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Thread: Mechanical Advance Distributor

  1. #1
    Enjoying Life Chief Hunglikmule 70-K5's Avatar
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    Mechanical Advance Distributor

    How much mechanical advance should a stock HEI distributor have?

    I always thought it was in the 20-21 degree range... But I've also heard that some emissions changes decreased the mechanical to 10 degrees.

    Is there a way to measure advance on the bench?

  2. #2
    72' Yea its a convertible Senior member jackedjimmy72's Avatar
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    Not sure. Always heard that the medium springs are a good fit to a mild engine in general.
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  3. #3
    Enjoying Life Chief Hunglikmule 70-K5's Avatar
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    Yea, the spring kits can change the advance curve but I don't see how they could change the *total* mechanical advance...

  4. #4
    Eric Senior member shovelhead77's Avatar
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    it should be more than 10 dont you set the timing some where around 8 with vacume advance unhooked
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  5. #5
    Knows their $hit MrK5's Avatar
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    IIRC there some kits that have bushings or spacers that will limit the total travel of the mechanical advance. But I'm not sure this is something that can be done on a stock HEI. That's why I prefer the aftermarket units.
    ~Scott

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  6. #6
    Enjoying Life Chief Hunglikmule 70-K5's Avatar
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    Yes, you set the timing with the vacuum advance disconnected.

    Typically I set the initial around 10-18 and then run up the rpm's until I get a 'all in' reading, using the dial on my timing light to tell me what that figure is. Or if you don't have a fancy light you can get a tape strip that goes around your balancer, only like $4 at any auto parts store.

    I'm leaning towards getting a new distributor, MSD makes a good looking HEI unit for under $150, since I'm never going to be spinning over 5K I figure a base after market will probably do the trick.

  7. #7
    Knows their $hit MrK5's Avatar
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    Yep, I think you're looking at the same one I am. Long story, but I had a billet MSD distributor, but in a unfortunate accident - through no fault of the distributor - I had to get a parts store distributor so I could get the truck home. I wound up selling the damaged MSD distributor and keeping the parts store unit. Now I'd like to go back to a new MSD, but I don't want to spend them money on another billet distributor. I think the MSD HEI unit you're looking at is the same one I am. I agree it should be good enough.

    I set my initial timing the same as you. Add in the vacuum advance and you are sitting in the mid-20's, or at least I am with the vac adv hooked to manifold vacuum. The interesting thing is if you were to look at the idle timing on a TBI motor it would be approaching 30 degrees.
    ~Scott

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  8. #8
    Enjoying Life Chief Hunglikmule 70-K5's Avatar
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    All most of us need... this is actually the old version, the newer version have a adjustable vacuum advance plate inside of the distributor instead of a adjustable diaphragm.

    http://www.summitracing.com/parts/MSD-8362/


  9. #9
    Shadetree Mechanic
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    Sounds like you got some pretty good info already... On the 383 I just built I went with a cheaper eBay HEI from some guys in Iowa (can't remember the name but I think it's a proform or something)
    Anyway, per my carb tech folks set my initial timing with vacuum connected to 16 at idle and when it's a full speed (2500 rpm or so) my total is right at 36-37 where I wanted it so stock my HEI is adding 20-21 mechanical

    Of course my BG demon carb is CRAP but that's another matter that a Holley hopefully will fix today

  10. #10
    Enjoying Life Chief Hunglikmule 70-K5's Avatar
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    Yea, your timing sounds right... There must be something up with my weights or springs or something not getting all that mechanical advance kicking in.

    I'll be off work all next week so I should have some good time to get back there, pull the cap, and see what is up with my weights. Hopefully I can get away with some $2 springs and not have to pop for a new distributor but under $15o isn't bad..

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