Toyota FE Series Engines

(3/5SFE / 4/7AFE / 4/5EFE / 1ZZFE / and V6 / V8s)
 The various FE series engines (using the FE head design) are the most thoroughly developed and purpose tuned Toyota power plants.  In the USA, 98% of current models Toyotas use this engine/head design.  The FE 4 valve per cylinder, narrow-angle Twin Cam heads (on the various Toyota blocks) are the reason for the amazing response and smoothness of the current generation Toyota motors.  The high torque characteristic designed into these engines give the driver all the advantages of the Twin Cam head design- plus low-end torque and fuel economy.  Torque is the reason why these engines respond quickly and smoothly.  The performance band has been engineered to provide power from low RPM to the designated redline.
There has been a lot of requests for parts and modifications for these engines, but unfortunately trying to raise the RPM band (or changing cams) will negate all the built-in attributes of these engines.  A camshaft change to raise the power band higher, will result in the loss of low-end torque and idling problems.  Drivability will suffer and the trade off will leave the customer with a compromised engine, trying to work against the ECU program and engine design.
By comparison, the performance oriented GE versions of the same series engines, (if available on the sporty models)- offer about a 20% horsepower advantage- but at a loss in low RPM response and torque.  The GE heads are more of the true Twin Cam design: wide-angle valves, long duration cams- suited for high RPM and high output- but at the sacrifice of throttle response in the lower RPM levels.
There are improvements that can be made to the FE engines- but the Toyota engineered power band should not be altered.  The ECU program and Camshaft profiles, if changed will result in a loss of drivability and risk internal damage.  You cannot do a better job than Toyota on coaxing power from these series engines, and needless to say, stay street-legal.
Upgrading these engines, is of course still possible:  intake systems, exhaust components, ignition upgrades all help in fine-tuning these engines.  The rule to follow and keep in mind is that all modifications are basically external in nature.  The only exception being pistons- to increase or decrease compression- within the same RPM band.   Turbocharging and/or supercharging will help- but keep in mind that based on the design parameters (again) these engines were designed for response- meaning lightweight internals: con rods/crankshaft (as compared to the sportier GE series engines).
The short answer is- if you are seeking a true high performance engine and high HP outputs- upgrade to the GE version of your engine (if available).