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Thread: engine efficiency with wasted spark vs. sequential ignition systems

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    engine efficiency with wasted spark vs. sequential ignition systems

    Hi!

    Can someone refer to some scientific research or, at least, some dyno measurements, that shows if theres engine efficiency variation between wasted spark and sequential ignition systems? Im focusing specifically in results related to these two firing configurations, supposing the same other parameters (ignition discharge energy, output voltage, spark plug electrodes gap, compression ratio, A/F ratio and so on).

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    Look behind you... Milkman Don's Avatar
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    Arrogant wankeler Slides's Avatar
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    If wastespark was of benefit to efficiency or emissions manufacturers would still be using it. There is nothing stopping them with coil per plug arrangements, they could even multi strike in the power stroke with modern inductive coils if it was beneficial especially as operating speed ranges are being reduced in a lot of stuff to reduce frictional losses.

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    Hi, Slides.

    There are some specific scenarios that require or strongly recommend sequential ignition approach, but I wont mention them here, since I am focusing on some hypothetical engine efficiency difference related to wasted spark and sequential ignition usage.

    Most cars, specially those are not in a higher price range, uses wasted spark approach. Then, sequential ignition is a configuration typically (not mandatory) found in high(er) priced vehicles. As we all know, car makers apply effort to reduce production cost, even on high end cars. So, they wont let cost raise regarding ignition subsystem for nothing, and sequential ignition system is more expensive then wasted spark one. Thus, I suppose that, except for those specific scenarios I mentioned above, makers will always opt for wasted spark configuration IF NO BENEFIT exist with sequential ignition approach.

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    I would have thought it was a tradeoff of cost and redundancy.

    Using a four cylinder as an example, only two coil packs are required for wasted spark, vs 4 for sequential, saving cost.

    However, if a coil pack fails, a sequential fired car with 4 packs can keep running as it still has 3 cylinders working. A wasted spark setup would only have two cylinders running, so less redundancy.

    Just my thoughts, happy to be corrected.

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    Hi, Sprinkles!

    Sure, there are many points-of-view regarding firing approaches, also including what you've considered. When safety is a concern,usage of individual coils is an advantage, not necessarily it means a sequential configuration, since its possible an arrange with individual coils but with wasted spark firing. But thats not the point here, since this thread intends to discuss on engine efficiency.

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    Waste spark coils are more expensive than a sequential coil as they normally operate at higher voltages and they have to fire twice as much which is why sequential coils are tiny in some cases. Yes 4 small coils might be more expensive than two larger more powerful waste spark coils but coil for coil the waste spark coils would cost more so the overall price difference would be negligible imo which is highlighted in the fact I have not seen a waste spark car after 2012. All new cars are sequential these days.

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    if you are after dyno power i probably wouldn't be spending too much time worrying about wasted vs sequential there is stuff all power there if the system is implemented properly
    E30 325is M20 3.1L

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    sack riding 10sec rx7's Avatar
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    Quote Originally Posted by E30is View Post
    if you are after dyno power i probably wouldn't be spending too much time worrying about wasted vs sequential there is NO power there if the system is implemented properly
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    might be able to do individual cylinder tuning better with fully sequential but thats gonna be spendy and not worth effort for most mere mortals
    E30 325is M20 3.1L

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    Hungry Hungry Hippo Tripper's Avatar
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    Quote Originally Posted by E30is View Post
    might be able to do individual cylinder tuning better with fully sequential but thats gonna be spendy and not worth effort for most mere mortals
    but you would probably pick the same amount if you indexed your spark plugs.
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    Quote Originally Posted by Tripper View Post
    but you would probably pick the same amount if you indexed your spark plugs.
    According to the snap-on junkie he used to index plugs on a drag team then moved to another team where they just through them in and he said it made no difference.

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    sack riding 10sec rx7's Avatar
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    Quote Originally Posted by E30is View Post
    might be able to do individual cylinder tuning better with fully sequential but thats gonna be spendy and not worth effort for most mere mortals
    depending on the ecu you can still do cylinder trims with waste spark
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    Quote Originally Posted by S View Post
    According to the snap-on junkie he used to index plugs on a drag team then moved to another team where they just through them in and he said it made no difference.
    I suspect it's a function of a number of factors as to whether there is any benefit to indexing plugs. Location of plug in combustion chamber, airflow characteristics.. I'd think the most benefit would come on engines with really poor head design and low air speed / swirl characteristics.

    There is down sides to indexing - the more you index the plug the lower the compression ratio in the cylinder - with the washers you're pulling the plug further out of the combustion chamber. Also the spark is further away from the center of the mixture.

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    Quote Originally Posted by 36 View Post
    I suspect it's a function of a number of factors as to whether there is any benefit to indexing plugs. Location of plug in combustion chamber, airflow characteristics.. I'd think the most benefit would come on engines with really poor head design and low air speed / swirl characteristics.

    There is down sides to indexing - the more you index the plug the lower the compression ratio in the cylinder - with the washers you're pulling the plug further out of the combustion chamber. Also the spark is further away from the center of the mixture.
    The way justin the snap-on junkie explained it they had thousands of spark plugs and would match them to each chamber then put them aside in labelled containers so no washers were used.

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    Look behind you... Milkman Don's Avatar
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    Id imagine when manufacturing your own heads you would factor the threading to ensure plugs end up in the right place, unlike mass produced where you arent chasing every last percentile of efficiency.
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    Quote Originally Posted by 10sec rx7 View Post
    depending on the ecu you can still do cylinder trims with waste spark
    This guy knows whats up. Just run whatever you have, if it breaks fix it or upgrade it...As long as your existing system is designed to operate how you are running it then nothing to worry about and nothing to be gained.

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    indexing plugs is for clearance so many engines dont need this
    E30 325is M20 3.1L

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    Quote Originally Posted by E30is View Post
    indexing plugs is for clearance so many engines dont need this
    Thats not indexing depth setting the plugs is different indexing is to do with making sure the tang in the same spot on every cylinder. Some engine builders believe it makes flame propergation even across all cylinders some say BS.

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    Quote Originally Posted by S View Post
    Thats not indexing depth setting the plugs is different indexing is to do with making sure the tang in the same spot on every cylinder. Some engine builders believe it makes flame propergation even across all cylinders some say BS.
    its for clearance as the ground strap is only on 1 side on most plugs (old school ones) you need to orientate it so nothing hits/swipes it
    Last edited by E30is; 16-01-18 at 04:25 PM.
    E30 325is M20 3.1L

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    I've seen dyno results of 2-3% that were clear and repeatable for side-gapped and indexed plugs on an sr20. I don't recall whether the gap was pointing at the inlet or exhaust though.

    On my Youtube channel I will be trying to measure this on the road via datalogs.

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    Quote Originally Posted by BLSTIC View Post
    I've seen dyno results of 2-3% that were clear and repeatable for side-gapped and indexed plugs on an sr20. I don't recall whether the gap was pointing at the inlet or exhaust though.

    On my Youtube channel I will be trying to measure this on the road via datalogs.
    I'm going to say imo that 2-3% might not be there on a different engine as I assume it would have a lot to do with chamber design.

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    Maybe, maybe not. But with the central plug location and... roundness... of the SR20 combustion chamber it seems like a prime candidate for *not* being sensitive to plug direction.

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    Non Compos Mentos Gammaboy's Avatar
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    Quote Originally Posted by E30is View Post
    its for clearance as the ground strap is only on 1 side on most plugs (old school ones) you need to orientate it so nothing hits/swipes it
    Alfa 2ls with fitted big valves will eat the ground strap if you're not careful.
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