A turbocharger is basically an air pump or alternatively an exhaust gas driven supercharger. Choose whichever you can relate to. Hot exhaust gas leaving the engine after combustion is routed via the exhaust manifold directly to the turbine wheel side of the turbocharger to make it rotate. The turbine wheel is connected to a compressor wheel by a common shaft and as the turbine spins faster and faster, so does the compressor wheel. which sucks air in and compresses it before pumping it, under pressure into the engine's combustion chamber. The air leaving the compressor gets quite hot due to compression and friction and this has the effect of thinning the air molecules. To get more air into the engine it needs to be cooled (made dense) which achieves a higher charge of air. This is achieved by fitting an inter-cooler (air to air heat exchanger) between the turbo compressor and the intake manifold. With more air forced into the combustion chamber, more fuel needs to be added to achieve the correct A/F ratio. More Air, more fuel = more horsepower. As a rough guide, a 10deg F drop in charged air temperature is equal to an increase of 1% horse power.
How much power increase is dependant on how much boost pressure is used and this is governed by mainly how much stress the engine is engineered to take. More power puts a hell of a lot more stress on engine parts. Standard unmodified engines can generally safely take 7PSI of boost. The boost is regulated by a wastegate. This is an internal valve fitted to the turbine housing and when boost pressure reaches a pre-defined limit the actuator opens this valve. This opens a passage for exhaust gas to by-pass the turbine wheel which stops the wheel spinning faster and therefore ceases to increase boost.
Turbos must have good quality oil. Use oil that meets the MIL specification for a turbocharged engine and don't miss a scheduled service. If you like to cane your engine regularly then change your oil more often. On the subject of making your turbo work, I have come across two thoughts about how to shut down the engine.
Do you need to use a Turbo Timer??? Interesting question. Some say No and I can understand their argument for against. For normal driving around with moderate turbo use they say that by the time you pull up and park the car the turbo has cooled and spinning at normal idle speed and therefore is safe to turn the engine off. On the Yes side, some say the turbo is still too hot and has not dissipated its heat. Shutting down the engine in this state will eventually lead to pre-mature failure of the turbo bearings.
My view is that it will not hurt to have one as a precaution. If you race or participate in motor sports then I would definitely fit one. Turbos are expensive and a little insurance by fitting a turbo timer would be wise.
Another piece of insurance that is very important is the quality and flow rate of the air filter fitted. The flow rate becomes an important factor once you start modifying the system for more power as the original filter may not flow enough air. Poor filtration will also cause the turbo compressor blades to wear prematurely, resulting in reduced turbo efficiency. If you are contemplating fitting a high flow filter with superior filtration, then I strongly recommend a Uni-Filter. Read my review of this product in the Product Reviews menu.
If you would like to increase your boost pressure you will need to fit a bleed T valve. This little sucker bleeds off some of the pressure signal to the actuator that controls the wastegate. This is a way off tricking the actuator and has the effect of increasing boost. But be careful you don't go too far. You can purchase these suckers as a kit. They are called 2 stage boost controllers from turbo smart. Easy to set up and once that is done, you can flick a switch on your dash for more horsepower only when you want it. Switch it off and your car has normal boost. Switch it on and you can have as much as you set it to. Once again remember more boost requires more fuel, make sure your engine management system is compensating for the extra boost. If you have a carburetted car then ensure you have it re-jetted. My sons 180SX has a 2 stage boost controller set at 10 & 15PSI. To compensate for the higher boost he has an Air Flow Controller (AFC) fitted. This device is easier and best to adjust on a dyno but can be setup on the road, not recommended however. Any further boost will require a money bucket to improve the engine internals and improve the fuel delivery.
Some vehicles have a device known as a blow off valve. You know when a car is fitted with one. If it is fitted legally you may not hear it as it should be plumbed back into the intake duct. A non so legal one is plumbed to atmosphere and make a distinct hissing or high pitched scream when the boost pressure is released. It sounds pretty cool. The purpose of the valve is to relieve back pressure between the compressor outlet and the throttle butterfly as the throttle is suddenly closed. Not all turbo systems are fitted with it.
One of the typical early symptoms of a turbocharger problem is blue smoke being emitted from the exhaust pipe while the engine is idling. Here are some photos of a failed turbo. The problem started with a whining noise, then a rattle sound every now and then, a loss of boost and finally the clouds of blue smoke and embarrassment while limping the car back home.
|
|
The rattle sound was the compressor nut trying to get past the impeller. No damage was done to the nut.It screwed easily back on the shaft, however the compressor wheel copped a hiding. With no nut, the impeller was free to move laterally and rub on the compressor housing. The bearing support for the shaft gave way and now the turbo was spinning out of balance all over the shop. |
|
|
The turbo partially dismantled. On the left is the compressor housing, the main body of the turbo in the middle and the exhaust turbine housing on the right. |
|
|
Another possible cause for no boost can also happen when the wastegate valve comes off and goes down the exhaust system to the catalytic converter or muffler as the case may be. I have only seen this happen once, very rare occurrence. Get a soft faced hammer if available and tap your exhaust system around the area of the first muffler. If you hear a rattle it could be the valve. To make sure, remove the outlet pipe from the turbine housing and have a look inside. This pic shows what it should look like with the valve in place.Not all turbos have this type of wastegate. |
