dandan Posted August 21, 2010 Share Posted August 21, 2010 No sweat, I hope it's useful. I may well have missed this bit but how and where are you measuring pressure J ay ? Quote Link to comment Share on other sites More sharing options...
jevansio Posted August 21, 2010 Author Share Posted August 21, 2010 No sweat, I hope it's useful. I may well have missed this bit but how and where are you measuring pressure J ay ? My boost/vacuum gauge secured into the dipstick hole. Quote Link to comment Share on other sites More sharing options...
jevansio Posted August 21, 2010 Author Share Posted August 21, 2010 (edited) Right I'm having problems replicating the stock system. I have a link from the in cam to the plenum with a check valve. The blue hose loops round and connects to one of the manifold barbed nipples. I have a large -10 fitting from the ex cam to the turbo intake pipe. On idle I see 0 crank pressure, on boost I see 0 to small +ve crank pressure. What is going on Something I don't understand. How does the stock system pull vacuum at idle when the ex cam link to the turbo intake is in essence a link to ambient? There can be no great vacuum in the airbox system when the car is idling? I introduced a check valve between the ex cam & turbo inlet. It had the effect of blocking that vent on idle so I could see 8 inHg vacuum in the crankcase. The valve is too small however to vent the crankcase pressure on boost and the crankcase pressure rises (a little over what it did when I had 2 x -10AN breathers to atmosphere). Really appreciate any help on this Edited August 21, 2010 by jevansio (see edit history) Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted August 21, 2010 Share Posted August 21, 2010 AFAIK the stock system doesn't pull a vacuum at idle, and to my understanding its not necessary, at idle and lower loads (off boost) providing there is no positive pressure its not a problem, and i would have said that 0 or very slight positive pressure at full boost is fine, just my opinion though, going bu my set up. Quote Link to comment Share on other sites More sharing options...
jevansio Posted August 21, 2010 Author Share Posted August 21, 2010 Many thanks to Dick I now have clear in my head how the system works. I was totally under the wrong impression that the stock system pulls around an 8 inHg vacuum all the time Quote Link to comment Share on other sites More sharing options...
jevansio Posted August 23, 2010 Author Share Posted August 23, 2010 With my new understanding of how the PCV system works, I did a test to see how much vacuum 2 x -10AN breathers straight into the turbo intake @ 45 deg slash (as the Moroso valve above) could pull. On idle it was negligle (as you would imagine). At full boost I would hazard a guess at it being around 6 to 10 mmHg (basically exactly the same as the figures Ricky measured on his stock engine). This does however lead me to believe that the 8 inHg I was hoping to achieve is only going to be possible with a mechanical/electric pump Quote Link to comment Share on other sites More sharing options...
dandan Posted August 23, 2010 Share Posted August 23, 2010 Were they flush with the ID of the turbo intake pipe Jay? If so, are you able to get something there that protrudes in further to see if that pulls more? Quote Link to comment Share on other sites More sharing options...
Swampy442 Posted August 23, 2010 Share Posted August 23, 2010 On the pulling a vac at idle thing, it must pull some as the link into inlet manifold is open i.e the check valve is open so it must pull something, I dont know what my boost gauge shows but its way below 0psi. Unless the pressure is equalised and balanced across the engine by the pipe in the inlet pipe? Quote Link to comment Share on other sites More sharing options...
jevansio Posted August 23, 2010 Author Share Posted August 23, 2010 Were they flush with the ID of the turbo intake pipe Jay? If so, are you able to get something there that protrudes in further to see if that pulls more? No mate, they stuck in around 10-15mm and were angled at 45 deg with a slash cut, exactly the the image of the exhaust valve Also do you think the take off being closer to the compressor may increase the vacuum? On the pulling a vac at idle thing, it must pull some as the link into inlet manifold is open i.e the check valve is open so it must pull something, I dont know what my boost gauge shows but its way below 0psi. Unless the pressure is equalised and balanced across the engine by the pipe in the inlet pipe? That's exctlywhat happens swampy, if you block off the ex cam side yes you get a vacuum, but leave it open to the turbo inlet pipe and the best you get is 0, all that is happening is there is a flow of air through the engine Quote Link to comment Share on other sites More sharing options...
Swampy442 Posted August 23, 2010 Share Posted August 23, 2010 There may be lower pressure closer to the face of the compressor but the slash cut creates a low pressure area anyway so the increased velocity of the air creates more low pressure etc. Quote Link to comment Share on other sites More sharing options...
TLicense Posted August 27, 2010 Share Posted August 27, 2010 I've found this doc which explains the PCV system quite nicely... http://www.autoshop101.com/forms/h63.pdf Quote Link to comment Share on other sites More sharing options...
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