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Old 02-26-2007, 05:58 PM   #1
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Default Put the PCV back in....

So the BEGI intake manifold didnt have a spot for a pcv valve so I have been running it with a breather on both sides of the valve cover. I found that by doing this I am leaking oil from the cam cover and have also seen lower oil pressure as well. This to me is unaccpetable so I decided to drill and tap a hole for the PCV valve. I also decided to run a T fitting off that same port so that the valve cover vent on the driver side is also incorporated into the flow. This should provide better oil vapor evacuation. I got it all back on but realized that I have a leak at my throttle body because the threads in the BEGI manifold for the TB got all effed up somehow. I didnt feel like messing with it anymore today but I will be running helicoils in there when I get the chance. Ill let you guys know the results when I get it all done.

I didnt honestly think missing a PCV would matter but I think it really makes a large difference. Turbo cars see a lot of blowby so we need to have a PCV in the system to catch it all.
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Old 02-26-2007, 06:14 PM   #2
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I'm very anti PCV system within a turbo system. Where it would normally be open and breathing on a NA car... it'll be close on a turbo car.

Its something many honda people overlook and get increased crank pressure and have problems from that.

Picture this... PCV system closes under boost... blowby and crank movement build pressure inside the motor... where does it go? Last time my lines got clogged (frozen stuff in lines to small)... my turbo became my PVC valve. I turned into Spy Hunter with the smoke screen upgrade.

Open PCV system for me... or ideally... slashcut or vacuum pumped.
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Old 02-26-2007, 06:18 PM   #3
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I'm very anti PCV system within a turbo system. Where it would normally be open and breathing on a NA car... it'll be close on a turbo car.

Its something many honda people overlook and get increased crank pressure and have problems from that.

Picture this... PCV system closes under boost... blowby and crank movement build pressure inside the motor... where does it go? Last time my lines got clogged (frozen stuff in lines to small)... my turbo became my PVC valve. I turned into Spy Hunter with the smoke screen upgrade.

Open PCV system for me... or ideally... slashcut or vacuum pumped.
I use a 323gtx pcv valve so it does its job. I need some way to evacuate excess oil vapors in the crankcase. I used a PCV valve with great success until I got the BEGI manifold and it didnt have a place for the PCV vacuum port. I dont really want to use a oil catch can, I think the PCV will do the job just fine, and a lot better than not venting it at all.
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Old 02-26-2007, 06:20 PM   #4
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I use a 323gtx pcv valve so it does its job.
Similar to a saab pcv valve i wonder. I've found that catch canning my breather box (shortblock) and the breather on the valve cover... works fine for me. Ideally I'd like some vacuum draw... but it works.
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Old 02-26-2007, 06:35 PM   #5
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well you get the vacuum draw as soon as you let off the gas, right?

by the way, there's a PCV that goes to the intake manifold from the pax side and then the hose on the driver's side that goes to the intake tube.

what is the latter and why do they go different places?
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Old 02-26-2007, 06:38 PM   #6
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well you get the vacuum draw as soon as you let off the gas, right?

by the way, there's a PCV that goes to the intake manifold from the pax side and then the hose on the driver's side that goes to the intake tube.

what is the latter and why do they go different places?

Right the hose that would normally go to the intake tube has not been used on my car for 3 1/2 years. My intake tube is all sillicon so i just teed off the PCV port that I drilled. It should be better than just using a breather filter on the end of it.
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Old 02-26-2007, 06:39 PM   #7
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Originally Posted by y8s View Post
well you get the vacuum draw as soon as you let off the gas, right?

by the way, there's a PCV that goes to the intake manifold from the pax side and then the hose on the driver's side that goes to the intake tube.

what is the latter and why do they go different places?
The one on the driver's side pulls fumes when you don't have vacuum on the PCV side.
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Old 02-26-2007, 07:25 PM   #8
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damn it...and I was getting ready to get rid of my PCV valve lol. I guess I'll be leaving it in there for awhile
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Old 02-26-2007, 08:44 PM   #9
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The one on the driver's side pulls fumes when you don't have vacuum on the PCV side.
OK so then what is the one on the passenger's side for? just closer to the combustion chamber to prevent nasty oil in the intake?
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Old 02-26-2007, 08:46 PM   #10
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OK so then what is the one on the passenger's side for? just closer to the combustion chamber to prevent nasty oil in the intake?
Yup, and it did most of the work pre-turbo.
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Old 02-26-2007, 08:49 PM   #11
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See, Andy? Scott and I haven't been blowin' smoke all these years after all, huh?
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Old 02-26-2007, 09:25 PM   #12
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OK so then what is the one on the passenger's side for? just closer to the combustion chamber to prevent nasty oil in the intake?
The PCV works in different ways depending on engine load. At and near WOT, the intake manifold is at/near atmospheric pressure. The PCV valve is shut, so excess crankcase pressure is vented out the drivers side vent.

When the engine load is low (the majority of the time) pressure in the intake is also very low (below atmospheric). Crankcase fumes are pulled through the PCV into the intake, and fresh air enters into the crankcase through the drivers side vent.

The valve is needed because it forces a one-way flow of gases through the crankcase during low-load engine operation. Without a one-way valve, moisture and acids from combustion will accumulate in the engine.
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Old 02-26-2007, 11:58 PM   #13
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No, "fresh air" would never enter the driver's side vent, as it is intended to be connected to a source of constant vacuum (you can see this on any stock car, including the Miata).

Why would you want said "fresh air" to enter the crankcase anyway? You want to pull a vacuum in the crankcase, hence the term Positive Crankcase Ventilation...we're trying to vent/get rid of the positive crankcase pressure, as it's not good for anything.
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Old 02-27-2007, 12:38 AM   #14
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he said it flows through... the point of the pcv is to remove pressure and, I believe, corrosive gases from the revaporization of condensation during cold startup.

I guess the flow doesn't matter as long as it's mostly OUT and never net IN.

Matt
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Old 02-27-2007, 12:47 AM   #15
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The driver side vent is connected to vacuum? How so? On an AFM car, I guess the crossover tube may be a few kPa lower than atomospheric, but nothing close to a vacuum. On a MAF car, I doubt you could even measure it.

You need fresh air in the crankcase to replace the fumes you are removing via the PCV.

Wikipedia to the rescue: http://en.wikipedia.org/wiki/PCV_valve
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Old 02-27-2007, 03:26 AM   #16
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I used to have problems with filters melting above the turbo manifold, so I ran a fuel hose from the driver's side PCV outlet to the other side (where the shock brace is mounted) and put a cylindrical filter there near the shock tower brace mounting point.
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Old 02-27-2007, 09:03 AM   #17
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The driver side vent is connected to vacuum? How so? On an AFM car, I guess the crossover tube may be a few kPa lower than atomospheric, but nothing close to a vacuum. On a MAF car, I doubt you could even measure it.
Huh? Yeah, look at a picture of the Miata engine bay; the driver's side vent is connected to a source of vacuum, on both AFM- and MAF-equipped cars, as far as I know. I'll find some pics to look at in a bit, but I can't imagine why the '90-'93 cars would be any different from the '94-'05 cars

Why would you want to re-introduce "fresh air"/pressure back into the system from which you're trying to remove pressure?
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Old 02-27-2007, 09:46 AM   #18
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Originally Posted by mschlang View Post
The driver side vent is connected to vacuum? How so? On an AFM car, I guess the crossover tube may be a few kPa lower than atomospheric, but nothing close to a vacuum. On a MAF car, I doubt you could even measure it.
Really you dont think 20 ~hg. of vacuum is a lot? The only time your reach 0~hg. of vacuum on the crossover is under load at close to WOT.

The whole point of the valve is to relieve pressure form the crankcase. You'll never "add" fresh air in. The pcv closes as your throttle increases, so no air enters the through the valve...on the flip side, the breather line is under a constant source of vacuum.
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Old 02-27-2007, 11:23 AM   #19
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Quote:
Originally Posted by mschlang View Post
The driver side vent is connected to vacuum? How so? On an AFM car, I guess the crossover tube may be a few kPa lower than atomospheric, but nothing close to a vacuum. On a MAF car, I doubt you could even measure it.
I follow you. Unless you have a tiny, dirty air filter you're not going to see vacuum in the CROSSOVER TUBE. if you did, it'd flatten like your straw suckin up a strawberry in a strawberry milkshake.

but it's there to keep whatever small amount of gases coming OUT of the drivers side vent going back into the motor.

So my problem is that I have my filter mounted directly onto my turbo.

no nipple.
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Old 02-27-2007, 11:56 AM   #20
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I have my pass side PCV hooked up normally with the miata valve, and the drivers side has a hose that connects to my intake. It works fine. I kind of want to get a catch can hooked up, as my turbo is now getting some oil in it.
-Michael-
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