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I have not seen one of the Mallett SC's in real life, but they do have a dyno of the kit posted on their website which really shows the difference between positive displacement superchargers and centrifugal superchargers.

For those that do not know the difference, a positive displacement supercharger moves a fixed volume of air for every revolution kind of like your engine. What this means is that as soon as you press the accelerator no matter what RPM you are at, the positive displacement supercharger is forcing more air into the engine. This is what gives positive displacement superchargers their great throttle response and big torque gains in the low to mid range that makes the engine feel much bigger.

The Mallett kit uses a centrifugal supercharger which does not move a fixed volume of air per revolution, and is more like a turbo since its flow rate is dependent on the speed of the impeller. The downside of this on a centrifugal supercharger is that unlike a turbo its speed is directly related to engine RPM. A turbo can spool independently of the engine and can reach its desired pressure as soon as there is enough exhaust energy to spool the turbo. When setting up a centrifugal supercharger you have to figure out what you want your max pressure and flow to be at engine redline and set your pulley ratio for that engine redline. Unfortunately for the centrifugal supercharger that means that it does not move much air at the lower engine RPM's and therefore does not ad much power in the low to midrange. It does have an advantage in the higher RPM's because it is more efficient than the positive displacement supercharger and because it makes its peak torque close to redline you will see higher horsepower numbers with a centrifugal set-up than a positive displacement supercharger set-up at similar pressures (since horsepower is calculated based on torque and engine RPM). Although the centrifugal set-up will have a higher horsepower number, the positive displacement supercharger will have massive amounts more power under the curve.

I have attached a chart showing the Mallett SC vs. The DDMworks stage 2 intercooled supercharger set-up. For those that have not seen a chart like this, it shows the power under the curve. We use charts like this to determine shift points in racing. The red line on the chart is the DDMWorks stage 2 intercooled set-up and the black line is the Mallett SC set-up. It shows the power to the wheels in all 5 gears. Looking at the graph you will see that the positive displacement supercharger (red line) has much more power to the wheels through most of the power band, only just at the very top of a gear will the centrifugal have more power to the wheels. As soon as both cars shift gears though, the advantage goes back to the positive displacement supercharger.

I don’t want to say that centrifugals have no place as they do work really well on bigger engines that tend to run out of breathe up top as if you look at most of the kits they are for larger V8's that have lots of torque down low and fall off up top. When you put a centrifugal on those it fills in the upper RPM's and flattens out the torque curve nicely. There is also a newer generation of centrifugal that is more efficient than the older style centrifugals used in most of the kits. This newer style fills in the mid range better than the older style but still suffers from the same limitations all centrifugals do.

Otherwise on a small 4 cylinder positive displacement superchargers will have more power under the curve then their centrifugal cousins.

Hope that helps everyone out.

	Dave@ddmworks Supporting Tuner Join Date: Jul 2007	I have not seen one of the Mallett SC's in real life, but they do have a dyno of the kit posted on their website which really shows the difference between positive displacement superchargers and centrifugal superchargers. For those that do not know the difference, a positive displacement supercharger moves a fixed volume of air for every revolution kind of like your engine. What this means is that as soon as you press the accelerator no matter what RPM you are at, the positive displacement supercharger is forcing more air into the engine. This is what gives positive displacement superchargers their great throttle response and big torque gains in the low to mid range that makes the engine feel much bigger. The Mallett kit uses a centrifugal supercharger which does not move a fixed volume of air per revolution, and is more like a turbo since its flow rate is dependent on the speed of the impeller. The downside of this on a centrifugal supercharger is that unlike a turbo its speed is directly related to engine RPM. A turbo can spool independently of the engine and can reach its desired pressure as soon as there is enough exhaust energy to spool the turbo. When setting up a centrifugal supercharger you have to figure out what you want your max pressure and flow to be at engine redline and set your pulley ratio for that engine redline. Unfortunately for the centrifugal supercharger that means that it does not move much air at the lower engine RPM's and therefore does not ad much power in the low to midrange. It does have an advantage in the higher RPM's because it is more efficient than the positive displacement supercharger and because it makes its peak torque close to redline you will see higher horsepower numbers with a centrifugal set-up than a positive displacement supercharger set-up at similar pressures (since horsepower is calculated based on torque and engine RPM). Although the centrifugal set-up will have a higher horsepower number, the positive displacement supercharger will have massive amounts more power under the curve. I have attached a chart showing the Mallett SC vs. The DDMworks stage 2 intercooled supercharger set-up. For those that have not seen a chart like this, it shows the power under the curve. We use charts like this to determine shift points in racing. The red line on the chart is the DDMWorks stage 2 intercooled set-up and the black line is the Mallett SC set-up. It shows the power to the wheels in all 5 gears. Looking at the graph you will see that the positive displacement supercharger (red line) has much more power to the wheels through most of the power band, only just at the very top of a gear will the centrifugal have more power to the wheels. As soon as both cars shift gears though, the advantage goes back to the positive displacement supercharger. I don’t want to say that centrifugals have no place as they do work really well on bigger engines that tend to run out of breathe up top as if you look at most of the kits they are for larger V8's that have lots of torque down low and fall off up top. When you put a centrifugal on those it fills in the upper RPM's and flattens out the torque curve nicely. There is also a newer generation of centrifugal that is more efficient than the older style centrifugals used in most of the kits. This newer style fills in the mid range better than the older style but still suffers from the same limitations all centrifugals do. Otherwise on a small 4 cylinder positive displacement superchargers will have more power under the curve then their centrifugal cousins. Hope that helps everyone out.