It could be something as simple as that the HR16DE engine was developed with the ports being the most effecient size to begin with. By making them bigger you slowed down the velocity of air which made the engine slightly less effecient.Guys, i had port and polished my HR cylinder head, also slip the cylinder head around 0.5mm . and i found some difficulties,
on the dyno run, the power decrease 4 HP and the tq decrease 20 Nm after i did that works..
how the maximum limit in slip cylinder head on HR? and it just need to be polished only (no need to oversize the in and ex on the cylinder head )?
so i need your help,guys.. thanks..
I'm not saying that this IS what happened, but modern engines are made to be very effecient from the factory in order to meet the tough emmision requirements of EU and US.