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lots of people are always asking me questions about turbos, so I thought this woudl explain some stuff......if you guys want to put this in the database or whatever, it would be nice.....
turbochargers do not use engine horsepower directly. This is good in that there is no parasitic loss but there is lag time. You can tune a turbocharger to provide boost almost instantly and therefore no lag. Between shifts on my 5 speed car, it comes back into boost faster than any supercharger I've ever seen, if you have seen my video riding inside the car you can observe this. This is because the turbo is spinning fast enough to make a certain pressure at the higher airflow required at higher RPM. It does slow down a little but because between the shift, the turbine is actually pulling the exhaust out of the cylinders. However it's still freewheeling super fast and as soon as you are back into it, that RPM and pressure is there.
Beyond the little things, turbochargers are much more configurable that superchargers are. When designing your turbocharger, you have 4 variables you can adjust to make it do exactly what you want it to do vs at most 1 on a supercharger. On a turbo, you can adjust the compressor wheel configuration, the compressor housing configuration, the turbine configuration, and the turbine housing configuration.
First you choose a compressor wheel that is well suited to your application. Then you choose a turbine wheel also suited to your application. Choose the carefully because once on the turbo, they are there. However you can also adjust the size of the housings which makes a marked difference.
On the turbine side, you can put a smaller housing which will cause the turbo to spool quicker. It's like a smaller gear. However, the smaller the housing, the less max boost the turbo will put out and the more restrictive the turbo will be to higher RPM exhaust flow. You balance this between how fast you want boost, how much boost you want, and how much back pressure you can take before it hurts performance.
On the compressor side, you have to match the compressor to your engine. You need to make sure that it is large enough to support your engines air flow efficiently but small enough that it doesn't surge at lower RPM. Surging can cause turbo damage. You will often find several compressor wheels that will work with your engine and then you can decide what suits your needs. You can also adjust the compressor housing size. The smaller housing allows the compressor to accelerate the are more rapidly thus reducing lag time. The larger housing accelerates the air more slowly but lets releases it at a higher pressure. It works like a venturi.
The nice thing is that you can swap housings on a turbocharger to reconfigure it as your needs change. Once the turbo if off the car, it takes about 5 minutes each to change housings.
Turbos control the amount of boost they produce by using a wastegate to let exhaust bypass the turbine. This is a wonderful thing because you it takes about 15 seconds to change the amount of boost the wastegate will let the turbocharger produce. The wastegate uses manifold pressure to open and close the valve. If your wastegate is set at 5 lbs but you use a boost controller to bleed off some of the air before it hits the wastegate, you can change the boost. You might up the boost to 15lbs by bleeding off 10lbs before it gets to the wastegate. Because of this, it is advisable to have self control. Believe me, the temptation to crank the boost up is very powerful.
turbochargers do not use engine horsepower directly. This is good in that there is no parasitic loss but there is lag time. You can tune a turbocharger to provide boost almost instantly and therefore no lag. Between shifts on my 5 speed car, it comes back into boost faster than any supercharger I've ever seen, if you have seen my video riding inside the car you can observe this. This is because the turbo is spinning fast enough to make a certain pressure at the higher airflow required at higher RPM. It does slow down a little but because between the shift, the turbine is actually pulling the exhaust out of the cylinders. However it's still freewheeling super fast and as soon as you are back into it, that RPM and pressure is there.
Beyond the little things, turbochargers are much more configurable that superchargers are. When designing your turbocharger, you have 4 variables you can adjust to make it do exactly what you want it to do vs at most 1 on a supercharger. On a turbo, you can adjust the compressor wheel configuration, the compressor housing configuration, the turbine configuration, and the turbine housing configuration.
First you choose a compressor wheel that is well suited to your application. Then you choose a turbine wheel also suited to your application. Choose the carefully because once on the turbo, they are there. However you can also adjust the size of the housings which makes a marked difference.
On the turbine side, you can put a smaller housing which will cause the turbo to spool quicker. It's like a smaller gear. However, the smaller the housing, the less max boost the turbo will put out and the more restrictive the turbo will be to higher RPM exhaust flow. You balance this between how fast you want boost, how much boost you want, and how much back pressure you can take before it hurts performance.
On the compressor side, you have to match the compressor to your engine. You need to make sure that it is large enough to support your engines air flow efficiently but small enough that it doesn't surge at lower RPM. Surging can cause turbo damage. You will often find several compressor wheels that will work with your engine and then you can decide what suits your needs. You can also adjust the compressor housing size. The smaller housing allows the compressor to accelerate the are more rapidly thus reducing lag time. The larger housing accelerates the air more slowly but lets releases it at a higher pressure. It works like a venturi.
The nice thing is that you can swap housings on a turbocharger to reconfigure it as your needs change. Once the turbo if off the car, it takes about 5 minutes each to change housings.
Turbos control the amount of boost they produce by using a wastegate to let exhaust bypass the turbine. This is a wonderful thing because you it takes about 15 seconds to change the amount of boost the wastegate will let the turbocharger produce. The wastegate uses manifold pressure to open and close the valve. If your wastegate is set at 5 lbs but you use a boost controller to bleed off some of the air before it hits the wastegate, you can change the boost. You might up the boost to 15lbs by bleeding off 10lbs before it gets to the wastegate. Because of this, it is advisable to have self control. Believe me, the temptation to crank the boost up is very powerful.
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