Explanation of Rotor Rub Blower Noise:

When new, an Eaton has .0025 rotor to case clearance. (.0025 is equal to the thickness of a piece of paper.) With that said it is easy to understand that when you assemble all pieces adjoined to the blower it is going to pull the case somewhat out of round. A similar scenario would be bolting heads on your block and the cylinders are pulled somewhat out of round. This is why your machinists will recommend you hone your block cylinders with torque plates to simulate this stress. This technique can not be used on blower cases so exact torque specs and tightening sequences are critical. We do many different styles of Eatons and all have their rub areas which are consistent case to case.

The pictures referenced below are stock Cobra and Lightning cases.


When you look at the Cobra case you will notice a Shadow at 3 & 9 O’clock; this is common to every Cobra. The shadow was made by the rotors rubbing the case due to torque stress. There are many of you who bought your car new and may or may not have noticed this because it eventually went away and you forgot about it. It generally takes about 500 miles to break in.


Every blower either Rebuilt or Ported is blueprinted to address such issues while we have it at the shop.At times a customer may still have a slight rub after a rebuild and re-torque but I assure you it is less of a noise than when your car was new. It will just go thru a normal break in period.


Another noise which is bad and should not be ignored is a rear case grind. The following picture shows this at the rear of case. This happens when a pulley is installed incorrectly. Always have your pulley installed at the time of porting service.


Most often a noise that is constant and does not go away is an idler pulley bearing. A good check is to lubricate one idler bearing at a time restart the engine and listen. If you have a loud whistle coming from your K&N it is bypass valve flutter. It is better to control the valve thru the tune and not the vacuum lines. Do not do both.

Every Lightning blower case has rotor rub at the rear of the roof. Anyone in doubt just remove your plenum and feel the roof.

This is not a critical performance area so we machine the added clearance needed. Never run a phenolic spacer between a Lightning plenum and blower, this will cause extra heat to remain in the blower case and will lead to failure. The rotor stripping on the Lightning’s has been 100% positive with no power loss and zero failures. Cobra rotors do not flake and rotor stripping is not required.


Other Possible Reasons for Blower Noise:

  • Rotor to Case Rub
  • Belts
  • Idler Pulley (or other pulleys)
  • Unadjusted Bypass Valve
  • Bad Bearings
  • Rotor Fazing
  • Front Drive Pulley Interference
  • Low Oil
  • Belt to Tight
  • Excusive Heat

Blowers are loud in general if you feel you have a “odd” noise of concern remove the belt and turn the front drive pulley by hand. If you feel a rub of any kind you should remove the blower and send it in for servicing as it will only get worse in a short amount of time.