[racerc2000]

I agree magic plugs wont make a diff on their own. and in most new cars the efficient nature is pre built in.

however. engines not specifically built for economy may find larger improvements then the ones that have been tweaked already.

for instance. hondas k24 (2.4L I4 with I-VTEC) (intake side only valve timing the economy vtec)

ranges from
Displacement: 2,354 cc (143.6 cu in)
Bore and Stroke: 87 mm x 99 mm (3.43x3.90 inches)
Compression: 9.6:1
Power: 160 hp (120 kW) @ 6000 rpm
Torque: 162 lb·ft (220 N·m) @ 5200 rpm
Redline: 7500 rpm

to

Displacement: 2,354 cc (143.6 cu in)
Bore and Stroke: 87 mm x 99 mm (3.43 x 3.90 inches)
Compression: 11.0:1
Power: 201 HP @ 7000 rpm
Torque: 170 lbs·ft @ 4400 rpm
Redline: 7000 rpm

with about 10+ variants between them not including the models that use intake and exhaust cam timing.

how would each one effect fuel economy or how would they react to such economy mods like these plugs etc?

I would assume the lower rpm torque could work out as better FE. would this be a wrong way of thinking? even though with the higher compression and higher peak HP its obviously not the economy engine.