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Plug gap for 1978 302 in '67 Mustang?

Old 07-04-2019, 05:05 PM
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danube7
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Default Plug gap for 1978 302 in '67 Mustang?

Hi all,


This is my first post in this Mustang related forum. I'm going to try a few others as well, as I work to get my car back out on the road.

Here's the story. I have a 1967 Mustang C-code convertible. In the 1980's the engine died and it was replaced with a 1978 Mercury 302. It has a replacement "2150"-like 2bbl carburetor. Since I can never get the original engine back, my goal is to make the current one "better" with stock parts. Years ago the distributor failed so I now have a HiPo dual point centrifugal advance distributor. Sitting on the shelf ready to be put in (in winter) are an Autolite 4100 carb and a 289 HiPo 4bbl intake manifold. But that is for later.

Now, I need to replace my spark plugs. Originals were 18mm BF42 (BF32 in the HiPo). But the 1978 vintage 302 has 14mm ASF52 plugs. But what gap???? My 1967 shop manual clearly has 0.032-0.036" for the gap, but I cannot find the gap for the 1978 vintage engine anywhere. I looked through the 1978 shop manual Engine volume and it is not listed. Does anyone know where I can find the right gap for my engine? (And I can't tell you what engine I actually have, unless I can figure it out from the block casting numbers somehow).

Some guidance would be very much appreciated. Thanks in advance!

Dan

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Old 07-05-2019, 06:08 PM
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Gun Jam
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34-36 would be quite acceptable for a points style ignition

If you were running MSD with blaster 2 45k coil and an a6 digital box you might run 40 to 45 tho.

-Gun
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Old 07-05-2019, 08:51 PM
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CtCarl
 
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FWIW, if you're talking about a standard copper plug like the Motorcraft SP425A from a 1978 Cougar or a Monarch, the gap for that application is .050, except for California cars which are .060.

Last edited by CtCarl; 07-06-2019 at 04:04 PM.
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Old 07-05-2019, 11:01 PM
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imp
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Originally Posted by CtCarl View Post
FWIW, if you're talking about a standard copper plug like the Motorcraft SP425A from a 1978 Cougar or a Monarch, the gap for that application is .50, except for California cars which are .60.
This may have been because Ford began using electronic ignition systems in 1978. My '78 Fiesta had one. But, you don't mean .50 because that's a HALF-INCH. Or .60, which is nearly 5/8 inch. You mean 0.050" and 0.060".
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Old 07-06-2019, 04:03 PM
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Originally Posted by imp View Post
This may have been because Ford began using electronic ignition systems in 1978. My '78 Fiesta had one. But, you don't mean .50 because that's a HALF-INCH. Or .60, which is nearly 5/8 inch. You mean 0.050" and 0.060".
Yes, that's right. As incredible as it may seem, I made a typographical error. I've fixed it now.

Thanks for the correction.
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Old 07-06-2019, 07:55 PM
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imp
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Originally Posted by CtCarl View Post
Yes, that's right. As incredible as it may seem, I made a typographical error. I've fixed it now.

Thanks for the correction.
Not to worry! It is easy for one not working with such numbers constantly to make a little error.
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Old 07-07-2019, 01:20 PM
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danube7
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Default Plug RESISTANCE. WAS: Plug gap for 1978 302 in a '67 Mustang?

Howdy folks, and thanks for the advice.

I am gapping my ASF52 plugs to 0.036 to go with my 1978 302 and points-based ignition.

I got a set of NOS plugs, same ones, from e-bay. I figured I would check them before putting them in since they are resistor plugs. They all read 12.5 KOHms except one, which reads 20KOhms. Is this too high? This seems like a pretty high value considering the plug wires are about 1 KOhm and the Ford shop manual specs those at <5000Ohms per foot (so they can be up to 10K Ohms for the longer ones). Should I use the 20 KOhm plug or get another one?

But the ASF52 plugs that came OUT of the engine, and are very old, are all between 4 and 8 KOhms (except one which is very low at 250 Ohms). But it's the same plug. Does the internal resistance get lower with use, or did my NOS parts get higher by sitting on the shelf for 40 years?

Interestingly, I can find out just about anything about spark plugs on the interwebs. Plug thread diameter, length, gap, tip type, temperature,... everything except core resistance of resistance type plugs. Is there some reference manual for Motorcraft spark plugs that lists the specified core resistance of the plugs across model years? What *should* it be for a points-based ignition system from the 1960's? The problem as I see it is I have too many different parts from different years. I have a 1967 ignition system, feeding a 1978 engine, with aftermarket plug wires from the 1980's. I'd really like to know what the specs of the system *should* be for a stock 1967 points based ignition.

Thanks in advance for the help.

Dan
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