Bluetop is in fact a term that has been thought up by 4A-GE enthousiasts..

 But actually, this name that has been given to the first generation 4A-GE engines, isn't correct! 

The first generation 4A-GE engines (build somewhere between '84 until '89) had blue '16 Valve' characters on top of the valvecovers.

Some people use these blue characters to indentify the different generations of the 4A-GE (first generation is called 'Bluetop'. Second generation is called  'Redtop').

But the differences between the different generations go further than just the valve covers.

My bigport 4A-GE under construction, with the blue characters restored to their former glory!

On top of that, the valvecovers are interchangable between the different generations and the valvecovers can be painted in a different colour in their lives. Even Toyota sometimes used the two colours for both generations. 

This is why I preffer to call the two generations by their biggest difference: 'Bigport' for the first generation and 'Smallport' for the second generation.

This is always correct because this difference between the two generations is that the first generation had larger intake ports than the second generation.

In these pictures you might be able to see the difference between the intakeports of the Bigport (left) and the Smallport (right)

You could also look for the T-VIS system, which is only used on the Bigport engines.

But then you must keep in mind, that some tuners remove the T-VIS system all together, so this is not a guaranteed difference to indentify the engine by.

I'll post the specifications of the Bigport engines below (apart from the slight differences between the engines of different years of construction):

Enginecode                              : 4A-GE

Fuel                                                : Petrol

Poweroutput                           : 125hp @ 6600rpm with MAP

                                                           : 115hp @ 6600rpm with AFM

Torque                                         : 138Nm @ 5000rpm

Number of cylinders         : 4 Cylinders

Displacement                         : 1587cc

Throttle diameter                : 55mm

Number of valves                 : 16 valves (4 per cylinder)

Valve operation                     : DOHC

Camshaft drive                      : Belt drive

Camshaft duration             : 240° in- and exhaust

Camshaft lift                            : 7,56mm in- and exhaust

Valve angle                               : -45°

Diameter intake valve      : 29,5mm

Diameter exhaust valve  : 25,5mm

Material cylinderhead    : Aluminium

Bore x stroke                            : 81,0 x 77,0 mm

Compression                           : 9,4 : 1

Diameter pistonpins          : 18mm with early, and 20mm with later engines

Fuelsystem                                : Fuel injected (L- Jetronic)

Ignition                                        : Elektronic ignition (ESA/TCCS)

Intake system                          : AFM with early engines or certain markets, and MAP with later engines

Material cylinderblock    : Castiron

Cylinderblock                         : 3- Ribs cylinderblock with 40mm cranckshaft bigends, or 7- Ribs cylinderblock with

                                                              42mm krukas bigends

Injector capacity                  : 182cc/min (1 Ohm with early, and 2 Ohm impedance with later engines, topfeed)

Fuelpump pressure            : 75 psi

Fuelrail pressure                  : 35 to 38 psi

Engine dry weight                : +/- 123 to 126kg