Sxynerd

On a Stage 2 head from "X" company, is it the Porting w/ a valve job that gives you the power OR does the oversized Valves makeup a substantial amount of the total gains?

02WhiteGTVert

They're both equally important in flow. "Porting",is opening up the ports,thus allowing more flow,same thing with larger valves,they both allow your motor to breath alot easier.

racer02GTstang

bigger valves will not gain as much as the porting but when you think about it they work together because if you find a shop who knows what they are doing they actually cut the heads as well so the bigger valves will fit, thus giving you more airflow.

35thAnni99GT

A valve on a 2v head cannot be oversized more than 1 or 2mm in most cases, meaning unless you running full out race at high RPM's the whole time you don't realize most of your gains from this. However, you may gain some power by changing the backcut on the valve.

You gain most of yourpower by manipulating the input passage which, cut from the factory, has some flaws. The passages are normally cut by CNC machines from one direction creating an abrupt turn in the intake passage. By smoothing out, enlarging, or changingthe shape of the passage, it changes the way the air "tumbles" into the combustion chamber and what the velocity of the incoming air is. Both those factors will change your final power numbers and WHEN that power is created. A good speed shop will realize whatyour goal is and adjust the porting accordingly.One port may yield better numbers faster in the powerband while another port will be better for road race cars that spend more time higher in the RPM's

Ehmark

you cant do too much with a 4v either because the valves will touch not sure about 3v though.

35thAnni99GT

The valves really arent the problem.... Its the reshaping of the passages that you see most of your gains from.

Chopper

Look at the link in my sig.
This gives an idea of what head porters are up against when trying to maximize power output of a 4.6 2v engine.

I think a higher port roof on the intake side to allow airflow to be as parallel to the valve stem as possible would be a big improvement,but there are coolant and oil passages in the way.

High tulip valves in the head might make up for some flow separation problems but this would increase weight in the valve train.This would require higher strength valve springs which would increase theinternal resistance of the engine.
A bigger bore to unshroud the valves would help,this would make even bigger valves possible but bringing back the cylinder wall clearance problem.
You see where this is going.There are some improvements but you always have consequences.