NastyZ28.com - GM Ignition System Tuning
There were two types of ignition systems used by GM during the 1970s: 1) the old style single point Delco-Remy distributor, and 2) the High Engergy Ignition (HEI) distributor. You should consider using the HEI if you have one handy, however we're supposed to be saving money by using what we have on hand... anyway, the concepts or tuning objectives will be similar for either model distributor. If you decide to change to an HEI distributor, make sure your tach is compatible with the transistorized HEI.
The ignition system on smogged motors is very retarded. Advance is usually still zero (0) at 1000 rpm, and full (10 degrees) at 4000 rpm.
In general, you want full advance around 2000 - 2400 rpm for good throttle response and good performance throughout the engines rpm range. On the other hand, dialing in too much advance too quickly will burn holes in your pistons if you're not careful.
Other items which affect how quickly you want the advance to come on are compression, rear axle ratio & gasoline quality. High octane gas can help prevent detonation even on engines with radical timing dialed into the distributor.
Remove the stock centrifugal weights and springs. Replace them with high performance (heavier weights, lighter springs) items. Lubricate the centrifugal weight base and distributor cam lobes.
With the new weights and springs, advance should begin just off idle and be fully advanced (13 degrees) at around 2000 rpm. Set dwell at 28 degrees, replace the cap and rotor with a quality cap with brass contacts.
Look at electrode for excessive burning.
Look inside header primaries from the flange side, you'll get an indication of flow distribution and fire.
First, get a baseline in timing, if you want more off the line and less top end, advance the timing a degree at a time, just remember running out of timing on the bottom end, limits your amount of timing on the top end.
Once you establish a baseline, check the ignition and decide on a starting point. In most cases 34 - 36 degrees total timing will be in the ballpark.
Author: MadMike Maciolek
North Georgia Classic Camaro
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