I've got an EM1. Should I keep the stock breather hose connected or to the CAI or get a breather filter, why or why not? The breather filter sure does look nice and a ton of people run them, but I'm not gonna sacrifice engine efficiency for that.

 

It doesn't matter. It makes literally no difference, performance-wise. The breather hose from the valve cover to the intake is there for emissions reasons.

 

Just wanted to make sure that it wouldn't hurt the engine somehow. A lot of people seem to think they don't allow the engine to breathe properly because they eliminate the positive vacuum.

 

I have the hose on my swap. I had the filter on my old D series. My friend has a filter on his boosted B series. Another friend has a filter on his NA B series. Another friend had the filter on his turbo MR2.

I think that whoever says it "causes damage" is just looking for something to blame other than a **** tune, or abuse.

 

Yeah I've got a buddy with a supercharged b18c hatch that has the filter. I assume he wouldn't put it there if it caused damage. Just thought I'd ask before I buy one. Thanks for the input.

 

It wont do anything now, but down the road it could be a accessory to internal oil consumption. It has not one single advantage, but a disadvantage some people's eyes. Its basically apart of your pvc system, taking air from the VC and transferring it to the intake, so why stop that? Honda put it there for a reason, and even when you buy a true aftermaket intake it comes with it, not a filter.

 

Positive....vacuum......

Go on...

 

Its there for primarily for crankcase ventilation. It is already a breather.

The reason why it is plumbed back to the intake:
-emissions.
-more difficult for moisture to work itself into the intake system.

It is in front of the throttle plate. The only time this would experience actual vaccum (negative pressure) is if the engine out-flowed the air filter. You'll never see appreciable positive pressure on a NA car that's running properly.

For FI cars, the intake plumbing is pressurized and it will keep the crankcase from venting.

Leave the stock breather tube in place. Water getting into your oil doesn't look cool. Oil fumes also don't smell cool when they make their way into the cabin.

Cars with high crankcase pressures or cars that often have liquid oil slosh into the intake system via the stock breather can benefit from an open breather that goes into a catch can. For example....the oil slosh that happens to S2000's on hard right handers at certain race tracks.

Is your car FI? Or do you track it and find that liquid oil sloshes into the intake, making you lose power?

 

 

We had a pretty solid discussion on this topic not so very long ago.

The positive vacuum associated with the intake is a misconception. That portion of the breather is to allow air flow for the vacuum created by the intake manifold on the other end of the pvc system.

If you put a plug on the valve cover instead of the hose or a breather, then you would be preventing the free suction of air into the crank case when the vacuum of the IM is greater than the blow by of the pistons.

Like NAR said. The breather filter or tube from the intake tube to valve cover has no difference in effect. You are still limited by the opening into the valve cover/head.