Bernhard

Is there any performance advantage to running the dual PCV set up like the 1969 H/O?
I have seen a few engine pictures of JR stock engines with extra breathers to help evacuate the crank case.

74sprint

No, but it looks pretty.

Ray

Bernhard

I wonder why the factory went with the dual PCV set up on the H/O?
I wonder if it could hurt performance as in weaken the intake vacuum.

VC455

Cutlasses had only one PCV system regardless of whether touched by Hurst or not.

The PCV system consists of a heavy vacuum hose that connects the PCV valve from the intake manifold (or valve cover) to a fitting on the front of the carburetor.

That is a basic pollution-control system that takes fumes from the crankcase and then to the carb; this keeps blow-by from escaping into the atmosphere. This works when the carb is at part-throttle.

When you are at full throttle the carb has no vacuum to pull the blow-by out of the crankcase. That function is in the following part of the answer...

Your question probably refers to the dual crankcase breather system that Hurst and W-30 cars had. Those breathers do not connect to the carburetor, so they cannot affect intake vacuum or any carb function. If you trace those breathers you will see they connect to the external part of the air cleaner housing.

The purpose of the breather system is to allow air to flow into the crankcase to replace the fumes taken away by the PCV system. Under full throttle, the breather system runs in reverse--all the blow-by goes from the valve cover(s) into the air cleaner housing.

So, why did some cars have dual breathers? It was only high-performance cars that had these, so it must have been something the factory engineers thought was necessary on high-performance cars. I would guess that the looser clearances in those cars produced more blow-by and they wanted an extra exit so crankcase pressure would not build up.

Crankcase pressure causes oil leaks--and the dual breathers would help prevent those.

FStanley

First the 1969 H/O never ran two PVCs.

1. The early prototype used a PVC in the drivers side valve cover and a breather element on the passenger side valve cover, then via tubes up to the air cleaner. Identical to 1969 442.

2. Production 1969 H/Os had a breather element in both valve covers and tubes up to the air cleaner. The intake manifold had a fitting for PVC, next to the water outlet, where the thermostat housing is connected. A rubber 90 deg elbow connects into this, then the PVC valve, then a small hose to the carburetor base fitting. Similar to 1970 W30 cars


Hence, two PVCs were never used only one.

Why they did this I do not know. If you don't have to worry about smog inspections, two breather elements probably won't hurt a thing. But keep in mind the factory carburetors were calibrated to work with the PVC valve. So you may have to tune a bit... if you do not use one... probably not much of a concern in WOT race conditions...

Bernhard

Thanks for the reply I thought they were running two PCV valves.

Bernhard

A good PCV systeam lowers pressure in the crankcase and prevents leaks.
It works better than breathers on both valve covers and might even free up some hp.

Bernhard

Aftermarket PCV
http://www.engineprofessional.com/ar...Q315_34-44.pdf

There was a stock unit that performed quite well and keeping the crankcase under vacuum.

Bernhard

I fixed the link
http://www.engineprofessional.com/ar...Q315_34-44.pdf



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