Re: Why do HEMI Rams have two spark plugs per cylinder
[Re: 340Scamp]
#340048
06/07/09 09:35 AM
06/07/09 09:35 AM
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Joined: Feb 2003
Posts: 12,675 Columbia, CT
moper
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They've been doing it for years. Nissan 2.4L had it in the 80s. My impression is they need the burn time of the mixture to be as fast as possible while still being a controlled burn, so they make sure the mixture is squished and moved during hte last few degrees of the compression stroke, then they light it from opposite ends so it takes 1/2 the time with less loss of efficiency.
Well, art is art, isn't it? Still, on the other hand, water is water! And east is east and west is west and if you take cranberries and stew them like applesauce they taste much more like prunes than rhubarb does. Now, uh... Now you tell me what you know.
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Re: Why do HEMI Rams have two spark plugs per cylinder
[Re: DZJim]
#340051
06/07/09 02:58 PM
06/07/09 02:58 PM
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Joined: Sep 2007
Posts: 14,889 up yours
Supercuda
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About to go away
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Posts: 14,889
up yours
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Airplanes require two independantly powered ignition systems for safety reasons, nothing more. If your plane ran better when you switched the other mag in then your first mag setup has problems. Not that mags are all that great an ignition system.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
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Re: Why do HEMI Rams have two spark plugs per cylinder
[Re: Supercuda]
#340052
06/07/09 08:25 PM
06/07/09 08:25 PM
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Joined: Aug 2006
Posts: 247 DuPont, Washington
DZJim
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Posts: 247
DuPont, Washington
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Quote:
Airplanes require two independantly powered ignition systems for safety reasons, nothing more. If your plane ran better when you switched the other mag in then your first mag setup has problems. Not that mags are all that great an ignition system.
Hmmm...yeah; I screwed up my first post. I inadvertently took off running on one magneto. You use both magnetos; switching each off in turn for the pretakeoff check. When I selected both "on" was when I picked up that little bit extra power.
I suppose safety is the reason behind the independent self-powered ignitions for airplane recip engines, but its a fact that you get a 50-75 RPM drop when switching one mag off during a runup.
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Re: Why do HEMI Rams have two spark plugs per cylinder
[Re: DZJim]
#340053
06/07/09 09:01 PM
06/07/09 09:01 PM
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Joined: Jan 2003
Posts: 256 Cary, NC
hemifever
super street
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super street
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Posts: 256
Cary, NC
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The second is a "wasted spark". It fires 1/2 degree after the primary.
1971 Plymouth Cuda - 451 stroker
2008 SRT8 Charger - B5 Blue SuperBee
2010 Challenger - 6 spd Plum Crazy RT-C
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Re: Why do HEMI Rams have two spark plugs per cylinder
[Re: GO_Fish]
#340056
06/07/09 11:21 PM
06/07/09 11:21 PM
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Joined: Oct 2007
Posts: 3,877 Oregon
hooziewhatsit
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Oregon
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I know in rotary engines, since the combustion chamber is fairly long and flat, it would take too long for the fire from one plug to fill/burn the entire chamber, so they have two plugs to speed up the burn. Could be something similar with the Hemi's? Either way, there's probably a list of benefits of using two plugs
If you ever find yourself in a fair fight, your tactics suck.
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Re: Why do HEMI Rams have two spark plugs per cylinder
[Re: hooziewhatsit]
#340057
06/07/09 11:44 PM
06/07/09 11:44 PM
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Joined: Jan 2003
Posts: 14,610 Not2farfromNashville, TN
Rug_Trucker
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The Nissan (Datsun back then) called their's the NapZ. It was a DOHC Hemi IIRC.
"The only thing to do for triumph of evil is for good men to do nothing"
"NUNQUAM NON PARATUS!"
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Re: Why do HEMI Rams have two spark plugs per cylinder
[Re: ZIPPY]
#340062
06/11/09 09:02 PM
06/11/09 09:02 PM
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Joined: Nov 2003
Posts: 2,937 GA
roadrunninMark
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6.7 jigawatts? Hey DZ, you also have 2 plugs/mags a cylinder in ur prop so you dont foul a plug and lose the engine since you are usually taking off and landing with full rich (unless high elevation). I am sure when you've done your run ups before you ran into a semi fouled plug, then had to run up and lean the mixture, let run for a little till it cleaned up, then did your mag checks again. Now if only cars could have that leaning knob to coax a few more miles a gallon. Mark
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Re: Why do HEMI Rams have two spark plugs per cylinder
[Re: ZIPPY]
#340063
06/12/09 12:47 AM
06/12/09 12:47 AM
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Joined: Jan 2003
Posts: 14,610 Not2farfromNashville, TN
Rug_Trucker
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I Live Here
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Quote:
Wow, that's quite a mixed bag of responses.
Anyone want to take a guess what the power difference is between waste spark and firing both plugs in all 8 at the same time, on an otherwise stock 5.7?
Well? How to keep the Rug_Trucker in suspense!
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