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Old 07-23-2013, 01:41 AM   #1
Serkan
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Default Speed density and catch can (open loop) ?

I will be going with Cobb speed density once I finish building the car.

Trying to figure out what to do with blow by and venting system.

Since the system won't be on maf, I can use catch can and not return the nasty blow by back to the intake.

But than it will not have vacuum in the head and block breathers. Is there going to be an ill affect if I just use catch can without return to intake system (open loop) ?


I want to get an SMC catch can (3" dia and 6" tall) with 2 inlets and hook up the block and head breathers in one unit.

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Last edited by Serkan; 07-23-2013 at 03:45 PM.
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Old 07-23-2013, 02:08 AM   #2
kellygnsd
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Even on MAF cars you don't have to run the return back to the intake. The blowby gas is already combusted gases and in no way affect your MAF tune. You don't need to account for gas that has already been consumed by the engine.

You can VTA if you like but I'm SD and I still plumb my AOS back to the intake just because I prefer a little PCV effect
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Old 07-23-2013, 02:16 AM   #3
Alistairh
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I'm MAF, have absolutely no ports on my intake, and vent my catch can to atmosphere.

OP, be aware that venting your catch can to atmosphere gets smelly.
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Old 07-23-2013, 02:37 AM   #4
Serkan
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What about the metered air that's been talked about in every thread ?

With stock configuration that air circulates in a closed loop (after maf). I am no expert but that is what i have been reading.

Never thought about the smell. Is it really that bad ?

Thanks for the replies.
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Old 07-23-2013, 02:39 AM   #5
Ryan321
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Running MAF or speed density will not effect your catch can. Sorry if I miss read what you were saying. As for brining it to the intake I would suggest ATM, let it sit in the can.
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Old 07-23-2013, 02:43 AM   #6
kellygnsd
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Quote:
Originally Posted by Serkan View Post
What about the metered air that's been talked about in every thread ?

With stock configuration that air circulates in a closed loop (after maf). I am no expert but that is what i have been reading.

Never thought about the smell. Is it really that bad ?

Thanks for the replies.
Post a link to a thread you are talking about. I guarantee they aren't talking about post combusted air. If they are, they don't know what the hell they are talking about. You may be confused on the effects and symptoms of pre and post MAF leaks. Blowby is neither.
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Old 07-23-2013, 02:56 AM   #7
Serkan
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I could be, it is pretty late. But I am sure i am not getting confused by bov vs bpv :P

So how come people go catless but still return the nasty blow by back into intake, since emission is no concern ?

Also what about going open loop and not having vacuum in breather lines ? Any bad effects ?
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Old 07-23-2013, 10:46 AM   #8
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They are using the intake to pull vaccum.
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Old 07-23-2013, 10:51 AM   #9
CatfaceType-R
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Wat...the op's posts aren't making much sense.
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Old 07-23-2013, 11:08 AM   #10
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I have seen great results with more crank venting then with minimal crank venting! Seems they wanna breath bad!
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Old 07-23-2013, 03:50 PM   #11
Serkan
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Looks like you guys are more confused than I am. I didn't ask where we get the vacuum from.

If you don't get what I mean by open loop, don't even post how it doesn't make sense to you.


I do not want blow by routing back into intake. I always thought the air in the system has to been in closed loop because of the maf. Kelly says combusted gases has no affect in maf tune.

Than I asked why the heck ppl with catless exhaust return their blow-by back to intake since emission is not a concern for them.

Than I asked if there is any bad affects running breather lines to a catch can without vacuum ? Do the heads and block need the vacuum to get rid of pressure ?

Pretty easy question.
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Old 07-23-2013, 05:00 PM   #12
kellygnsd
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I'm on my phone and don't feel like typing a novel at work so

1. You need to learn about positive crankcase ventilation and its benifits and how it works.
2. How pre and post maf leaks affect you AFR
3. What blowby is and where it comes from
4. Why being catless has no bearing on whether you vta or plumb your can back to the intake.
5. Ask coherant questions and not jump from bov to bpv to catless this to blowby.

I think the reason you don't understand what we are saying is because you don't have full understanding of what is going on.
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Old 07-23-2013, 05:16 PM   #13
Serkan
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You are right about 1,2 and 3. I am doing as much research and reading on this.

4-5 is partially right because I never said catless exhaust has anything to do with breathers. Anyways i gave up getting an answer in this thread.
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Old 07-23-2013, 06:46 PM   #14
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To answer your question. A catch can/AOS will perform more effectively with a vacuum source on it. But, you can also simply vent the crank case pressure to atmosphere and it's 90% as good.
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Old 07-23-2013, 09:53 PM   #15
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Ideally you should have minimal to no blowby if the motor is built right. In the case you do... Having a vacuum source using a good catch can that doesn't simply suck that junk back in the intake could have some benefit. But do you need it... Nope. Mine vents to the wheelwell.. So do many others. If you do hook it up to the intake you run into the issue of how much vacuum are you actually sucking... Are you sucking oil out by mistake now... It's a mess. Hope for a good build with no blowby and vent it however you want.
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Old 11-13-2013, 10:31 PM   #16
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i have the smelly issue with my setup, running speed density and a catch can vented to the atmosphere, and this is on a bone stock ej257, what i'm thinking is on using the rear 02 sensor bung on the downpipe to screw in a nipple and run a hose from my catch can instead of having the filter, that way the smelly gases are going to be pushed out from the exhaust.
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