Project C7 Corvette Stingray, Gaining octane with Moroso’s Air Oil Separator

Getting oil in your intake tract is never a good thing.  The worse thing is that an oil mist that gets sucked into your cylinders can cause the engine to detonate.  You all know that detonation is the #1 killer of high performance engines. Oil has a significantly lower auto ignition point than gasoline so when it is introduced into the combustion chamber during the intake stroke it acts just like low octane fuel in your tank. Oil also causes sludge that gums up your intake manifold and fouls your ports, contributing to performance hampering valve deposits.  Since our LT1 engine has a high 11.5:1 compression, it needs all the help it can get to avoid detonation on our crappy 91 octane California pump gas. To make sure as little oil mist gets into our intake manifold as possible, we installed Moroso’s air oil separator into our C7’s PCV crank vent to clean the engines blowby gasses before they are introduced into the intake manifold.

The Moroso air oil separator is a polished billet aluminum can that basically acts like a filter for blowby gasses.  It is machined in two parts so it can be disassembled for cleaning.  It is full of stainless steel mesh which is rolled like a jelly roll and acts like the filtering medium.  When blowby is introduced into the can, the oil sticks to the mesh and any water vapor in the blowby gasses condenses on the mesh and flows to the bottom of the can.  It’s very simple but effective.

The air oil separator kit comes with all the fittings, and hoses to do the installation.

A bracket specific to the C7 assures that this will be a clean and simple installation.

First we applied liquid teflon thread sealer to all of the fittings.


  1. The Moroso “catch can” is probably one of the WORST designs out there. It really saddens me that you didn’t use one that actually works. If you look at the SAE paper on crankcase ventilation filters, you can see how awful that design is. Something like the Mann+Hummel ProVent 100 is not significantly larger than the Moroso catch can, and at least an order of magnitude better at getting oil vapor out of the blowby gasses. Not to mention that, when properly installed, it automatically drains back into the sump, which means you don’t have to drain it. You just need to replace the filter element when it gets clogged, which isn’t very often. (Get the pressure relief version, and it will start to dribble out the side, letting you know when to change the filter)

    1. In track testing the Moroso works flawlessly so far, not one bit of oil mist past it. Do you have any empirical evidence that it doesnt work well? I feel there is nothing at all wrong with the design and would not hesitate putting it on any car. I would run something else with a higher volume, more baffles and an oil return on flat engines that have venting problems like Subaru’s and Porsche but no problem for most things. Provents are designed for diesels that do not have a vacuum in the intake manifold so there is a check valve that must be removed. Then you have to make brackets and buy hoses, etc. to adapt it to the car. Times money and this is a simple kit that installs in about 30 minutes.

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