whats the theory behind a hi-speed retard?

Discussion in 'Competition Camaros' started by 4-71/Z-28, Jun 8, 2008.

  1. 4-71/Z-28

    4-71/Z-28 Veteran Member

    Jul 16, 2005
    i know its supposed to help with mph towards the end of the track, but how does it help? and does it saccrifice et for mph? im just looking for those last hundredths to officially be in the 9's on motor!!
  2. Mwilson

    Mwilson Veteran Member

    wow 9's on motor!
  3. GetMore

    GetMore Veteran Member Lifetime Gold Member

    Nov 8, 2004
    Patterson, NY
    At the lower engine speeds you need to advance timing to make sure peak cylinder pressures are just after TDC. As the engine gets faster you need to light off the mixture sooner to achieve this.

    Now, for some reason, as the engine speeds increase past a certain point you actually need to decrease timing, since the higher mixture speeds and temperatures (IIRC) make it so that the mixture burns quicker.
    That is how the high speed retard works. It takes a few degrees of timing away so the engine isn't fighting itself too much. This gives you more power at the top end.
  4. KansasTwister

    KansasTwister Veteran Member Lifetime Gold Member

    Oct 7, 2006
    Lawrence, ks
    my old man (ex ahra three world record drag racer, hasnt raced now in 30 years, still got all 4 cars) was trying to figure out what this was a few years back. I dont think he ever did. How do you do it? what triggers it? i know he said sometihng about a switch on a 4 speed to trigger it in 4th gear.
  5. Dirt Reynolds

    Dirt Reynolds Veteran Member Lifetime Gold Member

    Jan 17, 2003
    BC, Canada
    The high-speed retard deal is something the older racers used to use a lot. It does work, usually adding a few mph at the lights. The Hays Stinger ignition was the first to incorporate this feature. It pulled 2° out at the top of the tach and was popular with the GS Buick guys for many years. Pretty much as GetMore said, at high engine RPM there is physically not enough time for the burn cycle as there is at lower RPM's, so taking a couple of degrees of timing out at the higher RPM range would allow the engine to build more power.
  6. rustbucket79

    rustbucket79 Veteran Member

    My theory, engine load is at it's highest (least amount of gearing) and RPM climb rate is at it's slowest, contributing to combustion heat and detonation. I believe it was more prevalent back in the early days when it was common to be running 40+ degrees timing and perhaps not the best fuels and combustion chambers. I do know my 327 was a timing hog, kill the timing, kill the torque. My 14.5:1 406 is happiest at 34.5 degrees, one of the 14:1 565's I built was happiest at 32 degrees, I doubt a retard would help either of those 2 combos, but despite having the ignition boxes to try a retard, I have never bothered. Gotta eliminate the variables in bracket racing as much as possible hehe.
  7. TheFly

    TheFly Guest

    "whats the theory behind a hi-speed retard?"

    Last edited by a moderator: Jun 9, 2008
  8. hhott71

    hhott71 Veteran Member Lifetime Gold Member

    Mar 30, 2001
    Joplin Mo. 64801

    Rust's theory sounds pretty good.

    They used to run dual points "back in the day"
    and would kill one set of points in high gear to reduce timing a few degrees.

    With the computers / electonics of todays ignitions, a bit of playing may yield results and easily tell what's happening on a datta-logger.
  9. Dirt Reynolds

    Dirt Reynolds Veteran Member Lifetime Gold Member

    Jan 17, 2003
    BC, Canada
    It has to do with time -- the higher the RPM the less time there is to get the burn cycle completed. As GetMore said, the engine spends less time "fighting itself" with the timing retarded a few degrees in high-gear at the top of the tach. If I remember correctly Hays had this same type of basic description included with the Stinger boxes they sold, explaining the reasoning behind the high-speed retard function.
  10. mrdragster1970

    mrdragster1970 Veteran Member Lifetime Gold Member


    As said, it does work, I will vouch for that. It can give you a tiny bit of ET, but more for MPH. I've seen guys do it to break a certain mark,
    130, 140, 150 ect. Guys used to think it helped trick guys when bracket racing, like a small N2O hit.
    To me, it's just something else that can go wrong. Unless you're a big power N2O, boost type engine, most guys don't bother anymore.
    Even if everything is set up automatically, it's just more headaches in my book.
    Good luck.


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