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Thread: Ported or non ported for vacuum advance

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    Ported or non ported for vacuum advance

    Finally got to spend some time fine tuning my white truck. To recap - 3.5ltr 20 thou over 9.75:1. Crower 50230 cam heads etc edelbrock performer carb and inlet manifold. Recurved dizzy with pertronix ignitor 1. Cars been running well but not perfect. A little hesitant on hot start and plugs look rich. So - carby and cam came from D&D Fabrications in US( also known as AluminiumV8). He re jetted carby knowing engine specs and cam. And marked on carby box what was to go to each port. He'd marked the ported vacuum for the vacuum advance. He'd also fitted smaller jets and metering rods to suit my engine. However i recently saw video of JEGS where they said to connect manifold vacuum to vacuum advance. Did a bit of research, swapped vacuum advance to manifold. Left static timing untouched. A much better running engine starts easier sounds a bit crisper such a small thing made a big difference. The article below was one of a few i found there are others saying use ported vacuum however the more scientific all recommended manifold vacuum.
    Will give it some time then re check plugs.
    http://www.superchevy.com/how-to/add...nition-timing/

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    Vacuum advance is only needed on cruising at partial throttle when the mixture is lean. So I agree with part of your link.

    But don't agree with the rest of the article

    Vacuum advance is ALWAYS ALWAYS ALWAYS connected to a ported outlet on the carbs.

    And and setting your timing at say 12 deg BTDC is all well and good but what is your total advance??

    When I set timing I'm looking at total advance. Yes 12 deg BTDC is a good place to start but you want to look at total advance.

    Set the timing up so the car runs nice but then rev it up until about 3000rpm until the mechanical advance it maxed. That should be 32 - 35 degrees. Engines are engines and they all work the same. Our Rover engine is a GM engine after all.

    If you engine is running better with the vacuum advance connected to manifold vacuum and of course it is you might have it to far retarded. Dose it ping at all? If not keep advancing the dizzy until it dose and them back it off a little.
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    Sorry mate don't agree with you and nor do many. Mine runs better on manifold its got 12 degrees static at idle that when i hook up vacuum advance rises to 16-18 degrees. No pinging. It'll stay where it is thanks

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    To clarify i contacted Performance Ignition in Nunawading who built the dizzy and spoke to the owner. He recommended manifold vacuum and IF that didn't work then go to ported. Heres another article by GM engineer Fyi which seems pretty thorough.

    Ported vs manifold vacuum advance - The BangShift.com Forums

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    Quote Originally Posted by FisherX View Post
    Vacuum advance is only needed on cruising at partial throttle when the mixture is lean. So I agree with part of your link.

    But don't agree with the rest of the article

    Vacuum advance is ALWAYS ALWAYS ALWAYS connected to a ported outlet on the carbs.

    And and setting your timing at say 12 deg BTDC is all well and good but what is your total advance??

    When I set timing I'm looking at total advance. Yes 12 deg BTDC is a good place to start but you want to look at total advance.

    Set the timing up so the car runs nice but then rev it up until about 3000rpm until the mechanical advance it maxed. That should be 32 - 35 degrees. Engines are engines and they all work the same. Our Rover engine is a GM engine after all.

    If you engine is running better with the vacuum advance connected to manifold vacuum and of course it is you might have it to far retarded. Dose it ping at all? If not keep advancing the dizzy until it dose and them back it off a little.
    That’s how I do mine, no idea what the actual figures are. In Winter I can wind in a couple extra degrees as well, it’s only when it’s stinking hot and the vehicle is under high load I can’t get away with that so end up keeping it in its ‘Summer’ setting mostly but I can notice the difference if I faff with it and get a bit more in there. 😇
    If you need to contact me please email homestarrunnerau@gmail.com - thanks - Gav.

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    My POS ran on gas with manifold vac for years with standard points / coil / condenser. Ran much better than ported vac.

    Recently converted the dist to electronic with a great kit from the US (FAST brand) with their module and coil.

    Wasn't totally happy with the performance outcome so went back to ported and it's great now. Really good idle and plenty of poke.

    cheers, DL

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    Intent of thread was that it seems that either work in some situations its not black and white. But also in my case not even something I'd have considered

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    In 'theory' on gas you want all advance in with low revs reducing to something like 10 or something degrees at cruise. Light mech weights in the dizzy help to do this (apparently........haven't tried this yet) along with initial static timing.

    Petrol needs more advance at cruise revs apparently, and less down low.

    Where the vac comes from does make a good deal of difference IME. All a bit of a black art all the same.

    DL

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    I just found this, Uncle Tony backs me up.\

    The Vacuum Advance Debate! - YouTube
    04 L322 Vogue V8 - Work truck
    07 Freelander 2 TD4 SE - The wifes
    74 Leyland P76 Targa Florio - Aspen Green
    91 Kawasaki GPZ900R


    Previous LRs = 78IIa series - 81, 93, 95 RRC - D2V8

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    Thats the issue. There's opinion on both sides. I've seen Uncle Tony comment. And frankly anyone that leaves lit cigarette in fender while talking/adjusting I lose interest. But thats all it is opinion. I'm saying - try both see which works best for your engine.

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