The
4AGE / 4AGZE- 1600cc DOHC 4 VALVE, plus the 5 VALVE
The 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!
The 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.
As 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.
Toyota 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.
The 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.
The 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.
In 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.
The 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.
We 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.
The 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
ratios.
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 fine
for 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 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.
Cylinder Head:
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.
There 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.
Camshaft 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.
On 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.
The 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
Japanese engines).
Supercharger / 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.
Fuel System-
If 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 pressure). The 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.
Ignition System:
Even 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.
Some
Recommended Set-ups:
For 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.
For Modified
configuration- Use
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 upgrade.
Modifying 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.
The 7A conversion is not
recommended.
The 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.
There 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.
For 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 available.
Any 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
(19mm). For supercharged or turbo
applications stay with the 20mm pins. Lightened
flywheels are available, to ensure the fastest throttle response.
Cylinder 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.)
For
Formula Atlantic engines, see the Formula Atlantic sheet.
More
detailed 4AG topics can be found in- www.club4AG.com.