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Kyle Saenz's Avatar
 
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Question carrera 3.2 turbo crankcase vent?

I have a turbo'd carrera 3.2 and as it sits It runs fine and pulls great but i was wondering about something... With the stock intake boot I believe there is an input hose in the back that acts as a crank case vent, I know these cars have a dry sump system so that should create a vacuum in the crankcase naturally but does anyone know if blow-buy would be an issue if boost pressure is going into the crankcase? would I be better off putting a filter on the hose and venting it to the atmosphere while plugging the hole in the intake boot or would that be a bad idea?
thanks so much for the help,
-Kyle
Old 12-02-2011, 04:14 PM
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well i bit the bullet and tried it out, i put an old mini cone filter on the hose and plugged the hole in the intake boot with a giant bolt. I have to say It was much better! it built boost faster and ran better, unless there are any adverse affects I am going to leave it like this. Anyone think having it vent to atmosphere is going to cause any damage in the long term?
Old 12-02-2011, 08:46 PM
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Not really, but you shouldn't have had any performance difference between the two setups?? Do you have positive crankcase pressure at idle coming out of the breather?
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Old 12-03-2011, 04:49 AM
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no, It's a pretty tight engine. I think the reason i saw a gain is the turbo has less area to pressurize now and now there isn't positive pressure in the crankcase under boost preventing blowby?
Old 12-03-2011, 12:04 PM
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The turbo doesn't have less area to pressurize it is a fixed area. The crankcase will have some degree of blowby on a turbo engine, but nothing excessive unless there is a problem. Why now there is no positive pressure in the crankcase? What was changed?
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87 911 Carrera platform
Twin Garrett's, Big Valve, Xtreme Cylinder Heads, JB Racing cylinders and machine work, custom JE pistons, GT2 EVO cams, GT3 oil pump, modified 3.2L intake, 80mm TB, custom Intercooler, equal length headers, DFI, KEP Stage 2 custom twin disc, G50 custom gear set, LSD, Tilton trans pump, Fluidyne cooler
Old 12-03-2011, 04:34 PM
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from what i understand, when there is a hose directly connecting the intake to the crankcase when the turbo spools puting positive pressure in the intake, it will also put positive pressure into the crankcase (which is bad and can cause blow by) when they are not connected the turbo has less area in the intake to pressurize causing it to build boost faster and less blowby. it takes less air to pressurize less area correct?

Last edited by Kyle Saenz; 12-03-2011 at 07:41 PM..
Old 12-03-2011, 07:38 PM
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An aspirated engine has the breather line from the crankcase to the oil tank and from the oil tank to the air filter box. If this isnt rerouted then that creates a boost leak. Yes you have boost going to the crankcase but also it is being bleed off though the air filter. The only thing you needed to do is block off the breather line from the intake. The breather needs to go from the crankcase breather tube to the oil tank and from the tank to the air filter housing or intake housing where the filter connects. It is only to help pull a vacuum on the crankcase. What most people do is vent the crankcase to a filter canister and tie the oil tank breather line to it then vent to atmosphere. If it went from the intake to the crankcase and that's it . Then yes you were pressurizing the crankcase and that is not good. But that would not create piston ring blowby. It would try to Push oil out any location it could. Yes if that was the case it would also take spool up some time for the added area of the crankcase. As long as you severed the line from the intake you'll be fine.
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Old 12-03-2011, 08:50 PM
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You have done the correct thing, I did the same, it stops you pressurising the oil tank, someone told me this can cause a big mess in the bay, also you're engine will stop breathing the blowby gases, instead you will.... Those cone filers clog up pretty quickly and you will start smelling it in the cabin. The solution seems to be a catch can and divert the gases out of the engine bay and under the car as far back as possible.
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Old 12-03-2011, 09:56 PM
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okay thanks so much, this is what i wanted to hear.
Old 12-03-2011, 10:17 PM
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I would suggest using a check valve on that hose so part throttle and idle conditions your crank see's vaccum. On boost it would prevent your crank case from being pressurized. Ideally a "suck through" turbo design would eliminate the issue altogether.
Old 12-05-2011, 11:26 AM
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crankcase breather

I just recently converted a carb VW to fuel injection. I also removed the tubes from the case to the intake and plugged the intake nossels. There are aftermarket kits out there that will put a valve and filter on the breather hose. Any blowby gasses are vented to atmosphere thru the filter instead of going back to the intake and robbing some power. I would not let the oil tank see any boost either.
Old 12-05-2011, 01:47 PM
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Quote:
Originally Posted by cliyde View Post
I would suggest using a check valve on that hose so part throttle and idle conditions your crank see's vaccum. On boost it would prevent your crank case from being pressurized. Ideally a "suck through" turbo design would eliminate the issue altogether.
Hey Cliyde, hope your beast is still traveling well!

This is true with a suck through but you really don't want the crankcase venting into the intake pressurized or not, it'll lower the octane rating of your fuel.
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Old 12-05-2011, 01:55 PM
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Hi Spence,
She's still running very strong and goes like a "stabbed rat", normally aspirated life will never be the same. Agreed oil "misting" lowers octane. I've seen this being an issue if there's blow-by or oil level is too high. Otherwise low boost might not be a factor... I once vented my crank case in the 928 and that worked great. I purchases a Jaz catch can from Jeggs for $50. Only issue i had with doing a vent is the Fuuuuumes!
CheersI
Old 12-05-2011, 03:58 PM
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we had this same discussion going on another board. crankcase vents to intake for two reasons - emissions (combust environment-harming gasses) and to create a vacuum in the crankcase. the vacuum helps the rings seal. as you noted, you were pressurising your crankcase by doing what you did, which can cause a lot of parasitic loss (your pistons were trying to push against that pressure).

venting the crankcase to atmosphere, however, loses the vacuum. if you want to get the vacuum back, reconnect the hose to before the turbo; the air rushing by to get to the turbo creates a vacuum as it passes the breather opening.
Old 12-05-2011, 04:59 PM
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Quote:
Originally Posted by cliyde View Post
Hi Spence,
She's still running very strong and goes like a "stabbed rat", normally aspirated life will never be the same. Agreed oil "misting" lowers octane. I've seen this being an issue if there's blow-by or oil level is too high. Otherwise low boost might not be a factor... I once vented my crank case in the 928 and that worked great. I purchases a Jaz catch can from Jeggs for $50. Only issue i had with doing a vent is the Fuuuuumes!
CheersI
Great news, yep, imagine going back to NA!

So what I have seen someone else on here do is run a pipe from where the filter usually sits on the catch can, out of the engine bay to under the back of the car, I think that does the trick... I need to try it, so the jaz fits fine, same inlet pipe size? I'll grab one, did you put any steel wool in it, not the fine stuff the courser type, I read that can help with the oil/air separation.
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Old 12-05-2011, 05:13 PM
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