Go Back   The Ford Barn > General Discussion > Early V8 (1932-53)

Sponsored Links (Register now to hide all advertisements)

Reply
 
Thread Tools Display Modes
Old 11-21-2018, 05:10 PM   #1
fordv8j
Senior Member
 
fordv8j's Avatar
 
Join Date: Jan 2015
Posts: 211
Default Vacuum reading

I put a vacuum guage on our 38 coupe today with 59A engine,warmed up and idling, it read 20, is that good?
fordv8j is offline   Reply With Quote
Old 11-21-2018, 05:17 PM   #2
Kahuna
Senior Member
 
Kahuna's Avatar
 
Join Date: May 2010
Location: NorCal
Posts: 2,617
Default Re: Vacuum reading

Ford, That's great
Kahuna is offline   Reply With Quote
Sponsored Links (Register now to hide all advertisements)
Old 11-21-2018, 05:20 PM   #3
Ggmac
Senior Member
 
Join Date: Jul 2016
Location: Lake worth Florida
Posts: 702
Default Re: Vacuum reading

As long as it's a steady needle at idle . Any dip could be indicating a problem
Ggmac is offline   Reply With Quote
Old 11-21-2018, 06:38 PM   #4
Talkwrench
Senior Member
 
Talkwrench's Avatar
 
Join Date: Aug 2012
Location: Perth, Western Australia
Posts: 2,628
Default Re: Vacuum reading

Vacuum gauge is a very under rated tool .. 20Hg is great , 21 Hg at idle is even better ; ) [if you have a standard cam]
__________________
"Came too close to dying to stop living now!"
Talkwrench is offline   Reply With Quote
Old 11-21-2018, 08:42 PM   #5
fordwife
Senior Member
 
Join Date: Dec 2015
Posts: 250
Default Re: Vacuum reading

Most motor or Chilton manuals will have a page that will tell you what various vacuum guage readings indicate. Or google vacuum guage.
fordwife is offline   Reply With Quote
Old 11-21-2018, 11:14 PM   #6
petehoovie
Senior Member
 
petehoovie's Avatar
 
Join Date: May 2015
Posts: 3,316
Default Re: Vacuum reading

Sponsored Links (Register now to hide all advertisements)
http://www.vanpeltsales.com/FH_web/F...auge-chart.jpg
__________________
The only thing nice about being imperfect is the joy it brings to others....

"Silver rings, your butt! Them's washers!"
"We shot our way out of that town for a dollar's worth of steel holes." - from 'The Wild Bunch' - 1969

https://www.youtube.com/watch?v=7NReUd2_0u0
petehoovie is online now   Reply With Quote
Old 11-22-2018, 04:23 PM   #7
Flathead Fever
Senior Member
 
Flathead Fever's Avatar
 
Join Date: May 2010
Location: Yucaipa, CA
Posts: 599
Default Re: Vacuum reading

20-inches is perfect. You can also try the throttle snap test like the first gauge describes. This cause the piston suck the air in faster. When the throttle slams shut the vacuum increase a little. This is an additional test to see how well the rings are sealing. If the vacuum goes up your rings are sealing as good as they were when they were new. This why in the old-days, before you bought a car, you took it to your mechanic to have it checked out first. That vacuum reading quickly told the mechanic if the engine was good or worn out.

You will not see 20-inches of vacuum with a high performance cam. The reading will be quite a bit lower. That changes when the power valve opens. So then you need to change the power valve to one that opens that matches your cam's vacuum reading.

I see nice vacuum gauges at estate sales for cheap. Nobody knows what they are used for anymore. Especially the "millennial mechanics". But you can't hook them to laptop so the new mechanics don't have a clue where to plug them into. They diagnose new vehicle engines just as good as they do flatheads.
Flathead Fever is offline   Reply With Quote
Old 04-10-2021, 09:09 PM   #8
Pdstark
Member
 
Pdstark's Avatar
 
Join Date: Jun 2020
Location: CA & MN
Posts: 46
Default Re: Vacuum reading

Quote:
Originally Posted by petehoovie View Post
On the 8BA or 8RT what should the idle RPM be (I think I remember something around 411?) - how would an idle RPM affect the vacuum reading?
__________________
“Wherever you go - there you are”
Pdstark is offline   Reply With Quote
Old 04-10-2021, 10:18 PM   #9
Pdstark
Member
 
Pdstark's Avatar
 
Join Date: Jun 2020
Location: CA & MN
Posts: 46
Default Re: Vacuum reading

Disregard... found what I needed.
__________________
“Wherever you go - there you are”
Pdstark is offline   Reply With Quote
Old 04-11-2021, 05:32 AM   #10
51woodie
Senior Member
 
51woodie's Avatar
 
Join Date: Apr 2018
Location: Chelmsford, ON Canada
Posts: 383
Default Re: Vacuum reading

My '46, with a stock 59AB, runs a steady 21" at idle, and 15" to 16" at 50 mph.
Attached Images
File Type: jpg Mech Gauges at Idle.jpg (42.8 KB, 27 views)
File Type: jpg Mech Gauges at Speed.jpg (54.3 KB, 27 views)
51woodie is offline   Reply With Quote
Old 04-11-2021, 05:51 AM   #11
Desoto291Hemi
Senior Member
 
Join Date: Oct 2019
Location: Carthage , Tennessee
Posts: 132
Default Re: Vacuum reading

That is a fine engine with reading like that .
Th3 temp and oil pressure are excellent as well .
It’s good to see a Flathead that is operating like it was designed.
Good job .
Tommy
Desoto291Hemi is offline   Reply With Quote
Old 04-11-2021, 06:36 AM   #12
Terry,OH
Senior Member
 
Terry,OH's Avatar
 
Join Date: May 2010
Posts: 3,715
Default Re: Vacuum reading

The vacuum gauge is not simply a go or nogo gauge it should also be used to adjust the carburetor idle mixture adjustment screws. Under the same conditions you took your reading just slowly turn the mixture screws, one at a time, in or out until you get the highest vacuum reading.
Terry,OH is offline   Reply With Quote
Old 04-11-2021, 07:48 AM   #13
big job
Senior Member
 
big job's Avatar
 
Join Date: Sep 2013
Location: Dighton, Mass
Posts: 1,081
Default Re: Vacuum reading

Quote:
Originally Posted by 51woodie View Post
My '46, with a stock 59AB, runs a steady 21" at idle, and 15" to 16" at 50 mph.

exactly as my 46 runs
big job is offline   Reply With Quote
Old 04-11-2021, 10:19 AM   #14
Pdstark
Member
 
Pdstark's Avatar
 
Join Date: Jun 2020
Location: CA & MN
Posts: 46
Default Re: Vacuum reading

Quote:
Originally Posted by 51woodie View Post
My '46, with a stock 59AB, runs a steady 21" at idle, and 15" to 16" at 50 mph.
That's the reading on my '51. Thanks for the confirmation!!
__________________
“Wherever you go - there you are”
Pdstark is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Sponsored Links (Register now to hide all advertisements)


All times are GMT -5. The time now is 06:02 PM.