Big trucks have always been home base for haulers of freight and big tires, while small trucks like the Ranger have long been the go-to conveyances for hauling butt. The 4.0-liter V-6 was the most powerful ever offered in Ford's signature mini-truck, making it a prime target for go-fast parts like the NGK Iridium.
The NGK Iridium is one of the highest-end spark plugs out there, offered as standard equipment in both the Evo VIII and Lotus Elise and Exige. It uses a 0.6 mm iridium electrode wire and a platinum disc welded to the bottom of the ground to produce a very intense spark without sacrificing durability. However, that quality comes at a price: a little over $17.00 per plug as of 2014.
A relatively stock 4.0-liter Ranger doesn't have the compression or cylinder pressures to make a plug like the NGK really necessary, as it might be in an 8,000-rpm four-cylinder with a massive turbo or nitrous. Assuming you don't have a blower, nitrous or 15-to-1 compression pistons in your Ford, you might want to go with a set of Denso Iridium plugs instead. The Denso Iridium is based on NGK's design, and offers about 95 percent of the NGK plug's performance and longevity at less than half the price.
