Hot rodding the HEI distributor
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==Overview== | ==Overview== | ||
| − | This article deals primarily with | + | This article deals primarily with 1980-back cars and some '86-back trucks, using (or donating) a non-computer controlled [[HEI distributor]]. There are a large number of modified vehicles that no longer use an ECM (engine control module) to oversee the emissions and performance parameters of their vehicles. Because of this, the pre computer-controlled type HEI distributor is often used; it is a relatively cheap, stand-alone unit with very good performance potential and a good track record for durability and reliability. |
==Non-computer controlled HEI setup for performance== | ==Non-computer controlled HEI setup for performance== | ||
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DON’T USE A COMPUTER CONTROLLED DISTRIBUTOR IF YOU HAVE REMOVED THE ECM!!!! You will get NO ignition timing advance AT ALL from the computer-controlled distributor, plus lousy performance and lousy mileage. If you have disconnected the 4-wire ECM connector going in the side of the distributor or the wiring between the ECM and the distributor is damaged you will, again, get no advance (and a check engine light). | DON’T USE A COMPUTER CONTROLLED DISTRIBUTOR IF YOU HAVE REMOVED THE ECM!!!! You will get NO ignition timing advance AT ALL from the computer-controlled distributor, plus lousy performance and lousy mileage. If you have disconnected the 4-wire ECM connector going in the side of the distributor or the wiring between the ECM and the distributor is damaged you will, again, get no advance (and a check engine light). | ||
| − | Yes, you can remove a non-computer controlled HEI and drop an old-style mechanical advance distributor in its place; it will physically bolt right in. But it will cause the ECM to throw a code (the check engine light will be illuminated) because the ECM senses the computer-controlled portion of the distributor is functioning every time you start the engine. Once you begin to take things out of the ECM’s control you pretty much have to go all the way with it and replace the computer controlled distributor, the computer controlled carb (Q-jet or | + | Yes, you can remove a non-computer controlled HEI and drop an old-style mechanical advance distributor in its place; it will physically bolt right in. But it will cause the ECM to throw a code (the check engine light will be illuminated) because the ECM senses the computer-controlled portion of the distributor is functioning every time you start the engine. Once you begin to take things out of the ECM’s control you pretty much have to go all the way with it and replace the computer controlled distributor, the computer controlled carb (Q-jet or Dualjet) and deactivate the check engine light. |
That being said, the NON-computer controlled HEI can be made into a great distributor for a street or street/strip car. It's simple, easy to tune, and plenty powerful to light off any naturally aspirated engine up to 7000 RPM if properly equipped. | That being said, the NON-computer controlled HEI can be made into a great distributor for a street or street/strip car. It's simple, easy to tune, and plenty powerful to light off any naturally aspirated engine up to 7000 RPM if properly equipped. | ||
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Can you just leave it unplugged? Yes. Your highway mileage will be off by about 5 MPG and your plugs will load up with carbon 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-driver street car, using a vacuum advance is always recommended. | Can you just leave it unplugged? Yes. Your highway mileage will be off by about 5 MPG and your plugs will load up with carbon 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-driver street car, using a vacuum advance is always recommended. | ||
| − | Vacuum advance for the street, using a relatively mild camshaft and compression ratio matching the cam: You want about 12 (crankshaft) degrees total vacuum advance if you run WITHOUT a functional EGR system, 16 degrees if you run WITH a functional EGR system. Regardless, you want it to come in between about 5 and 15 in/Hg of manifold vacuum. Crane has an adjustable vacuum advance can kit, [http://www.summitracing.com/parts/CRN-99600-1 p/n 99600-1]. Install the advance can with about 9 turns (tighter than the loosest setting) of the adjustment screw as a starting point. Another adjustable vacuum advance can for the GM HEI is the Accel [ | + | Vacuum advance for the street, using a relatively mild camshaft and compression ratio matching the cam: You want about 12 (crankshaft) degrees total vacuum advance if you run WITHOUT a functional EGR system, 16 degrees if you run WITH a functional EGR system. Regardless, you want it to come in between about 5 and 15 in/Hg of manifold vacuum. Crane has an adjustable vacuum advance can kit, [http://www.summitracing.com/parts/CRN-99600-1 p/n 99600-1]. Install the advance can with about 9 turns (tighter than the loosest setting) of the adjustment screw as a starting point. 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 w/instructions and tool. |
Also, if you find the ''amount'' of vacuum advance being supplied by a particular vacuum advance can (be it a stock or aftermarket can) to be excessive but otherwise OK for tip-in and rate of vacuum advance, use the adjustable vacuum advance "limiter" cam [http://www.summitracing.com/parts/CRN-99619-1/ (also available separately)] that comes with the Crane vacuum advance. | Also, if you find the ''amount'' of vacuum advance being supplied by a particular vacuum advance can (be it a stock or aftermarket can) to be excessive but otherwise OK for tip-in and rate of vacuum advance, use the adjustable vacuum advance "limiter" cam [http://www.summitracing.com/parts/CRN-99619-1/ (also available separately)] that comes with the Crane vacuum advance. | ||
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File:Hei mechanical ADVANCEslots and pins 0011.jpg | File:Hei mechanical ADVANCEslots and pins 0011.jpg | ||
| − | '''[[Hot rodding the HEI distributor# | + | '''[[Hot rodding the HEI distributor#Mechanical, aka "centrifugal" advance|Return to top]]'''. |
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