How to Time a Big Block Chevyby Don Bowman
Big-block Chevy timing is pretty well standardized unless major modification have been done. The timing on stock 396, 402, 427 and 454 engines is 32-34 degrees total advance at 3500 rpm. This is for an engine with stock camshaft, heads, stroke, and a compression ratio of 10:1. The high-performance versions are slightly higher with a maximum advance of 38 degrees on premium fuel, if the camshaft warrants it. It depends on the overlap of the valves as in a split centerline and total advance on the intake valve. Total advance is the most important setting; however, the engine runs better at an idle and off-idle retarded to an average of 18 degrees BTDC with the vacuum advance operating.
Find and identify top dead center on the timing plate, located on the timing cover. Top dead center will be 0 or a V shaped cutout on the plate. Mark the timing line on the harmonic balancer with a white marker to ease visual identification while timing. Connect the timing-light red lead to the positive terminal on the battery and the black lead to the negative. Connect the remaining end with the snap to the number-one spark plug wire, which is the closest wire to the radiator on the driver's side. Move all wires clear of all moving or hot parts and lay the timing light on the driver's fender.
Loosen the distributor hold-down plate using the 9/16-inch distributor wrench. Loosen the distributor just enough so that it can be rotated with little force, but will stay in place. Rotating the distributor counterclockwise will advance (increase) the timing. Rotating the distributor clockwise will retard (decrease) the spark timing. Start the engine and allow it to warm to operating temperature.
Shine the timing light carefully down the driver's side of the front of the engine at the harmonic balancer. Turn the timing knob on the timing light until the white line on the balancer is lined up with the 0-degree mark on the timing plate. Read the number under the pointer on the knob on the back of the timing light. This is the number of degrees before top dead center at an idle. The timing should be close to 18 degrees BTDC.
Grab the throttle linkage and raise the rpm to 3500 momentarily, and turn the knob again to bring the white line on the balancer to 0 or TDC. Bring the engine back to an idle and check the reading on the light. If the total timing is less than 32 degrees, rotate the distributor counter-clockwise to advance and check again. The opposite goes for a timing that is too high. Once set, re-tighten the distributor hold-down bolt.
Shut the engine off and give it a few seconds to rest, then start the engine again. If the engine seems to hesitate when turning over, the timing is too advanced or the vacuum-advance plate is stuck in advance.
Set the timing on modified engines with the procedure used in Steps 1 through 5 to start, followed by the advance-to-miss method. This has been proven to be the most popular method at all the racetracks. It takes a sense of feel and sound and can be incredibly accurate. With the engine running and warmed up, stand on the passenger side of the car. Place the right hand on the throttle linkage and the other on the distributor base.
Rev the engine to 3000 rpm and hold it there while rotating the distributor counterclockwise just until it begins to stumble. Turn the distributor clockwise until the engine rpm begins to slow down and stumble. Rotate the distributor counterclockwise again until the point of stumble and reverse the rotation just until all stumble is gone. Continue to rotate the distributor another ten degrees clockwise. Shut the engine down and give it a few seconds to cool, and restart. If there is no timing hesitation when starting, re-tighten the distributor hold-down bolt.
Drive the car and listen for pre-detonation (pinging). If there is pre-detonation, back the timing down just a few degrees and retry. If there is no pre-detonation, try advancing the distributor a few degrees and drive it again.
Things You'll Need
- 9/16-inch distributor wrench
- Advance timing light
- Whiteout or white paint or marker
Don Bowman has been writing for various websites and several online magazines since 2008. He has owned an auto service facility since 1982 and has over 45 years of technical experience as a master ASE tech. Bowman has a business degree from Pennsylvania State University and was an officer in the U.S. Army (aircraft maintenance officer, pilot, six Air Medal awards, two tours Vietnam).