Results 1 to 10 of 10

Thread: Ported or non ported for vacuum advance

  1. #1
    Join Date
    Oct 2011
    Location
    Sunshine Coast
    Posts
    1,087

    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/

  2. #2
    Join Date
    Apr 2015
    Location
    Hervey Bay
    Posts
    349
    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.
    04 L322 Vogue V8 - Work truck
    07 Freelander 2 TD4 SE - The wifes
    74 Leyland P76 Targa Florio - Aspen Green - project
    91 Kawasaki GPZ900R
    96 Seadoo HX Jet Ski

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

  3. #3
    Join Date
    Oct 2011
    Location
    Sunshine Coast
    Posts
    1,087
    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

  4. #4
    Join Date
    Oct 2011
    Location
    Sunshine Coast
    Posts
    1,087
    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

  5. #5
    Homestar's Avatar
    Homestar is offline Super Moderator & CA manager Gold Subscriber
    Join Date
    Aug 2010
    Location
    Sunbury, VIC
    Posts
    17,864
    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.
    Thatís how I do mine, no idea what the actual figures are. In Winter I can wind in a couple extra degrees as well, itís only when itís stinking hot and the vehicle is under high load I canít get away with that so end up keeping it in its ĎSummerí setting mostly but I can notice the difference if I faff with it and get a bit more in there. 😇


    1977 101 FC - 'Chucky'
    1986 Classic RR - 'Thing'
    1976 Series III Tray
    1997 Honda CBR1000F
    2003 L322 - Gone to a new home.

    'Love with your heart - use your head for everything else.' - CaptainDisillusion

  6. #6
    Join Date
    Mar 2008
    Location
    Bellarine Peninsula, Brackistan
    Posts
    3,153
    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

  7. #7
    Join Date
    Oct 2011
    Location
    Sunshine Coast
    Posts
    1,087
    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

  8. #8
    Join Date
    Mar 2008
    Location
    Bellarine Peninsula, Brackistan
    Posts
    3,153
    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

  9. #9
    Join Date
    Apr 2015
    Location
    Hervey Bay
    Posts
    349
    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 - project
    91 Kawasaki GPZ900R
    96 Seadoo HX Jet Ski

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

  10. #10
    Join Date
    Oct 2011
    Location
    Sunshine Coast
    Posts
    1,087
    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.

Tags for this Thread

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Search AULRO.com ONLY!
Search All the Web!