Editing Hot rodding the HEI distributor (section)
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==Parts of the HEI system== ===Cap and rotor=== Use caps and rotors that have brass terminals. Aluminum is cheaper- but in this case you really do get what you pay for. The center carbon electrode button, or "rotor bushing" in the drawing below is what transmits the current from the coil to the rotor, and should be a quality part. Cheap/offshore buttons can have excessive resistance; this causes heat and can in extreme cases melt the surrounding plastic of the cap and the engine will quit. The button has to be assembled into the cap first, then the rubber insulator. The small spring on the button goes against the bottom of the coil. Use dielectric grease on both sides of the rubber insulator. [[File:HEI CAP- ELECTRODE- INSULATOR- COIL DIAGRAM.jpg|thumb|330px||Drawing of cap and coil, related parts.]] ===Coil=== On the coil-in-cap GM HEI, the coil is located on top of the distributor between the plug wire towers under a plastic cover. Stock, it's capable of about 35,000 volts and so-so total spark energy. It's fine for a naturally aspirated street engine that uses a 0.035"-0.040" plug gap and has a compression ratio compatible with pump gasoline (</= ~10:1), and has a redline of around 5500 RPM. You can upgrade the coil with an aftermarket replacement that can produce more volts and total spark energy. On low budget builds, a replacement coil and module may give adequate performance, depending on the application. There are 2 different designs of the HEI coil. The only external difference is that one has red and white power leads, the other has red and yellow power leads. You will need to know which one of these you have stock to order up the appropriate aftermarket coil. ====Coil ground==== The coil is grounded through the center terminal of the connector under the coil cover. This ground may be a wire or a solid strap, as shown below. [[File:Hei coil ground center term.jpg]] ===Module=== This will be covering the 4-pin HEI module. There were also 5- and 7-pin modules used on computer-controlled applications, however they do not generally lend themselves to non-computer-controlled high performance applications. The module is the electronic controller that takes the place of breaker points. It is located under the distributor cap secured by a pair of screws. One of these screws also acts as a ground path. The module will have four wires going into it (two per side). The module senses the magnetic pickup signal from the magnetic pickup assembly and uses this signal to know when to trigger the coil. The module also controls how much "dwell" the coil receives between firings. A Delco module is a good choice for street/performance applications and is preferred over an auto parts store non-GM/Delco replacement, possibly unless it's a performance replacement. There have been reports of various quirks associated with some aftermarket modules, so research them beforehand. From "yeti" @ yellowbullet.com: <blockquote> The HEI modules vary the dwell to eliminate the need for a ballast resistor. This prevents the coil from overheating at low engine speed when a fixed dwell system would leave the coil turned on so long as to over-saturate it and cause excess heat.<br><br> The actual “Genuine GM” module controls the dwell by monitoring the signal from the pickup with an R/C circuit. Many aftermarket modules accomplish dwell control by measuring the amperage to the coil and cut the dwell to limit it to a preset amount. “High performance” modules have a higher amperage cut-off point to “optimize high RPM performance”. This can result in a situation where if a vehicle has low voltage or high resistance in the primary wiring to the coil, the module will increase the dwell time to the maximum, which approaches 45º and allows no time for the spark to burn. (Sort of an electronic version of "the rubbing block is worn out and the points are closed up”.)<br><br> Old points vehicles had approximately 30° of points closed time, which made 15° available for the spark to burn. The coil can't discharge when the “points” are closed, mechanical or electronic, because when they are closed it is grounded. </blockquote> ====Module part numbers==== Some part numbers for a stock-type "990" series module: *ACDelco D-1906/GM p/n 10482820 (used in the GM ZZ4 crate engine) *Standard Ignition/Bluestreak p/n LX-301 *Borg Warner CBE4 *Echlin TP-45 *Standard LX-301 [[File:HEI modules1.jpg|frame|left|If looking for an HEI, choose one that has the 4-pin module seen at upper left, above. The other modules all require an ECM to function correctly.]] <br style="clear:both"/> Use a [http://www.arcticsilver.com/as5.htm '''heat sink paste'''] (available from Radio Shack and computer shops) on the bottom of the module and be sure the surface of the distributor body where it mounts is clean. The heat sink compound (not ''dielectric grease'') helps transfer the module heat into the distributor body which acts as the heat sink. Failure to do this can lead to an early failure of the module. [[File:Artic Silver heat sink compound5.jpg|none|400px]] <br style="clear:both"/>
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