Crankcase breather ideas.
06-04-2015, 10:37 PM
#17
Former Vendor
Most pump makes state that there is a "level" of vacuum that is to much and can cause that amount of damage. but that is normally around 14hg and up. the pumps we have have a MAX of around 10-12 at redline. the pressure is limited by the sealed fresh air/oil return line from the separator to the sealed crankcase. bigger the hose, the more vacuum it will pull etc....
Try to understand that the pump manufacturers are making "generic" statements about their products.
I'm not talking generic here...I'm talking specifics.
I'm betting that none of the pump makers have ever seen the inside of a GTS engine....which have zero oiling from the oil return rings to the wrist pins....completely dependent on splash.
I'm betting that none of the pump makers have seen the blue wrist pins inside a GTS engine, from the lack of lubrication and excessive heat.
Anyone who promotes or uses a vacuum system, will freely admit that the vacuum reduces the oil mist flying around inside the crankcase.
Oops, tiny detail.....This is the ONLY thing lubricating a GTS wrist pin.
What percentage of oil reduction to a wrist pin that is already blue is tolerable?
I guess not very stinking much. Colin thinks it is a non-issue.
I know this. I stand behind everything I make. I can't afford to replace GTS engines with failed rods and failed pistons. My vacuum system sits on the shelf, because I can't afford the gamble.
Colin apparently can afford the gamble.
Buy it. Use it. I hope I'm wrong! I hope it works!
06-04-2015, 11:21 PM
#18
Pro
Thread Starter
And I completely understand that.
Try to understand that the pump manufacturers are making "generic" statements about their products.
I'm not talking generic here...I'm talking specifics.
I'm betting that none of the pump makers have ever seen the inside of a GTS engine....which have zero oiling from the oil return rings to the wrist pins....completely dependent on splash.
I'm betting that none of the pump makers have seen the blue wrist pins inside a GTS engine, from the lack of lubrication and excessive heat.
Anyone who promotes or uses a vacuum system, will freely admit that the vacuum reduces the oil mist flying around inside the crankcase.
Oops, tiny detail.....This is the ONLY thing lubricating a GTS wrist pin.
What percentage of oil reduction to a wrist pin that is already blue is tolerable?
I guess not very stinking much. Colin thinks it is a non-issue.
I know this. I stand behind everything I make. I can't afford to replace GTS engines with failed rods and failed pistons. My vacuum system sits on the shelf, because I can't afford the gamble.
Colin apparently can afford the gamble.
Buy it. Use it. I hope I'm wrong! I hope it works!
Try to understand that the pump manufacturers are making "generic" statements about their products.
I'm not talking generic here...I'm talking specifics.
I'm betting that none of the pump makers have ever seen the inside of a GTS engine....which have zero oiling from the oil return rings to the wrist pins....completely dependent on splash.
I'm betting that none of the pump makers have seen the blue wrist pins inside a GTS engine, from the lack of lubrication and excessive heat.
Anyone who promotes or uses a vacuum system, will freely admit that the vacuum reduces the oil mist flying around inside the crankcase.
Oops, tiny detail.....This is the ONLY thing lubricating a GTS wrist pin.
What percentage of oil reduction to a wrist pin that is already blue is tolerable?
I guess not very stinking much. Colin thinks it is a non-issue.
I know this. I stand behind everything I make. I can't afford to replace GTS engines with failed rods and failed pistons. My vacuum system sits on the shelf, because I can't afford the gamble.
Colin apparently can afford the gamble.
Buy it. Use it. I hope I'm wrong! I hope it works!
Sounds like the factory was at its wit's end with this problem.In an idle moments I've wondered about adding external breathing between the bays in the the bottom of the vee.
Done by putting hole(s) thru' the top of each bay, then interconnecting them with a flat, covering manifold.
Would really need two of those, one each side of the knock sensors (= more clearance of the TB plenum).
It's radical engine-out surgery but just a thought.
06-05-2015, 12:57 AM
#19
Nordschleife Master
When he realized that engine builders who use vacuum systems increase the wrist pin clearance and/or feed oil directly to the wrist pins when using vacuum systems, he was afraid that the oil supply to the wrist pins might be too marginal....especially since he's seen extreme heat and high wear at GTS wrist pins in the stock engines, when disassembled. (The wrist pins are invariably "blue" (from heat) in the small gap between the connecting rod and the piston pin, in GTS engines.
Additionally, I measured small end bushing wear on 4.5, 4.7, and 5.0L small ends, all had the same amount of wear as a completely destroyed set of GTS small ends that Rob E measured for you.
The pins also saw no excessive wear, or were worn out of spec. There is also zero recorded small end failures, or records of wrist pins requiring replacement upon opening any GTS engine. If this were a problem, I suspect Porsche would say to replace them like they say to do with the 1R rods whenever the GTS engine is opened......
In all fairness to Greg, he spends a tremendous amount of time developing his pieces and testing them. He's very concerned about "trading one problem for a new problem" and tends to error on the conservative side....especially when faced with evidence that there is already potentially an existing problem.
At any rate, it makes little difference, since there are plenty of used GTS engines out there for sale.....and Porsche has unlimited amounts of cheap crankshafts, rods, pistons, and blocks, in case the "experimental, without ever actually looking inside an engine with a vacuum system to see what the actual effects of the system actually are" thing doesn't work out.
But you know I REALLY REALLY had thought, and hoped that you had finally either taken your panties off so they couldn't be in a twist, or had just pulled them out, or taken meds to balance things out. Why would I think this?! OH I don't know, maybe because you have actually sent people my direction for information regarding the vacuum pump system for their GTS........ Clearly I was mistaken......
06-05-2015, 01:14 AM
#20
Nordschleife Master
Just so that some can get an idea as to what my system generates.
On a GTS, the system will see under full power at redline a maximum of between 6-8" Hg vacuum.
While cruising around it will generate 4-5" Hg vacuum.
At idle, it will be less than 1" Hg.
Now, another thing to look at, every inch of vacuum is very much the same as 1000' elevation. So during normal cruising, and seeing 4-5" Hg, it is the same as driving your car at 4-5000' elevation.
I installed the first vacuum pump on my 1987 928S4 in July 2011. I then drove that car to Sharktoberfest in 2011. I do not drive gently, as Tom M, Adam B, and others can attest. I drove the **** out of the car for many many miles. I have opened the bottom of that engine up, and there is no bluing to the wrist pins. Now before Greg can jump in and say that it is only the GTS's that he is concerned about. I have now had this system on a local GTSs 928 for a very long time. He drives aggressively as well. I have pulled the pan off the engine after running vacuum for a fair bit of time, and saw, you guessed it zero additional wear, and no detectable movement in the wrist pin either.
On this particular engine, it consumed roughly 370 miles per quart, it consumed the same amount with someone's GTS crankcase breather system on it, the only "fix" he was offered was to tear down and rebuild, on an engine with perfect leakdown. Post vacuum pump install, last we spoke, Joe told me that he couldn't measure any consumption, it was too low of a consumption to measure.
Now I will state, that with the vacuum pump system installed, I would strongly recommend that one sharktunes their vehicle, and ensures that post install, there is no detonation. As I do find that when the 928 starts to see knocks, the amount of oil that goes through the vacuum pump increases exponentially, and can overwhelm every air oil separator. However that said, I have yet to see a stock GTS with a stock map, running 91+ octane fuel detonate at all. As well, I strongly recommend sticking with the stock knock settings, being more aggressive with these settings drastically increases the problem.
Please keep in mind as well that the vacuum pump makers are also going to be conservative in their statements of 14-15" Hg vacuum. How much of a safety factor is there is a hard question to quantify. But I do feel confident that there is a large safety margin at the levels of vacuum we are running.
Should one be extremely worried, there are things that can be done to increase wrist pin oiling without pulling pistons etc.
On a GTS, the system will see under full power at redline a maximum of between 6-8" Hg vacuum.
While cruising around it will generate 4-5" Hg vacuum.
At idle, it will be less than 1" Hg.
Now, another thing to look at, every inch of vacuum is very much the same as 1000' elevation. So during normal cruising, and seeing 4-5" Hg, it is the same as driving your car at 4-5000' elevation.
I installed the first vacuum pump on my 1987 928S4 in July 2011. I then drove that car to Sharktoberfest in 2011. I do not drive gently, as Tom M, Adam B, and others can attest. I drove the **** out of the car for many many miles. I have opened the bottom of that engine up, and there is no bluing to the wrist pins. Now before Greg can jump in and say that it is only the GTS's that he is concerned about. I have now had this system on a local GTSs 928 for a very long time. He drives aggressively as well. I have pulled the pan off the engine after running vacuum for a fair bit of time, and saw, you guessed it zero additional wear, and no detectable movement in the wrist pin either.
On this particular engine, it consumed roughly 370 miles per quart, it consumed the same amount with someone's GTS crankcase breather system on it, the only "fix" he was offered was to tear down and rebuild, on an engine with perfect leakdown. Post vacuum pump install, last we spoke, Joe told me that he couldn't measure any consumption, it was too low of a consumption to measure.
Now I will state, that with the vacuum pump system installed, I would strongly recommend that one sharktunes their vehicle, and ensures that post install, there is no detonation. As I do find that when the 928 starts to see knocks, the amount of oil that goes through the vacuum pump increases exponentially, and can overwhelm every air oil separator. However that said, I have yet to see a stock GTS with a stock map, running 91+ octane fuel detonate at all. As well, I strongly recommend sticking with the stock knock settings, being more aggressive with these settings drastically increases the problem.
Please keep in mind as well that the vacuum pump makers are also going to be conservative in their statements of 14-15" Hg vacuum. How much of a safety factor is there is a hard question to quantify. But I do feel confident that there is a large safety margin at the levels of vacuum we are running.
Should one be extremely worried, there are things that can be done to increase wrist pin oiling without pulling pistons etc.
06-05-2015, 01:22 AM
#21
Nordschleife Master
I also wanted to make note to those following.
3 things that should be considered.
distance from piston top to wrist pin on GTS engine,
GTSs proneness to detonation,
and increased stroke.
3 things that should be considered.
distance from piston top to wrist pin on GTS engine,
GTSs proneness to detonation,
and increased stroke.
06-05-2015, 01:39 AM
#22
Former Vendor
I'd love to see pictures of this, because you claimed before it was a GZ motorsports pump you purchased, and when I spoke to them, they said they have never sold anything to you......
And yet, after you first stated that those who increase small end clearance for race engines using 20+in Hg vacuum, I called the companies which you referenced their material and asked them this. They stated they did not change the small end clearances for vacuum.....
Additionally, I measured small end bushing wear on 4.5, 4.7, and 5.0L small ends, all had the same amount of wear as a completely destroyed set of GTS small ends that Rob E measured for you.
The pins also saw no excessive wear, or were worn out of spec. There is also zero recorded small end failures, or records of wrist pins requiring replacement upon opening any GTS engine. If this were a problem, I suspect Porsche would say to replace them like they say to do with the 1R rods whenever the GTS engine is opened......
I won't even touch that one.......
I find it facinating how you seem to know what work everyone else has done.....
Everything has an experimental side to it. Including your pieces. Maybe I should recommend that eveyone with an "experimental" aka different crankcase ventilation system on there car open up the pan and change their rod bearings annually along with inspecting the pins for additional heat.....
Naw, he only makes up false information when he either has a product which competes with someone else, or doesn't like the person for one reason or another.
Why not give the jabs you make at myself, porken, and all the others a break too? It sure would be nice to get along instead of having to defend ourselves from your antagonistic posts!
You got a real kick out of me asking Carl if he was going to charge customers to make his pieces fit on customers cars. Yet I didn't see you offering to cover all the costs that Joe incured with both Scan Auto, and myself trying to make your system work. Instead you claimed that I sabotaged the system.
But you know I REALLY REALLY had thought, and hoped that you had finally either taken your panties off so they couldn't be in a twist, or had just pulled them out, or taken meds to balance things out. Why would I think this?! OH I don't know, maybe because you have actually sent people my direction for information regarding the vacuum pump system for their GTS........ Clearly I was mistaken......
And yet, after you first stated that those who increase small end clearance for race engines using 20+in Hg vacuum, I called the companies which you referenced their material and asked them this. They stated they did not change the small end clearances for vacuum.....
Additionally, I measured small end bushing wear on 4.5, 4.7, and 5.0L small ends, all had the same amount of wear as a completely destroyed set of GTS small ends that Rob E measured for you.
The pins also saw no excessive wear, or were worn out of spec. There is also zero recorded small end failures, or records of wrist pins requiring replacement upon opening any GTS engine. If this were a problem, I suspect Porsche would say to replace them like they say to do with the 1R rods whenever the GTS engine is opened......
I won't even touch that one.......
I find it facinating how you seem to know what work everyone else has done.....
Everything has an experimental side to it. Including your pieces. Maybe I should recommend that eveyone with an "experimental" aka different crankcase ventilation system on there car open up the pan and change their rod bearings annually along with inspecting the pins for additional heat.....
Naw, he only makes up false information when he either has a product which competes with someone else, or doesn't like the person for one reason or another.
Why not give the jabs you make at myself, porken, and all the others a break too? It sure would be nice to get along instead of having to defend ourselves from your antagonistic posts!
You got a real kick out of me asking Carl if he was going to charge customers to make his pieces fit on customers cars. Yet I didn't see you offering to cover all the costs that Joe incured with both Scan Auto, and myself trying to make your system work. Instead you claimed that I sabotaged the system.
But you know I REALLY REALLY had thought, and hoped that you had finally either taken your panties off so they couldn't be in a twist, or had just pulled them out, or taken meds to balance things out. Why would I think this?! OH I don't know, maybe because you have actually sent people my direction for information regarding the vacuum pump system for their GTS........ Clearly I was mistaken......
Worked in high school debate class, but is a waste of time when dealing with real world discussions.
I made two, very carefully worded posts, explaining my concerns, with theory and examples of why I believe what I believe....and all you can do is attack me personally?
Why not try to be a man and address my carefully and clearly stated concerns?
Oh, and BTW....your "test" on your own car doesn't count, does it?
Clearly, it doesn't have GTS pistons. Although your experience is tiny, you should know that your pistons do have oil returns to oil the wrist pins.
06-05-2015, 01:41 AM
#23
Electron Wrangler
Lifetime Rennlist
Member
Lifetime Rennlist
Member
OK so we have to have the train wreck again?
In stock configuration I have so much oil misting & flinging around the crankcase it isn't even slightly funny. All of it wants out... and a good amount actually makes it into the intake. Now this is 'really good' of course because it lubricates the cylinders really nicely - right? (Oh apart from the explosion thing...).
I run vacuum limiting valves - though I do acknowledge that they are hardly needed. I set them to ~7"Hg - at that point they flow fresh air into the cam cover to hold the vacuum level (and flush the crankcase). Get your mighty vac out and suck on the output tube until you get 7" Hg - it's nothing! It almost never runs even at that level in steady state general driving.
Context is all important here - this vacuum level is hardly more than the atmospheric difference between sea level & Denver CO, depending on the weather of course. As far as I know 928's survive just fine in Denver - even in the summertime.... This level of vacuum is just too low to be any kind of serious risk (it's a normal everyday occurrence in many places in the world). This low of a vacuum may help collapse a cloud of oil mist - but no reasonable amount of vacuum we will ever see here will stop oil being flung off the rotating masses or splashing as normal - the mechanisms are quite different - that much should be apparent.
Racers use vacuum for extreme ring sealing (often at 20-30 "Hg). In this application for a 928 it is only being used to ensure positive crank evacuation and oil separation - the purpose and necessary vacuum levels are totally different animals. If you get any ring sealing benefit it is relatively incidental to the primary goal IMO. The biggest power benefits here are from clean pistons and no ingestion to avoid power loss though timing degradations. The other benefit is keeping all the oil in the sump and not losing it out the tailpipe.
20K miles of hard driving says it works - better than any other argument I know.
I do know enough about the basic physics to not be particularly concerned - I was just surprised how well it worked out as a separation mechanism - it very much exceeded my expectations.
Could you make a vacuum system that could damage a 928 - certainly, but no one here is doing that - these are mild systems. I like the VLV's because I want to be sure its safe. I like my engine and I did this to save it - the stock configuration was torturing it every day - and forcing me to back off the gas all the time... now I don't have to do that anymore. As Roger said - it's like different car...
Alan
In stock configuration I have so much oil misting & flinging around the crankcase it isn't even slightly funny. All of it wants out... and a good amount actually makes it into the intake. Now this is 'really good' of course because it lubricates the cylinders really nicely - right? (Oh apart from the explosion thing...).
I run vacuum limiting valves - though I do acknowledge that they are hardly needed. I set them to ~7"Hg - at that point they flow fresh air into the cam cover to hold the vacuum level (and flush the crankcase). Get your mighty vac out and suck on the output tube until you get 7" Hg - it's nothing! It almost never runs even at that level in steady state general driving.
Context is all important here - this vacuum level is hardly more than the atmospheric difference between sea level & Denver CO, depending on the weather of course. As far as I know 928's survive just fine in Denver - even in the summertime.... This level of vacuum is just too low to be any kind of serious risk (it's a normal everyday occurrence in many places in the world). This low of a vacuum may help collapse a cloud of oil mist - but no reasonable amount of vacuum we will ever see here will stop oil being flung off the rotating masses or splashing as normal - the mechanisms are quite different - that much should be apparent.
Racers use vacuum for extreme ring sealing (often at 20-30 "Hg). In this application for a 928 it is only being used to ensure positive crank evacuation and oil separation - the purpose and necessary vacuum levels are totally different animals. If you get any ring sealing benefit it is relatively incidental to the primary goal IMO. The biggest power benefits here are from clean pistons and no ingestion to avoid power loss though timing degradations. The other benefit is keeping all the oil in the sump and not losing it out the tailpipe.
20K miles of hard driving says it works - better than any other argument I know.
I do know enough about the basic physics to not be particularly concerned - I was just surprised how well it worked out as a separation mechanism - it very much exceeded my expectations.
Could you make a vacuum system that could damage a 928 - certainly, but no one here is doing that - these are mild systems. I like the VLV's because I want to be sure its safe. I like my engine and I did this to save it - the stock configuration was torturing it every day - and forcing me to back off the gas all the time... now I don't have to do that anymore. As Roger said - it's like different car...
Alan
06-05-2015, 03:42 AM
#25
Nordschleife Master
Greg,
You attacked me first, carefully worded, basically saying I know nothing.
I have numerous times covered your concerns, and dispelled all the misinformation you have and have now again posted.
Why not see that how you are doing it is an attack.
If I was to openly state that your crankcase breather system risked blowing up the engine due to detonation, and then claimed you wouldn't fix the engine as you wouldn't, you would get your back up as well.
I have covered your concerns with data a number of times, and called your experts to ask them questions, their answers contradict what you post on this topic. I also went to others and got their responses too.
What you state does not align with any of the research I have done. I posted all that information before. So you cannot say I haven't gone through it!!
AO hit the nail on the head with his post regarding your posts on RL. You come in tell people it is crap, and troll the threads offering no real help. More and more are thankfully waking up to this.
Next time should i just take your approach and just go over all the reasons why your system doesn't work and is dangerous to run on the engine?!
You attacked me first, carefully worded, basically saying I know nothing.
I have numerous times covered your concerns, and dispelled all the misinformation you have and have now again posted.
Why not see that how you are doing it is an attack.
If I was to openly state that your crankcase breather system risked blowing up the engine due to detonation, and then claimed you wouldn't fix the engine as you wouldn't, you would get your back up as well.
I have covered your concerns with data a number of times, and called your experts to ask them questions, their answers contradict what you post on this topic. I also went to others and got their responses too.
What you state does not align with any of the research I have done. I posted all that information before. So you cannot say I haven't gone through it!!
AO hit the nail on the head with his post regarding your posts on RL. You come in tell people it is crap, and troll the threads offering no real help. More and more are thankfully waking up to this.
Next time should i just take your approach and just go over all the reasons why your system doesn't work and is dangerous to run on the engine?!
06-05-2015, 01:14 PM
#26
Former Vendor
I'm not going to argue with you about this.
You have your theory and I have mine. I directly address my concerns...I've seen the inside of many GTS engines and was genuinely concerned about any chance of reducing the oil volume to the wrist pins. Pretty simple. You've only seen the outside of a GTS engine, so you have very little data to refer to...leaving you with only personal attacks.
Let's leave it at that and see what happens. Like I said, in two posts, I hope you system doesn't do any harm. Time will tell.
You have your theory and I have mine. I directly address my concerns...I've seen the inside of many GTS engines and was genuinely concerned about any chance of reducing the oil volume to the wrist pins. Pretty simple. You've only seen the outside of a GTS engine, so you have very little data to refer to...leaving you with only personal attacks.
Let's leave it at that and see what happens. Like I said, in two posts, I hope you system doesn't do any harm. Time will tell.
Greg,
You attacked me first, carefully worded, basically saying I know nothing.
I have numerous times covered your concerns, and dispelled all the misinformation you have and have now again posted.
Why not see that how you are doing it is an attack.
If I was to openly state that your crankcase breather system risked blowing up the engine due to detonation, and then claimed you wouldn't fix the engine as you wouldn't, you would get your back up as well.
I have covered your concerns with data a number of times, and called your experts to ask them questions, their answers contradict what you post on this topic. I also went to others and got their responses too.
What you state does not align with any of the research I have done. I posted all that information before. So you cannot say I haven't gone through it!!
AO hit the nail on the head with his post regarding your posts on RL. You come in tell people it is crap, and troll the threads offering no real help. More and more are thankfully waking up to this.
Next time should i just take your approach and just go over all the reasons why your system doesn't work and is dangerous to run on the engine?!
You attacked me first, carefully worded, basically saying I know nothing.
I have numerous times covered your concerns, and dispelled all the misinformation you have and have now again posted.
Why not see that how you are doing it is an attack.
If I was to openly state that your crankcase breather system risked blowing up the engine due to detonation, and then claimed you wouldn't fix the engine as you wouldn't, you would get your back up as well.
I have covered your concerns with data a number of times, and called your experts to ask them questions, their answers contradict what you post on this topic. I also went to others and got their responses too.
What you state does not align with any of the research I have done. I posted all that information before. So you cannot say I haven't gone through it!!
AO hit the nail on the head with his post regarding your posts on RL. You come in tell people it is crap, and troll the threads offering no real help. More and more are thankfully waking up to this.
Next time should i just take your approach and just go over all the reasons why your system doesn't work and is dangerous to run on the engine?!
06-05-2015, 02:41 PM
#27
Former Vendor
Several times, you've referenced atmospheric pressure being the same as a vacuum...saying that the atmospheric pressure in Denver is the same as the vacuum you are pulling.
I don't see how this reference has anything to do with actual vacuum, which is the difference between the existing atmospheric pressure and any lower pressure you create.
It's the reduction of atmospheric pressure, regardless of what that initial pressure is, that is my issue.
I think that anything which had the potential to pull oil away from the wrist pins is a potential problem.
Just to be clear.....again....I'm not the enemy here.....I'm thrilled this idea is being tried and shows positive results.
I just happen to have some concerns....based on what I've seen inside GTS engines and these concerns caused me to "shelf" my own vacuum system, years ago.
Pretty simple. I do what I think is right....everyone else is free to do what they think is right.....
However, does that mean I can't freely express my concerns and support those concerns with my own personal observations?
I don't see how this reference has anything to do with actual vacuum, which is the difference between the existing atmospheric pressure and any lower pressure you create.
It's the reduction of atmospheric pressure, regardless of what that initial pressure is, that is my issue.
I think that anything which had the potential to pull oil away from the wrist pins is a potential problem.
Just to be clear.....again....I'm not the enemy here.....I'm thrilled this idea is being tried and shows positive results.
I just happen to have some concerns....based on what I've seen inside GTS engines and these concerns caused me to "shelf" my own vacuum system, years ago.
Pretty simple. I do what I think is right....everyone else is free to do what they think is right.....
However, does that mean I can't freely express my concerns and support those concerns with my own personal observations?
OK so we have to have the train wreck again?
In stock configuration I have so much oil misting & flinging around the crankcase it isn't even slightly funny. All of it wants out... and a good amount actually makes it into the intake. Now this is 'really good' of course because it lubricates the cylinders really nicely - right? (Oh apart from the explosion thing...).
I run vacuum limiting valves - though I do acknowledge that they are hardly needed. I set them to ~7"Hg - at that point they flow fresh air into the cam cover to hold the vacuum level (and flush the crankcase). Get your mighty vac out and suck on the output tube until you get 7" Hg - it's nothing! It almost never runs even at that level in steady state general driving.
Context is all important here - this vacuum level is hardly more than the atmospheric difference between sea level & Denver CO, depending on the weather of course. As far as I know 928's survive just fine in Denver - even in the summertime.... This level of vacuum is just too low to be any kind of serious risk (it's a normal everyday occurrence in many places in the world). This low of a vacuum may help collapse a cloud of oil mist - but no reasonable amount of vacuum we will ever see here will stop oil being flung off the rotating masses or splashing as normal - the mechanisms are quite different - that much should be apparent.
Racers use vacuum for extreme ring sealing (often at 20-30 "Hg). In this application for a 928 it is only being used to ensure positive crank evacuation and oil separation - the purpose and necessary vacuum levels are totally different animals. If you get any ring sealing benefit it is relatively incidental to the primary goal IMO. The biggest power benefits here are from clean pistons and no ingestion to avoid power loss though timing degradations. The other benefit is keeping all the oil in the sump and not losing it out the tailpipe.
20K miles of hard driving says it works - better than any other argument I know.
I do know enough about the basic physics to not be particularly concerned - I was just surprised how well it worked out as a separation mechanism - it very much exceeded my expectations.
Could you make a vacuum system that could damage a 928 - certainly, but no one here is doing that - these are mild systems. I like the VLV's because I want to be sure its safe. I like my engine and I did this to save it - the stock configuration was torturing it every day - and forcing me to back off the gas all the time... now I don't have to do that anymore. As Roger said - it's like different car...
Alan
In stock configuration I have so much oil misting & flinging around the crankcase it isn't even slightly funny. All of it wants out... and a good amount actually makes it into the intake. Now this is 'really good' of course because it lubricates the cylinders really nicely - right? (Oh apart from the explosion thing...).
I run vacuum limiting valves - though I do acknowledge that they are hardly needed. I set them to ~7"Hg - at that point they flow fresh air into the cam cover to hold the vacuum level (and flush the crankcase). Get your mighty vac out and suck on the output tube until you get 7" Hg - it's nothing! It almost never runs even at that level in steady state general driving.
Context is all important here - this vacuum level is hardly more than the atmospheric difference between sea level & Denver CO, depending on the weather of course. As far as I know 928's survive just fine in Denver - even in the summertime.... This level of vacuum is just too low to be any kind of serious risk (it's a normal everyday occurrence in many places in the world). This low of a vacuum may help collapse a cloud of oil mist - but no reasonable amount of vacuum we will ever see here will stop oil being flung off the rotating masses or splashing as normal - the mechanisms are quite different - that much should be apparent.
Racers use vacuum for extreme ring sealing (often at 20-30 "Hg). In this application for a 928 it is only being used to ensure positive crank evacuation and oil separation - the purpose and necessary vacuum levels are totally different animals. If you get any ring sealing benefit it is relatively incidental to the primary goal IMO. The biggest power benefits here are from clean pistons and no ingestion to avoid power loss though timing degradations. The other benefit is keeping all the oil in the sump and not losing it out the tailpipe.
20K miles of hard driving says it works - better than any other argument I know.
I do know enough about the basic physics to not be particularly concerned - I was just surprised how well it worked out as a separation mechanism - it very much exceeded my expectations.
Could you make a vacuum system that could damage a 928 - certainly, but no one here is doing that - these are mild systems. I like the VLV's because I want to be sure its safe. I like my engine and I did this to save it - the stock configuration was torturing it every day - and forcing me to back off the gas all the time... now I don't have to do that anymore. As Roger said - it's like different car...
Alan
06-05-2015, 02:54 PM
#28
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I have a big wedding tomorrow and I don't want to get pulled away from doing the Chicken Dance because my phone is exploding with you guys going full Robocop vs ED-209 on each other.
......or worse yet, Kibort going full Johnny-5 on everyone.
Greg, doesn't your head scavenging system pull any vacuum on the crankcase? Just curious, I'm not terribly familiar with either setup.
To help clarify this debate, the only reason why this setup could be detrimental to a GTS (and only a GTS) is because certain years do not have the oil drain holes in the pistons?
06-05-2015, 03:40 PM
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I have a big wedding tomorrow
06-05-2015, 04:12 PM
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