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Considering Distributor “ Upgrade “

Discussion in 'Early CJ5 and CJ6 Tech' started by Hondadoug, Sep 25, 2024.

  1. Sep 27, 2024
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Huh?
     
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  2. Sep 27, 2024
    Jw60

    Jw60 New Member 2025 Sponsor 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Rotating the actual distributor housing without any seal to the crankcase.
    Not a good idea for a jeep.
     
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  3. Sep 27, 2024
    jeepdaddy2000

    jeepdaddy2000 Active Member

    Eagle Point oregon
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    Vacuum advance:
    A mechanical advance is linear and cannot be load sensitive. Engineers found out early that engines under light load can use additional advance above the mechanical weights, which provide maximum advance for an engine under load. They developed a system that senses load through intake vacuum. This system was designed to be sensitive to high intake vacuum, which occurs under lighter loads and higher RPM's (thanks to ported vacuum). Most vac adv units provide between 15 to 20 extra degrees advance on top of the mechanical advance. As the load increases, the vacuum begins to drop and so does the added advance, which protects the engine from pinging and knocking (detonation).


    Vacuum advance provides better fuel economy under cruise conditions by providing additional advance in those situations. Whether an upgrade will pay for itself or not is directly related to how much driving you do under cruise.
     
  4. Sep 28, 2024
    amboynut

    amboynut Member

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    Well said. Thanks for adding the detail.
     
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  5. Sep 28, 2024
    amboynut

    amboynut Member

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    Ahh. Thanks for that. I always wondered why my Corvette used manifold vacuum for the vacuum advance.
     
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  6. Sep 28, 2024
    jeepdaddy2000

    jeepdaddy2000 Active Member

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    Side note:
    I'm going to refute this.

    The "it's an emissions thing" statement became somewhat of an obsession with me, since I've found ported vacuum as ther source of vacuum advances all the way back into the 40's when vacuum advances began to be installed on various engines. This was long before any questions on emissions began.

    I've had numerous conversations with all kinds of folks on various boards and in person and the consensus was fuel grades were so poor back then that the engines couldn't consistently run manifold vacuum on the advances without issues.

    I have no issue with someone refuting this if they can bring valid information to the discussion.
     
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  7. Sep 28, 2024
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    I don't know of a reference. I had thought it was emissions related, but presumed a different mechanism. The Motor Trend article that Fireball points suggests that the reason for the spark retard was to heat the exhaust. This might be correct if the catalytic convertors of the day needed the increased exhaust temperature to set off catalysis. Maybe. These early single-stage convertors only converted CO and HC.

    My understanding was that it's meant to reduce combustion temperature at idle and thereby reduce NOx emissions. NOx is a particularly nasty component of photochemical smog. I know that my '65 F100 in California was required to run an aftermarket spark controller in the radiator hose (like our spark CTOs now) and it was way way before the age of even the single-stage convertors. This requirement was justified by reduced emissions - California only. My '73 and '75 CJs both had spark CTOs and no convertors.

    I know that ported vacuum makes the engine run hotter at idle. Jeep used ported vacuum bypass as part of "heavy duty cooling" on some later vehicles. Presumably it would switch from ported to manifold vacuum as engine temperature climbed. Both this and my F100 retrofit device seem to argue against fuel quality being the controlling factor, at least on modern cars. Dunno - I'm sure this is not the whole story, but I have not found a better single-source discussion than the Motor Trend article.
     
  8. Sep 28, 2024
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Possibly, in the Dark Ages? But is that anecdotal, or documentable with evidence?

    Just a reminder, in my lifetime fuel "quality" (reflected as octane, which affects ignition timing) declined dismally since the golden era of high performance muscle cars. Roughly 50 years ago, and coincidentally, after the prime years of the CJ5 F-head, although the F-head was designed to run globally on potentially very low octanes.

    Not sure how relevant that is, but I query the basis of the statement "fuel grades were so poor back then."
     
    Last edited: Sep 28, 2024
  9. Sep 28, 2024
    jeepdaddy2000

    jeepdaddy2000 Active Member

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    All good points, but still doesn't explain ported vacuum on vehicles in the forties. I've a shop manual that specifically states that vacuum advance is provided above idle. This would indicate a ported vacuum source. This is the quote for all makes and models in the 46 model year.

    These distributors also had an "octane selector". designed to be a manual adjustment for various gas octanes.

    Back then being the forties and fifties.

    An interesting read starting on post 4
    https://www.jalopyjournal.com/forum/threads/octane-selector-for-dummies.659737/
     
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  10. Sep 28, 2024
    PeteL

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    Everything went to heck when they took the driver's 'spark lever' off of the steering column. Never a problem before that.

    Harrummmph.
     
  11. Sep 28, 2024
    Fireball

    Fireball Well-Known Member 2025 Sponsor 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Clearly I have to concede it existed before emissions. However, it may well have gotten more common because of emissions, I have no proof of it though.

    But that doesn't mean ported vacuum is a "requirement" for vacuum advance. There are lots of cars that use direct manifold vacuum. For example, the 1966 Buick 225 manual says the vacuum advance is connected to manifold vacuum. https://www.teambuick.com/reference/library/66_chassis/files/68-c.php

    I seem to recall my dad saying Ford like ported advance while GM preferred manifold (back in the 60s).
     
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  12. Sep 28, 2024
    Fireball

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  13. Sep 28, 2024
    nickmil

    nickmil In mothballs.

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    Think about how it works. Rpm increases in most applications you want more ignition timing advance (there are exceptions). You get this from a vacuum advance by having it hooked to ported vacuum as the vacuum to the advance increases as rpm increases. As the throttle plates open manifold vacuum drops decreasing vacuum advance when you typically need more advance.
     
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  14. Sep 28, 2024
    vtxtasy

    vtxtasy oldbee 2024 Sponsor 2023 Sponsor

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    Went way down this rabbit hole before. The 231 vacuum diagram show a TVS switch turning on ported vacuum when the engine is cool.
    This makes more heat and less hydrocarbons, so it is an emission function until the engine warms up and switches to manifold vacuum.
    The consensus is what does your particular engine like at idle. After the throttle opens, they are the same. My engine likes the extra
    advance at idle.

    A quick look in to this and found a couple good posts by Crazy Steve that sums it up very well.

    https://www.jalopyjournal.com/forum/threads/ported-vacuum-or-manifold-vacuum-to-dist.1019838/page-2

    https://www.jalopyjournal.com/forum/threads/ported-vs-common-vacuum-advance.1194253/
     
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  15. Sep 30, 2024
    CHUGALUG

    CHUGALUG Member

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    Keep in mind all Willys vehicles save the CJ used a Vacuum Advance distributor and ONLY the early ones rotated the whole distributor. The IAT-4405 I am using in my 134L operates exactly the same as the Distributor in our 67 Mustang or my 66 Chevelle

    The reason it was not put on a CJ was due to them being sold more as a tractor then all the other things people used them for. Including driving on the hwy to work. My dad drove my 48 CJ-2A to work 16 miles each way on State hwy 213 from early 1963 to late 1969 And when he set up the engine in it (from a 58-59 DJ-3A it had a Vacuum Advance distributor in it.
     
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  16. Oct 1, 2024
    jeepdaddy2000

    jeepdaddy2000 Active Member

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    I'm not trying to drive a point home, but to continue a discussion on the question. It seems there is a common statement that ported vacuum is directly linked to emissions. My replay is always "why did it exist prior to any emission issues?"

    The consensus I found after long discussions is gas was crap back then and engines didn't like full vacuum advance at idle because of this. The "octane selector" found on many models seems to bear this out.

    Very true and I don't question that later emission vehicles utilized ported and manifold vacuum to help manipulate exhaust gasses. Ford even had a dual diaphragm advance module that retarded timing under certain conditions.
    [​IMG]
    And this makes sense. If the vac adv were pretty much invisible due to the Jeeps usage, then saving the money by not having to redesign the dist, manufacture, and install the unit would make sense. As time wore on, roads got better, and performance became more important, installing vacuum advances was probably a cheap upgrade to help compete.
     
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  17. Oct 1, 2024
    timgr

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    Both claims can be true.

    Ported vacuum may have existed prior to the emissions era for reasons other than emissions. It's clear that, in many cases, ported vacuuum at idle has been used to meet emissions standards.

    Jeeps from the '70s are a good example. They all have a spark CTO that switches from manifold to ported vacuum as the engine reaches operating temperature. Extra advance at idle was needed at idle when the engine was cold. You can bypass the spark CTO and run manifold vacuum all the time, and the engine will run fine, but I predict you will not pass an emissions tailpipe test. The spark CTO appears in the emissions chapter of the TSM, and Jeep would not have added the extra parts and put the description in that section for no reason.

    You can find references alluding to this directly -

    upload_2024-10-1_12-14-21.png

    (This is at the Crankshaft Coalition wiki - I can't get the link without it being a huge mangled encrypted string - sorry. I can post the entire PDF if you want it.)

    These Jeeps also have TCS, transmission controlled spark, that disables vacuum advance entirely in high gear.
    TCS.png

    P. 4A-23 of the 1975 Jeep TSM.

    It's clear that retarding the spark lowers combustion chamber temperature, at the cost of lower performance. Indeed, my 1965 F100 required a retrofit device that turned off vacuum advance entirely at operating temperature. The ARB claimed it reduced HC 42%, CO 14% and NOx 10% ... maybe HC reduced at idle and NOX at cruise.

    upload_2024-10-1_12-31-28.png

    (Another link severely mangled and encrypted by Bing - PDF available if you want it. Includes a CARB document describing available VSAD devices.)

    It seems clear that retarding the spark by disabling vacuum advance was used as an emissions reduction tool, regardless of what purposes it had been put to prior to the emissions era.
     
    Last edited: Oct 1, 2024
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  18. Oct 1, 2024
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    I also have not come across any references regarding the purpose of ported vacuum prior to emissions concerns. Modern sources seem to focus on that, like any other purposes are incidental. Old sources that might discuss are not online, it seems. Maybe old automotive engineering textbooks, like from the 30s and 40s?
     
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  19. Oct 1, 2024
    jeepdaddy2000

    jeepdaddy2000 Active Member

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    My quote is from a shop manual from the late forty's. Rummaging through the various manufacturer sections, all use the statement about vacuum advance above idle.
    I won't dispute ported spark may have evolved into an emission component, but it's origins seem to have been used for another purpose.

    I would be interested in the effect of manifold vacuum on the "high performance" engines of the mid 60's and their high compression numbers. The 409 ran 11.25 compression. The manifold pulses while cranking may have caused kick back during cranking.
     
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  20. Oct 1, 2024
    Jw60

    Jw60 New Member 2025 Sponsor 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    I don't see how compression ratio would affect manifold vacuum. An aggressive cam would affect vacuum but i don't understand how compression ratio would directly affect vacuum.
     
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