Hot rodding the HEI distributor
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*20 degrees centrifugal | *20 degrees centrifugal | ||
*16 degrees vacuum advance | *16 degrees vacuum advance | ||
| − | + | The above equals 50 degrees total advance including vacuum advance) under light throttle cruse/high vacuum conditions. Using an adjustable vacuum advance unit, the vacuum advance can be adjusted for what vacuum the vacuum advance falls out and tips in. | |
If you are in the 45-55 degrees range (about 50 degrees is fine in most cases) of total advance, you’re in the ballpark. Each engine is different and what works for one engine might be a little different than what works for another engine. | If you are in the 45-55 degrees range (about 50 degrees is fine in most cases) of total advance, you’re in the ballpark. Each engine is different and what works for one engine might be a little different than what works for another engine. | ||
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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. | 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. | ||
| − | WATCH YOUR IDLE RPM WHILE YOU SET INITIAL ADVANCE TIMING!!! 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. | + | WATCH YOUR IDLE RPM WHILE YOU SET INITIAL ADVANCE TIMING!!! 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. |
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| − | The shim kits are sold through Summit and Jegs, etc. from Moroso, Mr. Gasket, Jegs brand, and others as well. | + | [[File:Dist shaftshim.jpg|thumb|300px|Distributor shaft shim selection]] |
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| + | ===Distributor shaft end play adjustment=== | ||
| + | This is done by measuring the amount of play between the distributor gear and the thrust washer. Take the measurements with feeler gauges. You want to end up with ~0.020" (no less than 0.015") on a Chevy distributor; some engines like the Olds need to have the end play adjusted differently. | ||
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| + | Take the measurement of the gap and subtract 0.020" from it, the result is the shim thickness needed. Shim kits are available from Summit, Jegs and probably the local parts store. There will be a selection of shims; use whatever combination needed to get as close to the target as possible. The kits typically contain 0.010", 0.020", and 0.050" (or 0.053", depending on brand) shims. | ||
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| + | Removal and replacement of the gear is covered in the link below, '''[[Hot rodding the HEI distributor#Resources|Description of an HEI rebuild]]'''. | ||
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| + | ===Distributor height adjustment=== | ||
| + | You can use extra distributor gaskets for this, but they are usually paper and will crush down and lose thickness after being used. The solution is to use nylon spacers that are ridged enough to resist crushing, yet pliable enough to seal the intake from oil leaking from the distributor hole. | ||
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| + | The shim kits are sold through Summit and Jegs, etc. from Moroso, Mr. Gasket, Jegs brand, and others as well. The kits typically contain 0.030", 0.060", and 0.090" (or 0.100", depending on brand) shims. | ||
[[File:Jegs pn 555-40082 nylon shims.jpg|thumb|left|[http://www.jegs.com/i/JEGS-Performance-Products/555/40082/10002/-1 Nylon distributor shims]]]<br style="clear:both"/> | [[File:Jegs pn 555-40082 nylon shims.jpg|thumb|left|[http://www.jegs.com/i/JEGS-Performance-Products/555/40082/10002/-1 Nylon distributor shims]]]<br style="clear:both"/> | ||
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