Nissan is modding its gas engines for 2010 with dual, "regular" pressure injectors (one per port) instead of a single injector.
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This reduces the diameter of the fuel droplets by about 60%, resulting in smoother, more stable combustion.
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(Left: One port of the Dual Injector Right: Conventional system injecting to both ports)
Source:
NISSAN | Nissan Introduces New Dual Injector System for Improved Fuel Efficiency in Gasoline Engines
How much better?
They don't quantify gains for the change in the fuel injectors alone, but in combination with variable exhaust timing, say it's worth a
~4% improvement compared to similar Nissan gas engines without the mods.
This is in line with what Tony has reported at fuelsaving.info on research into optimized fuel vaporization, where "the saving is a couple of percent at best."
Source:
Fuel saving gadgets - a professional engineer's view
Interesting side effect: that couple of percent improvement in the burn will permit Nissan to reduce the amount of rare (ie expensive) metals in the catalyst while maintaining its effectiveness.