Dual plug heads with single plug?

Discussion in 'Volkswagen' started by specter22, Mar 17, 2018.

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  1. Mar 17, 2018 #1

    specter22

    specter22

    specter22

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    Ok, this is a bit odd, but I'm soliciting opinions. Let's say a person had a VW engine with heads machined for dual plugs. Now let's say the person had a single-plug ignition system, and wasn't inclined to upgrade. What's a person to do? The way I see it, there'd be two options; option 1, put spark plugs in all the holes and ignore half of them (or make some dummy plugs to save half an ounce), or option 2, come up with a wiring scheme that allowed a flip of a switch to swap between banks of plugs as a backup (in the event that a plug failed mid-flight.) My concern is that you've got several small bits of metal hanging out in the ignition chamber just waiting to cause preignition; in addition, I'm curious as to whether you'd have excessive carbon build-up on the unused plugs, to the point where they wouldn't fire if called upon to do so. Has anyone played around with this, or something similar?
     
  2. Mar 18, 2018 #2

    deskpilot

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    Don't play with your safety. Upgrade to dual ignition, it's not hard not expensive compared to your funeral.
     
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  3. Mar 18, 2018 #3

    Hephaestus

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    Choose wisely... There are less expensive options.

    Crank triggered DIS leaving your distributor as alternate - makes good sense and not near as expensive as a mag kitm
     
  4. Mar 18, 2018 #4

    pictsidhe

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    Double ended coils is the cheap way to do it, but will only protect against fouled plugs. Leaving plugs unused will likely see them foul.
     
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  5. Mar 18, 2018 #5

    TFF

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    Turn a dummy plug and stick it in. Make life easy. Datusn 200s, Alfa GTAs, and Cosworth Vegas had duel plugs and distributers. Now days a lot more. Datsun was for emissions, the other two for performance. Not sure of the vega but Datsun and alfa had v8 cap and a rotor that would go to two plugs. I know the Alfa had duel coils to give enough fire power. The twin spark Alfa, similar but modern head to the GTA, had two distributers; one where the normal distributer was and a second driven off a cam.
     
  6. Mar 18, 2018 #6

    cheapracer

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    'cause they had crap designed combustion chambers. The Nissan Z20 series were certainly weird engines. We used to sell Z24 (2.4 liter) to the rally boys who would throw the head in the bin and use an L20 (Datsun L series engine) head on them.

    A back up spark plug lasts a surprisingly long time, was quite common on nasty old 1960's/early 70's 2 stroke motorcycles. If one fouled up, you just changed the lead over and went again.

    Even in the late 70's when they had them running a lot cleaner and they didn't chew plugs, the heads still came with 2 holes, but one had a blanking plug.
     
    Last edited: Mar 18, 2018
  7. Mar 18, 2018 #7

    Hephaestus

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    Hey... It wasn't just the Aussies ;) It was a common swap in North America too - ditch that z24(?) Head in the Datsun kingcab - install an old l20b head and distributor to loose the complexity and if I recall it bumped compression a touch.
     
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  8. Mar 20, 2018 #8

    specter22

    specter22

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    Deskpilot - Thanks for your concern. This engine is going on a KR2 with extended wings, so it will have a pretty solid glide ratio in the event of an engine out. I also can't remember the last time my car had an ignition problem. Let me add, this is a 2-seater, so I have no interest in saving a few hundred bucks in exchange for an unsafe airplane. I just haven't seen the kind of ignition issues with modern systems that you can often get with magnetos. There are a number of folks who run VW's in their planes with single ignition - Bob Hoover was a proponent of that, provided you built the engine to last, rather than to get every last HP possible out of it.

    Hephaestus and Pictsidhe - I should have specified. The engine is currently running a "distributorless" ignition system with dual plug coils, set up so that if a coil fails it only kills one plug in each of two cylinders, rather than both plugs in one cylinder. It's an old Hapi system that uses Hall-effect sensors and magnets in a 009 distributor body, with the mechanical advance left in place. The engine isn't running yet, but the components in the system all seem to function; I'm just looking at replacing some of them based on their age.

    TFF - If I recall, there's a thread (or two) on HBA where someone was advocating a method of adapting a Datsun distributor cap to a 009 distributor... I'll have to look that up again.

    Cheapracer - Swap the wire and keep on going, eh? I would think with a 2-stroke the plugs would take a lot more abuse than in a 4-stroke, but maybe that's my ignorance showing.
     

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