Hot rodding the HEI distributor
From Crankshaft Coalition Wiki
(→Limiting or locking the mechanical advance mechanism) |
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| − | + | [[File:GM Performance pn 93440806 HEI distributor11.jpg|thumb|300px||GM Performance p/n 93 | |
| − | [[File:GM Performance pn 93440806 HEI distributor11.jpg|thumb|300px||GM Performance p/n | + | |
==Overview== | ==Overview== | ||
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===Coil=== | ===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 ( | + | 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. | 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. | ||
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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. | ||
| − | *Put the probes between the | + | *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. |
| + | 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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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. | ||
| − | 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 | + | 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. |
<br style="clear: both" /> | <br style="clear: both" /> | ||
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*14-18 degrees initial advance | *14-18 degrees initial advance | ||
*18-22 degrees centrifugal | *18-22 degrees centrifugal | ||
| − | * | + | *all in by =/< 3000 RPM |
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The above gives 46-48 degrees of advance (including vacuum advance) under light throttle cruse/high vacuum conditions. You want the mechanical advance in as soon as the combination will allow, without causing pinging. Using an adjustable vacuum advance unit allows the vacuum advance to be adjusted for what vacuum the vacuum advance falls out and tips in. Set it so the vacuum advance starts to drop out at about the same point that the carb power enrichment circuit (Holley power valve, Edelbrock step up spring, or Q-jet power piston) starts to come in. | The above gives 46-48 degrees of advance (including vacuum advance) under light throttle cruse/high vacuum conditions. You want the mechanical advance in as soon as the combination will allow, without causing pinging. Using an adjustable vacuum advance unit allows the vacuum advance to be adjusted for what vacuum the vacuum advance falls out and tips in. Set it so the vacuum advance starts to drop out at about the same point that the carb power enrichment circuit (Holley power valve, Edelbrock step up spring, or Q-jet power piston) starts to come in. | ||
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*[http://www.sparkplug-crossreference.com/ Spark plug cross-reference] | *[http://www.sparkplug-crossreference.com/ Spark plug cross-reference] | ||
*[http://www.webrodder.com/article.php?AID=53&SID=60 Exploded view of an HEI distributor] | *[http://www.webrodder.com/article.php?AID=53&SID=60 Exploded view of an HEI distributor] | ||
| − | *[ | + | *[hpuppy.org/ignition2/Ignition%202b.htm GM HEI distributor notes, etc.] |
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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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