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Just a few pictures of my 92 Polo G40.
A fair few of ye probably know the car already, for those that don't:
Its a 1992 registered 1272cc supercharged Polo.
Original Irish car, one of only two officially imported into Ireland by VW.
This was the VW Ireland demo car (given to RTE as a promotional vehicle)
Only 500 rhd drive versions were built, based on the mk3 / 2f polo with revised suspension incorporating rose joints instead of bushes and uprated front and rear anti roll bars, thicker rear axle beam, heavier duty top mounts and lowered slightly over standard (40mm).
In May 1991, a G40 powered Polo finally arrived to displace the GT as the top Polo model available in the UK. It was based on the GT Coupe model, but with the assistance of the G-Lader and an intercooler, power was boosted to 113bhp (83kW). A characteristic of forced induction is a very wide spread of torque, which peaked at 111lb ft (150Nm) in the Mk3 G40. Other distinguishing features were lowered and stiffened suspension with a rear anti-roll bar, ventilated front brakes, and 175/60 tyres on 13 x 5.5 BBS alloy rims. Red striped bumpers, G40 badges front and rear, special 'Le Mans' interior trim, and a roof mounted 'bee sting' aerial completed the cosmetics.
To assist with publicity for the Polo range in general, Volkswagen introduced a one make race series for the G40 called the G40 Cup. These G40s continue to be raced in the Super Coupe Cup against performance models from Renault, Rover and Honda.
During the life of the UK Market Mk3 G40 there were only minor specification changes; for the 1992 model year clear front indicators and tinted rear lights were included along with a different stereo radio/cassette unit. Various options were available such as front fog lamps and a sunroof
G40 Engine
Although unique to the G40 model, the G40 engine (code PY) is closely based on the standard 1272cc Polo power plant. This conventional 4 cylinder water cooled design uses a cast iron block and alloy head. In the G40 it is transversely mounted, coupled to a manual 5 speed gearbox via an uprated clutch. Its main difference from other Polo engines is the addition of a supercharger to significantly boost power output.
Engine Management
Engine operation is controlled by an Electronic Control Unit (ECU). This ECU is a G40 specific version of the VW/Bosch Digifant Mk1 system. Similar ECUs are used on other VWs including the G60 powered cars and the Mk3 Polo GT. The Mk3 G40 Digifant is based on a Motorola MC68HC11 microprocessor and its control program is stored in a 32K byte EPROM device (type 27C256). This EPROM is normally referred to as the 'chip' and its contents include the ignition and fuelling maps that define the engine characteristics. 'Chipping' involves replacing the EPROM with an aftermarket version using new maps intended to improve performance.
The ECU uses a number of sensors to determine the engine's current operating conditions; knock sensor, distributor Hall sensor, air temperature sensor, coolant temperature sensor, MAP sensor, Lambda probe (oxygen sensor), throttle closed position (idle) switch, and throttle fully open switch. The signals from these sensors are then used to determine the appropriate fuel and ignition timings from the ECU's maps.
Cylinder Head
The alloy head uses a single overhead camshaft driven by a timing belt to operate 8 valves via hydraulic tappets. The use of a supercharger provides adequate power without needing the additional complication of a 16 valve head. To prevent problems with detonation the compression ratio is reduced to 8.0 to 1.
Air Intake and Supercharger
Cold air is fed to the air filter housing from an intake behind the driver's side headlamp. The intake ducting is specially shaped to reduce induction noise. The air is fed through a paper filter before entering the 40mm G-Lader supercharger. (Note that there is a restriction in the outlet pipe of the standard air filter housing.) It is essential that a good quality filter is used as the supercharger can be easily damaged by small particles; the engine should never be run without a filter. The supercharger compresses the air and feeds it to an air cooled intercooler located next to the charger behind the grill. (The intercooler inlet includes a coarse wire mesh filter to protect the engine in the event of a major supercharger failure!) The process of compressing the air heats it up and the intercooler removes this heat and so increases the air's density. The compressed and cooled air is then passed to the throttle.
The throttle system incorporates a bypass valve so that under normal operation any air excess to the engine's requirements is returned to a second supercharger intake (which is directly connected to the main supercharger intake from the air filter). On its way back the air pipe passes through the cam cover. This is purely for convenience of routing. Under normal conditions the air pressure is therefore low and supercharger is doing very little work. Fuel consumption is correspondingly low.
When the throttle is fully opened a mechanical linkage closes the bypass valve and the excess air from the supercharger causes the intake pressure to rapidly rise. The engine then operates at full boost and much higher power is available. If a boost gauge is used to monitor manifold pressure it can be seen that pressure is normally partial vacuum like a conventional engine (also allowing the vacuum servo to operate!) but builds rapidly to positive pressure when the throttle is fully depressed.
Dual 'V' belts are used to drive the supercharger from the crankshaft pulley as the loading is quite high when at full boost. As the supercharger displaces a fixed volume of air on each revolution and it is directly driven by the engine, the boost pressure available when the throttle is depressed is largely independent of engine speed. This produces a very good throttle response from any speed without the 'lag' associated with a turbocharger. A smaller pulley can be fitted to the charger to increase its speed relative to engine speed and so increase boost and performance (at the expense of supercharger life).
It now has a Stage 4 charger and K&N panel filter,
Power output is 114.4 @ the wheels and 129.9 @ the flywheel,
don't have the torque figures here but I'll get them later.
A few pictures:
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I'll stick it on there later Trev
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Here is a bit on the charger:
G-Lader History
The G-Lader was invented in 1905 by a Frenchman called Le Creux. Materials technology at the time prevented his design being a viable option. In the eighties once supercharging (as opposed to turbocharging) was decided upon as their route to performance Volkswagen decided to follow through with Le Creux's original design. Over 400 designs were produced before the current unit was settled on. The reliability of the current unit meets the following minimum requirement: Full boost at 10,000 rpm for 800 hours continuous. As a measure of what this means in real terms consider that one of the designs that fell by the wayside could only last 4 hours on the test bed under these conditions, but would still last 20,000 miles in a VW test car.
Principles
The lader (charger) unit has two air inlets and one outlet. One inlet is direct from the air cleaner box, the other recirculates unwanted compressed air. The lader is always spinning in proportion to engine revolutions (factor is 1.6 times crank speed). The unit is driven via two belts, which also drive the alternator. Outgoing air is driven through the intercooler (air cooled, using the same principle as the radiator, but without a fan) and then on to injection system. On the back end of the injection system is a bypass valve, which distributes the compressed air between the cylinders and the second lader inlet. The bypass valve is directly connected to the throttle. Only at full throttle opening is all the charge air directed to the cylinders, at other openings the air circulates, meaning the engine operates in pretty much a normally aspirated mode.
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Internally the G lader is a double spiral shaped chamber. Air is pulled into the outer spiral then forced inwards via a magnesium displacer, which rotates eccentrically, using a similar principle to the Wankel engine. The hot outgoing air is driven through the intercooler, which by cooling the air (by about 130 degress F) compresses it.
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A fair few of ye probably know the car already, for those that don't:
Its a 1992 registered 1272cc supercharged Polo.
Original Irish car, one of only two officially imported into Ireland by VW.
This was the VW Ireland demo car (given to RTE as a promotional vehicle)
Only 500 rhd drive versions were built, based on the mk3 / 2f polo with revised suspension incorporating rose joints instead of bushes and uprated front and rear anti roll bars, thicker rear axle beam, heavier duty top mounts and lowered slightly over standard (40mm).
In May 1991, a G40 powered Polo finally arrived to displace the GT as the top Polo model available in the UK. It was based on the GT Coupe model, but with the assistance of the G-Lader and an intercooler, power was boosted to 113bhp (83kW). A characteristic of forced induction is a very wide spread of torque, which peaked at 111lb ft (150Nm) in the Mk3 G40. Other distinguishing features were lowered and stiffened suspension with a rear anti-roll bar, ventilated front brakes, and 175/60 tyres on 13 x 5.5 BBS alloy rims. Red striped bumpers, G40 badges front and rear, special 'Le Mans' interior trim, and a roof mounted 'bee sting' aerial completed the cosmetics.
To assist with publicity for the Polo range in general, Volkswagen introduced a one make race series for the G40 called the G40 Cup. These G40s continue to be raced in the Super Coupe Cup against performance models from Renault, Rover and Honda.
During the life of the UK Market Mk3 G40 there were only minor specification changes; for the 1992 model year clear front indicators and tinted rear lights were included along with a different stereo radio/cassette unit. Various options were available such as front fog lamps and a sunroof
G40 Engine
Although unique to the G40 model, the G40 engine (code PY) is closely based on the standard 1272cc Polo power plant. This conventional 4 cylinder water cooled design uses a cast iron block and alloy head. In the G40 it is transversely mounted, coupled to a manual 5 speed gearbox via an uprated clutch. Its main difference from other Polo engines is the addition of a supercharger to significantly boost power output.
Engine Management
Engine operation is controlled by an Electronic Control Unit (ECU). This ECU is a G40 specific version of the VW/Bosch Digifant Mk1 system. Similar ECUs are used on other VWs including the G60 powered cars and the Mk3 Polo GT. The Mk3 G40 Digifant is based on a Motorola MC68HC11 microprocessor and its control program is stored in a 32K byte EPROM device (type 27C256). This EPROM is normally referred to as the 'chip' and its contents include the ignition and fuelling maps that define the engine characteristics. 'Chipping' involves replacing the EPROM with an aftermarket version using new maps intended to improve performance.
The ECU uses a number of sensors to determine the engine's current operating conditions; knock sensor, distributor Hall sensor, air temperature sensor, coolant temperature sensor, MAP sensor, Lambda probe (oxygen sensor), throttle closed position (idle) switch, and throttle fully open switch. The signals from these sensors are then used to determine the appropriate fuel and ignition timings from the ECU's maps.
Cylinder Head
The alloy head uses a single overhead camshaft driven by a timing belt to operate 8 valves via hydraulic tappets. The use of a supercharger provides adequate power without needing the additional complication of a 16 valve head. To prevent problems with detonation the compression ratio is reduced to 8.0 to 1.
Air Intake and Supercharger
Cold air is fed to the air filter housing from an intake behind the driver's side headlamp. The intake ducting is specially shaped to reduce induction noise. The air is fed through a paper filter before entering the 40mm G-Lader supercharger. (Note that there is a restriction in the outlet pipe of the standard air filter housing.) It is essential that a good quality filter is used as the supercharger can be easily damaged by small particles; the engine should never be run without a filter. The supercharger compresses the air and feeds it to an air cooled intercooler located next to the charger behind the grill. (The intercooler inlet includes a coarse wire mesh filter to protect the engine in the event of a major supercharger failure!) The process of compressing the air heats it up and the intercooler removes this heat and so increases the air's density. The compressed and cooled air is then passed to the throttle.
The throttle system incorporates a bypass valve so that under normal operation any air excess to the engine's requirements is returned to a second supercharger intake (which is directly connected to the main supercharger intake from the air filter). On its way back the air pipe passes through the cam cover. This is purely for convenience of routing. Under normal conditions the air pressure is therefore low and supercharger is doing very little work. Fuel consumption is correspondingly low.
When the throttle is fully opened a mechanical linkage closes the bypass valve and the excess air from the supercharger causes the intake pressure to rapidly rise. The engine then operates at full boost and much higher power is available. If a boost gauge is used to monitor manifold pressure it can be seen that pressure is normally partial vacuum like a conventional engine (also allowing the vacuum servo to operate!) but builds rapidly to positive pressure when the throttle is fully depressed.
Dual 'V' belts are used to drive the supercharger from the crankshaft pulley as the loading is quite high when at full boost. As the supercharger displaces a fixed volume of air on each revolution and it is directly driven by the engine, the boost pressure available when the throttle is depressed is largely independent of engine speed. This produces a very good throttle response from any speed without the 'lag' associated with a turbocharger. A smaller pulley can be fitted to the charger to increase its speed relative to engine speed and so increase boost and performance (at the expense of supercharger life).
It now has a Stage 4 charger and K&N panel filter,
Power output is 114.4 @ the wheels and 129.9 @ the flywheel,
don't have the torque figures here but I'll get them later.
A few pictures:
I'll stick it on there later Trev
Here is a bit on the charger:
G-Lader History
The G-Lader was invented in 1905 by a Frenchman called Le Creux. Materials technology at the time prevented his design being a viable option. In the eighties once supercharging (as opposed to turbocharging) was decided upon as their route to performance Volkswagen decided to follow through with Le Creux's original design. Over 400 designs were produced before the current unit was settled on. The reliability of the current unit meets the following minimum requirement: Full boost at 10,000 rpm for 800 hours continuous. As a measure of what this means in real terms consider that one of the designs that fell by the wayside could only last 4 hours on the test bed under these conditions, but would still last 20,000 miles in a VW test car.
Principles
The lader (charger) unit has two air inlets and one outlet. One inlet is direct from the air cleaner box, the other recirculates unwanted compressed air. The lader is always spinning in proportion to engine revolutions (factor is 1.6 times crank speed). The unit is driven via two belts, which also drive the alternator. Outgoing air is driven through the intercooler (air cooled, using the same principle as the radiator, but without a fan) and then on to injection system. On the back end of the injection system is a bypass valve, which distributes the compressed air between the cylinders and the second lader inlet. The bypass valve is directly connected to the throttle. Only at full throttle opening is all the charge air directed to the cylinders, at other openings the air circulates, meaning the engine operates in pretty much a normally aspirated mode.
Internally the G lader is a double spiral shaped chamber. Air is pulled into the outer spiral then forced inwards via a magnesium displacer, which rotates eccentrically, using a similar principle to the Wankel engine. The hot outgoing air is driven through the intercooler, which by cooling the air (by about 130 degress F) compresses it.
More
More again
