First L@@k >> ‘GTT R56 OIL CATCH CANS’ (N14 engine) + Article

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         ‘GTT ULTIMATE GUIDE TO R56 OIL CATCH CANS’ (N14 engine)

We are currently working on brand new design oil catch cans (x2) for the R56 Cooper S. These are needed to fully purge the system of oil mist, steam & other contaminants from re-entering the turbo & engine under all driving conditions from idle & part throttle to full throttle & boost. Unfortunately there are so many different types available with opposing and conflicting theories, resulting in much confusion for the consumer. Also the plumbing is often messy & not easy to install for the DIY mechanic. Whether standard or modified, these cars certainly need a good OCC system like no other! Re-mapping for more power and turbo boost without an OCC on this delicate engine, will almost certainly be a recipe for long term disaster. Continual contaminated ‘oil mist’ re-entering the inlet manifold & turbo compressor reduces the fuel octane causing ‘engine killing’ pinking & knock. It also produces much carbon build up on the back of the inlet valves which is a big problem with these cars and needs to be addressed. Here we will list a few things that are important to incorporate within the design, and also things that should be avoided!

    1. For The Most Effective Solution, Do not block off the port in the inlet manifold from the PCV valve. However we certainly don’t want all this rubbish being put straight back in the inlet manifold, so it needs to be trapped using an effective OCC.
    2. We believe the main reason for some people blocking this port off is: (A) They don’t understand fully understand its functions. (B) Because it requires custom hoses and complex fittings made to connect and seal well at both ends.
    3. The inlet manifold is the only place where a very useful natural vacuum source exists at idle & part throttle. Think of this vacuum as short for ‘vacuum cleaner’, and yes you have a useful ‘hoover’ that provides modest suck to remove the contaminated oil mist from the rocker cover & crank cases. This mist also contains much water vapour which unless extracted results in emulsifying of the oil. This is usually made worse in cooler conditions & with light driving .This breather circuit consists of a one way valve (PCV Valve) to allow fumes to be vented into the inlet manifold, but prevents reverse flow at higher throttle positions when positive boost exists in the inlet manifold. The second important function is to provide a very slight negative pressure within the crankcases & sump zone. This sucking assists oil returning from the turbo. Turbochargers use only gravity for the oil return, so any slowing or restriction here could cause the oil level to rise within the bearing housing of the turbo resulting in oil smoke from the exhaust, and long term build up of ‘baked on’ carbon deposits inside the turbocharger bearing housing reducing its lifespan.
  • Two OCC’s are needed to do the job 100% effectively! 


    1. We see some single OCC’s claiming to do the job of 2. Most involve blocking off the all important inlet manifold vacuum port so that can never be true and should be avoided. It is possible to do the job with just one OCC, whilst retaining the inlet manifold suck; however it requires two more ‘one way valves’. The downsides are: You only have half the tank capacity (i.e. 1 tank vs. 2 tanks). A lot of additional plumbing is required, and lastly those two extra valves could fail. For these reasons we feel 2 separate OCC’s are best.
  • Breather Filters Mounted On The Second ‘On Boost’ OCC Will Let Oil Fumes In The Cabin! Now here you have 2 design options: – Catch all the oil, water etc. in the OCC then return just relatively clean dry air back through the inlet. Or vent the fumes via a small filter to atmosphere. The filter option is actually very effective BUT creates oil smoke fumes that enter the cabin when driven hard, so is not ideal for road use. Also it could be a hazard if the engine blew and shot half a little of oil out of the filter either onto the hot exhaust parts, or onto the road getting under someone’s tyres. The first solution is therefore preferable.


    1. Note the re-entry point on the engine at the turbo compressor inlet is not a vacuum zone (many think it is), in fact it is almost exactly of atmospheric pressure under all driving conditions. The only time it is ever slightly in negative pressure, is if your air filter system is restricting at full rpm & boost…but that’s another story!
    2. Ok the second ‘On Boost’ OCC that is required connects between the other end of the rocker cover (i.e. the passenger side for UK cars), and the ‘ribbed’ induction hose between air filter and turbo compressor inlet. This is the only circuit that is in operation once you go beyond a certain amount of throttle as the inlet manifold goes from being in part vacuum to positive boost. At this point you’ve lost the suck from the manifold through the PCV valve on the other circuit, but the ‘blow by’ of combustion gasses leaking past the rings creates the flow out for the second OCC circuit.
  • Use Dipsticks to monitor oil level.


    1. Plastic tube slight glass is of little use on an OCC. Firstly it goes brown very quickly making it hard to read. Secondly it can leak. An Oil Level Dipstick is a much neater idea. Design should be of the screw in type, as anything less than a perfect seal will affect the operation on the PCV valve circuit.
  • OCC Design Should Have Internal Method of Trapping the Oil. GTT OCC’s point the oil mist downwards at the entry point; yet collect oil free air from the very top on exit. Many cheap designs have the inlet and outlets almost pointing at each other allowing some oil to bridge the gap rather than remaining in the OCC.


  1. Good internal design will prevent much more of the oil etc. getting past the OCC, ensuring it is stopped and stored in the OCC.
  2. Pipe Work Should Be Custom Designed Where Possible To Allow Optimum Shape & Diameters At The Various Connection Points. They should be made of a material designed for use with oil, and to be able to withstand both positive pressure & vacuum without expanding or imploding. The original breather pipes go very brittle with age, so are probably due for changing anyway.
  3. Custom Fittings Are Required To Connect To Inlet Manifold & PCV Valve. Not cheap or easy to design properly, but these are ‘a must’ on this car. With both vacuum and full boost, any leaks or pipes blowing off here would be a disaster.

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