Anybody know the purpose of this hose?

[dfiore]

There is a small hose going from th valve cover to th air intake box. I took the box out and managed to press a K&N clone filter on there. The ony thing I could do with the other hose was lay a small piece of paper towel over it and reinstall the clamp. All I can tell is that air is coming FROM the valve cover, and I don't have a way to link it back into the airflow. I'm guessing it's hurting my MPG???

[Insightful Trekker]

That would be part of the PCV system (Positive Crankcase Ventlation). In general air will enter art the valve cover and be drawn through the PCV valve back into the intake. This inlet point needs to have filtered air as its intake. Over the long haul allowing particulates into the crankcase will increase wear.

If at say 1500 RPM's air is exiting this point it reads like the PCV valve and or its related hoses are clogged. Venting the crankcase is essential for long oil life (combustion by products leak past the rings and "attack" the oil). A positive flow through this system is needed.

Also an engine in an advanced state of wear _will_ vent from the inlet hose regardless of the rest of the systems condition because of excess piston ring blow-by.

HTH!

[dfiore]

Am I losing mileage by just filtering with a paper towel and not running it back through the intake? I couldn't think of anything else to do with it, as long as I'm using that filter. Maybe the filter isn't really any better? It's labeled a high flow

[Insightful Trekker]

You _are_ loosing MPG _potential_ by removing the factory tuned intake system.

A paper towel as a PCV intake filter is almost worthless. There is no MPG impact based on the PCV intake filter (or not). I think I've explained the concept otherwise.

HTH!

[b1shmu63]

Here is my understanding regarding free flow filters.

Unlike older carburated engines, the fuel ratio in a computerised injection system is controlled by the computer, not the vacuum. Engine power is controlled largely by restricting the air flow. Reducing the the airflow with a restrictive filter will reduce the maximum power, and if it is significant enough cause the secondary Vtec cam to be engaged earlier.

The OEM filter is essentially oversized, so unless you live on a gravel road or drive in otherwise particulate filled air, the standard filter should work as well as a high flow filter. At least one member who tried a K&N filter found no difference. Another expressed concern that small particles of silica would get through the high flow filter and increase engine wear.

Blow by from the engine, routed by the hose to the air cleaner, is burned by the engine, reducing pollution and adding a tiny amount of power. Win, win.

[dfiore]

Sounds good. Think I'll put the airbox back in and toss the high flow filter. Thanks guys!

[Insightful Trekker]

To clairify further:

Both the intake and exhaust "air" flow is not "smooth". If you think about how the flow is produced you'll understand.

Air in drawn in only on each intake stroke of a piston. Therefore there is a regular pulse frequency associated with the intake air at any given engine RPM. There is also some relatively small power used in drawing in the intake charge.

Now here's how a tuned intake (and exhaust for that matter) works. If you adjust the intake chambers such that it is a resonant frequency of the intake flow at the desired engine RPM then you will see an increse in power / torque & MPG (as a consequence) since then pulses are now working together to improve overall flow. Again at the _designed_ RPM.

Honda has been doing this now for over 10 years with many of their models. The overall percentage gains are small, low single digits, and with MPG probably not discernable except under labratory conditions. But its essentially "free" for the taking. The've even done a duel stage tuned system whereby a secondary chamber was switched open & closed based on engine RPM to further improve the effect.

And just like as with the lean burn window if you drive outside the "box" you won't "see" it. An aftermarket high flow filter _will_ improve peak HP, at the high end of the tach. The "gain" will also be too small to "feel".

HTH!