![[Image]](GRAPHICS/intrcool.jpg)
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.
T-tops were installed on all Supercharged models.
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.
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.
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.
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.
Actual outlet temperatures were as follows with an outside air temperature
of 59 degrees F.
Partial throttle cruise at 70MPH (SC engaged, 8" vacuum) 100 F Partial throttle cruise at 70MPH after full boost run 130 F Idle, engine compartment fan on. 100 F Maximum observed outlet temperature (long uphill run, 10 PSI) 200 F
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".
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.
KRPM MPH Run 1 Run 2 ==================================== 2-3 14-22 0.99 0.98 seconds 3-4 22-30 0.99 0.97 4-5 30-38 0.90 1.00 5-6 38-46 1.07 1.02 6-7 46-54 1.17 1.17 Calculated horsepower RPM HP ============== 2500 52 3500 75 4500 101 5500 114 6500 121Source: Measured values.
If you install one, the fan should be set up to blow out through the top of the inercooler towards the rear deck lid. This is the natural airflow when the car is moving. Running in reverse caused higher intake charge temperatures as the fan slowed down the normal airflow over the intercooler. It has been suggested that a squirrel cage type blower can provide more pressure. Some bench tests with this fan type didn't look very promising either. An air scoop on the drivers side of the car would probably work best short of relocating the intercooler.
Belt slip manifests itself by a squealing or an air leaking type of sound over a particular RPM. The noise can be intermittent. A noticable drop in boost (around 2-3 PSI) is usually observed during the slip.
![[Image]](GRAPHICS/sc2.jpg)
Looking at the supercharger from the
top. Only the Air Bypass Valve (red and white sticker) is visible.
![[Image]](GRAPHICS/sc1.jpg)
The radiator overflow tank has been
removed. The Air Vent Control valve is the brown one on top of the supercharger
with three hoses attached to it. The ABV diaphram control valve is the blue
valve near the bottom with a hose running to the AVB. The brown valve in the
very bottom vents the fuel pressure regulator's compensation port to the
atmosphere.
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Dave Kucharczyk <ssr@netcom.com>