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Thread: spark dwell...can somebody give heavy details

  1. #121
    Advanced Tuner INTHERED's Avatar
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    Thanks for answering all of my questions - INTHERED
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  2. #122
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    For boosted applications and controlling knock I don't think dwell is going to help you - as RHS said. Problems arise when you have too little dwell causing misfires, but too much dwell will only burn coils.

    If I were you, I would fit a set of BFR7 NGK plugs.

  3. #123
    Quote Originally Posted by tjwong View Post
    I finally called MSD to find out what their rated maximum dwell time is for their coils. After speaking to one of their developement engineers in El Paso, I was told that their coils were rated at 3.5ms maximum dwell time.
    3.5ms at what voltage?
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  4. #124
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  5. #125
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    Any core only has so much flux it can store. Beyond this
    point current makes heat, not additional spark energy.
    You could determine the saturation current (or old-timey
    power supply guys still talk volt-seconds, which seconds
    are your dwell) pretty simply on the bench.

    Different coils have different cores, flux capacities and
    temperature withstand.

    Dwell is only the energy put into the hole (plus losses).
    It's not going to help spark knock any. A better burn
    may in fact do better at combustion and cylinder
    evacuation / fill, and make you -more- ping-prone if
    the burn is cleaner. That just says you need less advance.

    If you're "on the ragged edge" of KR it means you have
    gone past MBT timing and can back off some. Couple of
    degrees at least. Assuming everything is clean. Of course
    injector imbalances and such can give you a weak (lean)
    cylinder that does all the pinging, while the others are
    under-advanced or over-fueled.

  6. #126
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    Quote Originally Posted by jimmyblue View Post
    Any core only has so much flux it can store. Beyond this
    point current makes heat, not additional spark energy.
    You could determine the saturation current (or old-timey
    power supply guys still talk volt-seconds, which seconds
    are your dwell) pretty simply on the bench.

    Different coils have different cores, flux capacities and
    temperature withstand.

    Dwell is only the energy put into the hole (plus losses).
    It's not going to help spark knock any. A better burn
    may in fact do better at combustion and cylinder
    evacuation / fill, and make you -more- ping-prone if
    the burn is cleaner. That just says you need less advance.

    If you're "on the ragged edge" of KR it means you have
    gone past MBT timing and can back off some. Couple of
    degrees at least. Assuming everything is clean. Of course
    injector imbalances and such can give you a weak (lean)
    cylinder that does all the pinging, while the others are
    under-advanced or over-fueled.
    2016 Hellcat Challenger, automatic, black on black with brass monkey wheels

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  7. #127
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    So it is best to keep the dwell tables and multipliers stock?
    2016 Hellcat Challenger, automatic, black on black with brass monkey wheels

    10.13@ 140 DA 5000 feet
    2.75 pulley, tune, drag radials. 10 percent lower od crank pulley, 1050 ix. off road mid pipe. tune

  8. #128
    Tuner ari666's Avatar
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    hi im sorry to dig up an old thread, but i have a slightly different issue and there seem to be some smart guys in here.

    im running the L29 vortec 454 tune from the repository, and im trying to dial it all in. ive hit the dwell time tables and it interests me that the dwell time seems to fall over rpm, i was wondering if anyone could shed some light on why it would do this?

    the 454 runs a single coil, HEI spark and a dizzy. the coil is a msd 8231 but i cant find any solid prime ms figures for it, id guess 3.5ms. would it pay me to just drop 3.5ms in all rows and columns? since it was mentioned rpm has no affect on saturation? my guess would be that running 8 cylinders might start demanding too much from 1 coil and it starts interfering with each spark event, but id like to get other opinions.

    ive looked up the tune for a V6 astro which shared the same coil/dizzy setup and they also have falling ms responses over rpm, but only a single row, not many rows depending on voltage like my bastardised tune. they also start much much higher and fall faster.

    ill load up both tunes and hope someone has an answer, thanks in advance

    .26-03-17spark timing.hpt 1999 v6 astro.hpt
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  9. #129
    Advanced Tuner Obsolete489's Avatar
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    I don't have an answer regarding the spark dwell, but maybe I can help since its an L29. What issues are you having?
    2000 K2500 - 489 CI Vortec w/ comp XE270 cam - 0411 swap and rear mount turbo
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    2011 LML Duramax

  10. #130
    Tuner ari666's Avatar
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    not so much an issue, more just trying to get everything nailed so it runs like a clock.
    1966 impala. L29 454. 0411 pcm. 2.5" twin system. comp cams XR282HR. ported heads. 1.75 rollers. 60lb deka injectors. bosch 044 pump. standard intake (cos' looks cool in a 66')

  11. #131
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    Hi,

    Sorry I don't know the engine etc., but as you likely read, the main issue is too much dwell will fry the coil, especially in a single coil engine, where its working much harder. Thats why the dwell is less at higher RPM - so the coil doesn't melt, lol. More sparks per second = more heat...
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  12. #132
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    Quote Originally Posted by WS6FirebirdTA00 View Post
    I have tested this from stock cars to 700+ hp cars, NA, FI, nitrous, no power was gained.
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