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Answers to the KB oil questions
OIL LEAKS
Oil typically doesn’t “leak” out of a Twin Screw anymore than oil leaks out of your engine oil pan. So where does the oil go? And is using a little oil a big concern. Engines hold 6-8 quarts whereas a supercharger carries a mere 5-6oz.(1/6 quart) so there is a big difference in being “1 quart(32oz) low” or “2 oz’s low”. A mere 1 quart of oil would cover 6 supercharger fill ups. Higher engine and supercharger rpm increase the internal air pressure in both. The pressure and oil must exit somewhere. The engine simply blows it out the breather or burns it in the combustion chamber via the PCV system. The supercharger can lose a relatively small amount of oil by its front seals at higher racing/high boost applications. Again 1/3 of it’s oil capacity is a measly 2 ounces. The older design 1.5-2.4 KenneBell/Autorotor superchargers vented air pressure out a breather on top of the front gear case or the drive snout. Similar to an engine. At high boost and/or supercharger rpm with this elevated internal pressure-as during a 1/4 mile run- the air would carry some oil with it out the breather and onto the supercharger and engine. 5 years ago, we solved this problem with an orfice, a tube and a catch can. Same principle used on the new Shelby KR differential for high speed cornering. You vent the oil to a container. It works! Anyone who experienced this problem with our Kenne Bell Autorotor superchargers was sent the vent kit “at no charge”.We learned quickly that many of our superchargers were being used both for street (low boost normal driving) and for competition (high boost) on weekends. In many cases, VERY high boost (Up to 26psi)
We also realized that more and more of our customers were running higher boost levels for the street “normal” driving on a full time basis. This of course, meant the supercharger is spinning faster and developing higher boost and heat ALL OF THE TIME.
Finally, since we’ve been selling Ford Twin Screws at least 3x longer then any other company, we have more units and more applications out there than any other company.
To solve the problem-around 5 years ago-we re-designed new drives for the previous Kenne Bell Autortor 2.4,2.2, and 1.7. The new Kenne Bell BIG BORE 2.8,2.6 and 2.1 incorporated a new “vent bolt” design from the beginning (2005 and later). All these “new” drives incorporated a unique vent hole in the pulley bolt. The cross drilled hole now vented the excess air pressure from the high boost/rpm harmlessly and cleanly out through the pulley bolt. The centrifugal force of the air in the hole prevented the oil from entering the hole and exiting the supercharger but relieved the air pressure in the oil reservoir. Now there was no need for a catch can. Problem solved Better product.
ROTOR SEALS
Yes, if the rotor seals are doing their job, this pressurized oil doesn’t get sucked back into the rotors on decel.
And if they’re sealing, boost pressure in the rotor pac doesn’t blow by the seals and into the oil reservoir.
All Twin Screws and Eatons use the same basic seals. Contrary to what you may have heard, there is no better one. If there was we would be using it.
Seal damage
Seals will last a long, long time. We have many superchargers out there with 100-250,000 miles on them with the original oil seals and minimum oil use. But we don’t all drive our Kenne Bell superchargers around at low rpm and low boost. O.K., so what goes wrong? Why do the seals not hold back 100% of the oil? How can we prevent our supercharger from using oil? Any seal’s efficiency can be compromised by:
1.Heat
2.lack of oil
3.Oil contaminants
4. Abnormally high vacuum on decels.
HEAT(over filling)
The big one. Overfilling is the number 1 cause of seal damage. Heat hardens the seals and causes them to leak. That’s why there is a big red tag on the dipstick of any new Kenne Bell supercharger that says NEVER OVERFILL. When overfilled, the oil can actually “boil”. At 440o, the green plastic coupler in the oil case will shred and/or melt. Overfill an engine or transmission and oil WILL overheat and even blow out the dipstick hole vent. Same condition as the supercharger.
CONTAMINATES
The shredded coupler or melted plastic contaminates the oil from overfilling and may damage seals. And overfilling can damage seals with only one overfill. Keep that in mind when buying a used and abused supercharger. And if the supercharger is run with out oil, the gear shavings and heat will obviously damage the seals.
HEAT(High RPM)
To reduce windage and oil heating at higher rpm and in competition, we have specific oil level recommendations. It’s all about controlling oil windage (same as in engines, transmissions and differentials). Instructions are included in every kit.
HEAT( From boost)
The air charge temp of a Twin Screw or Turbocharger is approx 10o per psi of boost. Eatons are much higher. Example: Raise the boost 5psi and you increase air charge temp by 50o. 10psi is 100o. The oil reservoir is located at the discharge port so it sees the higher boost temps. We recommend 18psi max for the street 18psi X 10o=180o + supercharger “in temp”= discharge temp. e.g. 100o day = 180o + 100o = 280o. But inhaling 200o underhood heat the end air temp is increased to 380o. Read on.
HEAT(Exposed, hot air underhood filters)
I wish we could all charge the idiots who sell these “air charge heaters” for superchargers for damages they’ve caused over the years. However, not one has ever reimbursed an owner. They create problems for Kenne Bell and our customers. Again, refer to the 280o example above but instead of 100o use the 200o air ( +100o) from the underhood exposed filter. Now the air discharge temp is 380o! Oops! The absolute worst cars to use an exposed underhood filter on is the 03-04 Cobra and 96-04 Mustangs. Our Shelby is the lone exception but there was no where else to mount the filter, it has some openings.
Always remember that what reduces seal life is not high speed wide open throttle-cool air rushing into the supercharger. It’s instead idling and cruising with the inlet sucking in hot 200o underhood air with the throttle body almost shut. There is very little cool air entering the supercharger during these conditions.
Throw that hot underhood exposed filter in the dumpster and suck out of the fenderwell or in front of the valance. A hot air underhood exposed filter warning is included with every kit.
BYPASS VALVE
We use a Mercedes Benz bypass valve. An extremely reliable component. It has to be. We’ve never had a failure that wasn’t related to 1. Supply tube fitting leakage or 2. External damage.
All problems we’ve seen are the result of compromising the supply line with gages. NEVER tie into a bypass feed line. The #2 cause of a bypass valve staying closed (not good) is low vacuum cams. Ever see a cam company or engine builder pay for a supercharger damaged by a cam that didn’t generate enough vacuum to OPEN THE BYPASS VALVE? Our standard bypass valves open at 2" less vacuum than others. And we have a special no spring model that opens at a mere 2"Hg.
These are all examples of how superchargers are damaged and blamed for problems that weren’t their fault.
EXTERNAL OIL LEAKS (BIG BORE SERIES)
Our records clearly show there has been only ONE-a 2.1- returned for an actual leak. Our fault. We pressure test all the gear cases but left the bottom case plug loose we missed one. The gear case is sealed to the supercharger housing so oil leaks there are non-existent.
DRIVE LEAKS
The only place for oil to leak out the drive is by the front seal. We’ve had 3 BIG BOY drives returned. All 3 had “seal shred” The drive seal rides on a hardened bushing (seal ring) that hold the pulley. Re-install it without an oil film between the bushing and seal and the seal immediately shreds/wears from lack of oil. Replace the seal and properly oil the seal surface and the problem goes away. We’ve sent out 6 BIG BOY seals in 3 years. All no charge. No questions asked. Instructions for oiling the seal are included with every kit but they’re sometimes overlooked.
Since 1990, we’ve sold tens of thousands of these superchargers. No one has ever been screwed by Kenne Bell. Many superchargers are run hard and often abused. Like any product, a Twin Screw supercharger has its limitations. We NEVER run from a problem and do our best to help prevent them through education. Which is why we take the time to respond to any negative posts. We have records of every supercharger sent in for warranty and repair and what the problem was. And we answer questions honestly and to the best of our ability. We try very hard to educate our customers in all the aspects of supercharging, including preventive maintenance. We even include 2 pages of “How to avoid and analyze supercharger problems” in all our kits. All of the technical papers-and more-mentioned above can be found on our web under “General Tech”.
RELIABILITY
We believe that Kenne Bell now has the most knowledgeable Technical Department in the industry and the most honest and straightforward website. And after 18 years in this business, we’ve seen it all and feel qualified in our analysis of any supercharger issue, including tuning. Hopefully we have answered any concerns you may have had about “oil leaks”. Feel free to contact us anytime if you have any further questions.
Jim Bell
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