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4A-GZE Supercharged Engine |
[Taken from article: http://www.mr2.com/TEXT/SuperChargerInfo.html]Overview
The Toyota 4-AGZE motor was used in the 86-89 MR2 Supercharged edition MR2s. The motor
is a modified 4-AGE unit coupled to an electronically engaged roots type supercharger
(manufacturer currently unverified) and a Nippon Denso air-to-air intercooler. Static
compression ratio of the motor was dropped from 9.4:1 to 8.0:1. The camshafts are
identical to a normally aspirated car, although their timing may be different. The motor
is fitted with a different type of injector with a higher flow capacity. Boost level is
set at 8 PSI and achieved at 4000 RPM and higher, however the supercharger creates usable
boost from idle through redline.
The supercharger is driven by a serpentine belt off of the crankshaft and shares it's
drive belt with the water pump. An electromagnetic clutch is installed on the
supercharger, allowing it to freewheel when it is not needed. The clutch is controled by
the engine's electronic control unit (ECU). A combination blow-off/bypass valve is
provided to route air around the supercharger when the clutch is disengaged or when boost
exceeds 8 PSI (nominal). The valve is operated by manifold vacuum/pressure. The ECU has
the ability to force the bypass closed via an electronic vacuum cut off solenoid valve.
The rear engine cover was modified to increase the height of the vents to clear the
intercooler. The passenger side engine cover vent was closed off and the driver side vent
had moulding added on the inside to seal against the top of the intercooler. The engine
cover is also made from fiberglass rather than stamped steel.
An oil-to-water cooler was added, the transmission and drive shafts were upgraded and a
10mm larger clutch was was added along with a new flywheel. A green light emitting diode
indicator located on the tachometer and labled "Supercharger" is activated by
the ECU whenever intake manifold pressure is positive. An engine knock sensor and a fuel
octane selection switch were also added. The supercharger and transmission changes add
almost 200 lbs. to the car.
Components
Supercharger
Length: 249mm
Width: 148mm
Height: 254mm
Weight: 10.8kg
Displacement: 1200cc
The supercharger is a roots type unit, manufacturer is unknown at this time. The lower
vane is driven by the pully and drives the upper vane via gears located in the rear of the
housing. The gears are run in Toyota supercharger oil, Toyota part number 08885-80108. The
lubricant costs about $50 for 50ml. Total gearhousing capacity is 130ml.
Two special tools are required for disassmbly of the supercharger; SST 09504-00011 for
keeping the pully from rotating while you undo the nut that holds the clutch hub to the
supercharger. If you have an impact wrench you might be able to get by without this for
removal. However you will still need something to hold the pully when you tighten the nut
down upon re-assembly. SST 09814-22010 for removing the ring nut that holds the clutch
pully on. You can't get by without this short of having a set of ring nut sockets or
custom building the equivalent tool.
Vent holes are placed at three points in the housing. One in the rear gear housing and
one to each of the shaft ends of the vanes on the front of the supercharger. The vents are
all connected together via external metals tubes and hosing. An air valve is connected to
all the vents which can purge them to the intake system after the airflow meter but before
the throttle body.
The supercharger adds heat to the intake charge both by conduction of housing heat
since the supercharger is bolted onto the engine and also by pressurizing the intake
charge. With the bypass valve open and the supercharger disengaged the intake system
raises the intake charge temperature by about 30 degrees F once everything is up to
operating temperature. Running under full boost with an outside air temperature of 50
degrees F the air temperature of the SC outlet can get as high as 270 degrees.
Supercharger Clutch
The supercharger clutch works in the same way as an air conditioning compressor clutch.
The pully itself spins freely on the supercharger input shaft. A coil of wire sits behind
the pully and a metal disc sits in front. The front disc is connected to the actual input
shaft of the supercharger. When the coil is engergized, the disc is drawn against the
rotating pully and they then rotate together as a unit untill the coil is de-energized.
The ECU engages the supercharger based on intake manifold vacuum. When the vacuum drops
below 8" the supercharger clutch is engaged. The clutch stays on untill the intake
manifold vacuum has risen to over 10" for a period of 5 seconds. This time delay was
added to avoid cycling of the clutch during shifts and momentary throttle transitions.
The clutch is operated by the ECU via a relay that lives in the rear trunk right next
to the ECU unit itself. Both are located in the center of the engine/trunk behind the
pressboard trunk liner. The relay operates the clutch by grounding one side of the coil.
The other side of the coil is connected to +12 volts when the ignition is in the ON
position.
An intersting note is that the manifold vacuum will be low enough during highway
driving that the SC clutch will stay engaged all the time. This typically occurs at speeds
over 65 MPH. My cars milage ran around 26 miles per gallon under these conditions.
Air Bypass Valve
The air bypass valve (ABV) serves two functions. The first is to provide a route for
air to bypass the supercharger when it is not spinning. The second is to act as a blow-off
valve when boost exceeds aproximatly 8 PSI. The blow off point varies significantly
between cars from 8 to 10 PSI.
The valve is attached to the rear of the supercharger and is closed when the car is not
running. It is in effect, a spring loaded plunger that blocks a port that runs from the
supercharger inlet to the outlet. When the intake manifold pressure on the plunger exceeds
the spring pressure, the valve starts to open, allowing the outlet side to discharge some
of it's air back into the inlet. This sets the maximum boost pressure.
The bypass function is achived by adding a vacuum operated diaphram on the back side of
the valve, which pulls the valve open. As soon as the car turns over, intake manifold
vacuum is created, which is routed to the diaphram and opens the bypass port. As the
throttle is opened, vacuum in the intake manifold drops and the valve starts to close. The
valve starts closing around 4-5" of intake manifold vacuum and is fully closed by
1-2". Since the computer has activated the SC clutch when intake vacuum dropped to
8", the supercharger starts spinning while the bypass valve is still open. The valve
starts closing with the supercharger already spinning thus creating a gradual smooth
transition from an open to closed intake system.
The computer also controls a solenoid valve that vents the vacuum diaphram on the air
bypass valve to outside air. By doing this, the computer can cause the ABV to close
irregardless of intake manifold vacuum. This valve opens as soon as there is positive
pressure in the intake, thus keeping the diaphram from working in reverse and pushing the
ABV valve closed more tightly as intake pressure increases. The computer also holds the
ABV closed this way when there is sudden vacuum in the intake, such as when you release
the throttle during a shift. This way the intake system stays sealed to the supercharger
while you shift and the system does not have to re-seal when you step on the gas again.
After several seconds of closed throttle (constant vacuum in the intake), the computer
releases the valve and disengages the supercharger.
Interestingly, connecting the diaphram directly to the intake system, thus causing the
valve to cycle open during shifts does not produce any noticable change in throttle
response.
Intercooler
The intercooler is a Nippon Denso unit (part # 127100-0153) with 19 cores. Surface area
is 200mm X 290mm with a depth of 65mm. The inlet and outlet tubes run the length of the
intercooler and are 50mm in diameter.
When the car is in motion, air is drawn in via the side vent located on the passengers
side of the car and flows over the engine and out of the compartment via the intercooler.
The side vent has positive pressure and the area over the engine cover has negative
pressure.
At 65 MPH air entering the vent increases in temperature by about 10 degrees F before
reaching the intercooler. Suprisingly, the temperature increase stays below 15 degrees all
the way down to 20 MPH or so. Increasing speed over 65 does not make a significant change.
At idle the underhood temperature rises to about 120 at which point the fan installed
in the side vent activates, bringing the temperature back down to about 100 degrees before
shutting down. Note that the temperatures above were measured directly below the
intercooler. Under hood temperatures vary considerably by location, for example the the
fan sensor, which is located nearthe exhaust manifold activates at ~160 degrees F and
disengages at ~130 degrees.
Intake charge temperature drops between 100 and 50 degrees depending on conditions.
When the intercooler is cold, full throttle opening will yield a 100 degree temperature
drop which then falls back to a low of 50 degrees as the intercooler itself heats up. 10
seconds after 1/8 throttle to full throttle opening the intercooler temperature drop is
down to 75 degrees and within 30 seconds falls to 60 degrees, falling at a slower rate
after that. Unfortunatly I did not have a data logger available at the time so I cannot
provide any chart data.
Air Vent Control Valve
The valve connects the supercharger gear case and end seals to the intake system before
the throttle body. The valve is operated by the ECU. With the valve closed, pressure
inside the vent system runs about 1/2 of the manifold pressure (or vacuum as the case may
be).
I suspect the reason for this is to minimize the pressure differential between the vane
end seals and the outside air. The ECU opens the vent line when manifold intake vacuum is
betwen 0 and 3".
Knock Sensor
The knock sensor is attached to the engine block and sends the ECU an electrical signal
that corresponds to engine vibration. The ECU filters the signal for frequencies of
interest during a time window that is syncronized with crankshaft rotation to look for a
characteristic signal that is produced during knocking.
If knocking is detected the ignition timing is backed off and then slowly returned to
normal unless knocking is detected, in which case the cycle starts over. The detection
time for knocking is in the 1-2 second range. I don't have values for the amount of timing
back-off or the return-to-normal speed. No attempt is made to drop the boost level when
knocking is detected.
Gas Selection Switch
A switch is provided on the dashboard to select what type of gasoline is in use (high
or low octane). Function is currently unknown, although changes in ignition timing would
be expected. Note: This switch does not appear on the Japanese cars.
Supercharger Oil Replacements
The cost of Toyota SC lubricant is quite high. Other types of SC lubricants may work
satisfactorily. Other places to try for lubricant are Ford (a roots type supercharger was
used on the Thunderbird), GM (the Bonneville SC uses a roots supercharger) and any of the
aftermarket roots supercharger manufacturers such as BI, Magnuson or Weiand. I expect any
decent hypoid gear oil will work. I plan on using 90 weight synthetic gear oil the next
time I am in the supercharger. After talking with several people who run roots type
superchargers on race cars and change their gear oil frequently I could not find any
reason why the Toyota unit would need something special. Maybe the $50 price tag is for
the special syringe packaging and low volumes they sell. Or maybe they used whale oil or
something
I have also sucessfully used the Jaguar Supercharger Oil, it costs 15.16UKP for 118ml,
the part number is: JLM12290
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