1966 BB Vacuum Specifications

[Mark Zediker]

I have a 1966, 427 / 435 motor and I have been trying to set the timing. Setting it according to factory specs with a timing light has produced poor results including overheating. I adjusted the timing until the vacuum was maximized at idle, with the idle running at spec. No overheating at idle like it did when set according to specs. The problem is the timing mark on the harmonic balancer is now past the end of the scale on the block. I suspect the harmonic balancer needs to be replaced, but I want to make certain I have not made a simple mistake, so it is best to ask a few questions. I am using premium fuel, 93 octane plus a 2 octane number (not points) booster to give 95 octane. The engine is completely stock except the exhaust manifold was replaced with headers and factory side exhaust system. I am measuring the vacuum from the manifold not the carb vacuum advance port. After a cold start, the engine runs at 1500 rpm and the vacuum measures 18". After it warms up, the vacuum falls back to 12" and the idle is at 800 rpm. The engine runs strong with no pinging when loading the engine at low rpm. The valves were recently adjusted with the engine hot. There are no apparent vacuum leaks around the carb or manifold. The problem is this vacuum reading seems low to me, but this is the first 427 I have played with. So, does anyone know what the manifold vacuum should be at idle

[Duke W.]

Re: 1966 BB Vacuum Specifications

All '66 L-72's, CA and 49-state configuration, have ported vacuum advance, so there is none at idle. Buy a foot or so of 1/8" tubing and build a new vacuum can and choke vacuum break harness by teeing them together. This will provide full time vacuum advance and lower idle and low speed operating temperatures.

With the vacuum can disconnected set the initial timing at 10 degrees at less than 800. Be sure it is not into the centrifugal advance by increasing revs after the timing is set. It should not begin to advance until higher than the speed you set the timing at.

Now connect the vacuum can and set the idle speed and mixture.

Recommend idle speed of 800-900. Your manifold vacuum should be about 14-15"

Duke

[Mark Zediker]

Re: 1966 BB Vacuum Specifications

Thanks for the suggestion and the info.

Mark