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What spark gap? ‘69 302 with mustang 5.0 EFI

hahnn6

Newbie
Joined
Jan 22, 2016
Messages
10
I have my original ‘69 302 (and heads) that I’m putting 5.0 intake, coil, and EFI on. My question is with the 69 factory plugs what do I gap them at when running a 5.0 coil/computer?
 

Yeller

Contributor
Bronco Guru
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Mar 27, 2012
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4,296
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Rogers County Oklahoma
.035 would be my go to with stock components. With aftermarket higher power stuff, up to .045.

Edit: apologies, didn't read close enough.... I'd go .045 with your set up
 
OP
OP
H

hahnn6

Newbie
Joined
Jan 22, 2016
Messages
10
Ok thank you so with a stock 69 302 long block and a mustang 5.0 computer and ignition setup with EFI you’d recommend a .045 gap for the stock ‘69 302 spark plugs?
 

Yeller

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Rogers County Oklahoma
unless your doing crazy things with compression, head design and such spark plug gap is more bout the ignition driving it, not the engine that it is installed in. .045 gap will give you a cleaner, more complete burn than .035, in theory anyway. The more modern ignition components generate more energy than the components from 1969 allowing you to take advantage of the wider gap. If your worried or concerned do the .035 gap that was specified for 1969, it will run fine. Is there verifiable information to support using the larger gap? Yes. Is it earthshattering, life changing different? No. It is just simple research that .045 is the recommended gap for the EFI and ignition set up.
 

DirtDonk

Contributor
Bronco Guru
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Nov 3, 2003
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43,179
Agree. Or you could always compromise and run slightly smaller at .042 or something like that.

Paul
 

Broncobowsher

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Total hack
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Jun 4, 2002
Messages
33,193
Cylinder pressure is a major influence in gap, the other is ignition power. Your cylinder pressures are about the same, not doing anything crazy like putting boost or NOS into the engine. Pump gas is pretty much pump gas and you really can't crank up the cylinder pressure. So that didn't change.

The ignition system did get more powerful. But still just the standard electronic ignition system. So run the gap of a regular electronic ignition system. Mid to low .040" range. A little less gap will last longer, a little more will be more efficient. Too much and you will have misfire under load or burn up the rotor inside the distributor. If you open the spark plug and it is gapped anywhere in the .040-.046" range, just put it in as is.
 
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hahnn6

Newbie
Joined
Jan 22, 2016
Messages
10
Thank you everyone for your advice! I’ll set it to .045 unless it’s already set around .040-042
 

blubuckaroo

Grease Monkey
Joined
Jun 11, 2007
Messages
11,735
Loc.
Ridgefield WA
Some plugs take opening the gap better than others. When I gapped mine to the recommended .044", the ground electrode will be severely angled. I just gapped it at .035".
 

Broncobowsher

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Total hack
Joined
Jun 4, 2002
Messages
33,193
Some plugs take opening the gap better than others. When I gapped mine to the recommended .044", the ground electrode will be severely angled. I just gapped it at .035".
That is where the checking the gap out of the box comes in handy.
 
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