Over the years the 3S-GTE engine has evolved from it's original form in the ST165 Celica GT-Four, to it's current guise in the Japan-only ST246 Caldina GT-Four. The names given to the different generations are not official, but simply those commonly used to refer to them, and they are:

Gen 1: 1986-1989

As found in the ST165 Celica GT-Four. This engine produced 185HP, and 177ft-lbs of torque.

Gen 2: 1989-1993

As found in the ST185 Celica GT-Four and SW20 MR2 Turbo (until late 1993). Produced 225hp, and 224ft-lbs in the MR2 and regular GT-Fours, 235HP and 224ft-lbs in the GT-Four RC.

Gen 3: 1993-1999

As found in the ST205 Celica GT-Four and SW20 MR2 Turbo (late 93 onwards). Produced 245hp and 224ft-lbs in the MR2, and 255hp and 224ft-lbs in the GT-Four.

Gen 4: 1997-2002?

As found in the ST215 Caldina GT-T. Produced 260hp and 239ft-lbs of torque.

Gen 5: 2002-

As found in the ST246 Caldina GT-Four. I don't have a lot of information about this engine so will only include what I know.

Intercooler

Gen 1

Small top-mounted water to air intercooler.

Gen 2

GT-Four - top mounted air to air intercooler

GT-Four RC - large top mounted water to air intercooler, larger pump, water lines and radiator than Gen 1.

MR2 - side mounted air to air intercooler, same size as the GT-Four air to air but with different piping outlets

Gen 3

GT-Four - large top mounted water to air intercooler, slightly thicker than Gen 2 GT-Four RC one, but with the same size lines and pump and similar sized radiator

MR2 - same side mounted air to air intercooler as Gen 2 in earlier MR2.

Gen 4

Top mounted air to air, larger than Gen 2 in GT-Four and MR2.

Gen 5

Top mounted air to air, appears to be the same as Gen 4.

Intake Manifold

Gen 1

Central throttle body, T-VIS (8 runner).

Gen 2

Central throttle body, T-VIS (8 runner)

Gen 3

Central throttle body, non T-VIS

Gen 4

Side entry, non T-VIS.

Gen 5

Central throttle body, non T-VIS

Injectors/Fuel Rail

Gen 1

430cc/min top feed

Gen 2

430cc/min side feed

Gen 3

540cc/min side feed

Gen 4

540cc/min(?) top feed

Gen 5

Not sure, but apparently the engine uses central injection, which is a system that usually only uses one large injector, placed right behind the throttle body, however EPC drawings show the injectors have a fairly normal layout, so I don't know about this one..

Engine Management Type

Gen 1

Bosch L-Jetronic (uses airflow meter).

Gen 2

Bosch L-Jetronic (uses airflow meter) - GT-Four RC has a larger AFM

Gen 3

Bosch D-Jetronic (uses Manifold Absolute Pressure sensor)

Gen 4

Probably Bosch D-Jetronic (uses Manifold Absolute Pressure sensor). Direct Fire Ignition with crank angle and cam angle sensors.

Gen 5

Not sure, but appears to use a Manifold Absolute Pressure sensor. Direct Fire Ignition, (not VVT-i as previously stated)

Turbo

Gen 1

Single entry steel CT26 with 4 bolt exhaust flange. No Bypass Valve

Gen 2

GT-Four: Twin entry CT26, ceramic turbine/shaft (JDM only), with the same diameter turbine and impeller as the Gen 1. 6 bolt exhaust flange. No Bypass Valve

MR2: Twin entry CT26, ceramic turbine/shaft (JDM only), with the same diameter turbine and impeller as the Gen 1. 6 bolt exhaust flange. Bypass Valve fitted

GT-Four RC and some others had steel turbine/shaft, with a slightly larger impeller. 6 bolt exhaust flange. No Bypass Valve

Note: All export models had steel turbine/shaft, however it is not clear whether this is the same turbo as is used in the GT-Four RC or if it is the same size as the ceramic versions but with steel parts

Gen 3

GT-Four, MR2: Twin entry CT20B, ceramic turbine/shaft. 7 bolt exhaust flange. Bypass Valve fitted

GT-Four Group A (and other homologation models) had steel turbine/shaft. 7 bolt exhaust flange. Bypass Valve fitted

Gen 4

Unsure, appears to be similar to CT20B, exhaust manifold and turbine housing are single piece casting.. Bypass Valve fitted

Gen 5

similar to Gen 4, except there is an extra stud on either end of the manifold to help prevent warping. Bypass Valve fitted

Fuel Cut

Gen 1

Early JDM models were calculated from AFM signal, happens around 12psi, later models were the same as the Gen 2. Currently investigating this a little for clarity.

Gen 2

GT-Four, MR2: Taken from Turbo Pressure Sensor. If that's unplugged (electrically) it calculates from AFM signal. Happens around 12psi

GT-Four RC same as above but happens at about 18psi.

Gen 3

Taken from MAP sensor. Happens around 18psi

Gen 4

Unsure, but probably the same as Gen 3.

Gen 5

Unsure, but probably the same as Gen 3.

Oil Cooler

Gen 1

Small water cooled box on the front of the block, between cylinder 3 and 4, under the turbo.

Gen 2

Small water cooled oil filter base on the front of the block, around cylinder 2

Gen 3

Same as Gen 2 but oil filter no longer attaches to the oil cooler

Cams

Gen 2

Intake: 236 Degrees, 8.2mm lift, Exhaust: 236 Degrees, 8.2mm lift

Gen 3

Intake: 240 Degrees, 8.7mm lift, Exhaust: 236 Degrees, 8.2mm lift

Other

Crankshafts

Gen 1 had a crankshaft with a slightly smaller PCD than Gen 2 onwards. The flywheel bolts were also one size smaller (like M8 vs M10 or something).

Heads

Gen 1 and 2 heads are of a very similar design, with large intake ports (T-VIS) and shim-over-bucket cam followers. Gen 3 and 4 appear to be almost identical, and had smaller intake ports and shim-under-bucket cam followers.

Gen 1 and 2 exhaust and intake ports/flanges are the same layout and the manifolds are interchangable. Early Gen 2 had one extra exhaust stud, later Gen 2s had 2 more.

Gen 3 and 4 exhaust and intake ports/flanges are the same layout and the manifolds are interchangable. The port spacing is different to the Gen 1 and 2

Cambelt Tensioner arrangement

Gen 1s are tensioned by a normal sliding tensioner and spring. Gen 2 onwards have a hydraulic tensioner. The Gen 1 heads do not have the appropriate bosses

Sump

Gen 1 and 2 use a normal steel bowl sump. Gen 3 onwards have a two piece sump; the top half is alloy and has the oil filter mounted to it. They use a different oil pump that diverts oil to the new filter location. They also have a small steel bowl on the bottom.

Blocks

Late in 1997 the block casting for the 3S series was revised with added support around the head stud boss by the water pump. This is most likely due to the block cracking problems (not just in high HP motors, but occassionally even in stock NA ones). The issues seems to be with excessive cylinder pressure trying to lift the head and basically ripping the whole corner out of the block. Here's a picture courtesy of mrcontrols.com ( click ) This is not to be confused with the problem of high HP engines cracking between #2 and #3 cylinders.

Sources: Some of this comes from my own experience, but much comes from Richard Doig's website, cam specs posted on a message board from a Hyperrev magazine.