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I found my vac advance to be faulty on my hei dist.the old unit has ar 28 on it.I am assuming this is either a part # or # ditating what size spring/diaphram or inside.If this is correct is this the correct # or is there another I should try?I have a 70 bb auto with auto.
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Re: C3 HEI
Andrew - this number sounds like an aftermarket designator. The GM units have a 3 digit number such as "236" or "360" and the degrees of advance such as 16 also on the unit. I think the NAPA/ECHLIN VC-1810 Duke has mentioned in past posts carries a three digit desingator on the part, such as B28. I think the VC1810 would work well on your application, based on posts from Duke. -
Re: C3 HEI
Your '70 engine is set up for emission control, which may include AIR. As such it has a very different ignition map than pre-emission engines, and the VC1810 is not suitable. The VC1810 is suitable for SHP engines that generate 14" or less manifold vacuum at idle. Delco or aftermarket parts catalogs should include a correct replacement for the original. I infer from the post that you have a '70 LS5 454/390 engine.
Beyond this, if you do not have to be emission tested you could set up the ignition map IAW a pre-emission control antecedent engine, which would be the non-California '66-'67 427-390/400. This would include a different vacuum advance, different centrifugal springs, and different initial timing.
DukeComment
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Re: C3 HEI
i may be all wet here but i thought that the HEI system did not come out till 1974/75Comment
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