Best spark plug wires?
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Senior User
Joined: Dec 2015
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From: Longview WA
Best spark plug wires?
Got a 351m in a 1981 camper special f250..Edlebrock intake and 1406 carb, 2.75" straight pipe exaust, No emissions junk, 14 deg timing, Right at 19 on the vaccum gauge but still running a little rich..So i bumped the gap up to .050 from .042..Now im looking at wires..more voltage means less wasted fuel. So what are you guys running? Im currently at 10mpg my goal is 13..I got 57 gals of fuel on board id love to see 740 miles before empty.
Elder User
Joined: Aug 2016
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From: Cape Town, South Africa
This, which is one of many, will cover the plug wires :
https://www.ford-trucks.com/forums/1...lug-wires.html
I doubt that the gap increase and new wires will improve the mpg much.
Something like correcting under inflated tyres would have more effect.
19* vacuum at sea level implies that your dizzy vacuum advance is connected to ported vacuum, which is a waste of time.
Connect it to full manifold, and verify that it actually works.
Initially you should see the 14* increase to +/- 29* and the 19'' vacuum increase to +/- 21''.
You'll also see the idle rpm's increase, and simply needs adjusting down.
A vacuum advance that doesn't work ruins fuel consumption.
https://www.ford-trucks.com/forums/1...lug-wires.html
I doubt that the gap increase and new wires will improve the mpg much.
Something like correcting under inflated tyres would have more effect.
19* vacuum at sea level implies that your dizzy vacuum advance is connected to ported vacuum, which is a waste of time.
Connect it to full manifold, and verify that it actually works.
Initially you should see the 14* increase to +/- 29* and the 19'' vacuum increase to +/- 21''.
You'll also see the idle rpm's increase, and simply needs adjusting down.
A vacuum advance that doesn't work ruins fuel consumption.
Post Fiend
Joined: Apr 2002
Posts: 19,311
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From: Waterloo, Iowa
Careful increasing plug gap beyond spec. Wider plug gaps does increase the firing voltage, but it also increases wear and tear or strain on the ignition system components. Coil will run hotter. Can run into misfire or arcing at high RPM or under heavy load. If the fuel mixture is excessively rich, the carburetor probably needs adjusting i.e. jetting. Lean mixtures are harder to ignite but the stock OEM plug gap should already have this factored.
Post Fiend
Joined: Apr 2002
Posts: 19,311
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From: Waterloo, Iowa
For the money, Motorcraft wires are excellent.
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Senior User
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From: Longview WA
I changed specs to a Non emissions engine..sticker and truck used to be a emissions based engine but not one single component of that stuff remains.. 0.48-0.52 and 14deg timing is what i found for non emissions 351m's was i wrong? Truck runs alot smoother now with the better gap..and im noticing less raw fuel odor.
Elder User
Joined: Aug 2016
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From: Cape Town, South Africa
Hi there Ted,
I normally specify rpms, but this time it slipped my mind. Oops !
Yes, 19'' @ 600 rpms would be healthy indeed, and would probably be 21'' @ 800 rpms, if connected to full manifold.
I should have asked !
What I was actually getting at, was that when connected to ported, and a vacuum reading is observed, one might not be able to tell if the vacuum advance is actually working.
But, if connected to full manifold, one can see at a glance.
I had diaphragms repeatedly fail on a brand new Pertronix dizzy which I realised immediately. (Gotta permanent vacuum gauge in the cockpit.)
BUT !
The fuel economy went for a ball of sh$t while I waited on each new diaphragm.
You follow that ?
I normally specify rpms, but this time it slipped my mind. Oops !
Yes, 19'' @ 600 rpms would be healthy indeed, and would probably be 21'' @ 800 rpms, if connected to full manifold.
I should have asked !
What I was actually getting at, was that when connected to ported, and a vacuum reading is observed, one might not be able to tell if the vacuum advance is actually working.
But, if connected to full manifold, one can see at a glance.
I had diaphragms repeatedly fail on a brand new Pertronix dizzy which I realised immediately. (Gotta permanent vacuum gauge in the cockpit.)
BUT !
The fuel economy went for a ball of sh$t while I waited on each new diaphragm.
You follow that ?
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
I changed specs to a Non emissions engine..sticker and truck used to be a emissions based engine but not one single component of that stuff remains.. 0.48-0.52 and 14deg timing is what i found for non emissions 351m's was i wrong? Truck runs alot smoother now with the better gap..and im noticing less raw fuel odor.
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Post Fiend
Joined: Apr 2002
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From: Waterloo, Iowa
Yep. Did you ever get a read on the actual MPG loss, or percentage? I've read 20%, or 2 to 3 MPG on older V8. More?
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Elder User
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From: Cape Town, South Africa
I certainly did !! 
It dropped from 14 mpg to 11 mpg.
Funnily enough, I never read about it, but yes, it was similar to your figures posted (21% and 3 mpg).
My driving habits etc remained constant throughout.
I probably would have wondered WTF if the vac advance had been ported connected.
And to continue with the hijack, I returned 2 brand new dizzies to Pertronix and one to MSD.
The first Pertronix one had a faulty curve that could not be dialled in, same for the MSD one.
The second Pertronix one must have used weird quality diaphragms.
Pertronix' customer service was excellent. MSD's was crap.
Having realised that the 'big name' brands were hit and miss, I bought a $50 HEI dizzy, which so far has been perfect. (Makes up for the bad gas consumption. LOL)
It dropped from 14 mpg to 11 mpg.
Funnily enough, I never read about it, but yes, it was similar to your figures posted (21% and 3 mpg).
My driving habits etc remained constant throughout.
I probably would have wondered WTF if the vac advance had been ported connected.
And to continue with the hijack, I returned 2 brand new dizzies to Pertronix and one to MSD.
The first Pertronix one had a faulty curve that could not be dialled in, same for the MSD one.
The second Pertronix one must have used weird quality diaphragms.
Pertronix' customer service was excellent. MSD's was crap.
Having realised that the 'big name' brands were hit and miss, I bought a $50 HEI dizzy, which so far has been perfect. (Makes up for the bad gas consumption. LOL)
Elder User
Joined: Aug 2016
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From: Cape Town, South Africa
Good man !
Post up your results/observations as you go along.
When you drive with full manifold vac adv connected, you won't feel a 300 HP to 400 HP change (if you know what I mean), but you might feel subtle changes.
When you get new plug leads, look at the manufacturer comments about resistance in the leads, measure yours with a multimeter, and compare.
Post up your results/observations as you go along.
When you drive with full manifold vac adv connected, you won't feel a 300 HP to 400 HP change (if you know what I mean), but you might feel subtle changes.
When you get new plug leads, look at the manufacturer comments about resistance in the leads, measure yours with a multimeter, and compare.
Elder User
Joined: Aug 2016
Posts: 723
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From: Cape Town, South Africa
That was quick !
Ok, that cheap, quick, and easy change was simply testing that the vac adv works, and it does.
Drive around a bit with full manifold, then decide between that and ported which one you prefer.
There'll be little to no change to fuel consumption.
The ohms test is purely to ensure the quality of the leads.
No idea how to get from 10 mpg to 13 mpg without knowing a lot more about the vehicle specs and driving habits.
For example, I get 14 mpg with a 50/50 combination of 90 mph cruising with no overdrive, and around town driving, in an F350 dually.
It could do better and it could do worse.
Ok, that cheap, quick, and easy change was simply testing that the vac adv works, and it does.
Drive around a bit with full manifold, then decide between that and ported which one you prefer.
There'll be little to no change to fuel consumption.
The ohms test is purely to ensure the quality of the leads.
No idea how to get from 10 mpg to 13 mpg without knowing a lot more about the vehicle specs and driving habits.
For example, I get 14 mpg with a 50/50 combination of 90 mph cruising with no overdrive, and around town driving, in an F350 dually.
It could do better and it could do worse.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Problem is pickup aerodynamics are not good, and trucks are heavy, and 250s more than some.
If you know someone who has an ignition analyzer scope, they are very useful at looking at the overall ignition health. Some repair shops have one. If you look on that auction site, right now there is a Heathkit for under a hundred bucks, includes all the wiring probes + manuals. I paid $40 for mine, they take a little learning curve but they are REALLY good at exposing ignition defects. You'll need a good HOT spark, good grounds.
High voltage is really weird stuff, everything has to work together as a total package, inside the cap, rotor, plug wire, rotor gap, plug gap, coil resistance etc That's why it is really tough to beat the OEM genuine ignition parts, they were engineered to work together.
You can reach your mileage goal, but you'll also have to really dig into both the distributor mechanical and vacuum ignition timing curve, and then finally some careful carburetor tuning & jetting work. If the ignition system itself is weak, it won't be able to reliably fire normal air/fuel mixtures so work on that first, make sure it's bombproof.
If you know someone who has an ignition analyzer scope, they are very useful at looking at the overall ignition health. Some repair shops have one. If you look on that auction site, right now there is a Heathkit for under a hundred bucks, includes all the wiring probes + manuals. I paid $40 for mine, they take a little learning curve but they are REALLY good at exposing ignition defects. You'll need a good HOT spark, good grounds.
High voltage is really weird stuff, everything has to work together as a total package, inside the cap, rotor, plug wire, rotor gap, plug gap, coil resistance etc That's why it is really tough to beat the OEM genuine ignition parts, they were engineered to work together.
You can reach your mileage goal, but you'll also have to really dig into both the distributor mechanical and vacuum ignition timing curve, and then finally some careful carburetor tuning & jetting work. If the ignition system itself is weak, it won't be able to reliably fire normal air/fuel mixtures so work on that first, make sure it's bombproof.
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