Punctured Oil Pans Can Be A Thing Of The Past With Paxton's New Internally Lubricated Supercharger
Horse Sense: It doesn't matter if they're internally lubed or oil fed, centrifugal superchargers such as Paxton's IL deliver top-end horsepower without adding unmanageable torque down low. That typically translates into easy-to-manage traction on street tires.
Paxton's new internally lubricated (IL) supercharger (right) offers all the performance but fewer installation hassles compared to its familiar oil-fed Novi 1200 brother.
Mustang fans love supercharging, except when it comes to punching the hole in the oil pan for lubrication. Some do it, but it's an angst-filled moment; others just can't swing the hammer. Using the opportunity to sell more superchargers, Paxton has developed-or redeveloped-an internally lubricated supercharger. The blower carries its own supply of oil and doesn't require any communication between the engine oiling system and the supercharger. In turn, that means there's no need to plumb a pressurized oil feed line or return line to the engine's oil pan. It's a concept Paxton pioneered in the ball-drive days but abandoned for an engine-oil feed when the boost and rpm levels of modern hot-rodding proved too much for the friction ball drive.
A pressurized oil feed from the engine remains a viable way of lubricating a centrifugal supercharger, and Paxton has no intention of abandoning it. There are some good reasons for the company to add an internally lubed blower to its offerings. We've already mentioned the first: punching the hole. Putting a hole in a perfectly good oil pan to fit an oil return line is too much for many people, so providing a choice between an oil-fed blower and an internally lubed one should result in more Paxton blower sales.
Eliminating the oil-feed and return lines also means fewer steps during installation, making it quicker and cheaper. That's always a plus. Especially since Paxton is seeking to expand its sales to car dealers. Notoriously parsimonious, dealers demand quick-and-easy installations, and are resistant to what they perceive as mechanical mayhem-punching holes, for example.
Remove the cover on the IL and this is what you'll see: the large drive gear and the smaller impeller gear covered by the plain disc of the oil slinger. The cover provides the location for the two ball bearings seen here.
Finally, oil-fed superchargers rely on gravity to return drained oil to the engine. In Mustang applications, this isn't an issue. For Paxton, there are installations where a gravity drain is problematic. In those cases, an internally lubed blower offers the ability to mount the supercharger almost anywhere the drivebelt or jackshaft can reach, including lower than the oil pan.
Challenges & Solutions
Giving a supercharger its own oil supply raises questions of oil cooling, cleanliness, aeration, distribution, and-most importantly-control inside the tight confines of the supercharger transmission.
To understand how Paxton addressed these concerns, let's review what's happening inside the drive section of the company's centrifugal blower. The action begins at the supercharger pulley, driven by the blower belt. The pulley is mounted to a shaft that's part of a large drive gear inside the supercharger's transmission. It mates with a much smaller impeller gear, which is mounted on the impeller shaft and directly turns the impeller. The two gears feature helical (curved) teeth and form a gear ratio of 3.6:1. The relationship between the crankshaft pulley and the blower pulley is also a gear ratio, typically around 2:1, giving the overall 7.2:1 a step up between the crankshaft and the supercharger impeller. Therefore, if the engine is ambling along at 2,000 rpm, the impeller and its gear in the blower are turning 12,960 rpm. At 6,000 engine rpm, the supercharger is whizzing along at 43,200 rpm. There's tremendous energy whirring inside the blower's transmission and at its impeller.
Remove the gears from the supercharger housing and the details of the redesigned housing are apparent. The bottom of the housing is the oil sump at the bottom in this photo. The angled fences are anti-windage devices, as is the semicircle fence around the impeller bearing bore. This housing is used on oil-fed and IL Paxton superchargers.
It's this prodigious rotation inside the transmission that causes all the frustration when trying to lube and cool the gears and their ball bearings inside the blower trans. The big concern is the gears, as the ball bearings need only a mist of oil for lubrication. Oil-fed blowers spit oil through a 0.032-inch hole at the gear interface, with a constant flow of filtered oil supplied by the engine. The amount inside the blower is controlled by the small orifice, and it's constantly draining out the bottom of the blower to the oil pan. There's never a large volume of oil in the gearbox, just a heavy mist to constantly wet the surfaces.
With internal lubrication, the supercharger has 4 ounces of oil. Think of it as a wet sump compared to the dry sump oiling of the oil-fed blower. This volume is necessary to allow it to cool, but pouring this much fluid into an unmodified oil-fed blower transmission means the dervish of gears entrains the oil and races it around the perimeter of the transmission housing. This heats the oil, beats air into it causing it to foam, and doesn't put it where it's needed, at the center of the transmission where the gears and bearings are.
Paxton's solutions are to cast fences in the oil's path to stop the roundy-round flow, provide a slinger to fling oil where it's needed, and use specially formulated lightweight oil for its lightweight and anti-foaming capabilities. Oil filtering is addressed by regular changes.
To see how the new internally lubricated transmission housing and its oil-control fences are laid out, it's best to examine the photos and captions. Paxton arrived at this configuration, including the shape and volume of the IL supercharger's transmission housing, by beginning with a standard oil-fed blower fitted with a clear plastic cover. Once the flow was visually determined, trial and error gave the various shapes and angles needed to kill the roundy-round action, direct the oil flow, and shear or knife the air/oil hurricane inside the transmission.
The drive gear (left) and driven-impeller gear (right) are identical to those in the oil-fed supercharger. The only difference is the addition of the oil slinger-the large flat disc-to the impeller shaft assembly. The slinger dips into the oil sump and flings a fine film into the drive-gear portion of the blower. It's the only oil "pump" in the system.
Regular oil changes are required, but at press time Paxton hadn't determined the exact interval. It will likely be once a year/ 12,000 miles, but could be slightly longer or shorter depending on testing. It was sent to an independent test lab for several durability trials, each approximating 50,000 miles of use. Oil changes are facilitated by drain holes in the bottom of the blower. The regimen was promised to not involve pulling the blower out of its brackets to turn it upside down. We're expecting a hose and drain valve at the bottom of the blower. The oil is filled through the dipstick hole.
Paxton says the exact oil specifications are proprietary, but confirms the lube is a light synthetic oil designed to avoid foaming. Motor oil can't be substituted, as it would foam, cause more heat, entrain, and perhaps bubble out the vent.
Function & Reliability
Naturally, Paxton wanted the new IL supercharger to meet or exceed all the existing standards for power output and reliability. Because the blower uses the same pulleys, gears, impellers, and volutes as its oil-fed units, it's no surprise Paxton's testing showed no difference in power output between IL and oil-fed Paxton superchargers. We've included before and after dyno tests of the prototype IL Mustang installation in a sidebar; they show the expected gain at the rear tires.