Hot rodding the HEI distributor
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==Computer controlled HEI== | ==Computer controlled HEI== | ||
| − | A word on the internal coil computer controlled HEI distributors: A computer controlled HEI distributor work basically the same as a non-computer controlled HEI except for the lack of a mechanical or vacuum advance mechanism (some early versions did use a vacuum advance); the ECM determines the advance curve electronically. Other than buying an aftermarket performance chip for the ECM (or buying hardware and software to burn/tune a new chip), there is no way to change the advance curve of a computer-controlled HEI distributor. The only other change you can make in the advance curve is to manually advance the base timing (usually worth a little HP by itself). Check a repair manual/GM service manual for the correct way to set the base timing for your particular engine/year (this usually requires disconnecting a spark control wire before the timing is set to TDC). 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 | + | A word on the internal coil computer controlled HEI distributors: A computer controlled HEI distributor work basically the same as a non-computer controlled HEI except for the lack of a mechanical or vacuum advance mechanism (some early versions did use a vacuum advance); the ECM determines the advance curve electronically. Other than buying an aftermarket performance chip for the ECM (or buying hardware and software to burn/tune a new chip), there is no way to change the advance curve of a computer-controlled HEI distributor. The only other change you can make in the advance curve is to manually advance the base timing (usually worth a little HP by itself). Check a repair manual/GM service manual for the correct way to set the base timing for your particular engine/year (this usually requires disconnecting a spark control wire before the timing is set to TDC). 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 try to use a computer controlled HEI unless there is an ECM. Without the ECM there will be no mechanical ignition timing advance AT ALL from the computer-controlled distributor (and only a few early HEIs used a vacuum advance along with an ECM), plus a computer controlled distributor without the ECM will give lousy performance and 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 there will, again, be no advance (and the check engine light will come on). | Don't try to use a computer controlled HEI unless there is an ECM. Without the ECM there will be no mechanical ignition timing advance AT ALL from the computer-controlled distributor (and only a few early HEIs used a vacuum advance along with an ECM), plus a computer controlled distributor without the ECM will give lousy performance and 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 there will, again, be no advance (and the check engine light will come on). | ||
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==Finding/verifying TDC== | ==Finding/verifying TDC== | ||
*You will want to begin by knowing the timing tab and line on the damper are accurately indicating [http://www.crankshaftcoalition.com/wiki/Determining_top_dead_center TDC]. | *You will want to begin by knowing the timing tab and line on the damper are accurately indicating [http://www.crankshaftcoalition.com/wiki/Determining_top_dead_center TDC]. | ||
| − | *On the SBC there were three different combinations of damper lines and timing tabs that go together. [http://www.crankshaftcoalition.com/wiki/Timing_tabs_and_damper_TDC_lines_SBC This page] describes them. | + | *On the SBC there were three different combinations of damper lines and timing tabs that go together. [http://www.crankshaftcoalition.com/wiki/Timing_tabs_and_damper_TDC_lines_SBC '''This page'''] describes them. |
==Plug gap== | ==Plug gap== | ||
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Also, the wire from the starter solenoid “R” terminal can be eliminated. New HEI coil wire and tach hook-up pigtails are available. These pigtails are a better solution than using a crimp-on type female spade connector because the pigtail has a much more robust design that won’t break off even after repeated removals. They also have positive retention clips that prevent the connection to fall off. | Also, the wire from the starter solenoid “R” terminal can be eliminated. New HEI coil wire and tach hook-up pigtails are available. These pigtails are a better solution than using a crimp-on type female spade connector because the pigtail has a much more robust design that won’t break off even after repeated removals. They also have positive retention clips that prevent the connection to fall off. | ||
| − | Another neat wiring aid is the Accel p/n 170072. It’s a combination HEI battery/tach pigtail that has a connector for both current to the HEI | + | Another neat wiring aid is the Accel p/n 170072. It’s a combination HEI battery/tach pigtail that has a connector for both current to the HEI and the connection for the tach molded together. A tach wire connector isn’t needed if using an MSD box that has a separate tach hook-up; in that case use just the stock type HEI power supply pigtail. |
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|[[File:Painless 30809 hei power.jpg|thumb|center|200px|Painless p/n 30809 power]] | |[[File:Painless 30809 hei power.jpg|thumb|center|200px|Painless p/n 30809 power]] | ||
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Pay close attention to the firing order at the distributor cap and at the plugs themselves. In the case of the SBC, #5 and #7 are next to each other on the cap, at the head and in the firing order. The engine will run, although will have a miss and will detonate, with the #5 and #7 wires swapped. See [[How to install a distributor]] for more on how to install a Chevy V8 distributor. | Pay close attention to the firing order at the distributor cap and at the plugs themselves. In the case of the SBC, #5 and #7 are next to each other on the cap, at the head and in the firing order. The engine will run, although will have a miss and will detonate, with the #5 and #7 wires swapped. See [[How to install a distributor]] for more on how to install a Chevy V8 distributor. | ||
| − | + | {{Note1}}Pay attention to the idle speed while setting the initial timing! <br>If you try to set your initial timing with the engine idling ABOVE the RPM that the mechanical advance has started to come in, getting a correct reading will be all but impossible. So always start adjusting initial timing without the mechanical advance adding any timing. You can temporarily add a heavier spring just for the initial timing adjustment if you cannot lower the idle enough. | |
==Distributor shaft end play adjustment== | ==Distributor shaft end play adjustment== | ||
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==Rotor phasing== | ==Rotor phasing== | ||
*[http://www.msdignition.com/uploadedFiles/MSDIgnitioncom/Support/frm28392_tech_bulletin_rotor_phasing.pdf Checking and correcting rotor phasing] from MSD | *[http://www.msdignition.com/uploadedFiles/MSDIgnitioncom/Support/frm28392_tech_bulletin_rotor_phasing.pdf Checking and correcting rotor phasing] from MSD | ||
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| + | ==Holley idle transfer slot== | ||
| + | The drawing below shows the transition slot as seen with the carb held upside down. The drawing on the left shows an overexposed transition slot. Baseline the throttle blades to give a transfer slot that looks like the image below, right (approximately as long as it is wide, or about 0.020", up to 0.040"): | ||
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| + | [[File:Holley transferslot.jpg]] <br style="clear:both"/> | ||
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| + | From this point the idle speed can be increased to the point where the transfer slot becomes over exposed. If that occurs, the secondary throttle blades may need to be opened slightly to allow more idle air to be introduced into the engine. If the throttle blades are open too far, a poor idle and off-idle transition can be the result. Depending on the cam specs, adding initial timing in addition to or instead of tipping the secondary throttle blades open more may give the best results. | ||
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| + | {{Note1}}Other carbs have similar transition circuits, and they need to have the throttle blades in the 'sweet spot' same as a Holley. Regardless of the brand of carb, opening the primary throttle blades too far in an effort to get a good idle will result in the idle being OK in neutral but will drop too far when the transmission is put into gear, along with the carb having poor off idle response. | ||
=Ignition advance= | =Ignition advance= | ||
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*'''Initial timing''' is the amount of timing advance before the mechanical or vacuum advance is added in. | *'''Initial timing''' is the amount of timing advance before the mechanical or vacuum advance is added in. | ||
*'''Total timing''' is the initial timing plus the mechanical timing. | *'''Total timing''' is the initial timing plus the mechanical timing. | ||
| − | *The '''vacuum advance'''- while important- is usually considered separately from total advance in most discussions on setting up a performance timing curve. In other words, you might hear "the engine runs best with 38 degrees total advance". That's initial plus mechanical advance; the amount of vacuum advance isn't added to that figure. | + | *The '''vacuum advance'''- while important- is usually considered separately from total advance in most discussions on setting up a performance timing curve. In other words, you might hear "the engine runs best with 38 degrees total advance". That's '''initial''' plus '''mechanical''' advance; the amount of vacuum advance isn't added to that figure. |
==Tuning the advance curve for performance== | ==Tuning the advance curve for performance== | ||
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What happens sometimes is the initial timing is too low, causing the primary butterflies to be opened so far to get the engine to idle that the engine is not running on the idle circuit; instead it is running mostly on the transition slots. If this is the case, the engine will idle high when out of gear and then the idle speed will drop down once it's put in gear, and the off-idle response will be poor at best. This can be magnified by not having enough torque converter stall rpm and to a lesser extent not enough rear gear ratio. | What happens sometimes is the initial timing is too low, causing the primary butterflies to be opened so far to get the engine to idle that the engine is not running on the idle circuit; instead it is running mostly on the transition slots. If this is the case, the engine will idle high when out of gear and then the idle speed will drop down once it's put in gear, and the off-idle response will be poor at best. This can be magnified by not having enough torque converter stall rpm and to a lesser extent not enough rear gear ratio. | ||
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==Initial advance== | ==Initial advance== | ||
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