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Old 01-24-2023, 03:50 PM
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Default Fixed Orifice PCV

In the Facebook Sniper EFI forum I read that a fixed orifice style PCV is preferred when using EFI - apparently it helps with idle. Has anyone experimented with this and also is anyone aware of a fixed orifice style PCV that looks and fits in old Pontiacs like ours.

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'69 Firebird 400/461, JBP 290+ E D-Ports, HR 230/236, 4l80E, 8.5 Rear, 3.55 gears
'64 LeMans 400/461, #16 Heads, HR 230/236, TKO600, 9-inch Rear, 3.89 gears
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Old 01-24-2023, 04:09 PM
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I went from a standard PCV system to a draft style system that is close to a fixed oriface PCV on my FiTech. I didn't notice any change in idle characteristics, nor did I have to make any tuning changes.

The item that made the biggest difference in idle quality was moving to timing control. Being able to dump in idle timing and letting the system idle stabilize by adjusting advance relative to fuel made a fairly dramatic difference in both idle quality, temperature control and idle vacuum. I gained over 2" Hg at idle by going to timing control and commanding about 24 degrees of initial advance.

This worked so well, that my once "somewhat rowdy" 455 with a 232/238 112 cam behaves and sounds as if it has more of a factory type cam in it.

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Old 01-24-2023, 04:25 PM
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I've tuned mine with a pcv system and with a draft style open breather set up. They each react differently because of the vacuum differences, but I can attain a great idle with either.

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Old 01-24-2023, 04:36 PM
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I switched the Chevelle over to fixed orifice PCV, after I had run the Sniper setup for more than a year with a regular PCV.

On mine, going to a fixed orifice, basically made the vacuum leak much smaller and caused the IAC counts to rise a bit to bring the idle back up where it was commanding. Once warmed up it's not a big deal but when it's cold it really tightened up the window I had for a high speed cold idle, basically pegging the IAC at 100 when cold to barely maintain an idle.

What it boils down to for me, and something I complained about very early on when we bought these Snipers, is that the IAC could stand to be a bit bigger for these larger engines with big camshafts that have a bunch of overlap.

I've played around with drilling the fixed orifice, I think I'm up to 3/32" or so and it hasn't really made a bunch of difference. Of course that's not even close to the near 1/4" or 5/16 hole the regular PCV had, LOL

Funny this all came up because I was going to switch it back over to the regular PCV today. I never had any drivability or running issues with it so not sure why they preach that so much over on the Holley forum.

The GTO got switched over to a vacuum pump so the engine is totally sealed, eliminating the PCV. But that was done for other reasons.

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Old 01-26-2023, 08:41 PM
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Which fixed orifice PVC did you use?

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'69 Firebird 400/461, JBP 290+ E D-Ports, HR 230/236, 4l80E, 8.5 Rear, 3.55 gears
'64 LeMans 400/461, #16 Heads, HR 230/236, TKO600, 9-inch Rear, 3.89 gears
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Old 01-26-2023, 08:55 PM
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Quote:
Originally Posted by grivera View Post
Which fixed orifice PVC did you use?
Oooof, honestly I'm not sure if there are a bunch of choices or not. I grabbed one off the shelf at the local store with a straight up 3/8 hose nipple that would work on my Chevelle. Same thing you would see in a Pontiac valley pan.

From what I understand though, they all pretty much have just a 2mm or a 3mm hole size in them. Not very big at all. Basically they are just a gutted PCV with a tiny hole in the bottom. A controlled vacuum leak....

I removed mine yesterday and reinstalled the standard PCV. But I'm just sort of playing around with the differences to understand more how it affects the fuel table.

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Old 01-27-2023, 12:22 PM
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Thanks- I’ve been searching on line but will take a look at AA and AZ…

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'69 Firebird 400/461, JBP 290+ E D-Ports, HR 230/236, 4l80E, 8.5 Rear, 3.55 gears
'64 LeMans 400/461, #16 Heads, HR 230/236, TKO600, 9-inch Rear, 3.89 gears
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Old 01-30-2023, 01:05 PM
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Here is the link to the one I used: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

I used it form the get go so I don't have anything to compare it against. I just had to put a piece of electrical shrink wrap around the bottom to fit a bit snugger in my stock PCV gasket.

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Old 02-01-2023, 01:17 AM
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I have on many big cammed engines used a fixed orifice PCV. On street cars here, a working PCV is reqd for registration. I calculated the orifice area of a stock PCV at idle & came up with a round hole of 7/64" diam.
I cut open the PCV, discard the innards & braze in a disc, in which I drill a 7/64" hole. Then braze the PCV back together.

Have done many over the years & work well.

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Old 02-03-2023, 09:13 PM
jrh3405 jrh3405 is offline
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I've had good luck with the ME Wagner dual flow pcv valve for my Pontiac, it's adjustable and or fixed orfice for efi.

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Old Yesterday, 10:53 PM
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Thanks all

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'69 Firebird 400/461, JBP 290+ E D-Ports, HR 230/236, 4l80E, 8.5 Rear, 3.55 gears
'64 LeMans 400/461, #16 Heads, HR 230/236, TKO600, 9-inch Rear, 3.89 gears
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