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Old 08-30-2005, 08:01   #1 (permalink)
Joe
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Recommended ignition timing for 1972 351C-4V

What do you recommend for initial timing for a 1972 Ford Mustang
351C-4V? Right now it is real slow off the line. I've got an:

1. Edelbrock Performer alum. intake;
2. Edelbrock 750 cfm with vac. secondaries;
3. Pertronix Ignitor II (with adaptive dwell);
4. Pertronix Flamethrower II;
5. Edelbrock full-flow air cleaner with K&N filter;
6. 4-Speed toploard with Hurst shifter;
7. 3.25 Taction-loc diff.
8. Split-fire plugs gapped at .040 (stock is .034 gap)

I think it is currently set at 13 degrees BTDC. I'm also thinking
about upgrading the igition to an MSD 6al CDI and recurving the
distributor with new, ligher springs.

Should I advance the initial timing more than 13-16 degrees BTDC since
I've got the plugs gapped more? Any recommendations?

thanks...

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Old 08-30-2005, 10:01   #2 (permalink)
trippingtoo8track@yahoo.com
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Re: Recommended ignition timing for 1972 351C-4V

Once the original cam has been changed, I have the best success timing
an engine with a vacuum gauge.

i.e. with engine at idle and vacuum advance disconnected, turn dist. to
get maximum reading on a vacuum gauge, then back it off 3" HG and try
that.

If it pings or is hard to start, back it off a hair more at a time,
until it will start easily without binding, and there is no ping.

you now have the "knock point" for that specific engine and fuel used

ps- use premium pump gas in old V-8's, they run better.

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Old 08-30-2005, 12:01   #3 (permalink)
one80out@hotmail.com
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Re: Recommended ignition timing for 1972 351C-4V

I agree with the vacuum gauge method.

Using this method to set base timing on my '70 351C-2v, to avoid ping I
have to use the stiffest spring on my MSD dizzie, which as I recall
corresponds to all-in at 3000 rpm. All U.S. 2v heads are open chamber
and are ping monsters because of it. I don't recall if the '72 4v is
open chamber or not, but I think it is. Therefore you might need to
follow the same approach.

FYI, my cam is the generic "RV" cam: 204/214 @ .050, .484"/.510", 112
LSA. I include this info because cam timing is also a major factor in
making or avoiding ping. Greater duration bleeds off compression. A
wimp cam like mine does not.

180 Out

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Old 08-30-2005, 13:01   #4 (permalink)
Big Al
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Re: Recommended ignition timing for 1972 351C-4V


<one80out@hotmail.com> wrote in message
news:1125426083.808714.323580@z14g2000cwz.googlegroups.com...
>I agree with the vacuum gauge method.
>


I don't. You can't set the timing at idle without first knowing the total
mechanical advance in the distributor. Unless you're working with a
completely stock set up. Then the factory did all the calculating and gives
you the correct timing at idle.

You set total advance and then adjust the distributor advance mechanism for
proper timing at idle. If you need some help, just ask. First thing you will
need is a timing light that will work at around 4,000 RPM. Disconnect the
vacuum and find out what RPM the advance tops out at. Then you can decide
where to go from there. Rough numbers might be 12 initial and 36 total at
3,800 RPM. It's not real critical where the distributor tops out with a
stick shift car, but somewhere between 3,600 and 4,000 would be good for a
street driven car.

Al # 35


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Old 08-30-2005, 17:01   #5 (permalink)
David M
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Re: Recommended ignition timing for 1972 351C-4V

On Tue, 30 Aug 2005 11:21:23 -0700, one80out rearranged some electrons to
form:

> I don't recall if the '72 4v is
> open chamber or not, but I think it is.


Yes, it should be open chamber.

--
David M (dmacchiarolo)
http://home.triad.rr.com/redsled
T/S 53
sled351 Linux 2.4.18-14 has been up 32 days 20:17

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Old 08-31-2005, 05:01   #6 (permalink)
DesertBob Jr.
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Re: Recommended ignition timing for 1972 351C-4V

good post- once the cam is changed from stock, the factory timing specs
kind of go out the window- you have to find the new "knock point" of
the motor for your combination and gas type

the vacuum gauge method works really well, esp. for a huge cam with low
idle vacuum and poor idle quality- you'll find the timing needs to be
bumped up quite a bit over stock settings, to make the car tractable on
the street

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