What should timing be with vacuum advance?
What should timing be with vacuum advance?
This can be checked with the engine running at idle with a timing light. Make sure the vacuum advance connection is removed, and now rev the engine up to around 2,500 to 2,800 rpm. Ideally, the timing now should be somewhere around 34 to 36 degrees to total advance.
When to set initial timing on Summit HEI distributor?
We prefer to set the initial timing for most engines at 10 degrees Before Top Dead Center (BTDC). With that set, remove the cap from the distributor. We’re using a Summit HEI distributor.
Where is the VAC port on a Hei Trans?
Leave your trans hooked up to the full/manifold vac source on the carb baseplate. Hook your HEI up to the ported (part-time) vac port on the pass side front metering block port. No vac at idle, so you can set your initial timing and idle speed without any vac intterference. On this port, you only get vac advance when you hit the gas.
What does vacuum advance have to do with total timing?
Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the “total timing” equation.
How to install a distributor and set initial timing?
Leave a little extra room with the spark plug wires to allow freedom of movement in the distributor. For Chevys, be careful to make sure 5 and 7 are installed correctly. If the wires are accidentally switched, the engine will not be happy. Before we try to start the engine, be sure the distributor is connected to switched power.
We prefer to set the initial timing for most engines at 10 degrees Before Top Dead Center (BTDC). With that set, remove the cap from the distributor. We’re using a Summit HEI distributor.
Where does the HEI hook up to the VAC port?
Hook your HEI up to the ported (part-time) vac port on the pass side front metering block port. No vac at idle, so you can set your initial timing and idle speed without any vac intterference. On this port, you only get vac advance when you hit the gas.
How does vacuum advance timing work on a street car?
On a street car, a vacuum-advance and a centrifugal-advance system are used. The vacuum advance increases timing as the vacuum created by the engine increases (idle and low-load conditions). As engine load or throttle position increases, the vacuum decreases, and so does vacuum advance timing.
What happens to vacuum timing as engine load increases?
As engine load or throttle position increases, the vacuum decreases, and so does vacuum advance timing. The centrifugal advance adds advance up until about 3,000 – 3,200 rpm, and is not attached to vacuum advance. Centrifugal advance keeps the combustion process in time with the piston location.
