Author Topic: 2 plugs???  (Read 2386 times)

mikeatchison123

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2 plugs???
« on: December 30, 2010, 01:25:53 PM »
i got a 78 fl250 and i was just curious why they have 2 plugs and all the coils on ebay for this model only have 1 spark plug boot? i guess if 1 fouls out u can switch the boot over or what?

mikeatchison123

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2 plugs???
« Reply #1 on: December 30, 2010, 01:44:31 PM »
ok i did some research myself and i found out it is just to seal the hole up, i want to use a snowmobile 2 cylinder coil on it to make use of the plug, would this be safe to do? i dont see why it wouldn't but what do i know, any info would be great.
thanks to all with help,
mike

Adnoh

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2 plugs???
« Reply #2 on: January 01, 2011, 10:19:17 AM »
Thats an interesting point of view. Some highly moded engine do run dual plugswith an ignition modual for secondary spark tiiming. I do not or have not done it to a 250 so not sure if any thinng is to gain. As far as firing both at the same time goes I do not believe there much advantage to this with todays gas/oil mix's. Plug location,  heat range, proper jetting, ect is important to a healty running engine.  For discussion purposes and what if's, one could run an over rich air fuel and allow the additional spark to help for proper combustion. This usally is used in a high cranking compression and border line CR ( compression ratio) engine to help it from detanating. First thng to look at is if there is a pipe installed and the tuned lenght of the pipe. We all here about egt and the 1200 being the number your looking for. Basicly the math didcates that 1200 is the nunmber a pipe tune is built to so all try to math there egt to this so the pipe timing is at its peak for the greatest preformance. As far as it relates to the What If, the over rich mixture will lower the egt number cooling the combustion gases and slowing down the pipes tune. Then if the aditional  spark  can ignite some of these gases the temp will go up. Notice I did not say secondary spark or delayed spark from standand ignition timing. In order to not make a five page post I will shorten up the related events. The squish band, cumbustion chamber, port timing, crankcase pressures, CR,piston to cylinder clearence and the fuel it's self all relate to this event. Even the plug heat range plays a part to the heat transfer and the over rich fuel mix being combusted. What a secondary spark timing can do for you is help clear the cylinder and increase the combustion timing during the blow down phase  ( the amount of crank rotation degrees from TDC ( top dead center) to the the export port starts to open)of the piston. The static timing will allow a set peak combustion strenght at a given degrees of crank rotation. The misture that is compressed into the squish band and the piston rotates down mixes with the hot combusted gases cooling them down a little so the thermal load on the piston crown is reduced and controls the crown swell and as these gases flow across the crown and out the exhaust port is keep the edge of the piston from melting from excessive heat.  If you use secondary timing with a non over rich mixture this will lead to excessive heat adn do piston damage. Now if you set it up to for secondary ignition the over rich ( for a looser term) can provide a peak combustion and a secondary or longer burn duration and that is the advantage. Basicly more leverage duration on the piston and increasing the power output. This is as long as everything else is kept in check. The standard static timing and the curve is usally altered when this is down to keep the engine intact.  

Remember most of us are building to a set pipe tune instead of builiding a pipe to an engine tune.  If you alter things for a built engine than a custom built pipe is in order to take advange fo the engines tune or it's a jetting nightmare and usally ends in power reduction and waste of money.

Any way paly away and share your work and results I like new ideas and approches on old ones.