Ignition Systems - Ignition Magician - Pontiac Tech

Myth 5:I Don't Need No Stinking Vacuum Advance!Reality:For Best Cruise Efficiency, Yes You DoMany HPP readers believe that a vacuum advance has no place on a modified Pontiac, but each engine should be looked at individually. As you read in "Advancing Opportunity" in the Oct. '06 issue, the purpose of a vacuum-advance unit is to increase the ignition lead under part-throttle, light-load conditions when the volumetric efficiency (VE) or cylinder fill of the engine is low. VE impacts cylinder turbulence and thus the flame or burn speed. Low levels of VE mean slower burn speeds and a need to advance the ignition timing for the best throttle response, power, and fuel economy. At wide-open throttle (WOT), there is no pressure differential in the engine, so the vacuum advance has no impact on the timing curve.

Lower compression-ratio engines (10:1 and below) usually benefit the most from a properly tuned vacuum-advance unit. The first step is to connect a manifold-vacuum gauge. Drive around with the gauge duct-taped to the windshield and note the readings. If there are at least 5 inches of mercury present under most driving conditions, the engine will probably respond to a vacuum-advance unit. Try connecting the distributor advance to a full-time (manifold) vacuum source and then a ported (timed) outlet, as was done in "Advancing Opportunity." As you saw, the engine will let you know which one it likes better. A manifold-vacuum source will provide advance at idle and then ramp off slowly as load is applied to the engine.

Myth 6:All Hei Modules Are Created EqualReality:Not All Hei Modules Are Created EqualHEI is a brand name for High Energy Ignition, which was first introduced by General Motors on some '74 models. Though other makers had electronic ignition prior to this, namely Chrysler in '73, HEI stood alone as a brilliant new theory. Designed with transistors that would survive on full battery voltage, HEI didn't use any resistor to drop the system's running voltage. In addition, a unique concept called "expanding dwell" was incorporated. Unlike the other early Detroit electronic-ignition systems that used a fixed dwell time just as breaker points did, HEI increased the dwell period as engine speed was raised. On a V-8 Pontiac at idle, the module dwell (on time) would be 5-10 degrees and expand to 30-35 degrees by 2,500 rpm. The higher input voltage along with increased coil saturation (dwell) allowed HEI to fire the spark plug longer and with a larger gap. The increased gap created a larger ionization window, and since the ignition was very powerful, allowed a longer burn time. Higher ionization voltage with longer burn times equals more power, better fuel economy, and a smoother idle.

Just because an HEI-equipped engine runs doesn't mean the module is operating properly. To check the system, hook your old breaker-points-style dwell meter to the tach terminal on the distributor cap, and read the dwell scale at idle and as the rpm increases. Cheap replacement modules often do not have the proper dwell period and thus impact performance. This simple test should be part of a performance diagnostic routine, performed with every tune-up. However, if the engine has a capacitor discharge (CD) box, the current draw will cause the HEI module to assume a fixed dwell of around 35 degrees, making this test invalid.

Myth 7:The Bigger The Spark Plug Wire, The Bigger The CoreReality:This Is Often Not SoCommon sense would dictate that thicker spark plug wire can transport more electricity. That would be true if the mm dimension described the size of the core, but contrary to what many think, it represents the thickness of the insulation. A 7mm wire has thinner insulation than a 10mm design. Core and resistance specs are manufacturer-specific so all plug wires are not created equal. The benefit of thicker insulation is less radio frequency interference (RFI) and electromotive interference (EMI) and greater thermal protection. Interference can be thought of as stray voltage leaking from the wire. Some may argue that since electricity takes the path of least resistance, thicker insulation is required to keep the electrons flowing to the spark plugs on a very high cylinder-pressure application, and that is true. But don't look for any gain on your 350hp Pontiac by switching to a wire with thicker insulation.

Myth 8:Misfire? I Know What That MeansReality:Misfire Is Often MisunderstoodThe term misfire is used improperly by many hobbyists. It describes an ignition event when either the spark isn't jumping the gap of the plug instead going to ground, or there is a very short burn cycle of the ignition. Many factors can cause a non-ignition-related misfire, especially an excessively lean mixture. When there is not enough fuel present in the combustion chamber, the flame cannot travel across the bore, so it extinguishes even though the spark plug is still arcing. This causes a rough idle, lack of power, and poor driveability. When diagnosing a misfire, you need to determine if it's an ignition problem or a mechanical issue that is preventing the ignition from working properly.