Side (Valve) Cover Plate

[Dave Neptune]

Hanley, a "snubber", not sure what you mean here.

Dave Neptune

[hanleyclifford]

Hanley, a "snubber", not sure what you mean here.

Dave Neptune

Snubber, a restriction fitting to modulate instrument fluctuation. I have them on my fuel pressure gauge and vacuum gauge. I have a theory that the PCV does not need the full flow of a 1/8" pipe to do it's job so I intend to drill out a .015" snubber until the PCV valve just controls the blowby with minimum vacuum "leak".

[romantic comedy]

I like that idea Hanley. Keep us updated.

[Dave Neptune]

Careful

Hanley, I think you'll need a bigger bleed than that as the PCV works at high manifold pressures too. When operating at these lower vacuum a larger hole is necessary to allow the flow. At higher vacuum or low pressure the valve allows very little through via an internal control. I doubt the PCV and a snubber will work well together as a PCV valve is set up for displacement and manifold load profiles via it's internal mechanism controlled by vacuum.

You would probably be better off finding one for a similar engine but of less displacement. The amounts of air that a PCV introduces is easily compensated by the carb. This is because carbs are so far off even when they're close. Look at how much better an FI engine works for economy, a carb set-up may match it is a few spots but across the board the FI is superior.

Dave Neptune

[hanleyclifford]

Ran a test today on the PCV system which I have plumbed to the carb spacer plate via 1/8" NPT fittings. The engine ran at 1200 rpm with 15 inches of vacuum. Next I installed a snubber in the line drilled out with 3/32" bit. I saw 17 inches of vacuum at the same rpm. Of course I had to change carb settings, main jet and idle screw, to achieve the same fuel/air ratio. The engine runs smoother and achieves a lower idle without missing. I'm looking forward to sea trials on this with launch expected in about 2 weeks. The issue will be whether the now restricted PCV can handle the blowby at cruising rpm.

[romantic comedy]

Interesting Hanley, Why would you have a higher vacuum with a "leak"? How do you measure the air fuel ratio?

[hanleyclifford]

Interesting Hanley, Why would you have a higher vacuum with a "leak"? How do you measure the air fuel ratio?

The "leak", the PCV valve deprives the manifold of vacuum; thus depriving the PCV valve of some of it's flow restores vacuum to the manifold. I measure air/fuel ratio with a gauge and an O2 sensor. The O2 sensor is threaded into the end of the manifold. The gauge is just below the ammeter on the panel.

[romantic comedy]

That is right, I remember now, that gold engine with O2 sensor. Looks good!

I am still stuck about the vacuum. In my mind, when there is a leak, the vacuum would go down, but the RPM would go up. I have to think on this.

[ndutton]

I did a little testing on my engine with and without PCV. I discovered that in neutral at 1000 rpm the PCV was costing me 1 to 1.5 inches of vacuum.

Ran a test today on the PCV system which I have plumbed to the carb spacer plate via 1/8" NPT fittings. The engine ran at 1200 rpm with 15 inches of vacuum. Next I installed a snubber in the line drilled out with 3/32" bit. I saw 17 inches of vacuum at the same rpm. Of course I had to change carb settings, main jet and idle screw, to achieve the same fuel/air ratio. The engine runs smoother and achieves a lower idle without missing.

Ooh baby, be still my heart. SCHWEEN!!

Hanley, you may be in the unique position to perform actual comparative vacuum measurements because with your oxy sensor you can maintain a consistent fuel/air ratio. Please keep the results coming. This is great information regardless of the outcome.

[hanleyclifford]

Ooh baby, be still my heart. SCHWEEN!!

Hanley, you may be in the unique position to perform actual comparative vacuum measurements because with your oxy sensor you can maintain a consistent fuel/air ratio. Please keep the results coming. This is great information regardless of the outcome.

Actually, Ed has the same system. I'm beginning to form an hypothesis in my head to the effect that the usefulness of a PCV valve is proportional to the quantity of blowby. To put it another way, the PCV as installed from the supplier pulls more air and vacuum from an engine than necessary to handle the blowby - it is not adjustable. I suppose the next thing should be a carbon monoxide sensor to see when the PCV achieves it's desired result, and at what size orifice. Any thoughts on this?

[ndutton]

I'm beginning to form an hypothesis in my head to the effect that the usefulness of a PCV valve is proportional to the quantity of blowby.

I've been saying the same thing for years but not as eloquently. Well, that and the idea that the cause of excessive blowby is not because you don't have a PCV system. It will be great to get some real measurements instead of subjective opinion.

[hanleyclifford]

Lot to think about here

If you run a PCV valve unrestricted on an engine you never really know how much blowby you have because it is being "handled" by the system. The downside is that you are pulling oil into your engine unnecessarily which can dirty valves etc. Mounting the PCV vertical helps but does not eliminate the issue. The carb can be adjusted of course to enrich the mixture to compensate for the "air no fuel" input of the PCV but that still does not eliminate the oil getting into the combustion chambers. Still, I am convinced the PCV handling of blowby is better than a slash tube; protestations to the contrary notwithstanding I am sure that no arrestor remains "schmutzfrei" with oily air and dust collecting on the grille. The solution seems to be an "adjustable" PCV system to accomodate different blowby levels. But how to determine what level is not acceptable and how to modulate the flow thru the system such that only the crankcase vapor required to maintain an ever-so-slight negative pressure in the crankcase is being extracted? Instead of the snubber should I be thinking in-line valve? The crankcase is open to the atmosphere big time right at the flywheel housing (unlike automotive) so pressure sensor would not work, but a CO sensor might. Thoughts?

[ndutton]

HA! My thoughts would not contribute to the discussion. Still interested in how this plays out though.

[hanleyclifford]

A blowby situation rarely gets better on it's own unless the problem is rings and you have a magical potion to improve their grip. OTOH an engine with significant blowby can still be useful for our purposes for an unspecified period if a way can be found to keep the fumes out of the boat - hence the slash tube or PCV. Both solutions extend the working life of the A4 but other issues such as carb performance are raised. I suspect that slash tube engines acquire dirty arrestors and consequent richer mixures. PCV engines draw unnecessary crankcase fumes into the engine and create a lean but oily condition in the combustion chambers.