Nightmotorsport Air Oil Separating Billet Valve Covers for Subaru EJ Engines

Compare the stock separator with the Nightmotorsport part.  The flow path is over 2x longer.  With baffles to reduce the velocity and allow the oil to separate from the blowby grass. The baffles are angled so the oil cannot accumulate on them and can drain.  It is super obvious that the Nightmotorsport is many times more effective than stock at getting rid of the oil.

At the bottom of the separator, there are drain holes so the separated oil can drain right into the engine.  The drain holes are small enough so most of the gas is forced back through the whole separator.

This is the exit vent where the cleaned blow-by gas can return to the head.

The ports for the crankcase vent and the PCV system can use barbed fittings for the OEM hoses or AN fittings if you want to use AN hoses or are running a dry sump.


    1. Initially, I thought so too but the owner of Nightmotosport came by and walked me through the features and I was very impressed with how well thought out they were, especially being a Subie owner and living through all the typical Subie issues.

  1. Curious to see an update at some point of accumulation in the IAG AOS after a track day. Love the content as always.

    1. Well the IAG AOS continually drains back into the crankcase which is a great feature, this way no oil is going to blow out of the engine!

  2. Wouldn’t such a part actually have the ability to free up power considering that the intake charge is no longer being contaminated with oil?

    Although, I have heard that Ferrari (and Mercedes?) were purposefully using oil consumption to make more power, although I am certain that they were tuning for the oil and using some pretty special oil additives.

    “Oil burns when it’s introduced into a gas-powered engine’s combustion chamber, which helps generate more power at the expense of, well, oil. In F1 today, fuel is heavily regulated by the FIA, but there’s a lot more flexibility with oil used. In practice, this means that teams can use certain additives to their advantage and create a more volatile fluid, helping with combustion.”

    1. Just reduce the likelihood of detonation, it’s not going to make more power, just let the engine make its intended power. Buring oil doesn’t make power, it has less BTU than fuel.

      1. Couldn’t you then run more aggressive timing and make your power that way? Similar to running higher octane fuel.

        I imagine that they only did it in F1 to get around the regulations. Not the way anyone would prefer to make power. Makes a mess.

  3. Is this item available in the 2.0 XT in my 2016 Forester? I am also curious best build for track day, (Road America Excludes 2016 Forester XT being a SUV, from running on their track, due to roll over by their experience), Brakes, Engine oil pump, oil pick up tube, oil pan, intake hosing, ect?

  4. So does this mean this could be installed instead of using an AOS like something like IAG AOS systems?

    1. We are still going to run an AOS on our motor with these valve covers. Night Motorsports says you dont have to.

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