Catch cans and crank pressure
04-02-2015, 05:13 AM
#196
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Location: France
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I'm not sure you could see any vacuum in the MAF pipe. But if the port in the MAF tree coming from the AOS was facing more the turbocharger (45 degree or less angle), the turbocharger could draw more help more this line.
I'm thinking about this design
I'm thinking about this design
04-12-2015, 04:56 AM
#197
Drifting
Dip Stick Remedy
No more crankcase pressure, since last update. Wanted to make something to hold down the dip stick without using zip ties. Made this out of a coat hanger and a few hose clamps. Don't need this, as the crankcase pressure no longer creates issues EVERYWHERE, still like knowing the dip stick is secure.
G
G
Hey guys,
I asked Mario to review this post/comments/potential resolutions, etc.
I wanted to share exactly what was done to my car that worked (so far) as I wasn’t with him when the actual work was done. I’m too busy running my businesses and raising children with my wife to work on my cars at night, weekends, etc. We did the planning in my garage with my input. I do have over 20 years experience modifying these "nutty" cars and used to do most of the wrenching.
This solution likely won’t work with journal bearing turbo cars as Mario pointed out below. The car is currently at German Auto in Phoenix to diagnose the Drive Shaft Shop (LR) 968 axles that don’t fit, but the stock 968 axles fit as designed. They won’t honor the warranty until we measure the stock axle CV compression/expansion against the stock axles, and the balance shaft seal was seeping from the excessive crankcase pressure. Didn’t want to change out any more gaskets until we had the crankcase pressure under control.
Many of these cars are highly modified, and what worked for my car may not work for others. Hope this helps some of you towards remedy.
Below are Mario’s comments after reading the post/comments on excessive crankcase pressure issues:
If you don't have the restrictive barn door flow meter there is no crankcase vacuum (scavenging) provided by the j-boot connection. The crankcase is open to the atmosphere via the intake air filter. The engine ingests whatever the crankcase pushes out into the intake tract. There are other systems where this connection is made in a high vacuum area (after the throttle body with a PCV valve) but to the best of my knowledge the 944t is not one of them.
Vent to motor mount breaks the siphon effect that would otherwise draw oil out of the stock oil film bearing after shutdown. The stock bearing requires a high volume and pressure of oil to work. The motor mount vent also serves to release backpressure if the drain can’t flow fast enough. The ball bearing turbo does not rely on pressure, in fact it restricts the feed to just over 1mm before the ball bearing and flows oil over it for cooling purposes. We drain that 1mm pressurized volume into a 13mm hose. A sign that a turbo drain is not sufficient is turbo shaft seal failure.
Hope this helps some of you!
I asked Mario to review this post/comments/potential resolutions, etc.
I wanted to share exactly what was done to my car that worked (so far) as I wasn’t with him when the actual work was done. I’m too busy running my businesses and raising children with my wife to work on my cars at night, weekends, etc. We did the planning in my garage with my input. I do have over 20 years experience modifying these "nutty" cars and used to do most of the wrenching.
This solution likely won’t work with journal bearing turbo cars as Mario pointed out below. The car is currently at German Auto in Phoenix to diagnose the Drive Shaft Shop (LR) 968 axles that don’t fit, but the stock 968 axles fit as designed. They won’t honor the warranty until we measure the stock axle CV compression/expansion against the stock axles, and the balance shaft seal was seeping from the excessive crankcase pressure. Didn’t want to change out any more gaskets until we had the crankcase pressure under control.
Many of these cars are highly modified, and what worked for my car may not work for others. Hope this helps some of you towards remedy.
Below are Mario’s comments after reading the post/comments on excessive crankcase pressure issues:
If you don't have the restrictive barn door flow meter there is no crankcase vacuum (scavenging) provided by the j-boot connection. The crankcase is open to the atmosphere via the intake air filter. The engine ingests whatever the crankcase pushes out into the intake tract. There are other systems where this connection is made in a high vacuum area (after the throttle body with a PCV valve) but to the best of my knowledge the 944t is not one of them.
Vent to motor mount breaks the siphon effect that would otherwise draw oil out of the stock oil film bearing after shutdown. The stock bearing requires a high volume and pressure of oil to work. The motor mount vent also serves to release backpressure if the drain can’t flow fast enough. The ball bearing turbo does not rely on pressure, in fact it restricts the feed to just over 1mm before the ball bearing and flows oil over it for cooling purposes. We drain that 1mm pressurized volume into a 13mm hose. A sign that a turbo drain is not sufficient is turbo shaft seal failure.
Hope this helps some of you!
04-13-2015, 04:47 PM
#199
Burning Brakes
Those of you who have vented the cam tower. Have you driven on track with prolongued periods at high RPM?
I'm asking because I'm considering this mod, but I'm still not sure oil won't gush out from the tower during track driving.
I'm asking because I'm considering this mod, but I'm still not sure oil won't gush out from the tower during track driving.
04-14-2015, 02:14 AM
#200
Burning Brakes
I did an autox last week and the catch can is still empty. I haven't tried any long right hand sweepers yet. I'm a little worried too since I remember watching a vid of a 928 with a camera inside the cam tower and it filled with oil on a long sweeper.
04-14-2015, 02:58 AM
#201
Drifting
A few pictures of my cam tower to AOS setup. Understand I'm using a Garrett type turbo, and the oil feed is restricted, and I'm not using the factory engine mount. This setup is designed for the Garrett/Tial turbos.
The hose from the catch can is venting into a little K&N filter, not the intake. The little filter is clean and easily checked to see if not.
Hope this helps.
G
07-30-2015, 08:25 PM
#202
Rennlist Member
Thread Starter
Thanks for all the tips given in this thread. My engine also has some blowby under boost which pushes a little oil out of the AOS vent.
At first I wasn't sure if the threaded plugs on the cam tower were a good location for a vent, so I did a quick test. I simply removed one of the plugs and started the engine. I was prepared to see oil flying everywhere, but to my surprise there was no oil at all. I could feel a moderate puff of air coming out of the hole, but no oil. I revved the engine and still no oil flew out. Then I removed a second plug and started the engine. The puff of air was barely noticeable anymore and there was no oil flying out of the second plug either.
I bought parts and installed a catch can with -8AN fittings and hoses. Here's a couple pics. After 3 weeks of use and regular full throttle pulls there's no oil in the catch can at all. A nice benefit is the oil seals on the engine seem to leak less, probably because there's less crankcase pressure pushing oil past the seals.
Thanks again everyone, my car is a little nicer now.
At first I wasn't sure if the threaded plugs on the cam tower were a good location for a vent, so I did a quick test. I simply removed one of the plugs and started the engine. I was prepared to see oil flying everywhere, but to my surprise there was no oil at all. I could feel a moderate puff of air coming out of the hole, but no oil. I revved the engine and still no oil flew out. Then I removed a second plug and started the engine. The puff of air was barely noticeable anymore and there was no oil flying out of the second plug either.
I bought parts and installed a catch can with -8AN fittings and hoses. Here's a couple pics. After 3 weeks of use and regular full throttle pulls there's no oil in the catch can at all. A nice benefit is the oil seals on the engine seem to leak less, probably because there's less crankcase pressure pushing oil past the seals.
Thanks again everyone, my car is a little nicer now.
07-31-2015, 02:05 AM
#203
Burning Brakes
It's working great! There hasn't been a single drop of oil in the catch can, and the AOS vent hose rarely has any oil in it. Before I vented the cam tower the AOS vent hose would regularly drip a few drops of oil on the driveway. Now it's dry.
10-01-2015, 12:42 AM
#205
Rennlist Member
Thread Starter
Been meaning to update this thread. I tried using the AOS side port as shown in post #86, but the dip stick tube still pushed up under boost, and I was getting more oil than I expected. I guess the AOS does a good job of spinning the oil out the side and the pressure out the top after all. 
So I added an additional vent via the cam tower, and still it didn't really help. So while I was swapping out the turbo recently, I pulled the AOS and drilled the top port to the same diameter as the tube, and ditched the check valve. For now I have both the AOS and cam tower venting to the catch can (with no check valves) and the catch can venting to the j-boot. This seems to work well -- the dipstick is no longer pushing up and the catch can gets minimal oil. I wish I could say no oil, but I get about a shot glass per hundred miles would be my guestimate. Picture shows the set up now, along with a gratuitous picture of my tig welding before adding ports and powder coating the catch can.
So I added an additional vent via the cam tower, and still it didn't really help. So while I was swapping out the turbo recently, I pulled the AOS and drilled the top port to the same diameter as the tube, and ditched the check valve. For now I have both the AOS and cam tower venting to the catch can (with no check valves) and the catch can venting to the j-boot. This seems to work well -- the dipstick is no longer pushing up and the catch can gets minimal oil. I wish I could say no oil, but I get about a shot glass per hundred miles would be my guestimate. Picture shows the set up now, along with a gratuitous picture of my tig welding before adding ports and powder coating the catch can.
10-01-2015, 11:13 AM
#207
Three Wheelin'
Last week i made a write-up on things to do on my engine, catch can is one of them.
I'm making a hose from the AOS connecting at the engineblock and from the camcover and connecting them both to a Mishimoto catchcan.
After this i'll make a connection from the intake to the catchcan for vacuum when there is no boost.
For on boost, i'll make a hose from just before the turbo to the catchcan as well.
On both lines there will be a check-valve to make sure that i'm not sucking in air from the wrong side.
Only thing i'm thinking about now is; would it be handy to have a vacuum "can"?
I'm making a hose from the AOS connecting at the engineblock and from the camcover and connecting them both to a Mishimoto catchcan.
After this i'll make a connection from the intake to the catchcan for vacuum when there is no boost.
For on boost, i'll make a hose from just before the turbo to the catchcan as well.
On both lines there will be a check-valve to make sure that i'm not sucking in air from the wrong side.
Only thing i'm thinking about now is; would it be handy to have a vacuum "can"?
10-01-2015, 05:13 PM
#208
Burning Brakes
Last week i made a write-up on things to do on my engine, catch can is one of them.
I'm making a hose from the AOS connecting at the engineblock and from the camcover and connecting them both to a Mishimoto catchcan.
After this i'll make a connection from the intake to the catchcan for vacuum when there is no boost.
For on boost, i'll make a hose from just before the turbo to the catchcan as well.
On both lines there will be a check-valve to make sure that i'm not sucking in air from the wrong side.
Only thing i'm thinking about now is; would it be handy to have a vacuum "can"?
I'm making a hose from the AOS connecting at the engineblock and from the camcover and connecting them both to a Mishimoto catchcan.
After this i'll make a connection from the intake to the catchcan for vacuum when there is no boost.
For on boost, i'll make a hose from just before the turbo to the catchcan as well.
On both lines there will be a check-valve to make sure that i'm not sucking in air from the wrong side.
Only thing i'm thinking about now is; would it be handy to have a vacuum "can"?
10-02-2015, 04:12 AM
#210
Nice work Tom!
May I suggest to delete the vent from the cam housing? The catch can on mine is only fed from the AOS and it barely fills up at all.
How does the new hotside compare with the previous one?
May I suggest to delete the vent from the cam housing? The catch can on mine is only fed from the AOS and it barely fills up at all.
How does the new hotside compare with the previous one?