Im looking to put in 1mm oversized inlet and outlet valves when I do my 2.3 stroker and AMS GT35R build early next year.

What is the effect of putting in oversizeed valves? Increased top end power at the expense of torque or am i likely to see increase of power and torque compared to standard size valves?

Note that this is intended to be a 94oct pump gas only car.

Depends on what else you do to the head in the way of porting. Very generally stated, larger valves can reduce port velocity in the lower RPM ranges, often with a gain in the upper RPM ranges. It's not always true that you'll see an improvement, since port velocity is important, and you're looking at the area under the whole curve.

The exhaust ports will ported and polished.

Is it also true that oversized inlet is hard to put in as there isn't much meat in the valve seat that enables you to get a decent three/five angle on it. Which in turn means that the gains you may achieve from enlarging can be lost due to the poor flow over the seat ?

Yes agree with this fact as we used the 1mm oversized ferrea valves and the valve heads reached one an other also due to lack of spacen head..

If your planning on doing drag racing with the car and a heavy port job, it might be a worthwhile investment. Stock DSM heads have been 10s with no porting or increased valve sizes. The evo head I am sure flows much better stock for stock

The ports in a 1G head are considerably larger than the EVO ports. The configurations are substantially different as well. I don't have figures on ultimate flow, or port velocity comparing the 1G to the Evo head. I'd love to see some

Check out headdynamics.com he does awesome port work and has many options avl for the 4g, Also reasonable pricing

Its a well known fact that the 2g head is a better platform to start with because its port size yeilds a higher velocity. As crappy as the 1g heads are, they still go 10s with cams and no port wor or pocket portwork.