Crankcase Breathers |
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Crankcase Breathers |
McMark |
Sep 12 2017, 04:58 PM
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#1
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914 Freak! Group: Retired Admin Posts: 20,179 Joined: 13-March 03 From: Grand Rapids, MI Member No.: 419 Region Association: None |
I was looking at the factory manuals and talking with someone about crankcase breathers. We were talking about breather setups for carbs specifically. And I realized as I was looking at the breather diagram that it appears that the breather ports on the heads were included to supply extra air to flow through the engine case. And then I read this little snipped in the manuals which seems to support my thought:
QUOTE Crankcase ventilation has been considerably improved in the engine by ducting fresh air from the air filter. This modification reduces crankcase condensation and icing at low outside temperatures. So following that logic... If the crankcase breather (at the oil filler neck) isn't connected to a vacuum source, then the ports at the heads should/could be plugged instead of connected to a breather box. Thoughts? Contradictions? Agreement? I realize people have been connecting breathers all sorts of different ways and most work just fine. I'm more interested in the theory aspect, and refining an 'ideal' installation since we already know many ways to 'make it work'. Attached image(s) |
MarkV |
Dec 31 2017, 06:46 PM
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#2
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Fear the Jack Stands Group: Members Posts: 1,493 Joined: 15-January 03 From: Sunny Tucson, AZ Member No.: 154 Region Association: None |
I could be wrong but I believe you have to find a ported vacuum signal. I think ported vacuum is from above the throttle butterfly on the carbs. My Dellortos don't have a ported vacuum port. I went with centrifugal advance so that I wouldn't have to figure out how to drill carbs for a vacuum signal. (IMG:style_emoticons/default/confused24.gif) I have no practical experience with this, so just going from what I'm reading. Nearly everything I'm reading suggests manifold vacuum would be the more useful signal to the distributor. In stock engines manifold vacuum advances the spark when there is a lean mixture at idle or low throttle on the highway. According to what I read, advance is useful then because lean mixtures burn more slowly, benefiting from the head start of an earlier spark. I think we wouldn't want that advance for open throttle because the richer mixture would be prone to pre-detonation. In the 80s I had a 914 2.0 with the stupid single progressive carb and a Bosch 009. In the Arizona heat, the car would ping unless I dialed the advance back so far it affected performance. With a non-stock camshaft (like my Web cam) the vacuum would be weaker, but I'm speculating that the 123 distributor could be configured over Bluetooth to compensate for that. Anyway it seems fun to experiment with. I don't doubt that Vacuum advance may be a better set up. I just didn't want to try to drill my carbs and I am pretty sure that you cant use the vacuum signal from the intake manifold. I have never seen a car with vacuum advance that didn't have the signal coming from somewhere on the carb. Plus I have two carbs and four throats so where do you pull the signal from....just one, both or all four? I have a mechanical advance that is very adjustable. It is set to 12 degrees at idle and to 28 degrees all in at 2500 rpm. I have a little over 9-1 compression ratio with a WebCam and my car never pings. I usually run it on regular gas. My head temps run around 275 most of the time even in the heat of the summer. (IMG:style_emoticons/default/confused24.gif) |
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