Hot rodding the HEI distributor
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| − | Non- | + | ==Non-computer controlled HEI setup for performance== |
| − | + | This article deals primarily with older-style non-computer controlled [[HEI distributor]]s. This is because there is so much performance left in them vs. stock AND since many people have ditched the computer in their 3rd gen cars and gone with a totally non-computer controlled engine. Please note: All carbureted V8 F-bodies since 1981 came from the factory stock with a computer controlled, internal coil HEI distributor. Most Fuel Injected 3rd gen V8s use a modified version of the HEI known as a “divorced coil HEI” (these have the small cap with an integrated magnetic trigger - usually found on GM TBI engines). | |
| − | This article deals primarily with older-style non-computer controlled [[HEI distributor]]s. This is because there is so much performance left in them vs. stock AND since many people have ditched the computer in their 3rd gen cars and gone with a totally non-computer controlled engine. Please note: All carbureted V8 F-bodies since 1981 came from the factory stock with a computer controlled, internal coil HEI distributor. Most Fuel Injected 3rd gen V8s use a modified version of the HEI known as a “divorced coil HEI” (these have the small cap with an integrated magnetic trigger - usually found on GM TBI engines). | + | |
A word first about those internal coil computer controlled HEI distributors: Computer controlled versions work basically the same as the old non-computer versions except that they don't have any mechanical advance mechanisms inside them -- the ECM determines the advance curve electronically. Other than buying an aftermarket performance chip for the ECM or buying the proper hardware & software to burn a new chip, there is NO WAY to change the advance curve of a computer-controlled HEI distributor- timing is controlled ENTIRELY by the ECM’s programming! The only change you can make in the advance curve, is to manually advance the base timing (usually worth a little HP by itself). Check your GM service manual for the correct way to set the base timing for your particular engine/year. If you have a computer controlled distributor in your car right now you can’t do much to increase performance other than to make sure it is correctly communicating with your car’s ECM and upgrade the coil to a better unit. This is not a bad thing -- it leaves funds available for parts that WILL make the car faster! | A word first about those internal coil computer controlled HEI distributors: Computer controlled versions work basically the same as the old non-computer versions except that they don't have any mechanical advance mechanisms inside them -- the ECM determines the advance curve electronically. Other than buying an aftermarket performance chip for the ECM or buying the proper hardware & software to burn a new chip, there is NO WAY to change the advance curve of a computer-controlled HEI distributor- timing is controlled ENTIRELY by the ECM’s programming! The only change you can make in the advance curve, is to manually advance the base timing (usually worth a little HP by itself). Check your GM service manual for the correct way to set the base timing for your particular engine/year. If you have a computer controlled distributor in your car right now you can’t do much to increase performance other than to make sure it is correctly communicating with your car’s ECM and upgrade the coil to a better unit. This is not a bad thing -- it leaves funds available for parts that WILL make the car faster! | ||
| − | DON’T USE A COMPUTER CONTROLLED DISTRIBUTOR IF YOU HAVE DITCHED THE ECM OR ARE RUNNING WITHOUT ONE!!!! 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 because the ECM looks to make sure the computer-controlled portion of the distributor is out there 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 -- replace both the computer-controlled distributor, the computer controlled carb (Qjet) and deactivate the check engine light. | + | DON’T USE A COMPUTER CONTROLLED DISTRIBUTOR IF YOU HAVE DITCHED THE ECM OR ARE RUNNING WITHOUT ONE!!!! 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 because the ECM looks to make sure the computer-controlled portion of the distributor is out there 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 -- replace both the computer-controlled distributor, the computer controlled carb (Qjet) 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 RPMs 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 RPMs if properly equipped. | ||
| − | Let's start with the coil. It's located on top of the distributor between the plug wire towers under a plastic cover. It's the "engine" that makes the sparks. Stock it's capable of about 35,000 volts and so-so total spark energy. It's fine for a naturally aspirated street motor that rarely sees the high side of 5000 RPMs. It will provide the energy to jump a plug gap of .040-.045 with no problem in these applications. | + | Let's start with the coil. It's located on top of the distributor between the plug wire towers under a plastic cover. It's the "engine" that makes the sparks. Stock, it's capable of about 35,000 volts and so-so total spark energy. It's fine for a naturally aspirated street motor that rarely sees the high side of 5000 RPMs. It will provide the energy to jump a plug gap of .040-.045 with no problem in these applications. |
You can upgrade the coil with an Accell or MSD replacement coil that will jump the voltage up to about 42,000 volts and total spark energy will also jump about 10-15%. There are even hotter coils than this from Accell, MSD and others that will give you the same 42,000 volts but a LOT more total spark energy (like 50% more). Either one of these “super high output” coils is a worthwhile upgrade for a hot street motor- you'll get better response and HP especially at higher RPMs where the stock one hits a kind of "wall". A new coil is also a lot cheaper than a complete MSD ignition amplifier setup and at least 95% as effective at making HP in most naturally aspirated applications (the MSD will still give you slightly better mileage & emissions due to it’s multi-strike spark capability below 3000 RPMs). With either hotter coil you can open the gap up to .045-.050 for just a smidgen more HP. There are 2 different versions of the HEI coil and you need to make sure you get the right one. 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 upgraded coil. | You can upgrade the coil with an Accell or MSD replacement coil that will jump the voltage up to about 42,000 volts and total spark energy will also jump about 10-15%. There are even hotter coils than this from Accell, MSD and others that will give you the same 42,000 volts but a LOT more total spark energy (like 50% more). Either one of these “super high output” coils is a worthwhile upgrade for a hot street motor- you'll get better response and HP especially at higher RPMs where the stock one hits a kind of "wall". A new coil is also a lot cheaper than a complete MSD ignition amplifier setup and at least 95% as effective at making HP in most naturally aspirated applications (the MSD will still give you slightly better mileage & emissions due to it’s multi-strike spark capability below 3000 RPMs). With either hotter coil you can open the gap up to .045-.050 for just a smidgen more HP. There are 2 different versions of the HEI coil and you need to make sure you get the right one. 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 upgraded coil. | ||
| − | For blown or nitroused applications | + | For blown or nitroused applications it is recommended to use an MSD (or equivalent) ignition amplifier box setup. You can do it with a stock HEI + hi-po coil but you'll likely have to close the gap way down (.030-.035) to make it work well. |
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| + | ===THE ADVANCE SETUP: Centrifugal and vacuum advance (non-computer controlled distributors ONLY!)=== | ||
Centrifugal advance assy. on the HEI is pretty darned good. The stock weights and advance plate are perfectly acceptable for all but the highest HP/RPM engines. Centrifugal advance is used to advance engine ignition timing relative to an engine’s RPM. With more RPMs, more advance is needed -- UP TO A POINT (more on that later). ALL stock HEIs that were installed in V8s are designed to have a total centrifugal advance of 20 degrees, +-1 degree due to production line tolerances. This is as measured at the crankshaft (10 at the cam). | Centrifugal advance assy. on the HEI is pretty darned good. The stock weights and advance plate are perfectly acceptable for all but the highest HP/RPM engines. Centrifugal advance is used to advance engine ignition timing relative to an engine’s RPM. With more RPMs, more advance is needed -- UP TO A POINT (more on that later). ALL stock HEIs that were installed in V8s are designed to have a total centrifugal advance of 20 degrees, +-1 degree due to production line tolerances. This is as measured at the crankshaft (10 at the cam). | ||
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