Valve Cover Breathers

[Dart 65]

Is there any benefit (or detriment) to having two breathers, one on each V/C, on a non-emissions, non-PCV equipped, engine, other than symmetry? The engine in question is an '84 360 with the stock dished pistons. I'm building a mild four-wheeler out of it, and am keeping the budget super low, about $500 if possible.

[dave571]

If you aren't running PCV then you should have two breathers to help keep the crank case from pressurizing.

BUT... imho I would run PCV on that set up. Why? To keep the crankcase from pressurizing

There is no reason not to. You won't see any performnance gain by removing it.

The positive crankcase ventilation will help to keep the gaskets in place, less oil consumption etc..

[Dart 65]

It sounds almost redundant, then, doesn't it? Maybe I don't understand the purpose of a PCV valve. And I've never been able to find an EGR valve on my truck, either. Does it even have one?

[dave571]

pcv sucks crank case vapours from the engine. It keeps the crank case from pressurizing.

Pressurizing the crankcase, pushes oil past gaskets, rings, complete gasket failure etc.

In the old days a "road draft tube" was used. It stuck down towards the road. As the car moved down the road, crankcase vapours were drawn out.

The vapours aren't emmisions friendly, so they changed it so the intake sucked the vapours out.(60's emissions. Yes emmisons have been around for a long time)

Completely Evactuating the crankcase isn't much better than pressurizing it, so there is a breather on one side. Fresh air comes in and the vapours and pressure is drawn out through the PCV valve.

Removing PCV only serves a purpose on motors that don't make much vacuum (like big cam drag motors. Virtually no vacuum at idle, and certainly none at WOT)

On cars like that they don't work.

I run one on my 11 second drag car, and have never even considered removing it.

Your application won't see a benefit of not having one, and the maintenance on the motor will be much more than before.

I'm not sure if sb's all had EGR by 84, but It would think so.

If yours has it, (which it probably does) the valve is on top of the intake next to the carb. It goes into the crossover passage.. They can be removed, and replalced with a block off plate or pipe plugs in the holes. Someone may have removed it already.

Unlike PCV, EGR does have performance and economy drawbacks, and virtually NO positives (other than reduced NOx emissions) If it has it, ditch it with confidence.

[SSHAKERR]

A picture is worth a thousand words.

But what about crankcase evacuation using your exhaust. -->http://store.summitracing.com/egnsea...5&autoview=sku ?
Increase engine performance by reducing pressure buildup.
These Mr. Gasket crankcase evacuation systems are primarily drag race systems designed to reduce pressure buildup in the engine crankcase. They provide better piston ring seal, less intake charge contamination, and a reduced chance of oil leaks, while increasing your engine performance.
I wonder how this would work on a street car. I can't imagine any downside if the valvecovers are properly baffled inside and you have one filtered breather. Dave, why did you say "Completely Evactuating the crankcase isn't much better than pressurizing it" ?

[dave571]

Originally Posted by SSHAKERR

Dave, why did you say "Completely Evactuating the crankcase isn't much better than pressurizing it" ?

I was refering to the necessity of having a vent on the system.
The system is designed to have a contiuous flow through it.

In your diagram, If there was no vent, and manifold was vacuum applied, Vapour removal would not be optimized.