super_mike

I have no experiance with 2 plug heads... CMB 90.. whats the purpose and any other info anyone can provide me with.. THANKS

mopartybob

I'm not sure but I remember reading somewhere it was to help with the idle and transition to WOT......

Sean Bowf

I know when I saw one blow a plug that it started surging down the straights...

Sean

jetpack

My Feedback: (1)

Most will be seen on the larger displacements for better flame travel, and reliability during throttle transitions like mopartybob mentioned due to fuel soak. There gets to be a point where the displacement starts to outmatch the standard size glow plug, and there's no larger ones to choose from.

Ron Olson

My Feedback: (1)

I've seen them made for engines as small as .45's but theyv work best with the large displacement engines. Nitro is a slow burning fuel and the more "spark" that you can get to it, the better otherwise you won't have a complete burn. When nitro is used in Top Fuel dragsters or Funny Cars, by the time that they're off the starting line the plugs are already gone and the engines are dieseling, this is why they have to shut off the fuel to stop the engines..

super_mike

I have been doing some more reading into this and let me know if i am correct.. If u run higher nitro % say over 50% on the big engines there is so much slow buring nitro in there u need the extra glow plug to get a higher burn % ..If u run a lower nitro % say under 50% u can run a single glow plug and get a good burn..I have 3 old gp style CMB 90's.. 2 with single plug heads and 1 with a dual set up..Bought them used.. I wanna learn on an old motor so when i burn it up or blow it up no big $$$ lost..the dual is for high nitro % and the single is for low nitro %.. Lower % burn faster than higher %.. If i am in-correct in my thinking...Let me know what ya know..The old rule of thumb being the bigger the motor the lower the nitro % the smaller the motor the higher the nitro % because the volume is too big in the bigger motors for 1 glow plug.. Smaller motor less volume = less glow plug needed..Is there any posted info on this already??? Any info anyone has i will read it !!!

Ron Olson

My Feedback: (1)

You got it! There isn't a lot of info on dual plug heads as there aren't that many around. Besides the CMB .90 some were custom made heads made.
Most run well with 40% nitro.

super_mike

Yes my single plug heads are cast and the dual is billet..Just by looking at it, i would say its a custom piece.. thanks

mopartybob

Merco,Fox,and OS to name a few came out with dual plug heads as early as 1964, check deeper into the antique forum threads (airplane engines) here on RCU,you may find more relevant info on the theory of these engines.....