Higher ratio rocker arm?

[88bluestar]

Trying to gain about 3 hg of vacuum in regards to rules.

Would increasing rocker ratio on just intake help increase vacuum?
1.5 to 1.6

Lighter weight oil etc make any difference to vacuum?

[Tom68]

Opposite, if any change at all.

Lighter oil may help, not 3" though.

What's your current idle ignition advance ?

[mag2555]

How does the motor leak down test?
No reason you can not have 3% if the motor is built right and or fresh.

With heads off the motor if you pour rubbing Alky into the all 16 ports do any of the valves leak within 5 minutes?

What's your compression ratio, are you at the rule limits?
The smaller the chamber the more vacuum you will have .

[Tom68]

3'' that's probably 20 odd % depending on what the minimum requirement is.

That's a cam change unless he knows of others making the required vac with that cam.

[CamKing]

Things you can do to increase vacuum.
Increase valve lash
Lean idle circuit
Advance timing
Change carb

[Horder]

Dual plane? I just gained 1.5” by going from a 3/8” open spacer and a 3/16” milled down to divided to a full divider and a 1/2” 4 hole spacer.

[Walter R. Malik]

Trying to gain about 3 hg of vacuum in regards to rules.

Would increasing rocker ratio on just intake help increase vacuum?
1.5 to 1.6

Lighter weight oil etc make any difference to vacuum?

Running a distributor with working vacuum advance on the engine will help the most.

[Mummert]

Raising idle speed helps vacuum.

[Tom68]

If it's a vac rule motor there should be a stipulated rpm reference.

[PackardV8]

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[88bluestar]

14hg @ 900 rpm.

Crower cam saver hydraulic lifters, sbc.


I have a new cam, lifters and valvesprings through JRC-Jones, but not sure ill have time this week to get them changed out, so im looking for temporary way to increase at least the vacuum so its close enough to 14.

[In-Tech]

Things you can do to increase vacuum.
Increase valve lashyes
Lean idle circuitNo, use a vacuum gauge and give it whatever it wants/likes, Mike is correct to a point. Higher overlap cams don't like stoich
Advance timingYes, 32 degrees should be common at 900 rpm idle
Change carb

[88bluestar]

Would smaller vacuum port diameter make a difference. Hidden plug inside a 3/16 port with a much smaller hole?

[Rick!]

Would smaller vacuum port diameter make a difference. Hidden plug inside a 3/16 port with a much smaller hole?

No. The vacuum gauge deadheads the port so there is no flow. So, a smaller hole does not affect the vacuum gauge measurement. It may slightly dampen pulses, if present.

[RCJ]

I was in tech with the late model one night. I was watching them tech vacuum on pure stocks. The tech told the driver to raise the rpm a certain amount. The driver put his hand over the top of the 2 barrel like a choke.and worked the throttle with his thumb. I've always wondered if a manual choke work to raise vacuum.