dual spark plug head

Discussion in 'Performance Mods' started by Evil_Genious13, Apr 20, 2015.

  1. Evil_Genious13

    Evil_Genious13 New Member

    Has anyone used a "fred head" or similar dual sparkplug racing head? did the extra plug give a noticable increase in power/ speed? also are both spark plugs powered by a single CDI?

  2. miketaco

    miketaco Member

  3. Marine One

    Marine One Member

  4. skyash

    skyash Active Member

    I don't see how 2 plugs can help. How much spark dose petrol need to blow up. If I had 2 stock plugs should work as one.and won't there be a power drop.split between 2.ensted of one strong one
    Timbone likes this.
  5. 45u

    45u Active Member

    If you have a good head two plugs are not needed. I dual plug early Harley heads do to the type of chamber so you get good ignition from one side of the head to the other as you cannot put one in the center. On the later Harley s have a much better head and do not need dual plugs. I have seen many dyno test and spark plugs have nothing to do with performance unless they are cheap after market.
  6. Marine One

    Marine One Member

    If you were using a stock CDI I doubt that you would be able to get enough voltage to make both of them spark at all. However I'm using a step up CDI with a much better coil. There is no real difference in top end performance but it seems to help with torque fairly well on the low end.
  7. Marine One

    Marine One Member

    I did mine partly for the looks and because you are right, it is a Much better head. The pinch/ squish zone around the head and the cylinder head is almost as large as the rest of the space around it. Mine is a medium compression head and it really opens up the chamber for a better, much more even burn during combustion. More fuel burns faster= more power. Like I said in an earlier post, there doesn't seem to be any difference in top end performance at all but on the bottom end it does help out.
  8. 45u

    45u Active Member

    What CC head are you using or do you know? I have a 6cc head I am going to run on my second build but only on plug.
  9. HeadSmess

    HeadSmess Well-Known Member

    no matter how many plugs you stick in there, you will still only get ONE spark.. whichever gap is the smallest will be the first to breakdown and conduct. until all gaps are even at which point it is just pure randomness which one will spark.

    unless you run separate cdi or have both ends of the coil exposed, so the current has to flow from earth, across one gap, through the coil, then across another gap, back to earth.

    the stock standard CDI will not allow this.

    an aftermarket CDI with separate coil should, if it has a separate earth wire but probably wont, unless its off one of these new wizz bang car engines that use one coil per two cylinders.

    you have also doubled the voltage requirements, so the coil needs heavier insulation, the magneto has to supply extra power that it cant produce...

    all in all, rather pointless.

    but, if you have a strangely shaped combustion chamber, or really big pistons... then dual sparks do make a difference. the biggest example being aircraft that standardly have two plugs per cylinder, as well as two separate magneto/ignition systems. if one plug fouls up, or a magneto fails...the other one still produces spark. you dont have to try gliding and landing with no engine.

    pre-flight check is to start on both magnetos, then switch one off...the engine RPM drops to almost half! and kicks straight back up when both are turned on again.

    why? because they cylinders are usually huge... having two flame fronts means the air/fuel charge burns faster, faster burn means faster pressure rise, faster pressure rise is more force on the piston.

    another method is to simply use high frequency sparks, multiple sparks on one plug... but the whole concept is rather pointless on tiny little 50mm or less cylinders. and really does require a special coil and circuitry.
  10. butre

    butre Well-Known Member

    Fred made a good cylinder head by chance, he's a machinist not a tuner. some of his designs don't do anything special. dual spark being one, copper squish band being another
  11. HeadSmess

    HeadSmess Well-Known Member

    mmm, i dont get the logic behind the copper inserts... oh, its more conductive for heat... yes, but the join between the two metals defeats the purpose!

    ha ha, solid copper head... be a tad on the soft side...

    fred makes money. thats all that counts :) the extra gimmicks just mean more people are fooled and hand over the cash ;)
  12. butre

    butre Well-Known Member

    I'd do the same thing if I could get away with it.
  13. HeadSmess

    HeadSmess Well-Known Member

    pfft, ethics...who needs ethics?

    as long as people are willing to spend it...take it!
  14. Marine One

    Marine One Member

    I'm not sure what CC. I was mistaken though and went back to look for the CC for you but the one I have is a high compression head from Kingsmotorbikes.com
    I do not have the stock CDI. I have a screamingroo coil from pedalchoppers.com and a JetPack High Performance CDI from Pistonbikes.com but that CDI doesn't have a dual plug tail so I purchased the tail from Pedalchoppers.com also.
    There is a HUGE difference in performance from the stock set up especially on the low end. Plus the bigger fins on the head really help keeping it cooler.
  15. Steve Best

    Steve Best Active Member

    Headsmess, I like the way you talk, true engine p0rn!
    Ya know your sh1t! Well worth listening to folks.

    Fred is doing wonderful stuff by experimenting and putting his experiments out there for others to try.
    I don't believe he is misrepresenting them or getting rich off them, or making useless bling.

    So let's get a grip on what is happening at ignition.
    The mixture has been compressed.
    Hopefully it is whirling around to keep it in suspension.
    The tip of the sparkplug is glowing red, almost hot enough to spontaneously ignite the mixture.
    The spark is that small tipping point of energy that fires off an event that is primed to go.

    So what do you need for "sure fire" ignition"?
    1) The right fuel/air mixture (carb jetting from plug reading and plug chops)
    2) Compression
    3) Mixture turbulence (from chamber design squish area) to keep homogeneous mixture
    4) Compact combustion chamber (from chamber design bowl shape)
    5) The right heat range plug (from reading the plug electrodes and insulator)
    6) Enough spark to jump gap even with the effects of all of the above. More does not make more power.

    As for copper squish inserts, copper has twice the heat conductivity of aluminum, which is twice that of brass, which is twice that of cast iron, which is twice that of titanium and some specialty steels. More thermal conductivity lets you run higher compression ratios by sucking the heat out of the mixture where you don't want it to pre-ignite. It is an interesting area to experiment when everything else has been optimized.

    Greater thermal conductivity also sucks heat energy out of your engine too. Maximum efficiency would dictate all the energy should be kept in the engine, however pistons and lube oil would not survive. It is all a balance.

    Top fuel dragsters dump a near liquid mixture into their cylinders and light it with arc welder power. By the end of the run the plugs are burnt out and only act like a glowplug. The engine will continue to run after the spark is turned off. For maximum power, you want your engine on that ragged edge. Plugs almost hot enough to self ignite the mixture. How do you get there? Read the plugs.


  16. Rob H

    Rob H Member

    I agree I've been a ASE certified technician for 30 years
  17. butre

    butre Well-Known Member

    the problem with a copper squish is that the copper just gets heat soaked because the heat can't transmit to the aluminum quick enough and you're just back at square 1
  18. Marine One

    Marine One Member

    So we need to make a copper head. Simple.:D
  19. HeadSmess

    HeadSmess Well-Known Member

    exactly... the metal join has resistance,much more than solid metal has.


    you can lap the joints etc, but i dare say the insert is shrink fitted. hard to lap something that has no clearance.

    much like electrical resistance, thermal resistance increases dramatically as we add alloying elements.

    then copper is relatively soft, and rather expensive compared to aluminium. about 6-8 times the price... why you see a lot of cheaper welders etc wound with aluminium rather than copper.

    and machining copper is terrible... nasty sticky stuff that breaks tools far too easily.

    copper likes to oxidise and turn green... aluminium can be easily anodised that prevents further oxidation.

    now silver...mmmm, silver beats both copper and aluminium in thermal and electrical conductivity.

    silver heads :) no werewolves allowed.

    and diamond takes the cake!