HELP! 65 300 Timing with HEI and Vacuum Advance questions

Discussion in 'Small Block Tech' started by Matthew Taylor, Apr 20, 2020.

  1. So I installed an HEI Distributor in my 65 Special. Minor trimming to the front driver corner of the intake lets me adjust it just fine with no intake bolt replacement. Now I'm trying to set the vacuum advance with it. I know how to adjust the in and out part of the vac advance, and am trying to get them to work in sync with each other for maximum power and reliability.

    So, my question is:

    What is the maximum advance (Mechanical + Vac) I should be tuning for and at what RPM?

    I know initial is set at 2.5 Deg BTDC per the factory specs

    I did a few searches and am probably missing this exact question, so I apologize if this is duplicated.

    Has anyone done this on the 300?

    if anyone is interested, here's the Distributor:

    https://www.swperformanceparts.net/...40-350-HEI-Distributor-65K-Volt-Coi/553533481
     
  2. Jim Nichols

    Jim Nichols Well-Known Member

    Probably want more like 10-12 initial advance with the HEI. You can get an advance curve kit and adjustable vacuum advance. That distributor probably has a performance curve and may have an adjustable vacuum can. No instructions came with it?
     
  3. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Matt,
    Your post is typical, and the reason I wrote this thread over 15 years ago.

    http://v8buick.com/index.php?threads/power-timing-your-buick-v8.63475/

    Forget that 2.5* initial timing. That went out the door when you replaced the distributor with something else. Initial timing specs only apply with a completely stock ignition system, the most important part being the distributor that engine got at the factory. The amount of mechanical advance built into distributors varied widely depending on the year, engine, and car. Being your car is now 55 years old, the original distributor was likely history long ago unless you have owned the car since new and know better.

    Here is the bottom line. Your engine will want 30-34* of advance at wide open throttle to make best power. Vacuum advance doesn't even enter into this at all because at Wide Open Throttle, engine vacuum is at or very close to ZERO. So your best power will be a combination of your initial timing plus whatever mechanical advance you have in the distributor you are using. Not knowing what HEI distributor you actually have there, we don't know how much mechanical advance is in that particular distributor. GM HEI's typically had a lot of mechanical advance built into them. The best course of action is to leave the vacuum advance off for now. Use your timing light to set the maximum WOT advance to 30-34*. Then your initial will end up being what it must be for that particular distributor. Once you determine what maximum WOT advance the engine wants, then connect the vacuum advance and tune that. My initial post in the thread I linked for you has a WORD document on how to set your maximum advance. Read that and ask Questions.
     
  4. Southwest has pretty good customer service. While it only came with basic wiring instructions(I already had that part covered) The design is a knock off in the same quality as the Pertronix or Proform knock off of the MSD HEI. All have the same issues with 215/300 stock intake manifolds and required grinding a bit off the intake and head to give full adjustment swing. SO the recurve kits are abundant and any technical instructions out there are similar to MSD. It does have an adjustable can(Came at max advance out of the box, but I tuned it to half way for initial start)
     

  5. I will be asking them for sure. Reading it now, and thanks for all of that. I guess I have to test the springs and see which way I need to go.
     
  6. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Very good. The vacuum advance should be the last thing you adjust. It will depend on how fast you get all the mechanical advance in. In general, you will want you cruise timing up around low to mid 40's for best gas mileage.
     

  7. After looking at the doc and going through most of my notes, my question is this:

    What initial timing mark should I be aiming for on the balancer to begin attempting to start and time the engine and adjust the distributor? Should I just start at Zero and work from there? More questions are sure to come, but this is the only one concerning me as I'm looking to do a first start on the engine with the new distributor. I'm taking your advice and not using VAC.
     
    Last edited: Apr 25, 2020
  8. Mark Demko

    Mark Demko Well-Known Member

    Never mind shooting for an initial timing setting as Larry said.
    Take your dial back timing light, set it for 34 degrees advance, now point it at your balancer, open the throttle slowly until your timing mark on your balancer is at "0"
    If it isn't, rotate distributor a smidge counter clockwise ( you may wanna turn the engine off to do this)
    Restart, and repeat the above until your timing mark comes up to "0" with your dial back timing light set to 34 degrees advance.
     
  9. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    More advance will make it start easier. Turning the distributor CCW will advance the timing. Once it starts, let it warm up and then go from there. Use the lightest springs available. Then set the total advance WITHOUT the vacuum advance. Once you set the total advance, tighten the distributor hold down. Use springs that get the total in by 3000 RPM. Drive the car and make some full throttle runs to listen for audible ping. Adjust the total to eliminate any ping. Once you have tuned the total advance, then add the vacuum advance and again drive the car. Check for part throttle ping. Adjust the vacuum advance to eliminate any part throttle ping.
     

Share This Page