My head is about to explode
Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
Thread Starter
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
) that would goop on a whole bunch of RTV and put the cam and distributor in jeopardy. If that wasn't what you were talking about then disregard the above paragraph
So anyway I was all set to take the manifold off and decided to try and run a bead along the back where it was leaking like a sieve. Why not give it shot, it has never worked the last 20 times I tried it, no sorry it has never worked period.
I let it dry over night and went for a spin this morning and it is dry as a bone back there, no leaks no nothing and the other wet stuff I saw yesterday was the bottom rad hose going south on me. I should go out and buy a lottery ticket tonight
Burning Brakes
Joined: Aug 2005
Posts: 1,164
Likes: 1
From: Europe, France
Let's hope it'll be leakproof too when you use it full throttle...
7000 RPM at WOT isn't exactly the same condition as idle...
Don't buy the lottery ticket already, but keep your fingers crossed !
7000 RPM at WOT isn't exactly the same condition as idle...
Don't buy the lottery ticket already, but keep your fingers crossed !
Melting Slicks
Joined: Feb 2003
Posts: 3,053
Likes: 4
St. Jude Donor '03,'11
i don't know why people think there is some big pressure rise when the rpm's go up. If you have a lot of blowby maybe a few psi of pressure but that ain't going to blow out that silicone.
Burning Brakes
Joined: Aug 2005
Posts: 1,164
Likes: 1
From: Europe, France
Breathers or PCV valve system can then become restricted in a very short time.
This condition can cause oil leakage at gaskets and seals that would not normally have leakage.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
That might be an interesting and maybe useful test.
Crankcase pressures at varying RPM with and without PCVs , with and without breathers , acceleration and deceleration and whatever other conditions people can think up.
Probably not a very popular topic like heat or oil pressure but I don't ever remember seeing a crankcase pressure dash gauge.
Crankcase pressures at varying RPM with and without PCVs , with and without breathers , acceleration and deceleration and whatever other conditions people can think up.
Probably not a very popular topic like heat or oil pressure but I don't ever remember seeing a crankcase pressure dash gauge.
Thread Starter
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Or even a crappy PCV that isn't able to provide the flow when the motor is producing high vacuum, it then goes to the weakest point for the air ( for lack of a better term ) and sucks part of your RTV bead into the motor, instead of blowing it out, and viola, now it has a hole for the air it is looking for.The above is just speculation I have nothing to back it up but it kinda makes sense
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
A couple of times I have seen the oil dipstick pushed up out of the tube a few inches from crankcase pressure, but this was always in new engines when they thought they could get away without ventilation.
The seals front and rear on these new engines were leaking badly too, but not the manifold walls. I always blamed the extra pressure to a new build not seated properly yet.
The seals front and rear on these new engines were leaking badly too, but not the manifold walls. I always blamed the extra pressure to a new build not seated properly yet.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
A couple of times I have seen the oil dipstick pushed up out of the tube a few inches from crankcase pressure, but this was always in new engines when they thought they could get away without ventilation.
The seals front and rear on these new engines were leaking badly too, but not the manifold walls. I always blamed the extra pressure to a new build not seated properly yet.
The seals front and rear on these new engines were leaking badly too, but not the manifold walls. I always blamed the extra pressure to a new build not seated properly yet.
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
Several times in for diagnostic purposes, I have connected a vacuum gauge at the dipstick tube to test for pressure after a new pcv was installed when people still complained about excessive oil leakage. It;s just a simple crude way to test for too much blowby.
I'll see if I can dig up some info. Maybe I recorded something. I seem to remember that it was around the same time I strted stuffing the pot scrubbies down into the bafles to help condense the oil vapor a bit.
I'll see if I can dig up some info. Maybe I recorded something. I seem to remember that it was around the same time I strted stuffing the pot scrubbies down into the bafles to help condense the oil vapor a bit.
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
Didn’t find any of the very old results I had, but here's some from last year.
Agree, but you you would have to test to see if it were really significant. Would have to be a lot of blowby.
Or even a crappy PCV that isn't able to provide the flow when the motor is producing high vacuum, it then goes to the weakest point for the air ( for lack of a better term ) and sucks part of your RTV bead into the motor, instead of blowing it out, and viola, now it has a hole for the air it is looking for.
The above is just speculation I have nothing to back it up but it kinda makes sense
Have never seen a motor go past 26 on the manifold side but that doesn’t apply. On the crank side, you’ll always have a certain amount of blowby plus the pcv and opposite fresh intake, so I doubt the vacuum could build very high, but totally dependent on the blowby vs pcv.
Here is a previous discussion with some results.
Crankcase turned positive at a lag, only at wot and wasn’t much.
http://forums.corvetteforum.com/c3-t...ot-to-pcv.html
Tests started at pg 8
Or even a crappy PCV that isn't able to provide the flow when the motor is producing high vacuum, it then goes to the weakest point for the air ( for lack of a better term ) and sucks part of your RTV bead into the motor, instead of blowing it out, and viola, now it has a hole for the air it is looking for.The above is just speculation I have nothing to back it up but it kinda makes sense
Here is a previous discussion with some results.
Crankcase turned positive at a lag, only at wot and wasn’t much.
http://forums.corvetteforum.com/c3-t...ot-to-pcv.html
Tests started at pg 8
Here’s some more info to mull over.
Had a little time to get some reading on the road today. Traffic was pretty heavy, so I didn’t get a lot.
I connected my “lower than atmospheric pressure gauge” (because Z-man and FB007 contend vacuum does not exist) the same as before, to the oem passenger valve cover breather tube.
I taped the gauge over the shadowband, so it’s not as clear as should be with the bright Florida sun behind it.
At startup and idle I got the same reading of 6”
After the engine got to full temp (180°) it went up to 7”
At 2000 rpm steady cruise it went back to 5”
At 2500 rpm steady cruise it stayed at 5”
At 3000 rpm steady cruise it stayed at 5”
At 3500 rpm steady cruise it dropped to 4.5”
At 4000 rpm steady cruise it stayed at 4”
Traffic wouldn’t let me cruise at any higher rpm
Half throttle acceleration thru 1st, 2nd and into 3rd stayed at 4”
Full throttle acceleration brought it to .5# pressure.
Thru all of the cruising rpm’s the needle stayed pretty steady.
At WOT acceleration, thru the gears, there was a lag of 3 or 4 seconds to reach pressure.
Had a little time to get some reading on the road today. Traffic was pretty heavy, so I didn’t get a lot.
I connected my “lower than atmospheric pressure gauge” (because Z-man and FB007 contend vacuum does not exist) the same as before, to the oem passenger valve cover breather tube.
I taped the gauge over the shadowband, so it’s not as clear as should be with the bright Florida sun behind it.
At startup and idle I got the same reading of 6”
After the engine got to full temp (180°) it went up to 7”
At 2000 rpm steady cruise it went back to 5”
At 2500 rpm steady cruise it stayed at 5”
At 3000 rpm steady cruise it stayed at 5”
At 3500 rpm steady cruise it dropped to 4.5”
At 4000 rpm steady cruise it stayed at 4”
Traffic wouldn’t let me cruise at any higher rpm
Half throttle acceleration thru 1st, 2nd and into 3rd stayed at 4”
Full throttle acceleration brought it to .5# pressure.
Thru all of the cruising rpm’s the needle stayed pretty steady.
At WOT acceleration, thru the gears, there was a lag of 3 or 4 seconds to reach pressure.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Noonie is there a PCV working in your “lower than atmospheric pressure gauge” test above ?
Not sure how Motorhead is venting but he could also attach a LTAPG to his dipstick tube and go for a quick ride.
( I clicked on the link and just as quickly clicked off of it. Not in the mood to read through that 
)
Not sure how Motorhead is venting but he could also attach a LTAPG to his dipstick tube and go for a quick ride.
( I clicked on the link and just as quickly clicked off of it.
Not in the mood to read through that )
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
Noonie is there a PCV working in your “lower than atmospheric pressure gauge” test above ?
Not sure how Motorhead is venting but he could also attach a LTAPG to his dipstick tube and go for a quick ride.
( I clicked on the link and just as quickly clicked off of it. Not in the mood to read through that )
Not sure how Motorhead is venting but he could also attach a LTAPG to his dipstick tube and go for a quick ride.
( I clicked on the link and just as quickly clicked off of it.
Not in the mood to read through that )Yes the pcv valve was installed on that test, but I had the vacuum guage (LTAPG
) connected to the fresh air intake tube on the pass side.The results are a little skewed because of that. Connecting to the dipstick tube would be the ulitmate test as I have done with some previously severe blowby engines, but not on the road under load. I posted my tests and results in stages just so the thread wouldn't be all over the map.
Connected to the dipstick tube, at least on that engine, I would assume the vacuum at cruise and the pressure at wot would both be less. Both the pcv valve and the intake tube would be working as designed under all conditions and unless there was an extreme amount of blowby, the gauge probably wouldn't show pressure. You would need a real flow meter to test that function, which I don't have.
It would be interesting to see what an engine at 7000rpm connected both ways would read on that guage though. If it showed pressure at that 7000rpm with the system connected as oem, I would think there would be a lot of blowby.
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
This thread has progressed from a bad casting with improper machine work that no amount of rtv can cure to trying to fix it with sealant because of blowby problems.
I'm still interested in the bad casting and bad machining.
The only machining involved on that part of the intake is the flat bottom surface that meets the wall and the dist hole itself with the top faced off for the dist. From the bottom side there should be bare casting between any maching in that area.
I would really like to see this machining mismatch and casting flaw, but I understand MotorHead not wanting to remove the manifold.
I'm still interested in the bad casting and bad machining.
The only machining involved on that part of the intake is the flat bottom surface that meets the wall and the dist hole itself with the top faced off for the dist. From the bottom side there should be bare casting between any maching in that area.
I would really like to see this machining mismatch and casting flaw, but I understand MotorHead not wanting to remove the manifold.
Thread Starter
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
No the mystery continues, and I am not ruling anything out but I ain't touching nothing right now, dry as a bone back there
Burning Brakes
Joined: Aug 2005
Posts: 1,164
Likes: 1
From: Europe, France
Melting Slicks
Joined: Feb 2003
Posts: 3,053
Likes: 4
St. Jude Donor '03,'11
Yes the pcv valve was installed on that test, but I had the vacuum guage (LTAPG ) connected to the fresh air intake tube on the pass side.
The results are a little skewed because of that.
Connected to the dipstick tube, at least on that engine, I would assume the vacuum at cruise and the pressure at wot would both be less. .
) connected to the fresh air intake tube on the pass side.The results are a little skewed because of that.
Connected to the dipstick tube, at least on that engine, I would assume the vacuum at cruise and the pressure at wot would both be less. .
But you know that could be an excellent mod. Block the breather hole and run the PCV as normal and it looks like you're pulling 7hg of vacuum. That is a very good thing. Dry sump oiling systems pull closer to max vacuum to reduce crank and piston windage. I would assume 7hg while not being close to a perfect vacuum would help a little. And you'd have less leaks while the engine is running because you're always pulling in rather than pushing out due to the weight of the oil.
Another thing that experiment might be telling us is that rings seal better at operating temp. 6hg cold vs 7hg hot.
Last edited by turtlevette; Aug 1, 2010 at 10:10 AM.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
That is very interesting. I was thinking how the heck are you pulling vacuum when the breather is letting air in as fast as the PCV system is sucking it out. Without the breather blocked i would think the vacuum is nonexistent.
But you know that could be an excellent mod. Block the breather hole and run the PCV as normal and it looks like you're pulling 7hg of vacuum. That is a very good thing. Dry sump oiling systems pull closer to max vacuum to reduce crank and piston windage. I would assume 7hg while not being close to a perfect vacuum would help a little. And you'd have less leaks while the engine is running because you're always pulling in rather than pushing out due to the weight of the oil.
Another thing that experiment might be telling us is that rings seal better at operating temp. 6hg cold vs 7hg hot.
But you know that could be an excellent mod. Block the breather hole and run the PCV as normal and it looks like you're pulling 7hg of vacuum. That is a very good thing. Dry sump oiling systems pull closer to max vacuum to reduce crank and piston windage. I would assume 7hg while not being close to a perfect vacuum would help a little. And you'd have less leaks while the engine is running because you're always pulling in rather than pushing out due to the weight of the oil.
Another thing that experiment might be telling us is that rings seal better at operating temp. 6hg cold vs 7hg hot.
Burning Brakes
Joined: Aug 2005
Posts: 1,164
Likes: 1
From: Europe, France
The PCV system needs intake vacuum to create crankcase vacuum.
If you stay at WOT long enough, you won't create much vacuum this way.
You''ll still have positive crankcase pressure...
We have the same problem with all vacuum actuated devices : they rarely work on a high perf / race car.
Often because a wild cam generates low vacuum too...
If you stay at WOT long enough, you won't create much vacuum this way.
You''ll still have positive crankcase pressure...
We have the same problem with all vacuum actuated devices : they rarely work on a high perf / race car.
Often because a wild cam generates low vacuum too...
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
The PCV system needs intake vacuum to create crankcase vacuum.
If you stay at WOT long enough, you won't create much vacuum this way.
You''ll still have positive crankcase pressure...
We have the same problem with all vacuum actuated devices : they rarely work on a high perf / race car.
Often because a wild cam generates low vacuum too...
If you stay at WOT long enough, you won't create much vacuum this way.
You''ll still have positive crankcase pressure...
We have the same problem with all vacuum actuated devices : they rarely work on a high perf / race car.
Often because a wild cam generates low vacuum too...