SoopaCooga
Veteran CEG'er
We all know that forced induction devices work by compressing air, and that a supercharger is a belt-driven compressor, whereas a turbocharger is an exhaust-driven compressor. A centrifugal supercharger (e.g. Vortech, Paxton, Procharger) is an interesting animal in that its compressor is quite similar to that of a turbocharger. Because of these similarities, we may be able to borrow some turbocharger technology to improve the performance typically obtained from the centrifugal supercharger. onder:
Can turbo tech be applied to a supercharger? To find out, let's compare the typical processes for choosing a compressor. Let's say we want mild boost of 8 psi max.
The output of a centrifugal supercharger is dependent on engine speed (i.e. RPM). The faster the engine spins, the faster the supercharger spins, forcing more air into the engine. If we don't want to exceed our maximum pressure of 8psi, then we size the compressor and its pulley so that peak boost is made at peak RPM. The downside is that we don't get our full 8 psi until the red line.
Since it's not belt-driven, a turbocharger isn't constrained by engine speed. How then do we keep from pressurizing the engine above our 8 psi max? If we attempt to solve this problem in the same manner that we did the last time, then we would choose a compressor and turbine such that the pressure produced would not exceed our max. [The turbine is analogous to the supercharger pulley.] However, this is not what is typically done. Instead, the pressure is kept below maximum through the aid of a wastegate. The wastegate allows us to choose a compressor that outputs more pressure than our maximum, which is desirable so that we reach our maximum boost sooner. This is why a dynamometer chart for a turbocharged engine shows a characteristically flat torque curve, versus the peakier curve of the centrifugal supercharger. When comparing dynos from a Honda S2000, this becomes painfully clear! :laugh:
In theory, the dyno chart for the centrifugal supercharger could also be flattened out by using a wastegate. The wastegate would be setup to vent boost once we reached peak pressure, allowing us to use a compressor/pulley combo that could exceed our maximum pressure, which would in turn let us reach maximum boost sooner.
I got this idea from an article in Muscle Mustangs & Fast Fords. I hope I inspired everyone to buy a Blackcoog kit.
Can turbo tech be applied to a supercharger? To find out, let's compare the typical processes for choosing a compressor. Let's say we want mild boost of 8 psi max.
The output of a centrifugal supercharger is dependent on engine speed (i.e. RPM). The faster the engine spins, the faster the supercharger spins, forcing more air into the engine. If we don't want to exceed our maximum pressure of 8psi, then we size the compressor and its pulley so that peak boost is made at peak RPM. The downside is that we don't get our full 8 psi until the red line.
Since it's not belt-driven, a turbocharger isn't constrained by engine speed. How then do we keep from pressurizing the engine above our 8 psi max? If we attempt to solve this problem in the same manner that we did the last time, then we would choose a compressor and turbine such that the pressure produced would not exceed our max. [The turbine is analogous to the supercharger pulley.] However, this is not what is typically done. Instead, the pressure is kept below maximum through the aid of a wastegate. The wastegate allows us to choose a compressor that outputs more pressure than our maximum, which is desirable so that we reach our maximum boost sooner. This is why a dynamometer chart for a turbocharged engine shows a characteristically flat torque curve, versus the peakier curve of the centrifugal supercharger. When comparing dynos from a Honda S2000, this becomes painfully clear! :laugh:
In theory, the dyno chart for the centrifugal supercharger could also be flattened out by using a wastegate. The wastegate would be setup to vent boost once we reached peak pressure, allowing us to use a compressor/pulley combo that could exceed our maximum pressure, which would in turn let us reach maximum boost sooner.
I got this idea from an article in Muscle Mustangs & Fast Fords. I hope I inspired everyone to buy a Blackcoog kit.