• Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-

Vacuum

  • Thread starter Thread starter ProTechAutoServices
  • Start date Start date Aug 1, 2026
P

ProTechAutoServices

New Member
Aug 1, 2026
5
0
1
PR
Aug 1, 2026
#1
  • Aug 1, 2026
  • #1
Hi, I'm building a old school 5.0l engine, with a gt40p heads and gt40 intake manifold. My question is....Can I run the vacuum hose under the intake manifold straight to the pcv valve or I still need to use the by pass under the intake manifold. That by pass is actually hitting the valve cover ; the cover are not the factory ones, they are toller than the original. I know I can use some spacer on the intake manifold, but I'm wondering if I can do that, thanks.
 

Attachments

  • Screenshot_20260725_144143_Google.webp
    111.6 KB · Views: 22
Last edited: Aug 1, 2026

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
28,021
10,645
213
polk county florida
Aug 1, 2026
#2
  • Aug 1, 2026
  • #2
Yeah, not much room under there with tall valve covers, I guess you could plug them two off and hook to a vac source by itself, I don't know what effect it would have t'd into the main supply to the vac tree. You could thread a nipple into the core plug at the back of the upper, maybe use a 90* nipple pointed down to clean it up.
 

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor
Admin Dude
Jan 4, 1985
43,347
21,544
234
Box behind Walmart
Aug 1, 2026
#3
  • Aug 1, 2026
  • #3
Post an image when you have the chance.


If I am understanding your question correctly then, "Yes". You can plug the the PCV hole in the back of the intake and use another vacuum source to run the PCV valve.

However, lots of folks have just done away with the PCV system altogether and just vented the valve covers.
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
28,021
10,645
213
polk county florida
Aug 1, 2026
#4
  • Aug 1, 2026
  • #4
Speed dencity or mass air computer?
 
P

ProTechAutoServices

New Member
Aug 1, 2026
5
0
1
PR
Aug 1, 2026
#5
  • Aug 1, 2026
  • #5
Mass air
 
P

ProTechAutoServices

New Member
Aug 1, 2026
5
0
1
PR
Aug 1, 2026
#6
  • Aug 1, 2026
  • #6
General karthief said:
Speed dencity or mass air computer?
Click to expand...
Mass air
 
P

ProTechAutoServices

New Member
Aug 1, 2026
5
0
1
PR
Aug 1, 2026
#7
  • Aug 1, 2026
  • #7
Noobz347 said:
Post an image when you have the chance.


If I am understanding your question correctly then, "Yes". You can plug the the PCV hole in the back of the intake and use another vacuum source to run the PCV valve.

However, lots of folks have just done away with the PCV system altogether and just vented the valve covers.
Click to expand...
 

Attachments

  • Screenshot_20260725_144143_Google.webp
    111.6 KB · Views: 30

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor
Admin Dude
Jan 4, 1985
43,347
21,544
234
Box behind Walmart
Aug 1, 2026
#8
  • Aug 1, 2026
  • #8
Ok... The port you circled in yellow. If that is the one you want to eliminate then yes... eliminate it.

You can use the port from the center section and route the hose how you want for the PCV.

The image you have circled in black should have one just like it in the upper plenum. If so, you really don't need to do anything with that. If the upper plenum doesn't have it, the gasket will seal it.


Edit:
Later versions of that same manifold had a simple "L" vacuum fitting in that location (circled in yellow) exactly like the one on the opposite side.
 
Reactions: Mcmahst and ProTechAutoServices
P

ProTechAutoServices

New Member
Aug 1, 2026
5
0
1
PR
Aug 1, 2026
#9
  • Aug 1, 2026
  • #9
Noobz347 said:
Ok... The port you circled in yellow. If that is the one you want to eliminate then yes... eliminate it.

You can use the port from the center section and route the hose how you want for the PCV.

The image you have circled in black should have one just like it in the upper plenum. If so, you really don't need to do anything with that. If the upper plenum doesn't have it, the gasket will seal it.


Edit:
Later versions of that same manifold had a simple "L" vacuum fitting in that location (circled in yellow) exactly like the one on the opposite side.
Click to expand...
Thank you
 

Mcmahst

5 Year Member
Jan 19, 2021
695
276
83
Laguna Woods CA, fort Mohave AZ
Aug 1, 2026
#10
  • Aug 1, 2026
  • #10
Lots of PVC questions lately.
 
Reactions: Noobz347

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor
Admin Dude
Jan 4, 1985
43,347
21,544
234
Box behind Walmart
Aug 1, 2026
#11
  • Aug 1, 2026
  • #11
Mcmahst said:
Lots of PVC questions lately.
Click to expand...

We get things in groups a lot of times.
 

AeroCoupe

lube between the nut and the face. I know my lubes
Founding Member
Oct 28, 2001
6,099
4,192
183
Claremore, OK
Aug 2, 2026
#12
  • Aug 2, 2026
  • #12
Seems like most know this but just in case, with a mass air car you cannot vent the valve covers. This would be a source of unmetered air and it will cause idle/surge issues.
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
28,021
10,645
213
polk county florida
Aug 2, 2026
#13
  • Aug 2, 2026
  • #13
AeroCoupe said:
Seems like most know this but just in case, with a mass air car you cannot vent the valve covers. This would be a source of unmetered air and it will cause idle/surge issues.
Click to expand...
That's why I asked
 
Reactions: AeroCoupe

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor
Admin Dude
Jan 4, 1985
43,347
21,544
234
Box behind Walmart
Aug 2, 2026
#14
  • Aug 2, 2026
  • #14
AeroCoupe said:
Seems like most know this but just in case, with a mass air car you cannot vent the valve covers. This would be a source of unmetered air and it will cause idle/surge issues.
Click to expand...

You still can but vents should be one-way.

Something like this:

Billet Valve Cover Breathers for Ford, GM, Dodge, Chrysler, Jeep, Toyota, Mitsubishi, Nissan, Honda, Subaru, Audi and Volkswagen. - CFM Performance

www.c-f-m.com
 
You must log in or register to reply here.

Similar threads

N
Need stainless carb heat shield
  • newmex999
  • Aug 29, 2026
  • 1965 - 1973 Classic Mustangs -General/Talk-
Replies
2
Views
105
1965 - 1973 Classic Mustangs -General/Talk- Sunday at 10:02 PM
Mcmahst
Mustang II 4 cyl gear hunting and possibly messed up vacuum system
  • oesterreicher
  • May 31, 2026
  • 1974 - 1978 Mustang II Talk & Tech
Replies
11
Views
419
1974 - 1978 Mustang II Talk & Tech Jun 14, 2026
manicmechanic007
J
Intake
  • James S
  • Jul 10, 2026
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
Replies
10
Views
254
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- Jul 12, 2026
James S
J
Intake vacuum lines
  • cnorman31
  • Mar 9, 2025
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
Replies
3
Views
828
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- Oct 15, 2025
Scrapla347
F
Fox 1990 Mustang GT 5.0 A9L – Engine suddenly shuts off but immediately restarts when key turned
  • FishermansFriend
  • Aug 9, 2026
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
Replies
16
Views
493
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- Aug 30, 2026
General karthief
Share:
Bluesky Email Share Link
  • Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
Menu
Log in

Register

  • Forums
  • What's new
  • Media
  • Resources
  • Contact
  • Sponsor
X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?

X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?