Hot rodding the HEI distributor

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[[File:GM Performance pn 93440806 HEI distributor11.jpg|thumb|300px||GM Performance p/n 93440806 HEI distributor.]]  
 
[[File:GM Performance pn 93440806 HEI distributor11.jpg|thumb|300px||GM Performance p/n 93440806 HEI distributor.]]  
 
    
 
    
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===What vehicles came stock with a non-computer controlled HEI?===
 
===What vehicles came stock with a non-computer controlled HEI?===
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All carbureted GM engines in cars built from 1980 to about 1974-'75 and trucks from 1986-back use this type HEI distributor. Newer HEI distributors used the ECM and had no mechanical advance provisions, although early computer-controlled HEI distributors retained vacuum advance in some cases. These later HEI distributors are not covered in this article, other than to say they're generally not used in performance applications unless used a just a trigger for an aftermarket ignition amplifier box or with a modified computer.
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All carbureted GM engines in cars built from 1980 to about 1974-'75 and trucks from 1986-back use this type HEI distributor. Newer HEI distributors (1981-86 for passenger cars exc. some 1987/88 B and G-body passenger cars with 305s (or 9C1 Caprices with 350s) with the EST (electronic spark timing) small cap/external coil distributor associated with TBI (throttle body injection) induction) used the ECM and had no mechanical advance provisions (these distributors have a 7 pin module), although early computer-controlled HEI distributors retained vacuum advance in some cases. 1981-86 trucks/vans with 305s (RPO LB9) used a variation of the computer controlled HEI with electronic spark control with 5 pin modules. These later HEI distributors are not covered in this article, other than to say they're generally not used in performance applications unless used as just a trigger for an aftermarket ignition amplifier box or with a modified computer.
  
 
===Aftermarket HEI distributors===
 
===Aftermarket HEI distributors===
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To use the interrupter, the switch is depressed (or toggled, depending on the design) and the engine is cranked via the key/starter switch. Once the engine is turning over, the switch is released. This powers up the ignition and the engine will start without kickback.
 
To use the interrupter, the switch is depressed (or toggled, depending on the design) and the engine is cranked via the key/starter switch. Once the engine is turning over, the switch is released. This powers up the ignition and the engine will start without kickback.
  
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====Starter brace====
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====Using a relay====
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A relay that delays the ignition from being energized- giving the starter time to get the engine turning over- can be wired into the ignition feed wire. These relays may be found from any number of suppliers, one is [http://www.wolstentech.com/index.php Wolsten Tech] out of New Jersey.
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===Starter brace===
 
{|
 
{|
 
|[[File:Sbc starter brace.jpg|thumb|330px|left|SBC starter brace]]
 
|[[File:Sbc starter brace.jpg|thumb|330px|left|SBC starter brace]]
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===Coil===
 
===Coil===
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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.  
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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.  
  
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You can upgrade the coil with an MSD replacement coil that has a potential of about 42,000 volts and total spark energy will also jump about 10-15%. There are even hotter coils than this from the aftermarket that will give more total spark energy. On low budget builds, a replacement coil and module may give adequate performance, depending on the application. And it could be cheaper than a MSD-type ignition amplifier.
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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.
 
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.
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For high performance, blown or nitrous applications it is recommended to use an MSD (or equivalent) ignition amplifier box setup along with high quality plug wires.
 
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====Coil ground====
 
====Coil ground====
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*Standard LX-301
 
*Standard LX-301
  
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[[File:HEI modules1.jpg|frame|left|If looking for an HEI, choose one that has the 4-pin module seen at upper right, above. The other modules all require an ECM to function correctly.]] <br style="clear:both"/>
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[[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.  
 
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"/>
 
[[File:Artic Silver heat sink compound5.jpg|none|400px]] <br style="clear:both"/>
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==Testing the HEI components==
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'''[http://www.wellsve.com/ecatalog.html Wells catalog to be used for looking up representative part numbers to find specs for testing]'''.
  
 
===Pick-up coil assembly===
 
===Pick-up coil assembly===
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[[File:HEI pick up coil assy.jpg|thumb|left|300px|HEI pick-up coil assembly.]] The pick-up assembly doesn't often fail internally, however the small gauge wires that connect to the end of the 4-pin module get flexed each and every time the vacuum advance retracts or extends- in other words, millions of times during its lifetime. Because of the flexing and the stiffening of the insulation from heat over time, the wires inside the insulation can break. This will often manifest itself as a sporadic, transient miss or stall condition that might seem unrelated to the ignition system.
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[[File:HEI pick up coil assy.jpg|thumb|300px|HEI pick-up coil assembly.]] The pick-up assembly doesn't often fail internally, however the small gauge wires that connect to the end of the 4-pin module get flexed each and every time the vacuum advance retracts or extends- in other words, millions of times during its lifetime. Because of the flexing and the stiffening of the insulation from heat over time, the wires inside the insulation can break. This will often manifest itself as a sporadic, transient miss or stall condition that might seem unrelated to the ignition system.
 
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<br style="clear:both"/>  
  
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===Testing the HEI components===
 
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'''[http://www.wellsve.com/ecatalog.html Wells catalog for looking up representative part numbers to be used to find specs for testing]'''.
 
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;Pick-up coil<nowiki>:</nowiki>
 
 
[http://www.wellsmfgcorp.com/ds_pcoils.php?showall=yes '''Wells'''] has information on what the various pick up coils should read for resistance. Find part numbers from the Wells parts catalog PDF above.  
 
[http://www.wellsmfgcorp.com/ds_pcoils.php?showall=yes '''Wells'''] has information on what the various pick up coils should read for resistance. Find part numbers from the Wells parts catalog PDF above.  
  
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If the meter jumps around as the wires are flexed, or if the resistance is drastically higher or lower than 600Ω-1000Ω (or is infinite), or if there is a reading between either wire and the metal case of the pick-up coil, it's bad.
 
If the meter jumps around as the wires are flexed, or if the resistance is drastically higher or lower than 600Ω-1000Ω (or is infinite), or if there is a reading between either wire and the metal case of the pick-up coil, it's bad.
  
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;Coil (from [http://www.hotrodders.com/forum/testing-hei-coil-module-103662.html#post727460 docvette])<nowiki>:</nowiki>
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===Coil===
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[http://www.hotrodders.com/forum/testing-hei-coil-module-103662.html#post727460 Coil test procedure] written by docvette
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Find part numbers from the Wells parts catalog PDF above.  
 
Find part numbers from the Wells parts catalog PDF above.  
  
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Next measure the secondary side of the coil:
 
Next measure the secondary side of the coil:
 
*Set your DVOM scale to RX10K or higher.  
 
*Set your DVOM scale to RX10K or higher.  
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*Put the probes between the BATT terminal of the coil and the carbon pickup inside the distributor cap. It should read between 6000Ω and 30,000Ω. Outside of that range toss the coil and get a new one.
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*Put the probes between the Ground terminal of the coil and the carbon pickup inside the distributor cap. It should read between 6000Ω and 30,000Ω. Outside of that range toss the coil and get a new one.
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Test carbon pickup between carbon end and spring end - resistance will be 4000- 6000 ohms
  
 
[[File:HEI cap.jpg]]
 
[[File:HEI cap.jpg]]
 
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;Module<nowiki>:</nowiki>
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===Module===
 
Many parts stores can test the HEI ignition module at no charge. If that isn't possible, another way is to replace the module with a known good module.
 
Many parts stores can test the HEI ignition module at no charge. If that isn't possible, another way is to replace the module with a known good module.
  
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==Initial advance==
 
==Initial advance==
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The first thing to do is set the initial advance correctly- that often means an initial advance of between 12 and 24 degrees, with the remainder coming from the mechanical advance.  
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The first thing to do is set the initial advance correctly- that often means an initial advance of between 12 and 24 degrees (depending on mainly the camshaft), with the remainder coming from the mechanical advance.  The more radical the camshaft, the higher the initial advance for a given compression ratio.  
  
 
===Effect of initial timing on carb tuning===
 
===Effect of initial timing on carb tuning===
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===Limiting or locking the mechanical advance mechanism===
 
===Limiting or locking the mechanical advance mechanism===
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In many cases, the mechanical advance has to be modified to shorten the amount of advance it can give, After determining how much mechanical advance your HEI is giving you, and it's determined it's too much for the amount of initial advance you want to run, the mods to the mechanical advance are shown in the image below (thanks to 69-CHVL of [http://www.chevelles.com/forums/ Team Chevelle]).  
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In many cases, the mechanical advance has to be modified to shorten the amount of advance it can give. After determining how much mechanical advance your HEI is giving you, and it's determined it's too much for the amount of initial advance you want to run, the mods to the mechanical advance are shown in the image below (thanks to 69-CHVL of [http://www.chevelles.com/forums/ Team Chevelle]).  
  
 
[[File:HEIadvlimitlock2.jpg|thumb|left|400px|]] <br style="clear:both"/>
 
[[File:HEIadvlimitlock2.jpg|thumb|left|400px|]] <br style="clear:both"/>
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You can run without a vacuum advance but expect your highway mileage to suffer, possibly more. And your plugs can develop carbon deposits within just a few thousand miles. For a race or a weekend street/strip vehicle this is probably no big deal, as long as fresh plugs are installed when needed. For a daily driven street car, using a vacuum advance is always recommended.
 
You can run without a vacuum advance but expect your highway mileage to suffer, possibly more. And your plugs can develop carbon deposits within just a few thousand miles. For a race or a weekend street/strip vehicle this is probably no big deal, as long as fresh plugs are installed when needed. For a daily driven street car, using a vacuum advance is always recommended.
  
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{{Note1}} See link '''[[Hot rodding the HEI distributor#Resources|HEI-type vacuum advance can specs]]''', below.
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{{Note1}} See link '''[[Hot rodding the HEI distributor#Resources|HEI vacuum advance specs]]''', below.
  
 
===Vacuum advance for the street===
 
===Vacuum advance for the street===
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If there is no EGR being used, the amount of vacuum advance needed will be around 10-12 degrees. In many cases that means there can be as much as 50 degrees of advance when the engine is cruising under a light load. Crane has an adjustable vacuum advance can kit, [http://www.summitracing.com/parts/CRN-99600-1 p/n 99600-1]. Another adjustable vacuum advance can for the GM HEI is the Accel [http://www.summitracing.com/parts/ACC-31035/ p/n 31035] that is said to allow infinite adjustment to both the amount and rate of advance. Comes with instructions and an allen wrench to adjust it.  
 
If there is no EGR being used, the amount of vacuum advance needed will be around 10-12 degrees. In many cases that means there can be as much as 50 degrees of advance when the engine is cruising under a light load. Crane has an adjustable vacuum advance can kit, [http://www.summitracing.com/parts/CRN-99600-1 p/n 99600-1]. Another adjustable vacuum advance can for the GM HEI is the Accel [http://www.summitracing.com/parts/ACC-31035/ p/n 31035] that is said to allow infinite adjustment to both the amount and rate of advance. Comes with instructions and an allen wrench to adjust it.  
  
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Another thing that is often overlooked, is if the cruise rpm is less than the rpm where the mechanical advance is all in by, the vacuum advance has to make up the difference to get the best mileage and drivability. This is something n adjustable vacuum advance can help; adjusting it to give advance at a vacuum level just below the vacuum seen at cruise RPM will let the engine run smoother and get better mileage.
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Another thing that is often overlooked, is if the cruise rpm is less than the rpm where the mechanical advance is all in by, the vacuum advance has to make up the difference to get the best mileage and drivability. This is something an adjustable vacuum advance can help; adjusting it to give advance at a vacuum level just below the vacuum seen at cruise RPM will let the engine run smoother and get better mileage.
 
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*14-18 degrees initial advance
 
*14-18 degrees initial advance
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*22-18 degrees centrifugal
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*18-22 degrees centrifugal
 
*10-12 degrees vacuum advance
 
*10-12 degrees vacuum advance
 
*Mechanical advance all in by =/< 3000 RPM  
 
*Mechanical advance all in by =/< 3000 RPM  
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*[http://www.rustynutscarclub.com/HEI.htm Description of an HEI rebuild]
 
*[http://www.rustynutscarclub.com/HEI.htm Description of an HEI rebuild]
 
'''''Return to: [[Hot rodding the HEI distributor#Distributor shaft end play adjustment|Distributor shaft end play adjustment]], above'''''
 
'''''Return to: [[Hot rodding the HEI distributor#Distributor shaft end play adjustment|Distributor shaft end play adjustment]], above'''''
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*[http://www.hotrodders.com/forum/centrifugal-advance-177478.html HEI-type vacuum advance can specs]
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'''''Return to: [[Hot rodding the HEI distributor#Vacuum advance|Vacuum advance]], above'''''.
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*[[Media:Vacuum Advance Specs.pdf|HEI vacuum advance specs]]
 
*[http://www.corvetteforum.com/techtips/viewsubtopic.php?SubTopicID=115&TopicID=3 GM points-type vacuum advance can specs and info (Lars)]  
 
*[http://www.corvetteforum.com/techtips/viewsubtopic.php?SubTopicID=115&TopicID=3 GM points-type vacuum advance can specs and info (Lars)]  
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'''''Return to: [[Hot rodding the HEI distributor#Vacuum advance|Vacuum advance]], above'''''.
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;Crankshaft Coalition wiki articles<nowiki>:</nowiki>
 
;Crankshaft Coalition wiki articles<nowiki>:</nowiki>
 
*[http://www.crankshaftcoalition.com/wiki/Category:Firing_orders Firing orders] of various engines.
 
*[http://www.crankshaftcoalition.com/wiki/Category:Firing_orders Firing orders] of various engines.

Latest revision as of 13:34, 26 November 2023

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