timing a carb'd 5.0

[calpolymustang]

I'm not a spark plug expert, but from I'm reading, this looks like pre-ignition?
Some plugs are in different lighting.

I'm wondering if I should be stepping down to a colder spark plug (AL 24), or maybe adjusting the timing?

Here's my setup:
Stock 5.0 long block with edelbrock 1406
using driver side port for distributor.
Autolite 25 plugs gapped to .055
MSD 6A, Blaster 2 coil
Taylor wires
91 octane in San Francisco bay area

Timing is
29° total centrifigal
55° total centrifigal w/ vac advance (if i hold throttle to 3k RPM)

Idling in gear with the ebrake I have:
6° centrifigal
33° centrifigal w/ vac advance

When i had the distributor advanced 2° more, i could hear pinging when I floored it on the free way (floored it, then heard pinging, then it down shifted and pinging went away)

Any tips or words of wisdom is appreciated
The car seems to drive well for the most part, and doesnt have any stumbling that i know of

 

[ddonaca351]

(imho)...

I would back the vacuum advance off about 10 deg and then add 4-6 degrees more initial advance (turn the dist)... for a 10-12 degree at idle reading.

You note (if I understand you correctly) that you have 6 degrees initial (reading at idle) and you have 29 total centrifigal in the distributor. That would give you 35 total advance at wot, which is probably about right... depending on how modern your heads are. (newer heads/better design make peak power with less total adv: 32-34, older/poor designs like more adv: 36-38-40)

In my exp, most motors (espitially ones with older heads) like more initial advance 10-12-14 degrees. The idle quality will improve and it will be peppier around town. But as you add more initial advance you may need to reduce the mechanical advance slightly, to maintain the same overall total adv. (34-36-38 degrees)

Also 30deg of vac adv seems a bit, um... optomistic to me. What I mean is, if you happen to get a load of bad gas, etc and you get out on the hwy and cruise you could be doing some damage and not even know it. (audible ping is about a 6 or 7 on a 1-10 scale so you can be doing dammage over the long term, and never hear it)

Your sig says you run a 4.11 rear gear, so I'm guessing your not in this for the gas milage... lol Right?

I would think 20 extra in the vacuum would be safer, and also allow you to go a little more agressive on the mech / initial timing for some more pep between stoplights / around town. (32-34-36 total, all in by 2500)

Also worth mentioning is heavier cars, or taller (highway) gears, etc... are less forgiving of agressive advance curves, on the flip side lighter, shorter gear (3.9-4.1-etc) cars are more forgiving of agressive advance because they can get "up on the curve" quicker and not lugg behind it...

Jetting also affects it... lean is less forgiving, fatter gives ya more fudge room, etc...

Bigger cams can also allow a more agressive curve cuz the overlap will bleed off some cylinder pressure at lower rpms, etc...

...so alott of things come into play, but as a general rule of thumb.

Hope this helps,
D

 

[65ShelbyClone]

I'm not a spark plug expert, but from I'm reading, this looks like pre-ignition?

Timing is
.....
55° total centrifigal w/ vac advance (if i hold throttle to 3k RPM)

55° total would explain the pinging. That's about 15° more than it should be. I would aim for a total in the 35-40° range with 10-14° base timing. Base timing with the 5.0 HOs is 10°, fyi.

 

[jcode68]

Maybe I'm wrong, but the plug gap set at .055 seems really wide. Stock range is about .035 and electronic CD systems like my Crane HI6 suggest .042-.045 range. Your spark might be too weak to get a full burn. What do your plugs look like?

 

[calpolymustang]

(imho)...
You note (if I understand you correctly) that you have 6 degrees initial (reading at idle) and you have 29 total centrifigal in the distributor. That would give you 35 total advance at wot, which is probably about right... depending on how modern your heads are. (newer heads/better design make peak power with less total adv: 32-34
D

ddonaca351, I'm not following your math, please help me out. How can you sum 6° initial with 29° total centrifugal? The 6° is base at idle, and 29° is total cetrifugal. My math says total at WOT would be only mechanical, assuming 0" of vac: 29°

as for the heads, theyre E7TE heads

Please note that some plugs were taken in different lighting, so look at color, not shade.

Base timing with the 5.0 HOs is 10°, fyi.

But it seems like there's more to it, since the 5.0 original had a computer controlling timing, but now i have a vac/mech distributor?

I'm not sure theres a way of adjusting the vacuum diaphram, but let's assume i have an aggressive vacuum diaphragm... How do I tone it down?

 

[calpolymustang]

...still cant find a vacuum advance adjustment, but heres a pic inside the dizzy

 

[65ShelbyClone]

I'm not sure theres a way of adjusting the vacuum diaphram, but let's assume i have an aggressive vacuum diaphragm... How do I tone it down?

Probably like this:
Vintage Ford Mustang Engine Tuning Aftermarket Vacuum Advance Adjustment Photo

 

[calpolymustang]

actually, before you posted i discovered the diaphram adjustment with a 3/32 allen in the vac port on the canister. thanks anyways!

i dialed the car in to:
15 initial w/ plugged vac port
36 total mechanical, w/ plugged vac port
48 total with vacuum connected

i still have 91 octane in the tank...
should i still use 91? or is 89 all thats necessary for my configuration?

65shelbyclone and ddonaca351:
im not sure what octane your specs are matched for

im trying to tune it for street, while still breaking my 14.033 sec 1/4mil (99.86mph) OH SO CLOSE

 

[65ShelbyClone]

With the ignition timing sorted out, you should be able to run 87. That's what I use and that's all that stock 5.0 HOs require, although I can run a little more advance thanks to aluminum heads. Stock compression is fairly mild at 9.0:1