Vacuum with new cam?

J

joekurt

Member
Oct 28, 2021
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Pennsylvania
#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!
 

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#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.
 
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#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.
 
#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.
 
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#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.
 
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#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.
 
#15
2Blue2 said:
Lets seem some pictures of yours Blackhawkxx...
And welcome aboard.
Click to expand...
Two.jpg
Two-1.jpg
 
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#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 .....

www.compcams.com

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 www.compcams.com
 
#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 .....

www.compcams.com

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 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.....
 
#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!!!
 
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#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:

 
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