The Nissan QR25DE four-cylinder engine might not have reached quite the level of fame of its six-cylinder brethren, but it's certainly found a place in the hearts of Nissan enthusiasts everywhere. While it doesn't have quite the power potential of the big VQ and VR V-6 engines, the QR25DE has developed a reputation for smooth performance, impressive efficiency and the kind of broad powerband that makes performance and fun accessible without revving the engine to death.
At one time, a simple plug change was good for a serious improvement in performance, but Nissan, like many other Japanese manufacturers, leaves little on the table when it comes to selecting the right parts for its engines. Rather than pussyfoot around with inferior copper plugs, Nissan went right for the kill and dropped in a set of NGK double platinum plugs. The NGKs, part number PLFR5A-11, are at least as good as any other aftermarket platinum plug out there, so you'll want to stick with them unless you're willing to shell out big bucks for much more expensive iridium plugs.
The NGKs, with a plug gap of 0.043 inches, come in second only to fine-wire iridium plugs like the Denso IKH16 or IKH20. The Denso's 0.3 mm-thinner electrode wire concentrates the electrical current into a narrower and hotter spark, optimizing the system for maximum performance. The stronger spark might also allow you to increase the plug gap to about 0.05 inch, which will ignite more of the mixture more quickly, allowing you to tweak the timing curve a bit with a computer tuner for greater power and fuel efficiency.
