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Lets Talk Sparkplugs
#1
I have a question about plug gap. I have a 72 351C 4V. I have changed ignition to electronic with a 6AL box. What should I gap the plugs at? Should I buy the same plugs for the original motor and re gap them are should I buy a different year plug that is gapped for the electronic ignition?

72 Q Code Mach 1, 351C, Toploader.
69 Torino GT Convertible, 351W, FMX
03 Anniversary Harley Davidson
31 Deluxe Tudor
91 F350 Lariet Crewcab 4x4, 460, automatic
2012 Escape 4x4
92 Feature Edition Mustang
82 F100 Shortbed
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#2
usually with a electronic ignition and a higher powered coil you can increase the gap by .005

standard gap is about .035" so you can easily run a gap of .040 if you want to.

basically you can take your regular autolites or motorcraft plugs or whatever and just use a spark plug gap tool and bend the electrode arm out to regap.

you should always check your plug gap before installation they are never correct out of the box.

personally I've tired gapping wider and saw no change in performance or drivability , the last time i put the plugs in the engine i just gapped them to .035 so i could use my old points ignition in case of electronic ignition failure.



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#3
I DONT THINK CHANGING THE GAP WILL DO ANYTHING FOR YOU. BUT YOU MIGHT LOOK INTO A HOTTER PLUG. DONT ASK ME TO EXPLAIN IT, BUT WHATEVER PLUG YOUR CAR HAS THEY MAKE THE SAME PLUG (HOTTER) EVEN WHEN I WAS A KID ON THE FARM MY DAD WOULD GO TO A HOTTER PLUG IN THE SPRING WHEN WE WERE PLOWING AND SUCH, THERE FOR THE HEAVY DUTY USE. BUT I THINK YOUR STOCK PLUG IS FINE. UNLESS YOUR HAVING WILD THOUGHTS.LOL..
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#4
my understanding is the gap would effect the electrode tip if it keeps wearing out prematurely because of high spark voltage and the gap too narrow, alternative would be if the spark is too weak you could narrow the gap, but that would point to another problem in the ignition system.

a plug that runs too cold would need to be replaced with a hotter version of the plug. the depth of the isolator changes depending on the heat range of the plug.
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#5
A quick rule of thumb on plug heat range is to get the range where the color change line (where the steel turns blue) is at the second thread from the end of the plug. If it blues more threads the plug is too hot, if less the plug is too cold.

Jeff T.

Low buck, touring style, '73 Convertible "rolling restoration", 351c, 2v heads with a shave and a haircut, Performer intake, Holley 650(ish), roller rockers, screw in studs, guideplates, stainless valves, Duraspark / Motorsports MSD, T-5 conversion. 1-1/8" front, 3/4" rear swaybars KYB shocks and some home brewed subframe connectors. Future plans; JGC steering box, Cobra brakes and... paint, interior, etc.

When I die I want to die like grandpa, peacefully in my sleep... not screaming, like his passenger.

[Image: 1_12_09_14_10_15_11.png]
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#6
Great info. It runs like a top gapped at 35. I have not run it long enough to know if they wear out to soon.

72 Q Code Mach 1, 351C, Toploader.
69 Torino GT Convertible, 351W, FMX
03 Anniversary Harley Davidson
31 Deluxe Tudor
91 F350 Lariet Crewcab 4x4, 460, automatic
2012 Escape 4x4
92 Feature Edition Mustang
82 F100 Shortbed
  Reply
#7
MSD has a gap spec for their ignitions. I run mine at .050. I am not detecting any wear on my plugs, even with Nitrous. That is the point of having a hotter spark so you can open the gaps and get a bigger spark. On a performance note, I would run colder plugs not hotter. I run Autolite 24's in mine. With hot ignitions and hotter plugs the ground strap gets hot and acts like a glow plug causing detonation.
Andy
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#8
While we are discussing spark plugs on this thread I need some new ones.

They will be going into a stock 351C 2v engine from '73. I generally buy Autolite plugs. So what plugs should I buy?


[Image: 386_07_10_13_5_58_42.jpeg]
My Mustangs:
71 M-code Mach 1, Medium Blue/White Sport, 4R70W, 3L50, Factory Ram Air.
72 Q-code Mach 1, Pewter/Black Sport, 4-spd, 3L25.
65 Convertible, Britney Blue/White/White, more modified than original.
05 Convertible, Legend Lime/Tan/Tan, future classic??
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#9
You can't beat our Tech Advisor. He is spot on with his recommendations. Spark plug manufacturers are like sighting in a new rifle. My 700BDL Remington is dead on using Winchester vs. Remington shells. My old 73 car always ran best on Autolight. While I found the 289 in my 68 Cougar liked A-C plugs as far as longevity and performance.

[Image: 2rr7aiv.png]

Just cruising along minding our own business when BAM!!! The LAWS show up.
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#10
markmel;45111 Wrote:You can't beat our Tech Advisor. He is spot on with his recommendations. Spark plug manufacturers are like sighting in a new rifle. My 700BDL Remington is dead on using Winchester vs. Remington shells. My old 73 car always ran best on Autolight. While I found the 289 in my 68 Cougar liked A-C plugs as far as longevity and performance.

Which Autolite would that be? I have no knowledge of what these engines take except for what the guy behind the counter will tell me as he reads his computer screen. Undecided

What would be a good plug to stick in there for general purpose street driving?

[Image: 386_07_10_13_5_58_42.jpeg]
My Mustangs:
71 M-code Mach 1, Medium Blue/White Sport, 4R70W, 3L50, Factory Ram Air.
72 Q-code Mach 1, Pewter/Black Sport, 4-spd, 3L25.
65 Convertible, Britney Blue/White/White, more modified than original.
05 Convertible, Legend Lime/Tan/Tan, future classic??
  Reply
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