• Mustang Forums
  • 1974 - 1978 Mustang II Talk & Tech

Vacuum with new cam?

  • Thread starter Thread starter joekurt
  • Start date Start date May 1, 2023
J

joekurt

Member
Oct 28, 2021
54
20
18
Pennsylvania
May 1, 2023
#1
  • May 1, 2023
  • #1
Hello again. I'm beginning a complete rebuild of 302 out of a '76 Mustang II. We put a pair of AFR 165 heads on it (CR~10:1) and are going with their recommendation for a Comp Cams 268 grind. Their actual grind number is XE268H. We're wondering about vacuum for power brakes, etc. Has anyone done anything close to this? And how was vacuum at idle or off throttle?
Thanks!
 

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor
Admin Dude
Jan 4, 1985
42,979
21,160
234
Box behind Walmart
May 1, 2023
#2
  • May 1, 2023
  • #2
It's an entry-level street cam. I'm no cam guru but to me, that means good street manners and overlap. You should see about the same vacuum as (maybe a hair less) your OEM cam.
 
Reactions: optionizerSS

LILCBRA

I wish I didn't have all of these balls in the air
Mod Dude
Dec 6, 2005
6,347
5,322
194
Corn County USA
May 1, 2023
#3
  • May 1, 2023
  • #3
I don't have experience with that specific cam, but looking at the specs it appears to be fairly close, if not a little more radical, to the cam I run:

Adv. Intake Duration288
Adv. Exhaust Duration300
Intake Duration @.050214
Exhaust Duration @.050224
Intake Valve Lift w/1.6 Rocker Ratio [w/1.72].473 [.508]
Exhaust Valve Lift w/1.6 Rocker Ratio [w/1.72].497 [.534]
Lobe Separation Angle112
Cam TypeHydraulic Flat Tappet
Basic Operating Range2800 RPM

The tighter LSA will most likely net you less vacuum than my car produces, which is around 15 inches at idle.

My original build included a different cam:

https://www.summitracing.com/parts/cca-cl31-330-3/make/ford

With that cam, which has the same LSA, I had no issues to speak of with vacuum idle. I bought myself this vacuum canister anyway:

https://www.summitracing.com/parts/cca-5200

It's still mounted in my engine compartment, but I've never had to hook it up. I think it would be pretty easy to hide if you wanted to see about using it. You could mount it in the fenderwell where a lot of the emissions stuff is if you'd like to hide it, but I don't think you'd necessarily need it.
 
J

joekurt

Member
Oct 28, 2021
54
20
18
Pennsylvania
May 1, 2023
#4
  • May 1, 2023
  • #4
Noobz347 said:
It's an entry-level street cam. I'm no cam guru but to me, that means good street manners and overlap. You should see about the same vacuum as (maybe a hair less) your OEM cam.
Click to expand...
Thanks Noobs347. Music to my ears!
 
J

joekurt

Member
Oct 28, 2021
54
20
18
Pennsylvania
May 1, 2023
#5
  • May 1, 2023
  • #5
Thanks Noobs347. Music to my ears!
 
J

joekurt

Member
Oct 28, 2021
54
20
18
Pennsylvania
May 1, 2023
#6
  • May 1, 2023
  • #6
LILCBRA said:
I don't have experience with that specific cam, but looking at the specs it appears to be fairly close, if not a little more radical, to the cam I run:

Adv. Intake Duration288
Adv. Exhaust Duration300
Intake Duration @.050214
Exhaust Duration @.050224
Intake Valve Lift w/1.6 Rocker Ratio [w/1.72].473 [.508]
Exhaust Valve Lift w/1.6 Rocker Ratio [w/1.72].497 [.534]
Lobe Separation Angle112
Cam TypeHydraulic Flat Tappet
Basic Operating Range2800 RPM

The tighter LSA will most likely net you less vacuum than my car produces, which is around 15 inches at idle.

My original build included a different cam:

https://www.summitracing.com/parts/cca-cl31-330-3/make/ford

With that cam, which has the same LSA, I had no issues to speak of with vacuum idle. I bought myself this vacuum canister anyway:

https://www.summitracing.com/parts/cca-5200

It's still mounted in my engine compartment, but I've never had to hook it up. I think it would be pretty easy to hide if you wanted to see about using it. You could mount it in the fenderwell where a lot of the emissions stuff is if you'd like to hide it, but I don't think you'd necessarily need it.
Click to expand...
Thanks LILCBRA! I didn't realize those vacuum boosters were just a simple can with a checkvalve. Genius.
 
Reactions: 2Blue2 and LILCBRA

2Blue2

will be trying this sex one when I can find it
Mod Dude
Mar 5, 2019
4,430
2,893
163
Oahu
May 1, 2023
#7
  • May 1, 2023
  • #7
joekurt said:
didn't realize those vacuum boosters were just a simple can
Click to expand...
Don’t some M2 have one in fender cowl area already?
 

LILCBRA

I wish I didn't have all of these balls in the air
Mod Dude
Dec 6, 2005
6,347
5,322
194
Corn County USA
May 2, 2023
#8
  • May 2, 2023
  • #8
2Blue2 said:
Don’t some M2 have one in fender cowl area already?
Click to expand...

I think the thing you're referring to is more of a charcoal canister, but I could be wrong. I lost all of that stuff years ago.
 
Reactions: 2Blue2

2Blue2

will be trying this sex one when I can find it
Mod Dude
Mar 5, 2019
4,430
2,893
163
Oahu
May 2, 2023
#9
  • May 2, 2023
  • #9
LILCBRA said:
charcoal canister
Click to expand...

Oy you might b right
 
Reactions: LILCBRA
I

IICrew

Mustang Master
Mar 29, 2020
479
608
103
USA
May 6, 2023
#10
  • May 6, 2023
  • #10
I have the xe268 cam with edelbrock heads. 10:1 ish c/r. I have plenty of vacuum. Choppy Rough idle. I have the idle set to around 750rpm. With the rebuilt engine mounts it shakes the car at that rpm. If your okay with that get the cam. On a cruiser or automatic build I would probably go one step milder. On my car it fits the build.
 
Reactions: LILCBRA
I

IICrew

Mustang Master
Mar 29, 2020
479
608
103
USA
May 6, 2023
#11
  • May 6, 2023
  • #11
The booster is for brakes attached to the master cylinder. The round bulb or can is only on a/c cars and is a vacuum reservoir. Helps stop the vent going to defrost on heavy accel. Non ac cars are cable operated and dont need it.
 

Blackhawkxx

Advanced Member
Mar 3, 2023
464
461
73
May 6, 2023
#12
  • May 6, 2023
  • #12
Your brakes will be fine with that cam.
 
Reactions: IICrew and LILCBRA

2Blue2

will be trying this sex one when I can find it
Mod Dude
Mar 5, 2019
4,430
2,893
163
Oahu
May 7, 2023
#13
  • May 7, 2023
  • #13
Blackhawkxx said:
will be fine
Click to expand...
Lets seem some pictures of yours Blackhawkxx...
And welcome aboard.
 
Reactions: IICrew

Enzio

Dang it. I was hoping mine would get 3 more inches
5 Year Member
May 14, 2019
1,054
840
133
Minnesota
May 7, 2023
#14
  • May 7, 2023
  • #14
Pictures!
 
Reactions: IICrew

Blackhawkxx

Advanced Member
Mar 3, 2023
464
461
73
May 7, 2023
#15
  • May 7, 2023
  • #15
2Blue2 said:
Lets seem some pictures of yours Blackhawkxx...
And welcome aboard.
Click to expand...
 
Reactions: 2Blue2, Enzio, LILCBRA and 1 other person

2Blue2

will be trying this sex one when I can find it
Mod Dude
Mar 5, 2019
4,430
2,893
163
Oahu
May 8, 2023
#16
  • May 8, 2023
  • #16
She sure is sweet!
 
Reactions: Enzio and Blackhawkxx
P

pyrogestate

Member
Oct 13, 2021
4
1
13
Canada
May 25, 2023
#17
  • May 25, 2023
  • #17
joekurt said:
Hello again. I'm beginning a complete rebuild of 302 out of a '76 Mustang II. We put a pair of AFR 165 heads on it (CR~10:1) and are going with their recommendation for a Comp Cams 268 grind. Their actual grind number is XE268H. We're wondering about vacuum for power brakes, etc. Has anyone done anything close to this? And how was vacuum at idle or off throttle?
Thanks!
Click to expand...
DO NOT USE THAT CAMSHAFT it is a CHEVY GRIND!!!!!!...this is the camshaft you should use for your FORD SMALL BLOCK, it will have great torque and horsepower, and will match your AFR 165 cc airflow characteristics, TRUST ME, AND it will have excellent vacuum and GREAT street manners and low RPM drivability on the street....as well .....

Xtreme Energy Computer Controlled 216/224 Hydraulic Roller Cam for Ford 5.0L

Xtreme Energy Computer Controlled 216/224 Hydraulic Roller Cam for Ford 5.0L (For EFI). Mild modifications, larger throttle body, mass air, 3.27-3.73 gear. (Note: for 1985-95 Engines Originally Equipped w/ Hydraulic Roller Cams.)
www.compcams.com
 
P

pyrogestate

Member
Oct 13, 2021
4
1
13
Canada
May 25, 2023
#18
  • May 25, 2023
  • #18
joekurt said:
Hello again. I'm beginning a complete rebuild of 302 out of a '76 Mustang II. We put a pair of AFR 165 heads on it (CR~10:1) and are going with their recommendation for a Comp Cams 268 grind. Their actual grind number is XE268H. We're wondering about vacuum for power brakes, etc. Has anyone done anything close to this? And how was vacuum at idle or off throttle?
Thanks!
Click to expand...
pyrogestate said:
DO NOT USE THAT CAMSHAFT it is a CHEVY GRIND!!!!!!...this is the camshaft you should use for your FORD SMALL BLOCK, it will have great torque and horsepower, and will match your AFR 165 cc airflow characteristics, TRUST ME, AND it will have excellent vacuum and GREAT street manners and low RPM drivability on the street....as well .....

Xtreme Energy Computer Controlled 216/224 Hydraulic Roller Cam for Ford 5.0L

Xtreme Energy Computer Controlled 216/224 Hydraulic Roller Cam for Ford 5.0L (For EFI). Mild modifications, larger throttle body, mass air, 3.27-3.73 gear. (Note: for 1985-95 Engines Originally Equipped w/ Hydraulic Roller Cams.)
www.compcams.com
Click to expand...
remember to CHECK YOUR PISTON TO VALVE CLEARANCE, if it is an issue FLYCUT THE PISTONS!!!!! Whatever shop or whoever recommended that cam to you might not be the best choice especially if they are recommending CHEVY camshafts for FORD small blocks, lol just my opinion.....
 
P

pyrogestate

Member
Oct 13, 2021
4
1
13
Canada
May 25, 2023
#19
  • May 25, 2023
  • #19
pyrogestate said:
remember to CHECK YOUR PISTON TO VALVE CLEARANCE, if it is an issue FLYCUT THE PISTONS!!!!! Whatever shop or whoever recommended that cam to you might not be the best choice especially if they are recommending CHEVY camshafts for FORD small blocks, lol just my opinion.....
Click to expand...
Sorry I got mixed up that post about the camshaft was a comparison about a CHEVY grind, I just wanted to help im sorry i SHOULD READ and not jump to conclusions however your engine build sounds exciting!!!
 
Reactions: Noobz347

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor
Admin Dude
Jan 4, 1985
42,979
21,160
234
Box behind Walmart
May 25, 2023
#20
  • May 25, 2023
  • #20
pyrogestate said:
Sorry I got mixed up that post about the camshaft was a comparison about a CHEVY grind, I just wanted to help im sorry i SHOULD READ and not jump to conclusions however your engine build sounds exciting!!!
Click to expand...
Hehe... There does exist, a cam with the same number that is for Chevy applications. I'm pretty sure the one we're talking about is this one:

https://www.cjponyparts.com/comp-cams-camshaft-set-xtreme-energy-xe268h-hydraulic-flat-tappet-1600-5800-rpm-289-302/p/312423-V/
 
Reactions: Enzio
You must log in or register to reply here.

Similar threads

SURGING IDLE / NO IDLE CHECKLIST FOR 1996–1998 MUSTANG GT (4.6L 2V) - Work In Progress
  • Noobz347
  • Aug 30, 2025
  • 1996 - 2004 SN95 Mustang -General/Talk-
Replies
0
Views
709
1996 - 2004 SN95 Mustang -General/Talk- Aug 30, 2025
Noobz347
J
Exhaust Manifold search
  • joekurt
  • Apr 10, 2024
  • 1974 - 1978 Mustang II Talk & Tech
Replies
4
Views
1K
1974 - 1978 Mustang II Talk & Tech Apr 12, 2024
extra_stout
SURGING IDLE / NO IDLE CHECKLIST FOR 1999–2004 MUSTANG GT (4.6L 2V) - Work In Progress
  • Noobz347
  • Aug 30, 2025
  • 1996 - 2004 SN95 Mustang -General/Talk-
Replies
0
Views
860
1996 - 2004 SN95 Mustang -General/Talk- Aug 30, 2025
Noobz347
Engine An engine building combo with stock Speed Density (SD) system
  • Mcmahst
  • Jan 14, 2025
  • Fox 5.0 Mustang Tech
Replies
11
Views
919
Fox 5.0 Mustang Tech Jan 15, 2025
Mcmahst
SN95 Desktop 363 Engine Combination - Looking for input
  • WhiteCobra95
  • Sep 8, 2025
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
Replies
11
Views
1K
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- Oct 6, 2025
Habu135
Share:
Bluesky Email Share Link
  • Mustang Forums
  • 1974 - 1978 Mustang II Talk & Tech
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?