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Join Date: Jun 2009
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914 Evap System with Dual Carbs

Hey Guys, I have searched the forum for images and answers to my evap question but I still need some advice. I have a 1972 1.7 that was converted to a dual Weber 34 ICT set-up by the previous owner. All of the evap system ports in the engine bay are either plugged or just left open. Since I do not have the stock air cleaner, I need some advice about what to do with these ports.

From the previous posts, I am thinking I should connect the oil breather to a catch bottle. But what about the lines from the cylinder heads? Should these all be tied together? What do I do with the evap return line from the charcoal canister?

One website I found shows the oil breather and cylinder heads all tied together, but I am not sure where the system is actually connected (last photo, lower right hand corner).

(Van's Porsche 914 Engine Build)

Any help would be appreciated.

Thanks!
Old 11-28-2010, 03:31 AM
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It goes the the square tank under the battery tray that I made...

You can see that about 1/2 way down this page: Van's Porsche 914 Engine Build
Old 12-09-2010, 12:15 PM
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Van, your website is astonishing! What a gift to the 914 community. Amazing...

Last edited by penp; 06-16-2011 at 04:13 PM..
Old 06-15-2011, 09:28 PM
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Note that the evap system is different from the PCV system. The evap system deals with gasoline vapors; it traps them in a charcoal filter and then routes them to the air cleaner so they can get burned.

The PCV system deals with crankcase air, which usually contains a good bit of oil droplets. The stock system has the two head vents joined together, and then running to the air cleaner. The PCV valve itself lives in the oil filler tower, and it has a hose that is connected directly to the intake manifold.

With carbs, you obviously don't have a unified intake manifold. So you need a breather box mounted as high as you can reasonably make it, which encourages all of the oil to go downhill back into the engine. You can run the three ventilation lines into it, and then run a line out of the bottom into a "puke bottle". That should help control the amount of oil that gets spewed into the engine bay.

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Old 06-16-2011, 07:10 AM
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The 3 vent lines on my engine are T'ed together and vented to atmosphere under the car. That's how it was when I got it and it seems to work OK. I could not find a suitable box to mount in the engine compartment.
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Old 06-16-2011, 02:31 PM
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Quote:
Originally Posted by Michael7810 View Post
The 3 vent lines on my engine are T'ed together and vented to atmosphere under the car. That's how it was when I got it and it seems to work OK. I could not find a suitable box to mount in the engine compartment.
Many, many years ago my shop made a box using a generic w/washer bottle that we bought at Pep Boys. Worked great!

Like Dave suggested, we mounted it in an upper corner of the engine compartment, as high as we could get it.
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Old 06-16-2011, 03:00 PM
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Dave,

Just to see if your recommendation would be different for race car use only, what is ideal? Below are different options (some variations on a theme) that I've seen used, trying to decide how to go...

Three breather lines routed to a standard plastic catch tank, somewhat loose, haphazard fittings (like a race car radiator overflow tank).

Same as above but with a small K&N filter on top for air.

Three breather lines routed to aftermarket VW/914 "breather tank." Top lid does not shut flush is slight raised up to let air in.

Same as above, but with the tank modified so the lid totally shuts flush and seals up, so it doesn't blow oil at high RPM (and has a plumbed in drain line on bottom that goes back into motor).

Three breather lines to (whatever kind of) tank, but the tank has two additional lines that go into the top of the air Weber air cleaner (I assume this is for street legal, smog test cars)

And - a newer reco I have heard about - blocking off the head breathers altogether (race engines only), and only having a breather/overflow on the filler breather?

Thanks....

Last edited by penp; 06-17-2011 at 12:51 PM..
Old 06-16-2011, 04:06 PM
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