PCV VALVE... Really?

[ndutton]

Are you suggesting the vacuum measurements as reported have no merit? If so, why measure vacuum in the first place?

I accepted the numbers at face value and would not have discounted them if they did not support my position. Had the vacuum readings come back dead even I'd have admitted zero PCV air leak.

[67c&ccorv]

I'll choose not to deal with carb adjustment difficulties and choose not to install an adjustable main jet to compensate for the PCV. I'm happy with the way things are and will strive to keep them that way.

May I assume you'll not be interested in my new line of logo apparel?

PCV for President in 2016!

[67c&ccorv]

Actually, the Moyer manifolds have an exhaust flange on both ends. This allows them to accomodate both "nornal" engines and "backward" ones that have a V-drive with a single part. The unused flange is closed off with a flat plate.

This makes it really simple to add an oxygen sensor to an A4 with a Moyer manifold. The flange plate can be removed and drilled & tapped in the comfort of your home shop. I even bought a separate plate to drill out, so the conversion can be easily reversed if that's ever needed.

But what about the dreaded "hot spot" on the exhaust manifold Ed?

[roadnsky]

Again we need exact numbers (I mean gauge shows closer to 19 than 20)as I stated would be broke down into %'s

Well, the actual number for idle WITH the PCV was closer to 17 than to 18.
Basically, it was a 2" difference at idle between the with and without.

And just to be more exact I should have also post the 1500 RPM number...
WITH the PCV it was just a "tad" under 12"

Right now, I have to say that on my A4, I'm happier without the PCV.
Dialing in the idle mixture adjustment was a breeze after losing the valve,
and the throttle response thru all rpms is excellent.

I'm gonna run another 8-10 hours more and then check the plugs.
Again, I'm beginning to believe my "rich" condition was because of too much MMO added at refueling. Haven't added any more and will keep an eye on it.
BUT, that is another topic...

[edwardc]

But,,
shouldn't the O2 sensor be in the path of the out going air?
That way you are sampiling all the cylinders.
And not just getting a reading from one corner that basically only one cylinder is influencing.

Technically true, but the assumption is that since there's a single-throat carb feeding all four cylinders, the mix ratio should be the same for all four, at least to the level of precision that we are concerned with.

The real reason for mounting it there is that O2 sensors are notoriously sensitive to moisture, and degrade quickly in the presence of H2O vapor. Thus, you want to mount it as far as possible from the wet part of the exhaust.

[edwardc]

But what about the dreaded "hot spot" on the exhaust manifold Ed?

I don't know how that would affect an O2 sensor. It might even help it work better, as they have to reach a certain temperature before they start reading properly. Fancier ones have a built-in heating element, but the inexpensive one I used doesn't, so I have to wait a few minutes for the exhaust manifold to heat up before I can get a stable reading.

Based on the numbers I'm seeing on this thread, I'm beginning to form the conclusion that any engine that has a PCV valve installed should also have an adjustable main jet installed as well to allow getting at least the cruise RPM and the idle tuned to the right mixture. As Neil points out, it won't be possible to get all RPMs tuned properly, but if you can get the one you most commonly cruise at.

And in my own case, I just wasn't able to find the right combinations of idle jet, main jet, and timing advance to achieve this until I installed an O2 sensor and a fuel/air ratio gauge to tell me when I got it right.

[hanleyclifford]

Okay, does anyone want to offer an analysis of Jerry's vacuum measurements before I make a case that they support exactly what I've been asserting all along?

The numbers are the numbers, measured with and without a PCV and no other changes.

Neil, I want some points for my conspicuous absence on this thread.

[ndutton]

Hanley, your self restraint is duly noted. However, I won't get irritated if my reasoning is subjected to scrutiny. Been there before. Actually, I thought the mention of the oxygen sensor would have drawn you in for sure.

I just read Indigo's product description that claims improved engine performance. There's no supporting text beyond the claim though. I've also looked and looked for Don's PCV offering. It was part of a flame arrestor product but for the life of me I can't find it in the catalog.

[hanleyclifford]

Neil, right up front I agree the PCV valve does not improve engine performance. No way. That isn't it's purpose. The O2 sensor doesn't do anything either unless you have an adjustable jet to go with it, and a vacuum gauge.

[ndutton]

Thanks Hanley, I completely agree. Do we differ on the idea the PCV is there to essentially mask an internal wear issue?

[hanleyclifford]

Thanks Hanley, I completely agree. Do we differ on the idea the PCV is there to essentially mask an internal wear issue?

Even an engine with little wear will still put out some oil vapor. The PCV keeps that out of the interior of the boat. The more the engine wears, the more important this becomes. If you don't need a PCV your engine is damn near perfect...or else your nose is defective.

[ndutton]

I should have said beyond the ability of the slash tube. I'd say we likely differ as to where the line is drawn, that line being when the PCV system becomes a necessity.

[Ball Racing]

Are you suggesting the vacuum measurements as reported have no merit? If so, why measure vacuum in the first place?

I accepted the numbers at face value and would not have discounted them if they did not support my position. Had the vacuum readings come back dead even I'd have admitted zero PCV air leak.

Lets see,
the numbers given were a "slight" bit different than the pictures.
you took his numbers and made your own numbers for your argument.
That was my argument.
What ever the numbers really were, thats fine.

There was many days between the gathering of numbers with and without the device.
There is no way the weather, tide, and wind were the same.
So it may take more or less throttle plate to give the same rpms for the test.
You just breathe on the throttle and you can get way different readings
Thus why I said the test should be performed on the same day for REALLY accurate data gathering.
Since my hull will plane out, the weather makes a big difference ,somedays it take more throttle than others to maintain a cruise rpm once planed out.Thus a different vacuum reading.
I kinda thought it was a given that there would be a air leak to a degree given the front seal, and the vented oil cap.

Your next debate was there was no way you can tune it to have correct mixture at idle cruise and at higher throttle.
Well I am not sure we have that now.

Our carb is way oversized, and it may receive a different fuel signal if run @WOT of the reach of the carb over if the throttle was set to a stop once max rpms were reached.

When I had racing carbs on the flow bench, I would compromise throttle plate stop positions to also maintain a strong fuel signal.

And since I seem to be the only one keeping this going,
I am going to say Again, it is wrong to mask problems with a device..

"I" would like to keep all smell away,(I have no foggy blowby) and if possible, get a performance benefeit.

I may not be able to do it.
But not trying won't make it any better either.

But maybe more than anything, I want to see it work because you say it can't and won't try.

[ndutton]

you took his numbers and made your own numbers for your argument.
That was my argument.

I used Jerry's numbers exactly as reported. Please don't suggest otherwise.

There was many days between the gathering of numbers with and without the device. There is no way the weather, tide, and wind were the same.

Perhaps not identical but Jerry's sailing grounds in Lake Mead are as stable an environment as could be hoped for, devoid of tides and virtually zero current.

I kinda thought it was a given that there would be a air leak to a degree given the front seal, and the vented oil cap.

True, but where does the leak enter, before the carb where it is taken into account re: fuel/air ratio or after the carb where it is not. That's the issue.

I am going to say Again, it is wrong to mask problems with a device..

Agreed. No question.

I may not be able to do it.
But not trying won't make it any better either. But maybe more than anything, I want to see it work because you say it can't and won't try.

By all means, go for it. My goal here is someone in the future considering a PCV system who finds this thread can get the pro's and con's so he can make an informed decision. If you or anyone else can find a way to keep the fuel/air ratio in the correct proportion with air contributed in varying amounts to the mix after the carb - and bring the data to support it - that would be great. It would be helpful to those who have experienced the tuning difficulties described here.

[romantic comedy]

.
I kinda thought it was a given that there would be a air leak to a degree given the front seal, and the vented oil cap
.

We are talking about the manifold, so I dont understand this part. Any PCV valve would act as an air leak, in my experience.

I agree that we dont know the crabs performance at any or all RPMs. Most here are assuming that the carb gives the correct mixture. This is where we need a sensor.

A device to mask the problem is fine with me, as long as it does not damage the engine.