Full marks to Xulfiqar for trying best to hammer and defend the correct logic here.
spark plugs esp the Bosch 4 tip do not increase power. I have used them in japanese swift 1989 to a corolla to a Vtec Civic. from the time that they were a rare commodity.
the basic fact is this, Bosch plugs are just better quality than most stock or normal ND/NGK plugs, they last longer and offer lower resistance and NOT ALWAYS better consumption. Since you have installed brand new 4 tips, they are giving you a slight edge as fuel burning 'may' have becomore more efficient.
Additionaly these days there is a blind senseless craze to install even more expensive iridium plugs. On a stock engine they will do nothing. it is a waste of money. First thing you need is an 'engine' itself, 1000 cc, 1300 cc toyotas Very Vtec's (VVti) - are just not juicy enough for such a plug to support it. Even a stock 1.6, 1.8 Honda Vtec does not have much benefit any such performance plugs. So they end up just being jammed in the block doing there work as easy as a normal spark plug. These are used for hi revving hi HP engines.
Secondly the concept of enhancing power through plugs and wires if FIRST to install a high power ignition coil - usually a sports spec, backed up by e.g. 60 AH battery - . once that is in place, using high tension wires that leake the minimum of current and can carry that addional Juice from the voltage boost coil. - all this juice now goes to a 'better' quality plug Bosch 4 tip or titanium or iridium they will give one hell of a blast to the cylinder head and you 'may' feel the edge there.
One more thing is that dual/quad tips/ Titanium are suspected of lowering fuel economy. Other than the longer life and better quality material esp the ceramic, there is no point in using a 4 point Bosch. NGK does the job just fine for the cars here with better fuel economy for most Carbed engined.
W/o very high power coil and matching wires - sports plugs are useless expense.
