Nothing to do with the fuel, You big cone induction kits are sucking up the hot air from the car this makeing the ecu incorrecly fuel the car, Set up a duct pipe to the front bumper and box the cone to stop hot air from entering this way the ecu will get the correct air temp from the air mass flow, Also have the cars been re mapped for the induction kits as if not there is no increase in output power just more torque of the engine as the ecu does not know of the air pressure effect?
Moden engines don't work to well with exspensive air kits as the ecu is designed to get emmission contols down get rid of the emmissions and gas control and away you go but the advrage engine say at this point 1.8 straight 4 produces around 125bhp, remove all emmision contols and reset the air filters and you would have around 180bhp,