGK): Many classic Chrysler owners today prefer standard Autolite 85 copper plugs or NGK V-Power (XR4 or XR5) plugs. These modern copper plugs offer excellent performance, resist fouling well in older engines, and are very affordable. They are considered by many to be a slight upgrade over the original 1960s technology.
- Classic Choice (Champion): Champion was a common original equipment supplier for Chrysler during this era. Plugs like the Champion J11C or J12Y are a great choice if you are aiming for period-correct authenticity. They are dependable plugs that work well, though some modern owners feel they can foul more easily than NGK or Autolite plugs in engines that burn a little oil.
- Other Viable Options (ACDelco, Denso, Accel): These brands also produce quality spark plugs that are compatible with your Imperial. While not as commonly discussed in owner forums as Autolite or NGK, they are perfectly acceptable alternatives if your preferred brand is not available.
Common Ordering Mistake: Check Your Thread Reach!
The V8 engines in passenger cars like your Imperial use a spark plug with a 3/8-inch thread reach. Some industrial Chrysler engines from the same era used a longer 3/4-inch reach plug. Parts catalogs can sometimes get this wrong. Always confirm you are buying the shorter 3/8-inch reach plug to avoid engine damage.
🎬 See this guide for installing plugs on big block MoparsAftermarket vs. OEM Spark Plugs
For a vehicle of this age, the concept of "OEM" is different. The original Champion plugs from the 1960s are no longer made. A modern aftermarket plug from a quality brand like Autolite or NGK is manufactured to higher standards than the originals and will provide excellent, reliable performance. There is no quality or performance advantage to hunting down expensive New Old Stock (NOS) plugs; a fresh set of modern copper plugs is the better choice.
Spark Plug Cost Comparison
| Option | Estimated Cost (per set of 8) |
|---|---|
| New Aftermarket (Copper) | $28 - $65 |
| New Aftermarket (Iridium/Platinum) | $60 - $150+ |
| Shop Labor to Install | $100 - $200 |
Pro Tip: Resistor vs. Non-Resistor Plugs
Chrysler originally specified non-resistor spark plugs used with resistor spark plug wires to suppress radio noise. Most modern replacement plugs are resistor plugs (often designated with an 'R' in the part number). Using resistor plugs with your original resistor wires is generally fine and most drivers will not notice a difference.
Frequently Asked Questions (FAQ)
What should I gap my new spark plugs to?
The correct spark plug gap for most 1956-1965 Imperials is 0.035 inches. Always verify the gap with a wire-style gapping tool and adjust if necessary before installation.
🎬 Watch: The ultimate DIY guide to replacing your spark plugsHow often should I change the spark plugs?
With a standard copper spark plug and a points-style ignition, a good interval is every 10,000 to 15,000 miles or every 2-3 years. Since these cars are often driven less, it's wise to inspect them annually for fouling or corrosion.
Should I use anti-seize on the threads?
This is a topic of debate. Some plug manufacturers like NGK advise against it as their plugs have a special plating that prevents seizing. If you do use it, use only a tiny amount on the threads, keeping it away from the electrode, and reduce the torque setting by about 20% to avoid over-tightening.
Can I use modern Iridium or Platinum plugs?
While they will physically fit, they are not recommended. These plugs are designed for modern high-energy electronic ignition systems. The lower-energy points system in your Imperial will not benefit from them, and they may not perform as well as a standard copper plug designed for this application. Stick with copper for the best results and value.
Helpful Videos
Technical Specifications
OEM Part Numbers: XN-12Y (Champion, obsolete)
Thread Reach: 3/8 inch (9.5mm) Hex Size: 13/16 inch (21mm) Recommended Gap: 0.035 inches Common Cross-References: Autolite 85, NGK B4 / XR4, Champion J11C / J12Y
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- 🎬 Helpful Videos
- 🛍️ Shop This Part
- Signs of Failing Spark Plugs in Your Imperial
- Choosing the Right Aftermarket Spark Plug
- Brand Recommendations
- Common Ordering Mistake: Check Your Thread Reach!
- Aftermarket vs. OEM Spark Plugs
- Spark Plug Cost Comparison
- Pro Tip: Resistor vs. Non-Resistor Plugs
- Frequently Asked Questions (FAQ)
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