Making decision between 4AGZE or 4AGE 20V

There is no definite answers to such question as both engines are quite different and is just a matter of what your needs are and what you really enjoy in an engine.

The 4A-GZE in general, like most forced induction engines, provide very deep torque range from low to mid rpm, and provides the driver a similar feeling as larger displacement engines. The power output is provided low in the rpm range. By contrast the 20V and modified 16V engines, being naturally aspirated, requires much higher revs to get similar output and torque curve is steep and narrow at the top. The more aggressively you tune them the more this is apparent.

The 20V with it's VVT operating, provides more stable higher torque output than the 16V but is vastly lower than that of the 4A-GZE. Novice drivers will definitely be faster with the 4A-GZE while more experienced drivers will find very rewarding challenge from the 20V while showered with the concert of individual throttles all singing like the best of racing motors. All this however is provided that you had installed and tuned the engine well, which seems to be more of a problem for beginners. In any case, never budget your project short, or cut corners on parts needed, or else your project will just be that...a compromise, even when just installing it using OEM specs.

4A-GZE - Forced Induction (Supercharger)

A forced induction engine, especially that like the 4A-GZE which uses Roots-Supercharger, will have very low torque availability. This means much of the horsepower is available at the lower to mid rpm range just as if you had a larger displacement engine. The principle is just that, to force more air and gasoline mixture into the chamber than normal atmospheric pressure allows, and burn that much more fuel within a limited cylinder space of the small engine.

Having said that, the heat generated from the engine is quite a bit more in need of attention. Despite the power being created at lower engine friction state, the sheer combustive heat and pressures generate a lot of heat. Therefore, the engine is stressed, needing a much more robust and heavier internals. The 4A-GZE does have a forged piston, and reinforced skirt area as well as it being based on a later model 4A-GE connecting rods and bearing system. It is durable engine when properly operated with factory ECU with all the sensors properly connected or with professional aftermarket ECU integration. However, like any forced induction engine, it is very susceptible to failure from bad installations, calibrations, etc, since the forces are that much greater for each combustion cycle. Also massive heat generated requires a much more robust cooling system for oil and water, and still has issues if the engine is used for very long duration under heavy loads, (such as in sustained hours in spirited open road driving, or large number of laps in a closed race track.)

4A-GE - Normally Aspirated 16V-20V

Naturally aspirated engines in contrast, are much simpler in actual design and parts list. It is a design where extra air and fuel is burned more rapidly by spinning an engine capable of sustaining very high RPM. The torque curve is narrow and it takes a skilled driver to maintain a high power range consistently, the more busy and variable the race conditions get. Some find this a rewarding trait (I do) but others prefer easy, consistent power of a forced induction method as in supercharging or turbocharging. The benefits of a high rpm NA engine is instant response. The engine will respond quickly to throttle and a more experienced driver will find such merit a definite must when driving on a track that involve braking and turning. As side bonus, the wailing sounds of a properly tuned high-rpm engine is what dreams are made of for enthusiasts who enjoy a fine calibrated engine in a car or a bike.

However this is not to say the installation or care taken in installation is any less complicated. It has to sustain rather high internal forces from higher rpm operation, and careful assembly becomes much more critical in such engines than in a low-rpm forced induction engine. Spinning an engine efficiently at over 6000rpm is a very precise business and it most often is a very expensive proposition with work becoming much more reserved for experienced tuners to achieve good results. Simply slapping pats together from a catalog will most often never achieve the intended result. And every gram of fat and every 1/100ths of a gram of balance will affect significant amount of power.

20V and modified 16V naturally aspirated 4A-GE engines are much simpler in electronic control and regulation. However it still needs precise timing and delivery and slightly higher electrical needs at higher RPM. Sustaining high rpm requires a very good ignition system. This is because the high rpm engine will require the spark plugs to fire more frequently and more precisely. If the engine is spinning at 8000rpm, the plugs must fire 4000 times per minute. The time it takes to recharge a coil for a spark is greatly reduced the higher rpm we must go. The problem in modern ignition system is not so much the timing control as computers are much faster than 4000X per second in processing. However the great electrical draw required to charge the coils are sometimes lacking in home-brew projects based on a 1986 Corolla specification alternator and supply. Many reduce the size of the battery to save weight, adding to more issues at times.