Editing Determining top dead center (section)
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==Timing the engine== Hook up your timing light to #1 plug wire. Remove the vacuum advance rubber hose from the vacuum canister at the distributor and plug the end of the hose with a golf tee or other suitable plug. Adjust initial timing at the crank to what you want by rotating the distributor housing. Some use the factory setting while others prefer to set it a little more advanced for good throttle response. If using a little more initial advance at the crank, make certain you don't have so much mechanical advance in the distributor that you exceed the total timing (initial and centrifugal) specified for the engine. Most small block Chevy's will run best with around 30-34 degrees (initial and centrifugal) with fast-burn heads and 35-36 degrees with conventional heads. If using a camshaft with more duration, you may want to increase the ignition timing lead at the crank and limit the centrifugal advance in the distributor to achieve your total ignition timing. Some distributors, like those sold by MSD, use different bushings to control the ''amount'' of mechanical advance. The '''rate''' of mechanical advance is tailored by changing the springs and/or centrifugal weights. Usually just spring changes are all that is needed. If working on a GM HEI, the original weights are almost always a better choice than the weights sold in the various advance curve kits available from Mr. Gasket, Crane, Summit, Moroso, etc. If you are using a radical cam and/or a converter that allows the engine RPM to come up past where you would normally limit centrifugal advance (about 2800 rpm), you may want to modify the distributor so that centrifugal advance is locked out and put your total amount of ignition advance in at the crank. Of course, the engine will not want to crank against this much ignition lead, so you will want to install a momentary switch in the wire going to the "+" terminal of the coil to disable the coil while you crank the engine. Once the engine is spinning, release the switch and the engine will fire normally.
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