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Hot Rods BBC timing...

Discussion in 'The Hokey Ass Message Board' started by babblewon, Dec 13, 2015.

  1. babblewon
    Joined: Aug 19, 2007
    Posts: 202

    babblewon
    Member
    from cali

    Ok, so I need some help here with timing. I'm timing a pretty stock 454 with non hei distributor, but it's kinda a general question as well. No vac canister.

    So I have a basic timing light without ability to dial in timing, so light only. I want to set my initial timing.

    I pulled the vac line from the dizzy to carb and plugged them. I then set the timing on the balancer at 10 advanced. I can't do total with my light (that I know of) so I plug the vac advance back in and set my idle. So now when I shoot the timing light at the balancer the timing mark is advanced way before the any numbers start. Is this right? I feel like it is too crazy advanced now?!?

    Before I started this I checked the timing with the light on the balancer with the vac line hooked up to the carb like I drive it and it was reading at 10 advanced. I was having some hesitation issues which prompted me to check the timing.

    Should I buy a new light so I can set the total timing? I mean back in the day they didn't have fancy lights so I thought if I use my basic light and set a decent initial timing I would be good.

    If anyone can help, can you dumb down the answer, I am not too experienced with tuning. Thanks guys
     
  2. First of all, there are no easy answers without a little more info. Back in the day we used to put a timing tape on the balancer to check the total advance, but the minute you stood on the gas, the tape would fly off. lol

    It would be better to get a new adjustable light.

    Second, it sounds like there is way too much vaccum advance at idle. Most vaccum advances give about 20*. I like the adjustable ones and limit them to about 8*-10*. It also matters whether you hook the vaccum advance to the manifold vaccum or the ported source at the carb. I like the manifold vaccum.

    Third, I like a lot of initial advance (about 15*) with about 10*-12* mechanical advance. That gives a lot of torque at low speeds and a light accelerator pedal feeling and much better gas milage. Add the 8*-10* vaccum advance on top of that and things work pretty good. When you hit the gas for passing, the vaccum goes away and you're back to about 25*-27* for no pinging.

    Now, it all depends what altitude you're at, how much load you're pulling and what octane gas you're using. Plus, what cam you have, what heads you have, how much cranking compression you have, etc.

    See, it can get kinda complicated! Sorry, I don't know how to dumb down the answers, I only know how to educate the pupil.

    Last of all ,if you live where you need to have e-check, you aren't supposed to do this.
     
    Last edited: Dec 13, 2015
  3. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    I would get a light with a dial or knob or readout....if you don't have access to a distributor machine, then you have no way of knowing how much advance the distributor has.

    I aim for around 36 degrees or so on a big block Chevy, total timing "all in", but with the vacuum hose disconnected.

    Some engines like vacuum advance at idle, some don't.
     
  4. All in at what RPM?
     

  5. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

  6. GearheadsQCE
    Joined: Mar 23, 2011
    Posts: 3,375

    GearheadsQCE
    Alliance Vendor

    I'm a little confused about this. I believe you have a vacuum canister and correctly disconnected it.

    I'm not a big block expert but here is what you can do:
    1. Disconnect vacuum line (like you did)
    2. Plug the carb or manifold side of the hose (the distributor side can be left unplugged)
    3. Adjust the idle speed to what you want it to be when you finish.
    4. Check and adjust the initial timing. I would start with factory specs. You said that you are new to this so you can use the practice.
    5. Snug down the distributor clamp (enough so you can turn it , with effort)
    6. While watching the timing mark, speed the engine up a little at a time until it stops advancing. Note that speed.
    7. Still watching, let the engine return to idle. If the timing goes back beyond your initial setting, you have slop in the timing chain.
    8. Plug the vacuum hose back on the can. The timing will probably increase a bunch. (If you have a ported vacuum connection, it might not until you have opened the throttle a little)
    9. Reset the idle to your desired spec.
    10. If you're not tired of this by now, you can drive it and then bump up the timing a little at a time until you optimize it, whatever that is.
    Like Squirrel said, you probably want the to limit the total advance to about 36 degrees. This is centrifugal advance + base timing. The easiest way to do this is use a dial back timing light. If you do buy one of these, buy a good one. The cheap ones are very erratic. The other way is to mark the harmonic balancer. As Montanal said you can get a timing tape. These will fly off if you don't get the damper spotlessly clean.
    Here is another way:
    Measure the diameter of the balancer. The more accurately you measure, the more accurate you result will be.
    Then do this math;
    c=pi x d Circumference = 3.14 X diameter Example: 3.14 X 8" = 25.2"
    Now divide by 360 25.12/360 = .0697 rounded to .07 (tis gives you 7 hundrenths of an inch equals 1 degree.
    Multiply that by 36 (total advance desired) = 2.52"
    Now make a mark 2.52" (2 1/2" is close enough) from the TDC mark on the balancer (be sure you make it 'before' TDC)
    Now you can accurately check the total timing.
    A fair amount of work, but I taught Autoshop for many years. I had many students that had zero money and wanted to play racer. This is the exercise I put them through. The main reason, of course , was to make them "think" and understand what was going on.

    Also, when you make big changes to timing, you need to check and adjust idle mixture to optimize it. Then there is carb tuning. Don't get me started on that!
     
  7. babblewon
    Joined: Aug 19, 2007
    Posts: 202

    babblewon
    Member
    from cali

    Sorry for the confusion, I disconnected the hose from the vac on the dizzy.
    Awesome info thanks. I'm gonna do the math and mark the balancer. Now if I'm looking at the balancer from the front, would I mark it to the right of the factory line to make an advanced mark? (I'm marking the balancer itself right?)

    So now I would...
    1) do the math and mark my balancer.
    2) disconnect the vac line/plug it
    3) set the new mark on the balancer to 0 tdc
    4) plug vac line back in

    The only thing I don't understand is if I set my total all in with the vac line off, then when I plug the vac line back on, am I adding more advanced timing? Sorry I'm slow
     
  8. BobMcD
    Joined: Jan 25, 2013
    Posts: 322

    BobMcD
    Member

    Total advance is intial timing plus the mechanical advance. Vacuum advance would be additional.
     
  9. babblewon
    Joined: Aug 19, 2007
    Posts: 202

    babblewon
    Member
    from cali

    Ok just found and read this...

    http://www.jalopyjournal.com/forum/threads/sbc-mechanical-advance-timing.815611/

    I'm starting to understand, basically I was setting my initial timing with vac connected because I didn't understand that the vac advance added does not calculate into the total "all in".
    I was thinking my 36 or so total was including my vac advanced.

    Damn, no wonder I had hesitation, my initial timing was including vac advance at idle
     
  10. GearheadsQCE
    Joined: Mar 23, 2011
    Posts: 3,375

    GearheadsQCE
    Alliance Vendor

    I see the light bulb coming on. ;)
    You always use the TDC mark to set the initial timing. The mark at 36 degrees (or so) is just to verify that the centrifugal advance is correct. When you bump the initial timing up, the total timing can get out of hand. If that is the case, you have to rework the distributor to limit the advance. It can be done in the car, but it is a lot easier to do in a distributor machine.
    Then you have to learn how to remove and install the distributor.
    Read this thread to see many opinions on the best way to do that.:D
    http://www.jalopyjournal.com/forum/threads/sbc-distributor-and-the-one-tooth-off-myth.1000209/


    Sorry, I forgot to answer you about which way from TDC to mark the total advance. Look at the balancer while the engine is running. The new mark should be 'before' the TDC mark going by the timing tab. Just want you to think it through, so when someone tells you the wrong thing (here or anywhere else) you will KNOW.
    By the way, the direction the crankshaft turns is always determined from your prospective while sitting in the driver's seat. Report back on this. Clockwise or counterclockwise? :confused:
     
    Last edited: Dec 14, 2015
  11. theHIGHLANDER
    Joined: Jun 3, 2005
    Posts: 10,245

    theHIGHLANDER
    ALLIANCE MEMBER

    Squirrel is right, 36 total, but that assumes some hi perf work. Garden variety 454s like about 34 all in. Manifold vacuum makes the pod a load compensation device (desirable on a 4" stroke) and gives a clean crisp pedal feel
    It's also handy for towing which is a 454 strong suit. Good luck.
     
  12. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    thanks for the mention of high perf work affecting timing requirements.....I guess I've never worked on a stock big block :)
     
  13. So the timing was set at idle, we don't know what idle is or was but that is no problem. If you set the timing and the engine runs and pulls fine total advance makes absolutely no difference. It is running and pulling just fine.

    if you are building or tuning a performance engine then total timing is a big deal on a stock motor doesn't matter if it is a flathead 4 or a BBC what matters is if you can drive it and it makes you grin when you do.

    Now if one is serious about total timing, and one does not own a distributer machine one is only guessing with a dial up timing light. They are seldom accurate and to be accurate that need to be calibrated on a consistent basis. if total timing means the difference between winning or loosing and you don't want to spring for a distributor machine a timing tape on the balancer is what you use. You find true TDC and then add the tape to the balancer, light it off and hit it with your light.
     
  14. babblewon
    Joined: Aug 19, 2007
    Posts: 202

    babblewon
    Member
    from cali

    Ok so I got to mess with it a little tonight.
    I started by plugging the vac line. Then I retarded the timing down to about 6, then bumped idle until the timing stopped advancing (about 2500 rpm) that brought it 16 advanced. So would this make my mechanical advance about 22?

    I then set the idle at about 850 rpm and went about 8 advanced on initial. This is roughly 30 total? This of course is all an estimate, but it's a stock street motor. I then connected the vac back to ported and set my final idle. Seems to run good, exhaust has a little random pop to it now when idling. My biggest concern now is the bastard is a son of a bitch on hot start.

    I didn't re-mark the balancer, but figured if looking at it I would mark to the right or before tdc.

    I also have a kinda small cranking amp battery in it so that could be part of it. It's a 700 cca for a compact car. Used it for size, maybe a mistake. Before I advanced the timing it would hesitate a second on hot start, but not like this.
     
    Last edited: Dec 14, 2015
  15. GearheadsQCE
    Joined: Mar 23, 2011
    Posts: 3,375

    GearheadsQCE
    Alliance Vendor

    You are getting the gist of it now. What you are finding out, is that just setting the timing based on some number that someone said would make it a killer is a bunch of hogwash.
    My take on where you are now, is that you need to set the initial timing to where it starts easily, hot or cold. Then, you work with the vacuum and mechanical advance(s) to optimize the performance. Try retarding the timing by two degrees and see if that helps or hurts the hot start problem. If it makes it worse, advance it a couple of degrees from your 8 degree starting point. You should be able to see a significant change with a 4 degree swing.
    Reading some other threads on here reminded me of another common practice (from years ago). With the vacuum advance connected, set the timing to obtain the highest vacuum reading at idle. Then, disconnect the vacuum advance and see what the initial timing is, for future reference. Of course, this requires that you have a vacuum gauge. It doesn't need to be an expensive one, you are only looking for the highest reading. The actual number doesn't matter.

    You could probably use more battery but if it is a 700 CCA in good condition, it should crank your BBC quick enough to start it. Good tune up shops have low rpm tachs that measure cranking rpm. Somewhere around 175 should get that puppy fired up. If it is way below that you need to do a starter draw test. If the starter is pulling too much current then you won't have enough rpm to start. Also, if the starter draw is really high, it can leave the ignition system lacking.
    The occasional 'pop' at idle tells me that there is something else to find. Is it a lean misfire? Cross fire in the cap? Or leakage to ground from a spark plug wire? Or????????
    You are correct on the direction of the advance mark. 'A' for the day.
     
  16. babblewon
    Joined: Aug 19, 2007
    Posts: 202

    babblewon
    Member
    from cali

    Ok so I do have a vac gauge. I left the vac advanced hooked to the dizzy. I then hooked the gauge up and advanced the timing until the vac stopped increasing. This was at 21/22 on the vac gauge.
    Then I disconnected the vac advanced and checked timing. This was about 3/4 retarded. Being that I wanted an idle advance of 18-24 (I think from reading all night) I set my intial timing to about 1 advanced so at idle with vac advance I'm around where I should be.

    The exhaust noise went away and hot start isn't a problem. I'm gonna try to test drive it when the wife comes home and watches the kid.

    Sounds like I'm where I need to be. Basically I'm 5 more advanced from when I first checked it before all the shenanigans. Once I drive it and can feel it out and fine tune.

    I definitely learned a lot and can't thank you guys enough for the info. At least I have a better understanding of how this stuff works. I'd rather struggle and throw wrenches than pay someone to do it for me.
     
  17. babblewon
    Joined: Aug 19, 2007
    Posts: 202

    babblewon
    Member
    from cali

    image.jpeg 1930 built from scratch by me. Early iron frame 454/350 ford 9" 48-52 f1 front with bell drop axle.
     
    Last edited: Dec 15, 2015
  18. GearheadsQCE
    Joined: Mar 23, 2011
    Posts: 3,375

    GearheadsQCE
    Alliance Vendor

    I like that^^^^^^^
    I've been retired from teaching six years. I still love it when someone wants to learn.
    As you get used to it, you can try bumping the timing up a little and see what happens.
     
  19. Call me crazy but if you run manifold vacuum to the distributor at wide open throttle do you not just have the base timing plus the mechanical advance? If you ran ported vacuum you would have both and run into detonation? There must be a point that when vacuum advance drops off with throttle opening it crosses a point where the mechanical advance is coming into play? Boggles the mind...
     
  20. GearheadsQCE
    Joined: Mar 23, 2011
    Posts: 3,375

    GearheadsQCE
    Alliance Vendor

    Ported vacuum is delayed but only until the throttle gets open a little. This was done for emissions. Too much advance at idle pollutes the air.
    At WOT there is no appreciable vacuum signal at the manifold or ported vacuum ports.
     
  21. Blues4U
    Joined: Oct 1, 2015
    Posts: 7,589

    Blues4U
    Member
    from So Cal

    How did we ever set the timing before there were timing lights with dials on them???

    Like porknbeaner said, find true TDC, add the degree'd tape to the balancer, there you go.

    BTW, 18 - 24 seems like an awful lot of initial advance to me. Seems like 8 - 12 would be more like it. Basically, you want as much as it will take without detonating under hard acceleration. I would be very surprised if it would take 18 - 24 though. Or did I misunderstand what you wrote?
     
  22. babblewon
    Joined: Aug 19, 2007
    Posts: 202

    babblewon
    Member
    from cali

    18-24 is including the vacuum advance at idle. (Manifold vacuum) With the vacuum advance removed and plugged I'm at only 1 advanced.

    Oh and I just drove it. Runs great, tons of power from start through WOT. No pinging, no hesitation and not a bunch of raw fuel smoke when idling anymore.
     
  23. babblewon
    Joined: Aug 19, 2007
    Posts: 202

    babblewon
    Member
    from cali

    Oh and I tried to bring my vacuum down from 20, but the vac can on the distributor was already all the way to the right. Couldn't limit it any further.
     

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