I started this thread because it's namesake ( port and polished?? ) was locked. Why, I don't know.
First off, the link provided at the end of the thread refers to porting the exhaust manifold, not the cylinder head, which I think chris was asking about.
Scott, port and polish on the head will increase HP, and moreso than ANY Intake
tube, if it's done right.
The head will flow more air in, and more exhaust out of the cylinders after porting. Oversized valves & springs would be a must to match the port job, but, there is a downside...
As many people on this board are more than happy to point out, there are virtually no sources out there for reprogramming our ECU's, this is a hurdle, since you need to tune the ECU to add more fuel across the RPM range and compensate for the increased flow. Also, your fuel economy will drop like a stone depending on how intense the porting is. one way around the ECU issue is to get an aftermarket AFC, and tune it on a dyno manually, but the warranty will be a dead parrot at that stage. However, the benefits could be pretty sizeable if everything is done by a competent machine shop and the fuel system is properly tuned. since the Celica uses a MAF sensor, air flow shouldn't require much tuning, as the MAF will pick up on the increased flow, but fuel mapping is critical since you'd be going beyond the specs of the ECU's pre-set thresholds.
the 2zzge VVTL-i motor is about as radical as one can get, head-wise, so you can't go oversize too much, as stock, the head is ported very well, and there isn't much room for improvement, but there is some wiggle room for die-hard tuners. as for the 1zz, there is more room for improvement. also remember, if the 2zz head flows like mad after porting, when it goes into lift, the motor may not be able to handle the added flow, unless of course, you take precautions.
On the 2zz, I'd lower the compression a little, and get new cams that retard the timing a bit, you don't want any detonation. lower compression is easy, just get a thicker head gasket (racing copper seal type) or swap the pistons for dished out ones.
On either app, you'll probably need new injectors (higher flow rate, possibly just blueprinted ones) and an external fuel pressure regulator.
Keep in mind, this is in no way is a set list of parts you need, there may be other elements that need replacing, such as connecting rods, oil/fuel pumps, swapping in anti-pump lifters. it depends on the setup, and what will be needed to compensate for the increased flow.
Just my two cents, Hope this helps