Ignition Timing & Rotor Position Question - Vintage Mustang Forums
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post #1 of 14 (permalink) Old 09-14-2016, 12:16 AM Thread Starter
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Ignition Timing & Rotor Position Question

Quick question about rotor position in a "healthy" engine.
Timing set at 12 degrees BTDC on compression stroke. Rotor pointing to plug #1.
Crank turns twice for every one turn of the cam.
So after one turn of crank, stopping at 12 degrees BTDC, the rotor would be pointing at the #6 plug.
Is this correct or am I mistaken?
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post #2 of 14 (permalink) Old 09-14-2016, 04:24 AM
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after one crank turn you you turned cam 180 degrees so rotor pointing 180 degrees in other direction
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post #3 of 14 (permalink) Old 09-14-2016, 07:24 AM
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Originally Posted by Djohnyvonne View Post
Quick question about rotor position in a "healthy" engine.
Timing set at 12 degrees BTDC on compression stroke. Rotor pointing to plug #1.
Crank turns twice for every one turn of the cam.
So after one turn of crank, stopping at 12 degrees BTDC, the rotor would be pointing at the #6 plug.
Is this correct or am I mistaken?
This is correct if your firing order is

1 5 4 2 6 3 7 8

It should be mentioned , That is not the only possible firing order

Clock

Ford 302HO / 5.0L and 351W Firing Order


1 3 7 2 6 5 4 8

(Plug 6 is the same position)

http://www.gtsparkplugs.com/firing-o...0-289-302.html

http://www.gtsparkplugs.com/firing-o...d-302-351.html

Z

Last edited by zray; 09-14-2016 at 07:28 AM.
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post #4 of 14 (permalink) Old 09-14-2016, 07:31 AM
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Originally Posted by zray View Post
This is correct if your firing order is

1 5 4 2 6 3 7 8

That is not the only possible firing order

Z
Look at any V8 firing order you wish- AMC, Chevy, Ford or whatever. There is a 90% probability that #6 is the 5th cylinder in the firing order. If you find an engine that doesn't have 1 and 6 as the first and fifth cylinders please post it here.
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post #5 of 14 (permalink) Old 09-14-2016, 09:33 AM
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Quote:
Originally Posted by Djohnyvonne View Post
Quick question about rotor position in a "healthy" engine.
Timing set at 12 degrees BTDC on compression stroke. Rotor pointing to plug #1.
Crank turns twice for every one turn of the cam.
So after one turn of crank, stopping at 12 degrees BTDC, the rotor would be pointing at the #6 plug.
Is this correct or am I mistaken?
That is correct. It will be point to it's "piston pair".

1-6
5-3
4-7
2-8
post #6 of 14 (permalink) Old 09-14-2016, 12:37 PM
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That is correct. It will be point to it's "piston pair".

1-6
5-3
4-7
2-8
Pete's right you can change "when" you fire them but NOT when they are both at TDC. The cam lobes must be changed in orientation as well. Three different firing orders have been used on production V8s over the years. 15426378 is the most popular. Chevrolet uses the same sequence though their cylinders are numbered differently and the dist turns clockwise.

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post #7 of 14 (permalink) Old 09-14-2016, 08:23 PM Thread Starter
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Thank you to all that replied. My motor is a 1967 390 s code, so yes, #6 is 180 across from #1. Just double and triple checking everything before I break in this rebuild.(my first time)hope all goes well.
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post #8 of 14 (permalink) Old 09-14-2016, 11:21 PM
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Originally Posted by awhtx View Post
"........If you find an engine that doesn't have 1 and 6 as the first and fifth cylinders please post it here.

I'm hoping my next Mustang will have this firing order: 1-5-4-8-3-7-2-6


Hint: (think Voodoo)


Z
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post #9 of 14 (permalink) Old 09-15-2016, 08:55 AM
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If you find an engine that doesn't have 1 and 6 as the first and fifth cylinders please post it here.
Well, it seems like GM were the black sheep with the Buick Nailhead's whacky firing order. 1-2-7-8-4-5-6-3
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post #10 of 14 (permalink) Old 09-15-2016, 09:05 AM
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Well, it seems like GM were the black sheep with the Buick Nailhead's whacky firing order. 1-2-7-8-4-5-6-3
GM numbers their cylinders differently . . so you can' compare that to Ford. It may not be as wacky as you think.
post #11 of 14 (permalink) Old 09-15-2016, 12:55 PM
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Quote:
Originally Posted by PetesPonies View Post
GM numbers their cylinders differently . . so you can' compare that to Ford. It may not be as wacky as you think.
Quote:
Originally Posted by zray View Post
I'm hoping my next Mustang will have this firing order: 1-5-4-8-3-7-2-6

Hint: (think Voodoo)

Z

^^^^^. this ones a Ford.

Z
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post #12 of 14 (permalink) Old 09-15-2016, 01:04 PM
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just as you say Pete, not that wacky, the nailhead Buick #4 corresponds to the Ford #6



I am surprised no comment on my posted Ford firing order of 1-5-4-8-3-7-2-6. I guess everyone's already in the know.

Z
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post #13 of 14 (permalink) Old 09-15-2016, 01:11 PM
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Originally Posted by zray View Post
I'm hoping my next Mustang will have this firing order: 1-5-4-8-3-7-2-6


Hint: (think Voodoo)


Z
Yup , only with a flat crank.

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post #14 of 14 (permalink) Old 09-15-2016, 04:53 PM
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Originally Posted by GT350HR View Post
Yup , only with a flat crank.
With fewer cars having V-8's these days, I wonder if the engines that used to be considered just for exotic cars, like the flat plane V-8, will be used more often as the V-8 becomes more specialized & strickly performance oriented.

Z
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