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Kirkham Motorsports

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  • 1 Post By twobjshelbys

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  #1 (permalink)  
Old 09-14-2020, 04:05 PM
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Default Idle rpm changed with air/oil sep installation...

...in the PCV system. I have a QuickFuel SS750 carb that was tuned quite well until I needed to install an air/oil separator in the PCV system. The idle dropped from 850-900 rpm to about 700 and less, apparently due to the new restriction in the PCV line to the manifold. Sometimes it would just die. I used the curb idle screw to regain my target idle rpm, but then the engine would overrun/diesel when I shut it down.

I don't like dieselling, but having to heel and toe at every stop just to keep the engine running isn't a lot of fun.

Suggestions on how to recover idle rpm without the evil dieselling?

Thanks in advance
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Old 09-14-2020, 04:29 PM
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That's interesting. I'm assuming you have a regular old-style PCV valve stuck in the passenger side valve cover and not a fancy adjustable PCV valve. Here's a test: If you pull the hose off the PCV valve entirely, so that the hose is just sucking plain old air from the atmosphere, does your idle shoot up higher?
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Old 09-15-2020, 06:13 AM
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Patrick

I have the fancy adjustable PCV valve. I've been assuming the engine is working a bit harder to pull the crankcase gases thru the separator.

I'll give it a try, see what happens. May need to readjust the valve. Good thinking. Thanks!
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Old 09-15-2020, 06:38 AM
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I have the following plumbed into my Quick Fuel Q-Series with no issue
Idle stays at a solid 950 hot or cold.

PCV
Dual Flow Adjustable PCV Valve – M/E Wagner Performance Products

ADD W1 Catch Can With Dipstick
https://www.addw1.com/collections/al...-configuration
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Old 09-15-2020, 08:43 AM
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Originally Posted by Sledge View Post
Patrick

I have the fancy adjustable PCV valve. I've been assuming the engine is working a bit harder to pull the crankcase gases thru the separator.

I'll give it a try, see what happens. May need to readjust the valve. Good thinking. Thanks!
And if pulling the hose off the ME Wagner valve does nothing to the idle, try pulling the hose of the carburetor fitting and see if the idle changes. If it does, investigate whether you can breathe or blow through your separator or if there is some funky clog in it somehow.
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Old 09-15-2020, 11:41 AM
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I find it hard to understand that the PCV system is so misunderstood...The manifold sucks it in via the PCV, the air enters the engine via the valve cover breather , goes through the engine through the PCV to the intake?????
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Old 09-15-2020, 11:59 AM
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Patrick:

You were right on the money. The restriction was in the separator itself in the form of a sinterd metal "filter" that was severely reducing flow. I'm going to remove the sintered material and use the nut to mount a baffle that I intend to fabricate. I removed the filter and it ran fine.

Thanks for the help!
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Old 09-15-2020, 12:01 PM
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Quote:
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Patrick:

You were right on the money. The restriction was in the separator itself in the form of a sintered metal "filter" that was severely reducing flow. I'm going to remove the sintered material and use the nut to mount a baffle that I intend to fabricate. I removed the filter and it ran fine.

Thanks for the help!
Excellent. Glad you're fixed.
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Old 09-16-2020, 07:53 AM
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Just curious whose air/oil separator you were using . The one that comes to mind that has a mesh in it is the Moroso unit . I would also be curious what baffle system you come up with .
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Old 09-16-2020, 08:03 AM
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Quote:
Originally Posted by Bobcat View Post
Just curious whose air/oil separator you were using . The one that comes to mind that has a mesh in it is the Moroso unit . I would also be curious what baffle system you come up with .
If that was aimed at me, I do have the smaller of the Moroso separators, along with the ME Wagner adjustable PCV, and Blue Thunder valve covers baffled as shown below. I have no problems whatsoever with them, and they work beautifully, provided that I empty the separator every 500 to 700 miles. Any more than that and the separator fills up about half way (that's two ounces) and then I start getting oil sucked in to the engine. You can tell when that happens because there is a slight decrease in off-idle performance and hot idling along with an increase in exhaust smell.



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Old 09-16-2020, 01:38 PM
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I needed a small one so I got a Jegs 52206 separator. Other than the ultra-fine sintered filter (very restrictive) it works fine and is well-made. I also use the M/E Wagner PCV valve. I home-made a baffle with a small piece of aluminum I had hanging around but did not take pictures of it.
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Old 09-16-2020, 02:06 PM
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Thanks for both replies .... I also have the Wagner unit and Moroso separator . I took the Blue Thunder VC off as the baffles weren`t doing the job . I would go through about a half quart of oil in just over 100 miles . It wasn`t in the separator , just seemed to go right through the Moroso unit into the intake .
My BT covers are the plain shot peened competition ones and the baffles are what you have Patrick .
The big difference I see is that you ( Patrick ) have your Wagner unit mounted higher than mine as I just used the grommet they supplied . I suspect that if I did the same , the BTV baffles would be adequate for the rpm I turn ...redline is 6400.
It seems the big difference between the Jegs unit and Moroso is the filter media with the Moroso unit not being as restrictive .
So , thanks for the info .
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Old 09-16-2020, 02:08 PM
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The addition of the separator changed the vacuum.

Separators are the closest thing to snake oil in the automotive industry. The oil that is captured is miniscule and does not affect in any way the operation of the engine. It's built into the plan. If you're pulling a teaspoon of drainage every 1000 miles then the engine would have taken care of that just fine. That is the design of the PCV system from day 1.

Now, if you have a boatload of oil in the separator you've got a bigger problem. The separator isn't going to fix it. It is an alert though, but then so is the smoke you're getting from the tailpipe.

The exception is the case where you track the car under varying angles from horizontal and it might capture a little more than normal. But even that isn't a problem. Consider it top oil.

When Shelby American added them for the early GT500s I knew their VP that brought it in and explained this. He said something like "we know, they are bling, but people want to buy them so we will sell them".

PS. You will NEVER need one on both sides. One side is vacuum and the other is exhaust. (I dont remember). Everyone always says one side has some and the other side has none. If that other side has some then you've blown your engine.
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