4AG engines were introduced in 1984 as the replacement to the 2TG.
Although a lot of knowledgeable Toyota enthusiasts welcomed the 16 valve
head, many kept back their excitement because the engine looked fragile.
Internal pieces did not follow the usual Toyota robust design.
In less time than the engines needed rebuilding, modified units were
performing and surviving in competition. Toyota
has rewarded it's Twin Cam diehards- with a new engine!
secret in the 4AG's compact and lightweight design was better metallurgy.
This is how Toyota was able to guarantee 4AG durability equal to its
performance potential. The iron
block was preferred over all-aluminum units, with a minimal weight disadvantage.
The 4AG can be modified without the disastrous results of all-aluminum
blocks. For it's physical
dimensions Toyota was wise to keep the iron block.
with any Toyota engine design- the 4AG evolved.
The first generation and second generation can be differentiated by their
large or small ports, and third generation with 5 valves!
The later versions had piston oil coolers, and higher compressions.
The 4AG was very popular and during it's introduction and out ran any 4
cylinders 1600 with 16 valves.
Motorsports U.S.A. initiated a development program for these engines, and have
been rewarded with a successful Formula Atlantic series.
These heavily modified engines maintained all the 4AG dimensions, with
modifications to the original block and cylinder heads.
As a full racing engine the 4AG has proven itself.
4AG originally powered 3 distinct drive arrangements- RWD (Corolla GTS),
Mid-Ship (MR2), and FWD (FX16). There
is 2 possible 4WD conversion available, but must only be used with stock HP
output. The later model Toyotas all
went FWD, by which time the 4AG was in its 2nd generation (1990).
The 4AG disappeared from the U.S. market by mid-91.
By the 3rd generation, in Japan, the GTS 4A-GE and GTZ 4A-GZE
Supercharged engines were replaced by the 4AG 5 valve (1992).
The 5-valve has also a 2nd generation (1996).
The 4AG series evolved from 115HP to 170HP.
4AG, because of its lightweight and compact design, is a very popular choice for
diverse applications. Desert racing
buggies (qualifying for the Toyota Contingency program), Lotus 7 replicas, and
the older Toyota Corollas and Starlet all support the "modern" 4AG
engines. Engine conversion kits are
available. There is tremendous
respect for these power units, specially for RWD applications.
Japan there is resurgent interest based on a comic hero, whose 4AG Corolla has
taken and beaten all comers. This
fantasy based on reality. Japanese
performance parts manufacturers, after discontinuing sports part production,
have again scheduled 4AG parts for production.
Just like the engine it replaced, the 2TG, the 4AG is the Toyota engine
for a whole new generation.
U.S. 4AG-ZE in the MR2 developed 140HP with the supercharger and with strictly
bolt-on modifications produced 188HP. There
was available a Twin Charger kit from HKS that developed 210HP and after further
modifications produced in excess of 350HP!
Also available was the HKS 5AG kit (not a Toyota designation), which
included a stroked crank and over-size pistons for 1720cc.
have rallied the 4AG Corolla AE86 in many international FIA events.
The cars are very competitive in Group N. One of the first Corollas we
prepared was for SCCA GT 2, which ended up in South America.
We have exported prepared 4AG engines to 5 countries!
MR2s in SCCA IT (Improved Touring) are disadvantaged in the class, but
with a little tuning (late model blocks) become really competitive.
We have set-up both cars for SCCA Solo ! and II.
fastest set-up is the Twin Charged MR2, and is completely streetable.
Unfortunately the kit is no longer available. Turbo engines can be set-up
for ultimately more HP, but ac lot less tractable.
The turbo engines, with forged or supercharger pistons, easily outrun the
4AGZ, with the same psi output. The
4AGZE engined MR2 and RWD/FWD Corolla conversions with the HKS (10 psi) big
pulley puts out at least 175 to 200. There
are bigger pulley kits, example: Cusco
(14 psi), that will definitely need additional EFI programming.
Mild cams and injectors can be combined for phenomenal cc. to HP output
THE 4A-GE 20 VALVE
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).
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. The individual
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 surface area- the 5 valve design cannot be
beat- theoretically and geometrically.
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 iron block- the engines were still on solid foundation for
heavy and serious modifications.
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 lightweight block 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).
these engines were used in Formula Toyota, a series much like Formula Atlantic
where there is only one SPEC engine available 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.
of Toyota technology, the twin versions of the 20-valve engine- 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??
THE 4AG / 4AGZE
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 fine
for milder tunes. For
serious competition the rods should be replaced.
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
away from the 7AF to 7AG conversion since the crank is not forged and the
flywheel bolts are too small, with no provision available to upgrade.
The rods are potential failures also when subjected to real 4AG RPM
operation. It is an exercise in
creativity but a total sidestep for any real performance-oriented application.
If you like the torque of the 7AF, use the complete engine.
There are some issues about the Formula Atlantic head.
The Formula Atlantic head is a modified 4AG head- port and polished with
the valve adjusters changed to the under-the-bucket shim arrangement (similar to
the 2TG and 18RG). The
valves and springs are different too. This
modification is required when running camshafts with high lift and/or long
duration (above 300). For
street purposes there is no advantage converting to this adjustment method or
preparing the head to Atlantic specifications.
The port and chamber modifications will decrease performance- short of
preparing the complete engine to Formula Atlantic specifications, which will
render the package totally unstreetable.
is very minimal head preparation needed, aside from match porting and polishing
the runners. Porting the heads on
this 16 valve Twin Cam more often decreases the air velocity- resulting in
poorer throttle response. Despite
others claim of a 20HP or more increase- on modified heads alone, this is simply
impossible without camshaft or pistons changed.
Toyota has casted and machined all their 4 valve heads to very close and
accurate tolerances for street (and rally) use.
choices for stock EFI systems and pistons should be limited to less than 265
duration. Upgraded blocks with
pistons of at least 10.5:1 compression may use up to 288.
It is recommended to convert to under-the-bucket shims for durations over
300 (with corresponding higher compression pistons).
Installing high duration cams on the stock set-up will cause the shims to
fall-off and instant result in instant engine seizure.
As always stay away from reground cams with non-factory lobe centers, you
will have problems getting the correct adjustment shims.
the 4AGZ intake manifold- the #1 runner, which is dog-legged, must be filled and
recontoured. This is a simple
procedure that must be done. Be
sure to frequently check the supercharger oil also.
Many units have died because of oil starvation.
5 valve head is Toyota's bonus to the 4AG after the 4AGZE went away.
With the additional valve and independent throttle bodies- the 4AG 20
valve is a unique head design. This
head unfortunately has many proprietary pieces and the only way to do a
conversion to a 5 valve is only with a complete engine.
The distributor position may be a problem in RWD installations. (Note:
There are 2 versions of the 5-valve engine, see related information under
/ Turbo Upgrade- The
preparation for the turbo set-up is to lower the compression.
The 4AG / 4AGZ that will see boosts in excess of 10 psi should be set-up
with forged pistons. Blocks
with the oil squirters must be used as these come with the better rods.
For boosts higher than 18 psi, the rods have to be replaced.
Oil cooler is mandatory, and for all applications a bigger radiator is a
good investment. Use
the 4AGZ injectors and fuel pressure regulator for turbo conversions of the
normally aspirated 4AG.
550cc injectors are available for serious boost / engine outputs. The
fuel pump can be replaced with the Supra Turbo pump, a direct bolt-in.
at all possible avoid using the dual side-draft carbs.
The cost for the carbs / manifold plus ignition conversion will come
close to a new fuel injection system.
The EFI system will be adequate for minor tuning.
4AG/Z EFI systems use either an AFM (air flow meter) or MAP (manifold air
AFM model is actually preferred since it will allow the user some adjustability
for modified cams; there is no compensation available with MAP sensors.
There is no advantage to converting to a MAP sensor, the idea of loss HP
due to the AFM restriction is not true.
4AGZs equipped with DFI (direct fire ignition), will see a performance increase
with an ignition amplifier.
This is one of very few Toyota ignitions that are marginal.
Colder plugs must be used with any upgrade.
For carburetor equipped 4AGs the distributor has to supplemented with a
timing controller, MSD 6A, and a coil.
Stock configuration- Overhauling
the 4AG is straightforward.
Machine Shop experience in rebuilding the head is a must.
Bores should be kept at the maximum 83mm.
If available newer rods with the bigger wrist pin must be used- with the
later model high compression pistons.
Clean up the ports and EGR passages at the same time.
Verify crank pin sizes since there are differences.
the 2nd generation blocks.
The smaller port heads (non-TVIS) heads have better air velocity,
specially important when using carburetors.
Depending on the EFI system used, choose the mildest cam available- you
will have better results. Adjustable cam pulleys will ensure accurate timing and
cylinder pressure tuning.
Forged high compression pistons are reasonably priced and are a good
to a late model head will require fabrication of a new intake layout for RWD.
The throttle body can also be enlarged to maximize air intake.
4AGZE conversion for normally aspirated models will need the correct power
steering pump, air conditioning compressor, and alternator.
This pieces are unique to this application- and the proper bracket is
also a must. The top mounted
intercooler will fit under the normally aspirated MR2 hood and will need a hood
scoop on FWD Corollas (but a front mount intercooler is still the best set-up.
The bigger (14 psi) crank pulley is a must.
are as many tuning theories as there are tuning shops.
The most important step in preparing an engine is to finalize the exact
set-up before buying any part. Displacement
increase that does not affect the bore / stroke ratio, to the detriment of RPM
potential will give the engine the edge. The
stock 16 valve head has undergone a lot of development time in terms of cam
configuration- unlike a displacement increase (done properly), a wrong camshaft
choice will result in a completely unsatisfactory set-up.
Racing configuration- The
preparation of any engine in sanctioned Motorsport events are tightly regulated.
Know the rules before starting.
FIA Group A or N parts homologated for use in these engines are
serious preparation will start by converting the valve adjustment to the racing
type (TRD) under-the bucket shims.
This will allow the use of any camshaft combination.
Formula Atlantic spec con-rods may be used with the correct piston
supercharged or turbo applications stay with the 20mm pins.
Lightened flywheels are available, to ensure the fastest throttle
port and chamber configuration approaching Formula Atlantic specs can be used-
but never the full Atlantic spec if the engine is not going into a formula
chassis or dune buggy.
(The 5-valve engine, used in Japan's Formula Toyota, is also supported
with tuning parts.)
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