what's the diff?

 

A breather with a filter cannot draw a vaccuum on the crank case (or whatever it's connected to) whereas if you keep it sealed, you can use the intake or exhaust to pull a vaccuum, usually a good thing.

 

the difference is, one is environmentally friendly, one isnt and one will hurt your performance, one won't.

the breather releases hydrocarbons into the atmosphere, one of the reason why cars run a closed PCV system nowadays....they decide to kill the quality of your intake charge by letting the oily fumes go into your intake, so your cat can sort out the mess.

the problem is, if you dont have a breather atop your tank, and you route it back into the manifold (like stock), while you are seperating the oil from the vapors (like a seperator), you are STILL allowing slightly oily vapors into your intake, which is crap. This means if you are boosting, you are more prone to detonation, since your intake charge is now even hotter and has oil droplets in it, and...if you are high compression, you are losing horsepower since you could be running more timing, but since you are having to deal with the the hotter intake charge and oil vapor, you have to kill some timing.

here is my setup-

http://www.d-series.org/forums...14512

the way i have it, i have the stock seperator fitted with a brazed 5/8 fitting, then i have reinforced hose to the tank, and the breather atop. The other line going into the tank is the from the valve cover...

This setup will double seperate the oil from the crankcase vapors, and still allow the crankcase to breath properly without the oil vapors going into the intake manifold...

 

what brand caries the best catch can with the breather filter?