Spark Plugs

[BDnFL]

I know most here have their preferences. I’ll be pulling the plugs chasing a misfire to check compression.
I can’t seem to cross reference my current plugs.
Engine is a stroked 440 to 493.
I know the engine is running rich which I’ll address after compression check. Since plugs will be out maybe there’s a better suggestion.
Picture of plugs after about 75 miles. Current gap at .45.
Engine builder installed AutoLite AP 103.
Thanks.

 

[pnora]

What heads are you running?

 

[ruffcut]

What cylinder heads, compression?

 

[toolmanmike]

Long reach plugs for a big block? Yep, what heads?

 

[R413]

Aluminum with those plugs.

 

[RemCharger]

Those are taper seat plugs. I'd guess the heads are motorhome 452s. Aluminum heads take a gasket plug.

 

[BDnFL]

What heads are you running?

Promaxx heads

 

[BDnFL]

C

What cylinder heads, compression?

Compression unknown

 

[toolmanmike]

Promaxx heads

They are supposed to be gasket seat apparently.

• Common Applications: NGK BKR5E, BKR6E (colder), or Autolite 3923/3924.
• Plug Type: 14mm Thread, 0.750" (3/4") Reach, Gasket Seat.
• Hex Size: 5/8" (commonly preferred for aftermarket heads).
• Recommendation: Verify the specific part number based on your engine's compression ratio, camshaft, and fuel type.
  BluePrint Engines

 

[pnora]

Those are taper seat plugs. I'd guess the heads are motorhome 452s. Aluminum heads take a gasket plug.

452 should also be a shorter plug. Those look like 3/4 reach.

 

[BDnFL]

Just found some paper work on the heads
Promaxx #9440.
84cc chamber. 210 Intake.

They are supposed to be gasket seat apparently.

• Common Applications: NGK BKR5E, BKR6E (colder), or Autolite 3923/3924.
• Plug Type: 14mm Thread, 0.750" (3/4") Reach, Gasket Seat.
• Hex Size: 5/8" (commonly preferred for aftermarket heads).
• Recommendation: Verify the specific part number based on your engine's compression ratio, camshaft, and fuel type.
  BluePrint Engines

 

[RemCharger]

NGK 5671A-6 should work.

 

[BDnFL]

Cam info.

 

[BDnFL]

Thanks for taking the time to reply, I appreciate it.

 

[gtxrt]

why the .045 gap try a smaller gap with new plugs

 

[RemCharger]

why the .045 gap try a smaller gap with new plugs

100%
No need for more than .035. More power = less gap.

 

[Geoff 2]

The cam is mild for a stroker. Unless the engine will see periods of WOT [ such as circle track racing ] use a '5' heat range in NGK.

 

[MoparLeo]

Your picture is off center and only shows 1 spark plug end.
Platinum ? What is the rest of the ignition ? Distributor ? coil ? wires ?

FROM CATALOG :​

Common Issues Addressed by Autolite AP103​

• Engine misfires due to worn or inefficient spark plugs
• Reduced fuel efficiency caused by incomplete combustion
• Difficulty starting the engine in cold conditions
• Interference with vehicle electronics from spark plug noise
• Premature spark plug wear in high-performance or high-mileage engines

Installation Notes and Tips​

Before installation, verify the spark plug gap is set to 0.050 inches (1.30 mm) as specified. Use a torque wrench to tighten the plug to the manufacturer’s recommended torque to avoid damage to the tapered seat. Ensure the spark plug threads are clean and free of debris.

 

[BDnFL]

100%
No need for more than .035. More power = less gap.

Will do on the .035 gap.

 

[BDnFL]

The cam is mild for a stroker. Unless the engine will see periods of WOT [ such as circle track racing ] use a '5' heat range in NGK.

View attachment 1992054

Just street use, maybe a little tire smoke at times.