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Old 06-01-2011, 01:32 PM   #1
mug23
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Default 05 STI crankcase breather system

Hello,

I have a question for the motor guru as I do not have a good understanding of the 05 STI crankcase breather system.

I have a new build block but the block is not an STI block and my car is an 05 STI where the oem 701 STI block has another vent hole in the near the middle of the block.

Now this will be my race car where emission is not an issue and never be driven on the streets. I'm also planning to push 500-600 whp. Now, since the new block doesn't have the extra vent hole like the STI does, can I just cap off the stock STI hose since there's nothing to plug it in on the new block? Would there be problems with pushing this high HP?

Maybe if I get a good air/oil seperator like the Crawford or the Grimmspeed one and cap off the un-used hose will work? Or should I just get an actual STI block instead?

Here are the picture on what I'm talking about.

New block:


OEM Block:
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Old 06-01-2011, 01:48 PM   #2
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doesnt matter.
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Old 06-01-2011, 03:05 PM   #3
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why did you circle the oil pressure sensor? It's not part of the breather system

I'd want to have the breather hole, especially as it's a race car. High crankcase pressure isn't a good thing to have.
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Old 06-01-2011, 03:09 PM   #4
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Quote:
Originally Posted by Homemade WRX View Post
why did you circle the oil pressure sensor? It's not part of the breather system

I'd want to have the breather hole, especially as it's a race car. High crankcase pressure isn't a good thing to have.
The circle was for something else. Nothing related to my question.

I was told that it would be ok and the main breather vent is enough to vent out.
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Old 06-01-2011, 03:28 PM   #5
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The secondary vent on the 2.5 block is just used to equalize the pressure between the heads and crankcase. It doesn't actually vent to the outside world or the intake, it's just a head to crank to head line that keeps the pressure equalized. The 2.0s didn't have it for some reason, so you can probably just cap off the second breathers on the valve covers, or keep the valve covers connected to each other and just cap off the part that used to go to that crankcase breather.
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Old 06-01-2011, 03:41 PM   #6
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curious as to why you went with an N/A block..


just make sure you cap off the vents on the valve covers as well.
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Old 06-01-2011, 03:51 PM   #7
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Quote:
Originally Posted by the suicidal eggroll View Post
The secondary vent on the 2.5 block is just used to equalize the pressure between the heads and crankcase. It doesn't actually vent to the outside world or the intake, it's just a head to crank to head line that keeps the pressure equalized. The 2.0s didn't have it for some reason, so you can probably just cap off the second breathers on the valve covers, or keep the valve covers connected to each other and just cap off the part that used to go to that crankcase breather.
It does more than equalize if you plumb it as such

he said race car and I say why keep OEM emissions handicaps? Take advantage of the port.
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Old 06-01-2011, 04:08 PM   #8
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Well, I got a deal from Outfront Motorsports with fully closed decked Manly piston and H-beam rods. Nitrated crank, 11mm oil pump and once I saw that the block was a Z block which indicates a perhaps a RS 2.5 block rebuild by Outfront and I was wondering.

I did talked to them over the phone and they mention that once it's closed decked, it wouldn't matter as the block was be strong to hold up to 600whp. The only concern I have is the vent hole which the STI has and they said to me that I can cap it off and it will be fine. I'm just having second thoughts now on this as I think I really want an actual 701 block instead.

Any suggestion would be appreciated on what I should do...
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Old 06-01-2011, 06:15 PM   #9
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Doesn't that vent system have something to do with the avcs in the Sti heads? Iirc...
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Old 06-02-2011, 02:55 PM   #10
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for what its worth that more-centered hole i have just running to my catch can. other one just vents to atmo from underneath the car.

out of curiosity, couldnt you just route that centered one to one of the heads? it just would dump oil back in...
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Old 06-02-2011, 03:20 PM   #11
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Quote:
Originally Posted by cha86
for what its worth that more-centered hole i have just running to my catch can. other one just vents to atmo from underneath the car.

out of curiosity, couldnt you just route that centered one to one of the heads? it just would dump oil back in...
I don't have that at center hole on my new block but the valve cover still have the provision hoses for the center hole since my car is an sti not a wrx. So I need to see where I can route those extra hoses of the valve cover.
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Old 06-02-2011, 06:09 PM   #12
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you can plug it...I'm wondering why the NA block was chosen :chosen:
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Old 06-02-2011, 07:45 PM   #13
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Quote:
Originally Posted by mug23 View Post
I don't have that at center hole on my new block but the valve cover still have the provision hoses for the center hole since my car is an sti not a wrx. So I need to see where I can route those extra hoses of the valve cover.
right i got that...but im saying IF...im wondering if you could do that? or would that not really do anything as far as crank case pressure.. but i do understand you would plug the valve covers..

homemade...input? can you route that center port to one of the heads and then the other port on the head to *say* a catch can/whatever...
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Old 06-02-2011, 09:48 PM   #14
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Dave. I would think you would be fine just running a hose from one head to the other. When we do hybrid motors at work that center port gets capped off as the 2.0L heads do not have the extra ports.
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Old 06-03-2011, 10:08 AM   #15
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Quote:
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Dave. I would think you would be fine just running a hose from one head to the other. When we do hybrid motors at work that center port gets capped off as the 2.0L heads do not have the extra ports.
Thank Brody for the input. I can't wait to get my monster fired up and run few laps.
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Old 06-03-2011, 06:02 PM   #16
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You need to bring it back out to MMP! I'm still learning my car, made too many changes too quickly. Just waiting on my spoiler now.

Good luck with your motor build, what are the plans?
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Old 06-06-2011, 02:35 PM   #17
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Quote:
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homemade...input? can you route that center port to one of the heads and then the other port on the head to *say* a catch can/whatever...
2.0L heads only have 1 port per head...if meaing a 2.5 head, then I still wouldn't because you're now restricting the flow.
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Old 06-06-2011, 04:10 PM   #18
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You need to bring it back out to MMP! I'm still learning my car, made too many changes too quickly. Just waiting on my spoiler now.

Good luck with your motor build, what are the plans?
I missed MMP but out here in the Northeast, there are like over 10 tracks within a 5-10 hour driving distance. For example: Lime Rock, Watkins Glen, NJMP, Mt. Tremblent, Mosport, Calabogie, etc... Too many to list.

I'm planning to push somewhere around 500-550 or 600whp. Process West V-mount intercooler and run some local time trials with a local club for now. I'm hoping to run Redline Time Attack when they do come to the east coast again.

Maybe one day I will take a month or two off and trailer back out west to run MMP and other cali tracks... but I'm actually planning to do club racing something like the 944Cup or Spec E30 or even SCCA IT series.

What about you?
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Old 06-20-2011, 09:50 AM   #19
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Car is still running great at ~500whp. Havent gone to any other race tracks, so for now I will have some fun at MMP. Got the cage put in a few months ago, frame rail brake ducts and got the Kognition spoiler installed by eric @ jdm legends.
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Old 06-20-2011, 10:55 AM   #20
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For me I would LIKE to run the crank breather to the heads. It allows the hot gasses that hover at the top to make it's way to the heads. Without it the crank case, IMO would get a little fowl....but that's just me. You can still run the engine without the center no problem. It will NOT have any more pressure than before.

Remember the passage ways where the oil drains from the heads to the block is still open. Oil flows back to the pan, but the blowby travels from crank area to the heads via these passages. It also goes through the rear baffle chamber on cylinder #3 in the back of the engine.

The extra fitting that's on the STi head for the crank breather is not baffled like the fitting that goes to the OEM turbo inlet. If you vent the extra fitting, which connects with the crank breather one to a catch can you will fill up that can with oil.
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