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351M spark plug gap?

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Old Feb 7, 2009 | 11:34 PM
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Question 351M spark plug gap?
Hello,

Can anyone please tell me what the spark plug gap for a 351M engine is?


Thank You
 
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Old Feb 8, 2009 | 07:47 AM
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With the factory Duraspark ignition, .042 - .046
 
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Old Feb 8, 2009 | 10:10 AM
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hi sorry to buzz in. what do you think the gap should be when running an MSD system?
thanks
jim
 
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Old Feb 8, 2009 | 11:36 AM
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This truck has the factory ignition spark set-up. So, sounds like .042 - .046 will work?
 
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Old Feb 8, 2009 | 12:34 PM
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Hey OrangeJuice,
My 78 400 is set at .44 i belive i read that in some manuel
 
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Old Feb 8, 2009 | 02:51 PM
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Originally Posted by OrangeJuice
This truck has the factory ignition spark set-up. So, sounds like .042 - .046 will work?
Yes, somewhere in that range. I generally gap mine at .044.

As far as aftermarket ignitions (Mallory, MSD, Crane, Jacobs, etc.), some recommend opening up the gap due to more electrical current being available with their system. You'd just need to play with the gap based on the recommendations of the respective manufacturers.
 
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Old Feb 8, 2009 | 09:34 PM
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I believe 42-46 is correct, there should be a sticker on the radiator support and/or valve
cover that should specify.
 
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Old Feb 14, 2009 | 06:47 PM
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Talking I run a MSD Street Fire and TFI coil.........
Originally Posted by skunktruck
hi sorry to buzz in. what do you think the gap should be when running an MSD system?
thanks
jim
I run 8.5 mm wires and premium cap and rotor and have my plugs gaped at .60 the truck runs great with smooth idle and great performance.

The TFI coil is the difference, I could have bought a Blaster oil filled coil but the TFI Ford coil does a better job and you can pick one up at the auto wreckers for cheap, also make sure you remove the resistor form the ignition wiring it has one, the one that goes to the coil.

Rick.
 
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Old Feb 14, 2009 | 06:51 PM
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so you think going from .44 to .50ish might lean it out a bit?
 
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Old Feb 14, 2009 | 09:57 PM
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Yes I do believe.
Originally Posted by skunktruck
so you think going from .44 to .50ish might lean it out a bit?
Because it is multiple Spark Discharge(MSD) with the wider gap and longer spark jump time I believe the air fuel mixture will burn more completely or less raw fuel unburned.

You still require a good coil to give a great spark in order for this to work.


Rick.
 
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Old Feb 19, 2009 | 09:51 PM
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Originally Posted by skunktruck
hi sorry to buzz in. what do you think the gap should be when running an MSD system?
thanks
jim
Should be .10 more so aroun .50 to .54
 
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Old Apr 28, 2012 | 02:03 PM
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1978 F150 4x4 351m/400
I'm running a Mallory Dist, Accel Cap/rotor, and MSD 8.5 wires...
What should my gap be?

Also what is the 351m speck for spark plug torque?

Thanks!
 
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Old Apr 28, 2012 | 03:28 PM
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7-15ft.lbs.for 14mm and 15-20ft.lbs. for 18mm plugs.
 
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Old Apr 29, 2012 | 10:51 AM
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Originally Posted by mustang81
7-15ft.lbs.for 14mm and 15-20ft.lbs. for 18mm plugs.

Thank you! Time for a new torque wrench...
 
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Old Apr 12, 2019 | 09:35 AM
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2 different factory settings but bigger is better


Originally Posted by OrangeJuice
Hello,

Can anyone please tell me what the spark plug gap for a 351M engine is?


Thank You
 
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