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Hot Rods Myth and facts of ignition timing explained

Discussion in 'The Hokey Ass Message Board' started by 2FORCEFULL, Jul 24, 2024.

  1. Jack E/NJ
    Joined: Mar 5, 2011
    Posts: 963

    Jack E/NJ
    Member
    from NJ

    Hand cranking with too much initial advance.

    handcrank.jpg
     
    427 sleeper likes this.
  2. G-son
    Joined: Dec 19, 2012
    Posts: 1,475

    G-son
    Member
    from Sweden

    "Running great" does not in any way say it couldn't run better, and/or consume less fuel. I dare say that most modified engines never get the ignition and carbs perfectly adjusted, people just get it good enough and settle there. Some times good enough is actually pretty close to ideal, some times it's way off.
     
  3. Adriatic Machine
    Joined: Jan 26, 2008
    Posts: 806

    Adriatic Machine
    Member

    Thank you for this, definitely cleared up some confusion for me.

    I have to say you guys are the salt of car culture. I love reading the articles on fine tuning and tuning fundamentals in general. I worked at dealerships from 88-96 when tuneups had been simplified so I’m playing catch up. Big thanks
     
    2FORCEFULL likes this.
  4. And YOU know this how?

    Ben
     
  5. ALLDONE
    Joined: May 16, 2023
    Posts: 3,168

    ALLDONE
    Member

    What you about to read is the opinion, not factual data, nore has it been proven in any study''''''''''''''''
    I've always considered vacuum timing as fake timing, and never include it to my total timing because it's just not there,.. On my drag cars, never used it... but always use it on street cars... what I think it does is cleans up the cylinders on a off and on throttle situation, as it comes in when you let off the gas.and help burn up the unused fuel..So, I don't count it... it's also there in the bottom end of rpms... so it help to push the motor to when the mechanical kicks in... so if ever asked "how much timing you runn'n" like most racers, I reply what I have at WOT... Kind off a false state ment if you don't say all in at max RPM I have 35,... but in my 71 years never heard the reply....@ 1000 16 @2000 22 @3000 35, but @ cruising I have 50 and back to 35 at WOT.... so now I'll will answer What is timing????
     
  6. G-son
    Joined: Dec 19, 2012
    Posts: 1,475

    G-son
    Member
    from Sweden

    Most people run out of equipment, patience or skill long before everything is adjusted perfectly. Just look at the people who have set up their carbs just using trial & error on the street, and then put a lambda meter on it. Some of the adjustments can be pretty good, while others can be way off and they had no idea.
    Ignition can be rather complicated too, if you don't just take a distributor, put it in and dial in the static setting. There's a lot of work involved if you are going to test how much advance to add as rpm goes up, at what rpm it should start and at what rpm it needs to finish. Then the same for vacuum advance; at what vacuum to start, when to finish, and how much advance it should add.

    Lots of people can get rather good results by trial & error on the street, lots of people can not. Testing it very carefully on a dyno can get it perfect, but that's a lot of time involved and will be expensive if it isn't your own dyno. Almost everyone settles with good enough rather than perfect.
     
  7. ALLDONE
    Joined: May 16, 2023
    Posts: 3,168

    ALLDONE
    Member

    thats why I miss national speed in vegas... in the 70's they had a dizzy wizard , you take him your dist. and he would set the curve to match what you were doing..
     
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  8. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 5,992

    2OLD2FAST
    Member
    from illinois

    LOL , and every time the weather changes , it's not perfect , perfect is an illusion !
     
  9. G-son
    Joined: Dec 19, 2012
    Posts: 1,475

    G-son
    Member
    from Sweden

    Also true.
     
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  10. VI Lonewolf
    Joined: Sep 2, 2017
    Posts: 80

    VI Lonewolf

    To quote a guy I have immense respect for, "the best you know is the best you've had"
     
  11. gimpyshotrods
    Joined: May 20, 2009
    Posts: 24,403

    gimpyshotrods
    ALLIANCE MEMBER

    Exactly zero vehicles with carburetors that I have tuned since I started using a wideband Oxygen sensor were tuned properly when they came in.

    Most "ran great", according to their respective owners, when they came in.
     
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  12. ALLDONE
    Joined: May 16, 2023
    Posts: 3,168

    ALLDONE
    Member

    I would say that would be somewhere in the 90%, most don't drive the cars enough to care
     
  13. hrm2k
    Joined: Oct 2, 2007
    Posts: 5,366

    hrm2k
    ALLIANCE MEMBER

    Kind of reminds me of the old Germ threads.
    same substance without the cuss words or drug references :rolleyes:
     
  14. 1971BB427
    Joined: Mar 6, 2010
    Posts: 9,678

    1971BB427
    Member
    from Oregon

    I've built and owned numerous cars that I ran no vacuum advance on at all. Especially on lighter cars. I use a vacuum advance on my '39 Chev because it's a heavy car, but my lightweight 2300 lb. Austin with a very healthy SBC has never had a vacuum advance, and runs great now for 13 years without.
     
  15. G-son
    Joined: Dec 19, 2012
    Posts: 1,475

    G-son
    Member
    from Sweden

    Yes, vacuum advance is more important for fuel economy than how it runs. Without it you just have to step a bit harder on the pedal to get the same amount of power in low load situations, meaning you burn more gas to get the same performance. If you don't mind burning more fuel you'll be fine without it.
     
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  16. Marty Strode
    Joined: Apr 28, 2011
    Posts: 9,590

    Marty Strode
    Member

    Or don't flip the ignition switch until the engine is spinning over.
     
  17. ALLDONE
    Joined: May 16, 2023
    Posts: 3,168

    ALLDONE
    Member

    11070256_852738288096476_1368725074892055817_n.jpg
    when I was running A/f they put rollers in at the vegas strip... you get the back tires on and let them spin, hit the mag switch and hope she lights.... wasn't soon after you had to have a starter....then when running AA/BAD , rear engine We made the last pass at orange county where you didn't have to have reverse...battery boxes and starters... then had to back up on your own...
     
    Last edited: Jul 27, 2024
  18. ALLDONE
    Joined: May 16, 2023
    Posts: 3,168

    ALLDONE
    Member

    wwell, I did learn something, or something I wanna check.... made it back to vegas and I gonna hook up the timing light un plug vac adv on dist. and hook up a vacuum gauge...I gonna bet that with the cam I got that I won't be near 16'' vac. but gonna find out, then at 3000 rpms I'm gonna hook vac adv back up and see what the advance is at 1000,2000,3000 rpms...... interesting
     
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  19. gimpyshotrods
    Joined: May 20, 2009
    Posts: 24,403

    gimpyshotrods
    ALLIANCE MEMBER

    If this thread did anything helpful, it did bring together many in agreement that don't often agree with each other.
     
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  20. gimpyshotrods
    Joined: May 20, 2009
    Posts: 24,403

    gimpyshotrods
    ALLIANCE MEMBER

    Why does it seem like this phenomenon is on the rise?
     
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  21. ALLDONE
    Joined: May 16, 2023
    Posts: 3,168

    ALLDONE
    Member

    Ok, so now that everyone is being nice.....one more myth fact buster....

    question, do you run vac. adv.. if so why?? and if not why???

    next question... do you run ported or manifold vac...

    through the years, I've had mech. that would open the hood, see the vac line and switch it...and I'd get the same answer no matter which way they did it.... because it'll run better..
     
    G-son likes this.
  22. Straight eight Buicks == ported vacuum advance. So NO vacuum advance at idle.

    Ben
     
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  23. Driver50x
    Joined: May 5, 2014
    Posts: 541

    Driver50x
    Member

    How do you do that exactly. Do you have to weld a bung to their exhaust pipe?
     
  24. Fordors
    Joined: Sep 22, 2016
    Posts: 6,294

    Fordors
    Member

    I prefer manifold and the one on my 350 LT-1 built for around town and highway use has an Accel vacuum canister that was actually made by GM for the 1968 GTO. The engine has 8.6-1 compression, I switched to the 327-350 horse cam, it has '186 big valve heads and a 6-71 @ 15% under on a Weiand blower manifold with a 2" drive. Carbs are two 1850's with direct linkage and the distributor is an iron Delco with an old MSD-6 box. I have no idea what the engineers designed that vacuum can for.
    The Accel advance unit has a maximum of 20° advance and 8° retard @ 2° per pound of boost. With 3.36 gears and 31" tall tires the engine is loafing along at 2600 rpm/71 mph. @ 16" vacuum. The car hasn't been out in years but road trips were at 17.5-18 mpg. Accel marketed that unit for their turbocharger kits decades ago.

    Here's a link to the Accel can instructions- https://www.jalopyjournal.com/forum...m-advance-can-for-delco-distributors.1287885/ Scroll down to post #11.
     
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  25. gimpyshotrods
    Joined: May 20, 2009
    Posts: 24,403

    gimpyshotrods
    ALLIANCE MEMBER

    Yes.

    I bought a box of 100. I have 1 or 2 left.

    Some might cough at that, but I will no longer tune without it.

    I have now had three customers claim that I damaged their fuel gauge when I worked on their vehicle.
     
    Last edited: Jul 29, 2024
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  26. gimpyshotrods
    Joined: May 20, 2009
    Posts: 24,403

    gimpyshotrods
    ALLIANCE MEMBER

    I won't wire one with a toggle switch, unless it is through the 4th gear pressure switch.

    That's only if the customer plans on towing, and even then I always recommend not using 4th (OD) then.

    I know two people who had toggle-only, who forgot to switch off at a stoplight.

    Both hit the car in front of them. Both hit cars were totaled, and one hitting car was too. Both hit parties were injured.

    Don't do that.
     
  27. justpassinthru
    Joined: Jul 23, 2010
    Posts: 610

    justpassinthru
    Member

    Why? Could it be because its not going down as fast?

    Bill
     
    Last edited: Jul 28, 2024
  28. @2FORCEFULL , while some may not agree, here is how I like to run.
    Street driven quadrajet, crate 350 with 700R4 and 3:55 rear axle.
    Anyway, I use manifold vacuum as the extra advance coming in after the engine fires allows me to lower the idle speed. The extra advance is a big help with slower heat buildup while stopped at traffic lights.
    Vacuum advance, on top of some or all mechanical advance, also helps fuel mileage while cruising at light throttle highway speeds.

    I look forward to hear what you learn by playing with your vacuum gauge.
     
    Last edited: Jul 28, 2024
  29. gimpyshotrods
    Joined: May 20, 2009
    Posts: 24,403

    gimpyshotrods
    ALLIANCE MEMBER

    Yup.

    One filled his tank by his home before he drove it in. He rolled in on a half-tank.

    When he got home he was furious that I wrecked his gauge.

    He said it moved only the width of the needle, and he was driving it hard.

    I changed his jets, power valves, timing, and spark plugs.
     
  30. GlassThamesDoug
    Joined: May 25, 2008
    Posts: 1,868

    GlassThamesDoug
    Member

    Ironically, I had some fun with a big dome 283 a few years back. Would run 1-2gear a little 3rd. But what I found with a 5/8 deflector dome on old style camel hump heads, was it ran OK at 40deg, then bumped to 50drg pulled wheels in second. When I moved it to 55 deg, it carried the wheels in second. Old early 70s cam, high compression, good fuel.

    Now then, a Racer my Father raced with ran these domes, way back. He kept all his notes on every pass, build performance. While I was in Arizona, he pulled out his old books, looked up that piston and smiled. Look what it says, best performance was 55deg, to prevent double firing. His theory was the tall domes inhibit flame travel. Thought that was pretty neat, that 2x people 40yr apart arrived at same timing.

    Track only, short bursts obviously.

    Never say Never.
     
    Charlie K, G-son, rod1 and 4 others like this.

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