spark plug gap
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Postmaster
Joined: Nov 2001
Posts: 3,351
Likes: 1
From: Escondido, CA
spark plug gap
What should I run my spark plug gap at? I will have a 9.5-1 CR and a decent cam. I will be indexing the electrodes to make the flame swirl around the combustion chamber. ie... gap of plug facing away from the exhuast valve. Anything else I should think about before firing her up?
Senior User
Joined: Apr 2003
Posts: 432
Likes: 3
From: Oregon Coast
spark plug gap
The stock gap for a 460 with the Dura Spark ignition is .042" to .046"
As far as indexing your plugs that is usually only done to keep the gaps from getting closed by the pistons in a real high compression setup. I have dynoed my sbc a couple times and it makes 1.9 horses per inch and it doesn't need it with 14.6 to 1 compression. On engines that don't need it to run it is undetectable on the dyno. On engines that need it, the gap should face straight down or favor towards the exhaust valve.
As far as indexing your plugs that is usually only done to keep the gaps from getting closed by the pistons in a real high compression setup. I have dynoed my sbc a couple times and it makes 1.9 horses per inch and it doesn't need it with 14.6 to 1 compression. On engines that don't need it to run it is undetectable on the dyno. On engines that need it, the gap should face straight down or favor towards the exhaust valve.
Senior User
Joined: Apr 2003
Posts: 432
Likes: 3
From: Oregon Coast
spark plug gap
Also keep in mind the higher you go with compression the narrower you need to keep the gap for reliable ignition. I run an MSD on my dragster and I gap those at .035". The wider it is the harder it is to fire. It is also harder to create a spark under high cylinder pressure or high compression. Yours is not considered high but this is the rule of thumb. Electricity takes the path of least resistance so if you run really wide gaps be sure all your components are of the highest quality as it may be easier to fire another cylinder or just go through the side of the wire somewhere rather than jump your gap. On mine I took a wire of while it was running once and it would jump 3 to 4 inches before it would travel up the pliers to my hand. When I got longer pliers it just went right through the side of my coil to the body. It was a neat experiment.
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Postmaster
Joined: Nov 2001
Posts: 3,351
Likes: 1
From: Escondido, CA
spark plug gap
Thanks. I was thinking of running a .042 gap. I just didn't want to go too big or too small. I am running the Duraspark II still. Everything is brand new. In the future I will add a MSD as a secondary or just run that. I am in a time crunch now. I only have a month before I leave for Cali. My orders came in sooner then I was told they would.
Elder User
Joined: Apr 2001
Posts: 997
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From: texarkana, tx
spark plug gap
Yo, AirHarley ~~
This be the dood in Rome who sold you Bunny....sounds like your engine is in your F-100?......Be sure to upload some picture updates to your gallery so we can all drool over them before you go to the sunshine state!!
..... Did you end up using Bunny's rear end and transmission? exhaust?
air conditioning?....
Keep us posted....
This be the dood in Rome who sold you Bunny....sounds like your engine is in your F-100?......Be sure to upload some picture updates to your gallery so we can all drool over them before you go to the sunshine state!!
..... Did you end up using Bunny's rear end and transmission? exhaust?
air conditioning?....
Keep us posted....
Postmaster
Joined: Aug 2001
Posts: 2,882
Likes: 0
From: Nevada
spark plug gap
Rule of thumb on naturally aspirated engines is .035 for points and .045 for electronic ignitions. From there, it becomes like reloading for a particular firearm, what does a combination like best. Plugs are cheap, after you get the engine dialed in try your gap in .002 increments both ways until you find what works best. Then put in a new set with that gap.
Good luck on your move to Kalifornia.
Good luck on your move to Kalifornia.
