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THE 4A-GE 20 VALVE
The 20-Valve 4AGE replaced the 4AGZE Supercharged engines. Just like the early and late 16 Valve 4Ges, they also underwent revisions. The Silver Top was introduced in the Corolla AE101 (1992), and the Black Top in the Corolla AE111 (1997). Both engines used Toyota’s version of Variable cam timing- VVT. Bore and stroke remained as in the original 1st and 2nd Generation 4AGEs(early) big port (TVIS) and (late) small port (non-TVIS). Similarly compression was upped in the later models. The blocks are identical to the late model AE92 generation blocks (and naturally the SC blocks too).
The 20-Valve engines never came officially into the US (and many other foreign markets where the old 4AGEs were available- and of course it imparts a very exotic presence. Theindividual throttle bodies look like they came off the fabulous 503 race engines. Think about it, no Toyota factory RACE Engine had 5 valves per cylinder!! Yamaha- who works with Toyota on cylinder head design (and manufacturing), have been a very avid pioneer and supporter of the 5-valve design. The short-lived Yamaha Formula 1 engines had 5 valves per cylinder. In terms of maximum valve to surfacearea- the 5 valve design cannot be beat- theoretically and geometrically.
Aside from the obvious 5-valve and variable timing cylinder head design- the difference from the 4-valve is the dramatically reduced weight of the internal components. Pistons, connecting rods, and to a lesser degree, crankshafts have all been updated with lighter weight design. The good news is that it remained an ironblock- the engines were still on solid foundation for heavy and serious modifications.
Between the Silver and Black top- the later Black models came with still lighter rotating components. Laying out the engine components side by side…there are miniscule differences, Toyota was tuning the engines to a higher degree by rotational mass reduction, a lesson advanced from the earlier lightweightblock design (of the pre-multi-valve engines). The difference in the connecting rods between 16 and 20 valve engines is dramatically surprising. However for purposes of radical modifications a Silver top will probably be a better engine to work with (slightly stouter rod).
In Japan these engines were used in Formula Toyota, a series much like Formula Atlantic where there is only one SPEC engineavailable to all competitors. The magic of 20-valve is apparent on the ability to attain and sustain a high RPM threshold. The addition of variable cam timing allows the engine to surpass both low-end torque and high RPM horsepower figures of the older 4AGEs. This is the closest to race spec engine Toyota has ever produced.
In terms of Toyota technology, the twin versions of the 20-valveengine- out specified any previous offering in naturally aspirated form. This is the last true iron block with the ultimate head design and intake set-up. The newer 1ZZFE and 2ZZGE come with a more advance VVTi head set-up- but with 1 less valve (per cylinder) and aluminum blocks. The 4AG 20-Valve wins!! What will Toyota use for the next Formula Atlantic engine??
MODIFYING THE 4AG / 4AGZE
Block:The 4AG block is a free revving and strong bottom end. A stock block will survive in excess of 350 HP if air-charged in the 8000 RPM range, or 250 HP in the 10000RPM range. The 2nd generation blocks with oil squirters should be the minimum considered. The connecting rods are also beefier, similar to the 4AGZ. The 1st generation block had smaller wrist pins and rod journals, which should be finefor milder tunes. For serious competition the rods should be replaced.
Stroking the crankshaft to a maximum 81mm will keep the RPM capability intact. Bores can be brought out to 83mm, but try to keep it under 82.5mm. There is no need for the Formula Atlantic crankshaft. Reject blocks that will need 83mm to clean up, for sure there is head damage also.
Stay away from the 7AF to 7AG...