I decided to post this info on a seperate topic...
For those interested... and have a little time and patience and can pay attention to detail. If you have limited space above your distributor... but want/need to keep your HEI distributor functional. Then this may interest you. Nobody makes a low profile distributor cap for the GM HEI distributor. .... unless you get an aftermarket crab cap distributor (which will not use the stock pick up coil, or ignition module, vacuum advance, etc.)
I fabricated this distributor cap for my cadillac 4.9 engine .... but this same cap could be used on any classic chevy, buick, oldsmobile, pontiac, or cadillac that uses an HEI distributor...
Next... get a distributor cap from a 1997 chevy pickup with a V8.... ....or if you need a low profile distributor for your six cylinder... then get a cap from a 1997 chevy pickup with a V6
You will need to shave off some of the external ribs so that it will press into the 76 cap. .... You will also need to shave it shorter...How short depends on how low you need it to be...
Now shove it into the 76 cap... Don't epoxy it until you are sure it is clocked correctly and aligned with the rotor. I would recommend using a micrometer, and test fitting it on a free spinning distributor off of the engine.
The cap has to be clocked right in reference to the distributor.... Turning the whole distributor will not fix an incorrectly clocked cap. Thats why when you install a cap... it has a tooth that doesn't allow it to turn it once it is mounted to the distributor. If the cap is not referenced correctly...(If the rotor is not pointing to one of the terminals inside the distributor cap when spark occurs... then there will be no where for the spark to jump to. (spark will arch somewhere else) When spark occurs...The rotor must be pointing to one of the eight terminals inside of the distributor. Adjustment of timing... advanced or retarded.... is done by turning the whole distributor... not the cap alone.
Rotor height in relation to the terminals inside the cap is important also. ...but since the terminals are about a 1/4 inch tall there is room for error... as long as the rotor is within this margin...but the closer to center, the better ...There is a little vertical shaft play is most distributors.
The gap from the rotor pointer to distributor terminals is also important ...it should be about .015 to .030 ... if closer it may hit when spinning ... if much wider, spark may jump elsewhere.
Ok...this picture shows how the firing order should be on engines that spin the engine clockwise.... chevy small blocks and big blocks, buick V8s, older cadillacs (368's, 425's, 472's, 500's) . . . And this is the firing order for distributors that spin counterclockwise... oldsmobile V8's, pontiac V8's and cadillac 4.1, 4.5, 4.9
Really nice job. I used an Accel correct-a-cap to make things look neat on my sbc (87GT) I had no end of trouble trying to figure out why the engine just wouldn't run right. I checked resistance in the cap - all was fine. Finally found that the cap was sending spark randomly to wherever it wanted to. Your cap might be a perfect solution. The correct-a-cap used wires set in epoxy that crossed inside the cap. By using the factory crab cap, you have made a much better product. I think there are more applications than you might think.
------------------ woodys 427
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01:37 PM
Archie Member
Posts: 9436 From: Las Vegas, NV Registered: Dec 1999
Really nice job. I used an Accel correct-a-cap to make things look neat on my sbc (87GT) I had no end of trouble trying to figure out why the engine just wouldn't run right. I checked resistance in the cap - all was fine. Finally found that the cap was sending spark randomly to wherever it wanted to.
LOL, yeah I've been there. I had one of those on my Opel GT with an SBC. Then the next problem was when the replacement cap failed while on a road trip. You'll never find a replacement if you need one on the road.
why not just pick up another distributor body, and mod the body for the cap? that way you can run off the shelf wear parts.
That is a good idea... but there are obstacles. The first is that the floor on an HEI distributor is very uneven... so even if holes are drilled and tapped for a crab cap.... it would sit uneven, and there would be large gaps second problem... the igntion module would be in the way... so module would have to be externally located. third problem...crab caps are very short... none are tall enough to to reach the base without hitting the rotor first... unless a spacer is made (like the one I made from a 76 cap)
... it would require a very heavily modified HEI distributor to accept a bone stock crab cap... and after all that, you would still need a modified rotor.
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04:17 AM
fieroguru Member
Posts: 12127 From: Champaign, IL Registered: Aug 2003
third problem...crab caps are very short... none are tall enough to to reach the base without hitting the rotor first... unless a spacer is made (like the one I made from a 76 cap)
... it would require a very heavily modified HEI distributor to accept a bone stock crab cap... and after all that, you would still need a modified rotor.
I would suggest having an aluminum (or plastic) spacer/adapter made that will fill the open space from the shorter crab cap as well as change the mounting pattern/configuration so the adapter bolts to the dist and an un modified crab cap will fit on top. For the rotor, make a 1/8" spacer to bolt to the top of the dist shaft and then adapt the spacer to accept the stock vortec crab dist. The upfront work would be more involved, but for the life of the swap all wear components would remain stock.
Depending on how thick this adapter needed to be, you might start with a L31 distributor housing and cut it up (they are plastic) and bond it to the base of an HEI cap.
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06:41 AM
Will Member
Posts: 14219 From: Where you least expect me Registered: Jun 2000
That is a good idea... but there are obstacles. The first is that the floor on an HEI distributor is very uneven... so even if holes are drilled and tapped for a crab cap.... it would sit uneven, and there would be large gaps second problem... the igntion module would be in the way... so module would have to be externally located. third problem...crab caps are very short... none are tall enough to to reach the base without hitting the rotor first... unless a spacer is made (like the one I made from a 76 cap)
... it would require a very heavily modified HEI distributor to accept a bone stock crab cap... and after all that, you would still need a modified rotor.
What Eric and I are suggesting is to install the baseplate from the Vortec distributor onto the Cadillac distributor body/stem. That way the Vortec cap would attach directly to the Vortec baseplate and the Vortec rotor could be used.
Now if there's no pickup coil and module in the Vortec distributor, that could pose a problem.
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09:29 AM
fieroguru Member
Posts: 12127 From: Champaign, IL Registered: Aug 2003
Ahh... didn't know if the Vortec PCM still relied on the distributor for primary triggering and the 24x in the timing cover for misfire detection like the OBDII LT1's or used the 24x for primary triggering. Must be the latter.
Some progress today with my mutant ninja distributor cap...
Some good and bad news....
The bad... Looks like the cap will not work so great on the 4.9 Cadillac.... The thermostat housing is in the way where some wires need to pass... Unless it sat higher ( but that's defeating its purpose of being low profile )
The good... So I installed it on my 1980 Trans AM... and it runs great! Didn't really need it there... but since I made an HEI crab cap, I wanted to test it out. Looks cools though... and the wires go the right way.
