Twin Spark Plug Cylinder Head

Discussion in 'General Questions' started by Fabian, Oct 10, 2012.

  1. Fabian

    Fabian Well-Known Member

    Does anyone know if the member from the other site "crmachineman" is on this site.

    I want to purchase one of his twin spark plug cylinder heads but i can't get in contact because the chief moderator over there has banned me for not only this lifetime but a further 3 life reincarnations.


  2. BigBlue

    BigBlue Active Member


    Contact him through Ebay on the link ion my prior post on EFI, unless your banned from Ebay:)

    AKA: BigBlue
  3. Purple Haze

    Purple Haze Active Member

    What is the advantage of a dual sparkplug? I understand that a lot (most? All?) of fuelie type racers use them, but they run extreme cylinder pressures due to blower or turbo boost. The MSD or other multi-spark boxes provide the same benefits without all the extra parts that would be needed to support multiple sparkplugs. I think a single strong, long duration spark would be better for most of our small engines. That's why I'm so gung ho for someone to develop a high-quality sparkbox for our little wonders.
  4. Fabian

    Fabian Well-Known Member

    The advantage of a separated dual ignition system and a dual spark plug cylinder head is that of redundancy.

    This concept means little to those people who use their motorized bicycle for short trips or limited recreational use, but for those who travel to the middle of nowhere on long distance recreational journeys, the benefits of redundancy are significant.
  5. Fabian

    Fabian Well-Known Member

    Trust me, that moderator (on the other site) tried to get me banned from breathing, but i (less than politely) reminded him that he doesn't have a monopoly on oxygen.
  6. crmachineman

    crmachineman Member

    I've joined motoredbikes!

    Hi everybody.
    Thanks for getting a hold of me Fabian. I started a new thread talking about the twin spark plug head.
    Anyway, finally they will be available, probably within a few days. I don't have any turnkey ignition systems to offer, but I have attached a image of the schematic diagram. I know there are some very good electrical people messing with these engines, and would appreciate their input, development, ect.
    So, anyway I'd be happy to try my best to answer any technical questions about this.
    Thanks a bunch!

    Attached Files:

  7. Fabian

    Fabian Well-Known Member

    Hi Fred

    I am so glad that you have joined the site.

    I want to purchase one of your twin spark plug cylinder heads with the compression release system as soon as possible.

    Can you advise if the compression release mechanism is the same as that from a chainsaw, as in the photos, for these are a very compact and reliable system:




    JVROOM Member

    I would like to know more about the twin spark plug head, I'm driving it Dodge hemi V-8 with 16 spark plugs, what a pain to change, but beyond redundancy, I think there's more power, oh I put Paxton supercharger on it for fun, but that's a separate story.

    I think duel spark plugs, lead to a better ignition, and maybe with the hemi, lower exhaust pollution. I have read the spark plugs a few times, and they seem to be firing equally. Question, is the head of development compatible with the slant head? Currently I'm running an upgraded spark plug, it's one of those ones with three grounding electrodes, can't say that it makes much difference. John
  9. Fabian

    Fabian Well-Known Member

    You can spin the cylinder head around 90 degrees; having twin plugs poking out the left and right hand side of the bike.

    I've ordered two different versions of the twin plug cylinder head and two different versions of the beveled piston.

    It's going to be like Christmas soon, when the new twin plug cylinder heads, beveled pistons, Walbro carburettor with reed valve adapter and 5 amp electric start/generator combo with twin 8 amp lithium batteries and accessory power sockets arrive in the next few weeks.

    I'll be like a kid let loose in a candy shop.
  10. jaguar

    jaguar Well-Known Member

    For reliability it makes more sense to have plug-in connectors for the CDI and high voltage coil and just change them out if they fail. Having two spark plugs installed means only one of them will be firing which means the other is accumulating crud which will hinder its operation if/when it is used. I say the second one isn't firing because unless the magneto/stator combo is changed out (for something bulkier and more complex that can equally supply two systems with voltage/current) you will have half the power delivered to each of two CDI/coil/plugs which is not something you want. bad idea.
    Power-wise there is no advantage to a dual plug system on such a small engine. The distance from center to side of the cylinder is just too short. Dual sparks are advantageous when there is more distance/area to cover rapidly with the spark ignited flame.
  11. Fabian

    Fabian Well-Known Member

    Twin independent power supplies and twin Jaguar CDI's and twin spark plugs enables both spark plugs to fire simultaneously, just like any aero engine, and just like it's been done since World War One and World War Two and on every piston engine aeroplane after that to the current day.

    A twin spark plug engine will not add "any" power to an engine with a small bore size, however it is very useful for redundancy purposes.
    Redundancy capability isn't an issue for someone doing short trips, but you want the trouble free concept of redundancy on your side if you're 150 miles from the car or from home and a coil or CDI fails.

    I like the idea of redundancy, hence my bike will now be equipped with a dual spark plug cylinder head and dual CDI's and a dual power supply.
  12. crmachineman

    crmachineman Member

    Well, what Fabian said was somewhat true, however I have some interesting test results that add a little more to the story.
    When I was testing the first twin plug prototype on my test bike it was working fine, but I didn't really notice a power increase from the previous testing, using the single spark plug head. As time went on, I made improvements on port timing, the intake tract and the exhaust, and power started to become really awesome. This was when my motorized bicycle started to be capable of exceeding 50 MPH! Soon after all these upgrades were completed, I thought it would be a good idea to go back to the stock ignition system, with a single spark plug cylinder head, for testing purposes. Both of these heads had the same combustion chamber shape and size. It was then, when my suspicions of the twin ignition were confirmed: when I put the single spark ignition, I started getting partial detonation problems when the engine reached normal operating temperature. This was when I realized I had to make a stage 2, single plug cylinder head with lower compression. I did, and the performance for the single spark ignition engine improved, even though I had lowered the compression.
    The understanding I gained from these tests is that a twin spark ignition system will allow you to safely run higher compression. Detonation can sometimes be hard to detect when it is only a portion of your fuel mixture which is detonating. Whatever amount of detonation you have in your engine, it will not contribute to power gain, it will be a power loss. Instead it will punish your engine with high stresses and heat production, which could then lead to very noticeable detonation, if it is allowed to continue.
    Since twin ignition initiates the flame front from two places, it has the ability to complete the burn more quickly. This is the key to preventing detonation from starting.
  13. Fabian

    Fabian Well-Known Member

    It's interesting that you make mention of detonation with high compression cylinder heads, because i have experienced exactly what you've described: not just detonation issues but dieseling problems on two of the high compression cylinder heads that i've tried. I had to layer up four head gaskets to drop the compression ratio below a point where it would stop detonating and this was with the Jaguar CDI set on the lowest possible ignition advance curve.

    Since four head gaskets screws up the squish effect, i reverted back to the low compression cylinder head, with the Jaguar CDI set at it's maximum advance curve, which proved to be the best setting for the low comp cylinder head.
    In both cases, the jetting was adjusted for the high compression and low compression cylinder heads, eliminating air/fuel ratio as a potential source of detonation.
    Twin spark plugs should reduce the flame front travel distance and potentially reduce detonation problems with a high compression cylinder head.

    I can't wait to try out your twin spark plug cylinder head, not just for redundancy purposes, but with the other included benefits.

    In my opinion, some of the high comp heads out there are set up with excessively high compression ratios, forcing you to screw up the squish band when adding extra head gaskets to drop the compression ratio.
  14. crmachineman

    crmachineman Member


    Yes! That's right!
    It is likely that those high compression heads you have been using were optimized for clean, carbon deposit free engines using race fuel. All my testing with these cylinder head designs was using 93 octane fuel you can easily get here in the U.S. I wonder how your fuel in Australia compares to ours, but many people here consider our fuels to be pretty inferior to fuels common twenty years ago. And you are right to worry about what all those extra gaskets would do for your squish band; not good.

    Several people have requested that I make special high compression versions of the heads. Since it is not too much trouble for me to do so, I decided that I would make some of those as well. Those heads could work well for two scenarios; The special high compression versions could be used on advanced engines using race fuel, or could be used with engines using stock exhaust and pump fuel.

  15. Fabian

    Fabian Well-Known Member

    I completely agree with your assessment of the situation i.e. race fuel vs pump grade fuel.

    I am using a completely standard exhaust/muffler and the both of the high compression cylinder heads (using a single head gasket and Australian south eastern seaboard 98 octane fuel) dieseled at low vehicle speed with high cylinder head temperatures and under heavy load.

    I am not sure how Australian south eastern seaboard 98 octane fuel compares with American fuel, because there seems to be differences in the way fuels are tested and given octane numbers, depending on global location.
  16. crmachineman

    crmachineman Member

    Okay, well I guess it's mystery for now. So you are using stock exhaust on your bike? I hope you will get good performance from what you ordered. I'm thinking you might want a higher compression head. Well, since they are already on the way, you might have to get an expansion exhaust and get ready for a pretty big boost.
  17. Fabian

    Fabian Well-Known Member

    Hi Fred,

    I am perfectly happy with the cylinder heads you have sent me - if they have a lower compression ratio than the high compression cylinder heads i've previously used, i'll be a very happy camper.

    An expansion chamber exhaust is desirable but in Victoria (Australia), new legislation has been passed (after a police pursuit with a high powered electric bicycle), giving police extraordinary levels of subjective assessment in deciding if a motorized bicycle isn't law compliant with the 200 watt maximum power output, allowing the police to hit you up with a bunch of tickets/fines, simply on their "belief" that your bike is over specification, of which you then have to prove to police that your bike is law compliant if they confiscate the bike.

    An expansion chamber is such an obvious visual giveaway that you're trying to squeeze more power out of the engine, plus it's visible from the rear of the bicycle. At least with the standard exhaust and 2-stroke engine, it is not visible from the rear of the bicycle.
    Last edited: Nov 4, 2012
  18. crmachineman

    crmachineman Member

    Boy that makes me mad!

    Hi Fabian

    Oh, man! That is so wrong! I would be so unhappy if some police officer pulled me over and gave me a ticket because of what kind of equipment I had on my bike. That just hurts!
    Okay, well keep us informed of how it goes.
  19. KCvale

    KCvale Motorized Bicycle Vendor

    The head yes, but not the cylinder itself ;-}

    I can't really see 2 plugs on one of these 48 or 66cc motors being better, actually worse it would seem to me other than the higher compression because 2 plugs are in the head.

    Unless you boost the voltage from the Mag somehow you are going to get less spark from each plug when the whole point is to get everything that little mag makes to the plug.

    I have only built 50 or so of these 48-66cc 2-stroke bikes but one thing I can you for sure is the one best investment you make is an $8 NGK BPR#HIX Iridium spark plug.
    The # is a number between 5-8. Higher numbers like 7 are best for really hot climates where lower numbers like 6 are best for very cold places. I run 7's here in the desert.

    Unless you are running a way off gas mix or tiny NT like carb on a 66cc I can pretty much guarantee you will feel the difference and they go in most every customer bike I build but the bottom basement budget bikes which I don't build many of.

    Just a tip, and here's another, your biggest performance gain is going to be from a tuned Expansion Chamber Exhaust no matter what carb, head, ignition system, boost bottle, bla bla bla you try.
    Next to the cheap and easy plug change, it is straight to an X-pipe next on a performance build for me.

    Again, just my 2 cents but I make my living building high end MB's and that's how I do it.
  20. Fabian

    Fabian Well-Known Member

    @ crmachineman

    It makes me seriously mad, and it is utterly wrong that a police officer (in Victoria) can give you, not just one ticket, but multiple tickets totaling around $2,000 even if you have a valid car and motorbike licence and without any convictions or outstanding infringements, just because of the equipment you ride.
    If your bike is confiscated, you then have to pay the $600 it costs to get it out of the impound centre, but you can only do so if you can prove to the police that your bike makes no more than 200 watts maximum power.

    Every day, i ride my motorized bicycle, knowing that at some point (it's going to cost me $2,000 and) i'm going to come across a police officer who will throw the book at me, even if i'm riding the bike in a lawful manner; obeying the road rules.