Dwell angle is the amount of time (measured in degrees of distributor cam rotation) that the contact points in the distributor remain closed. Initial point gap determines dwell angle. If the points are set too wide, they open gradually and dwell angle (the time they remain closed) is small. This wide gap causes excessive arching at the points, and, because of this, point burning. This small dwell doesn't give the coil sufficient time to build up maximum energy and so coil output decreases. If the points are set too close, the dwell is increased, but the points may bounce at higher speeds and the idle becomes rough and starting is made harder. The wider the point opening, the smaller the dwell, and the smaller the point gap, the larger the dwell. Thus, a point gap of 0.019 in. on a V8 engine might produce a dwell of 28°, while a gap of 0.016 in. might produce a dwell of 34°. Adjusting the dwell by making the initial point gap setting with a feeler gauge is sufficient to get the car started, but a finer adjustment should be made. To make this adjustment, you need a dwell meter
Dwell angle is permanently set electronically on HEI distributors, requiring no adjustment or checking.
Six Cylinder Engines
- Install the new points as outlined earlier.
- Connect the dwell meter by hooking up one lead (usually black) to a good ground somewhere on the engine; connect the other lead (usually red) to the coil primary post. This is the one with the small wire that leads to the distributor.
- If the dwell meter has a set line, adjust the meter needle until it rests on the line.
- Start the engine and let it warm up. The dwell is checked with the engine idling.
- Check the dwell angle with the engine at an idle. If it needs adjusting, shut the engine off, and readjust the point gap. Start the engine back up and check the dwell again. Both point gap and dwell angle can be found in the specifications chart.
- Once you get the dwell correct, set the ignition timing. Remember that changing the dwell changes the ignition timing although changing the timing does not affect the dwell angle. Therefore, dwell angle adjustment must always be done before timing adjustment.
- After installing the points, hook up the dwell meter by connecting one lead (usually black) to a good ground and the other lead (usually red) to the distributor side of the coil If the dwell meter has a set line, adjust the needle until it rests on the line.
- Start the engine and let it warm up. The engine should be idling at normal operating temperature when the dwell is set.
- Raise the adjusting window on the distributor cap and insert a 1 / 8 in. Allen wrench into the adjusting screw. Better yet, use a long-handled flexible adjusting tool.
- Turn the adjusting screw until the specified dwell angle is obtained on the dwell meter. On 455 motors, it is easier and safer to shut the engine off while you are making the adjustments.
- Once the dwell is correct, adjust the ignition timing.