Greg checks the impeller to...
Greg checks the impeller to confirm that its points are good and there is no indication that it has touched down inside the volute.
Every supercharger, even our project car's Novi 2000, has critical operating limits that must be acknowledged if you expect the blower to have any type of longevity.
"Once you start to take a blower above our recommended maximum rpm, its efficiency starts to fall off, oftentimes to a point where we recommend moving up to another product that will give you the performance (blower speed and boost production) you want without imposing the same type of stress on its internal parts or generating the type of heat that can lead to damage or failure," says Ricky Best, Paxton/Vortech's Motorsports and Media relations manager. "A supercharger really is like a little book. Upon inspection, we're able to see where a failure has occurred and usually pinpoint exactly why (excessive belt tension, insufficient oiling, and so on). If you change your oil at regular intervals and take good care of your supercharger-don't overspin it, and keep it in its operating rpm range-there's no reason why the blower won't last 80,000 to 100,000 miles, but sending it to us for an inspection and refreshing is good, inexpensive insurance," Ricky says.
A wear mark similar to this one in the bearing bore for the supercharger's upper pulley bearing is a tell-tale indicator that the belt has been grossly overtightened. Since there is more load on this part of the bearing, heat builds up in this area and causes premature failure of the bearing.
Each supercharger that is returned for maintenance service is evaluated using this checklist that contains possible problems and the technician's assessment of the unit's external and internal condition.
The bent points on the impeller (left) and wear ring that has been ground into the volute in the background (right) are prime examples of an impeller that has "touched down" inside the volute. A touch-down is usually caused by an improperly sized bypass valve, and it isn't the kind deserving of a celebratory dance. If the bypass valve is too small, there's no way it can handle more than 8 psi of air. When you've got 10-plus psi being fed to a small bypass by a 3-inch discharge tube, the excessive air pressure is forced back into the supercharger and up under the impeller when the throttle is slammed shut. This backpressure forces the impeller off its base, sending it crashing into the volute at high speed.