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Why use cheap copper spark plugs?

Many are using standard copper core Autolite 24/25 or Motorcraft SP415 in their relatively stock 5.0L/5.8L engines. The main difference between the two are the Autolite has a copper tip and the Motorcraft has a nickel alloy tip.

These copper core spark plugs have many benefits, such as being inexpensive, easy to accuire, easy to read and a great electrical conductor in OEM Secondary Ignition applications. They have the proper manufacturer's recommended dimensions and heat range rating for OEM heads. Being inexpensive also motivates one to change them regularly and read them for signs of overheating or accumulation of deposits. Regular reading of your spark plugs allow for early identification of poor performance or potential engine damage. And, when your gap wears and becomes less efficient, you will know it both visually and by how your truck is running.

Autolite 24: 14mm Thread Size, 11.6mm (.460") Reach, 5/8" (16mm) Hex Size, Tapered Seat, Resistor, Power Tip, Copper Core, .044 Gap, Heat Range 4

Resistor plugs minimize electronic interference and can aid in reducing electrode erosion. Copper Core aids in cooling and improves resistance to fouling. Power tip or extended electrode plugs project the firing tip into the combustion chamber which not only aids in cooling but also cleaning so that fouling is reduced at low RPMs.

Autolite 25: 14mm Thread Size, 11.6mm (.460") Reach, 5/8" (16mm) Hex Size, Tapered Seat, Resistor, Power Tip, Copper Core, .054 Gap, Heat Range 5

On the other hand, many aftermarket heads require specific spark plugs of different dimensions, reach, seat and Heat Range. The length of the threaded portion of the plug should closely match the thickness of the head because if it extends too far into the combustion chamber it can potentially be struck by the piston. When using aftermarket heads, you must refer to the manufacturer's recommended spark plug and heat range. As an example, here are the recommended Autolite starting range spark plugs for my AFR 185 heads. Note the much longer reach and Gasket Seat vs Tapered Seat. Also note this is still a copper core spark plug with a copper tip. These Autolite Racing plugs have oversized ground electrodes for better heat transfer and a cut back ground electrode to reduce bridging (carbon fouling between ground electrode and center electrode) and ground electrode shadowing.

Autolite AR3924: 14mm Thread Size, 19mm (3/4") Reach, 5/8" (16mm) Hex Size, Gasket Seat, Resistor, Power Tip, Copper Core, Racing Plug with Nickel Plated Shell, Heat Range 4

Subsequently, I have upgraded to an equivilent NGK spark plug in testing for a more efficent heat range specific to my performance application. Note the projected V-Power tip, colder heat range and .040 gap. This unique design directs the spark to the edge of the electrode where it develops more rapidly and increases ignitability even in lean burn conditions. This is still a copper core spark plug, although with a nickel alloy tip like the Motorcraft. Regarding heat range, more power creates more cylinder heat. A rule of thumb is 1 heat range colder for every 75-100 hp increase, then read the plugs and adjust from there. It is important to remember that heat range numbers are not universal between spark plug manufacturers and you must cross reference equivalents when changing brands.

NGK FR5-7373: V-Power Plug, 14mm Thread Size, 19mm (3/4") Reach, 5/8" (16mm) Hex Size, Gasket Seat, Resistor, Solid Terminal Nut, Projected Tip, V-Power (V-Grooved Center Electrode), .040" (1.02mm) Gap, Heat Range 5

In summary, modern Iridium, Platinum or other expensive precious metal spark plugs are made for longevity, not necessarily performance, and are designed for very efficient and complex modern electronic engine control systems. The main problem with these spark plugs in our older Broncos is they are lesser conductors and produce a less powerful spark than copper plugs, meaning less engine power. They may work well in your late model 2010 modular EEC-VI engine, but not necessarily better in your older pre-1996 EEC-IV Bronco. Specifically in the older Ford Bronco having a relatively stock OEM engine, cheap copper core spark plugs have proven to be inexpensive, readily available, excellent electrical conductors, and have forced us to become more "in tune" with engine performance changes.

This is why everyone says "use cheap copper spark plugs" in your relatively stock Bronco. :thumbup

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