73 BB Vacuum

[Lynn S.]

Just got my 73 454 running after engine rebuild. Auto, Manual brakes, AC. How much vacuum should I have off the intake manifold? Cannot get enough vacuum to the front resevoir tank to make the headlights work? Thanks, Lynn Schwebach

[Mark E.]

Re: 73 BB Vacuum

The stock LS4 cam is a mild, low overlap hydraulic, so it creates plenty of vacuum for the car's accessories...expect 14" - 17" at idle.

Before blaming the engine for low vacuum, look for leaks in vacuum system. Start by disconnecting the supply lines at the intake and see if produced vacuum changes. If yes, leak check the car's vacuum system.

[Duke W.]

Re: 73 BB Vacuum

Maybe some moron installed a high overlap cam, and perhaps you know who it was. Measure and report vacuum idling in neutral if a manual trans and in DRIVE if a TH400. Be sure to specify the SPEED that you measure vacuum or your measurements are MEANINGLESS.

Duke

[Owen L.]

Re: 73 BB Vacuum

Just got my 73 454 running after engine rebuild. Auto, Manual brakes, AC. How much vacuum should I have off the intake manifold?

My nearly stock rebuild of my '72 454 LS-5 has about 18" at the manifold port. It could be an inch or so to either side of that but I recall it's a healthy pull.

Edit: as admonished below: at idle, ~750rpm, in park.

[Duke W.]

Re: 73 BB Vacuum

Your vacuum reading is MEANINGLESS because you didn't state the engine speed at which is was measured!

Didn't I just say that?

Also you need to specify whether it's a manual or auto trans. Manuals should be measured in neutral and autos in DRIVE!

Duke