soopachargen wrote:Would increasing the valve sizes on a 16v deliver a good performance increase?? what do you mean by the b16 valves not being masked??
An engine is the sum of ALL it's components. Optimally you want a charge to scream down a port at maximum velocity tumble and swirl as much as possible (while maintaing velocity) in order to keep the fuel as mixed as possible, at all RPM. A valve is part of that equation. There is little point in having a fast charge get lazy as it goes past the valve. So you want to run a small valve on an efficient low RPM engine and a large one on a screamer. Valve area is used as a general rule of thumb as to power potential.
On the down side, bigger valves need somewhere to sit and run further towards either each other or the port walls, effectively blocking part of the charge (masking). This may force the valve inclination to be increased. Which may in turn cause the valves to foul each other in cam overlap (very high performance cams). Or more likely charge to be directed striaght through to the exhuast. Squish bands, designed to keep the fuel tumbling and directed towards the spark are also forced to be smaller with a larger valve (or they too may cause masking), and with a higher valve inclination you typically have a larger combustion chamber so the dome on your piston gets bigger, which in turn affects flame propogation and detonation.... and so power drops. Complex, yep.. have I helped... nope.
Saying all that, TRD thought the 16 valve needed bigger valves for high performance use. I cant remember the size and I gave away my TRD 4AG Bible (Piece of shyte) but I think its 2mm on intake.
There are anomolies to manufacturers installation. Mainly depending on what is in the parts bin. My 6a10 for instance uses the valves from a 2ltr V6, same size as the 4age, but boy are they masked!