During the combustion process, some of the burnt gases will get past the piston rings and blow down into the sump and crankcase and in doing so they pick up some oil on the way.
In order to minimise emissions of these nasty smelly oily gases they are recycled back into the engine to be burnt again. To do this, a breather pipe is fitted (normally comes from the rocker cover) and returns any expelled gases back into the intake system. The oil that is inevitably present in this air is then put into the engine and can reduce power because it's not petrol and doesn't burn as easily. An oil breather tank fits into the breather line and removes the oil from the air before it gets back into the engine therefore giving a marginal increase in power.
You are correct in that it will be better for the engine not to try and burn oil and turn into a turbo diesel
As for the amount of increase, I would assume that it depends on how much oil is present in the gases that you are removing. IF you are getting a lot of oil in from the breather pipe then you will be able to substitute this volume with air/petrol and get a better combustion. The amount of oil picked up will no doubt vary depending on engine condition (worn piston rings etc) and so I would have thought that a precise answer could not be given unless you try it out. It will give an improvement but how much, I don't know.
The best route for the breather hose is straight to atmosphere to make sure that fresh air and not gases that have already been burnt once is put into the induction every time. Manufacturers recycle the gases because it is environmentally friendly to do so.
Yes, forged pistons do need extra clearance when cold to allow for expansion. As I have reported elsewhere, when I am doing lots of short journeys the oil consumsion goes up! I suspect that an oil breather tank might help.
Simon, you understood me! If I were you (old, anxious about engine failure and warranty, living in the city etc ) I would get a breather tank. I doesnt cost much and can only be beneficial. Check the breather tank often so it doesnt fill up!! Just kidding. Try it.
Actually, the two main reasons why you don't want oil to mix with the incoming air is that the oil will coat the inside of the intercooler and reduce its efficiency and most importantly the oil reduces knock resistance.
I think the best way to do it is to connect the vent hose and the PCV hose to an internally baffled catch can which is then connected to the intake. This way you get vaccum assisting the crankcase ventilation and leavethe majority of the oil behind.
The big problem is (especially for HKS racing suction kit users) the oil tends to coat
the inside of the induction pipe, any crap that manages to get through the HKS filter
then sticks to the oil on the inside of the pipe; building up over time and finally falling
off in a oily/dirty lump into the turbo.....OUCH !
Buy an oil breather/catch tank if you have an HKS induction kit. I can give 10% disc
on the Spec-R tank, it looks the nuts too, especially when aeroquipped.
Aero spec ss braided lines r not required on a breather system , there is no pressure , vacuum or temperature 2 speak of so it's unjustified expense. We do a much lower price ss braided tube for this sort of application , which is still compatible with those fake hose ends.
Just 2 b clear , the high spec stuff is the way 2 go 4 oil cooler and other oil and fuel lines.
BTW u can buy race rule spec breather catch tanks much cheaper than the Spec URRRGGGHHHH stuff .
Not trying 2 spoil any1's party here , just telling about alternatives
I quite agree, on my cossie all I had was a piece of rubber hose routed into a plastic pot which was tie wrapped to the inner wing! Cost me nothing but did the job. If the car blows out a lot of oil, which the cossie used to do being a dinasour running 1.7bar it's good to have another pipe at the bottom of the pot to drain the oil back into the sump. It's just a simple oil/air seperator.