Crankcase pressure gauge
Thread Starter
Safety Car
Joined: Feb 1999
Posts: 3,504
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From: Mexico Beach FL
Crankcase pressure gauge
Has anyone put a pressure gauge on the lower crankcase to see what kind of pressure may build up on a highly modified engine?
Normally, intake vacuum is used to keep the crankcase at a small negative pressure -- PCV.
But, at high rpm and throttle opening, ring flutter and blow-by may cause positive pressure.
It seems to me that it would be easy to use rubber tubing clamped to the dipstick tube and the other end to a pressure gauge to see what the reading is over a range of rpm and power.
Just wondering if anyone has tried this and what the results were?
Tom Piper
Normally, intake vacuum is used to keep the crankcase at a small negative pressure -- PCV.
But, at high rpm and throttle opening, ring flutter and blow-by may cause positive pressure.
It seems to me that it would be easy to use rubber tubing clamped to the dipstick tube and the other end to a pressure gauge to see what the reading is over a range of rpm and power.
Just wondering if anyone has tried this and what the results were?
Tom Piper
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
Crankcase vacuum/pressure monitoring with a gauge is not uncommon.
If you have the means to datalog, Performance Trends announced
an inexpensive crankcase blowby sensor at PRI this spring. I do not
see it in the product list on the website, but here is a link to the
PRI handout where they mention it and show a picture.
.
If you have the means to datalog, Performance Trends announced
an inexpensive crankcase blowby sensor at PRI this spring. I do not
see it in the product list on the website, but here is a link to the
PRI handout where they mention it and show a picture.
.
Large Impressive Member
Joined: Jul 2003
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From: Good health is merely the slowest possible rate at which one can die
St. Jude Donor '04-'05-'06-'07
Some diesel engine manuals have specs for this as a diagnostic test and so yes I've done it when working on them. I'm not sure what numbers would be acceptable in a high performance application, but I'd guess not over 3 lbs. Maybe a bit more in a radical, short run duration drag engine could be considered normal. Once again these are only guesses judging from specs for a healthy diesel. Also, they have open crankcase vent systems.
Le Mans Master
Joined: Feb 1999
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From: South Carolina
St. Jude Donor '03 & '05
Tom, are you trying to figure this out to reduce your blow by, by maybe seeing if you need a vacuum pump for the crankcase?
I am hoping the catch can I am putting in will reduce the oil contamination by reducing oil getting into the chambers from excessive crankcase pressure.
I am hoping the catch can I am putting in will reduce the oil contamination by reducing oil getting into the chambers from excessive crankcase pressure.
Thread Starter
Safety Car
Joined: Feb 1999
Posts: 3,504
Likes: 4
From: Mexico Beach FL
Tom, are you trying to figure this out to reduce your blow by, by maybe seeing if you need a vacuum pump for the crankcase?
I am hoping the catch can I am putting in will reduce the oil contamination by reducing oil getting into the chambers from excessive crankcase pressure.
I am hoping the catch can I am putting in will reduce the oil contamination by reducing oil getting into the chambers from excessive crankcase pressure.
I am just curious if the engine crankcase actually develops a pressure instead of the low negative pressure that is ideal.
My guess is the rings start to flutter above about 6200 rpm and the pressure goes up considerably from there.
I figured someone has already tried it on a high revving engine.
Tom Piper
Large Impressive Member
Joined: Jul 2003
Posts: 65,811
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From: Good health is merely the slowest possible rate at which one can die
St. Jude Donor '04-'05-'06-'07
There is no way that it cannot develope a pressure. Even with excellent ring sealing just the pistons moving up and down would tend to create pressure. Now whether any stock or modified venting system can fully compensate or even create a vacuum depends on the engine and it's CV system/type. It could be monitored by anywhere that you can tap into the parts of the engine which contain crankcase pressure. Via the dipstick hole as you mentioned, from a valve cover opening, etc. And knowing this as you've surmised could be enlightening. But if you're having no problems that could be attributed to this, I'm not sure it's worth the bother except for establishing a baseline in case there are problems down the road.
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Joined: Nov 2008
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I have a 1966 427 390 HP engine w/ stock casting, larger hydraulic cam but basically a stock motor w/ <5K on rebuild.
I measure 15 – 18 in Hg at 700 RPM idle.
I’m trying to resolve a persistent right side valve cover oil leak.
Last night, I found a cracked PCV hose which was replaced.
I verified the functionality of the PCV valve by placing my thumb over the PCV valve while the engine was idling. It had plenty of suction & the PCV was vibrating freely.
I replaced the PCV valve in the left valve cover & then connected a vacuum hose to the dip stick tube & measured 0 vacuum.
I did not block off the hose that runs from the right valve cover to the air cleaner or the oil cap.
What is the correct procedure to measure crankcase vacuum on a C2 corvette engine?
Thanks in advance for all your help!
Andy
I measure 15 – 18 in Hg at 700 RPM idle.
I’m trying to resolve a persistent right side valve cover oil leak.
Last night, I found a cracked PCV hose which was replaced.
I verified the functionality of the PCV valve by placing my thumb over the PCV valve while the engine was idling. It had plenty of suction & the PCV was vibrating freely.
I replaced the PCV valve in the left valve cover & then connected a vacuum hose to the dip stick tube & measured 0 vacuum.
I did not block off the hose that runs from the right valve cover to the air cleaner or the oil cap.
What is the correct procedure to measure crankcase vacuum on a C2 corvette engine?
Thanks in advance for all your help!
Andy
