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Anybody have factory ignition timing specs for 1974?
https://slantsix.org/forum/viewtopic.php?t=53799		 Page 1 of 1
Author:  Fab64 [ Fri Nov 08, 2013 6:10 pm ]
Post subject:  Anybody have factory ignition timing specs for 1974?
Hi all,

In preparation for recurving my distributor (a re-manufactured, stock 1974 electronic unit), I've taken baseline readings of my centrifugal advance at various rpm's, along with vacuum advance at various inches of vacuum.

Note, I am well aware that some on this board consider re-manufactured items to be junk, so please no flames. For my own curiosity, I'd like to verify how close my re-manufactured unit is to stock 1974 readings. I have a 1967 Factory Service Manual for my car, which provides the desired centrifugal and vacuum advance specifications. Note, the values given for cars without the Cleaner Air Package (C.A.P.) vs. with it, are a bit different. I will show both, but only for a 225 CID with Automatic Transmission:

Without C.A.P.:

Centrifugal Advance (the manual says this is degrees @ distributor rpm, but surely that's a mis-print??? Shouldn't it be crankshaft rpm?)
0 deg @ 325 to 475 rpm
0 to 2.5 deg @ 475
7.5 to 9.5 @ 960
10.5 to 12.5 @ 2200

Vacuum Advance (degrees @ in. Hg)
0 deg @ 4.9" to 7.1"
3 to 5 deg @ 10.5"
5.25 to 7.5 deg @ 13"

With C.A.P.:

Centrifugal Advance (degrees @ rpm)
0 deg @ 325 to 475 rpm
0 to 4.5 deg @ 475
8 to 10 @ 750
12.5 to 14.5 @ 2400

Vacuum Advance (degrees @ in. Hg)
0 deg @ 5" to 7.1"
3 to 6 deg @ 8.5"
6 to 8.5 deg @ 10"

My questions:

1.) Shouldn't "distributor rpm", referenced above, really be crankshaft rpm?

2.) Unfortunately, I am unable to locate this same type of data for 1974. I'm assuming these numbers would be different for a 1974 electronic distributor, correct? If so, and someone on this board has a 1974 Factory Service Manual, I'd be grateful if you could provide these numbers.

3.) Since my engine uses a PCV & breather cap, may I assume it is considered to have the C.A.P., and would use the C.A.P. specs?

As always, your help is sincerely appreciated.

Roger
Author:  ceej [ Fri Nov 08, 2013 7:12 pm ]
Post subject: 
Hi Roger,

Those would be the numbers on a distributor machine. The distributor, as you note would be turning at 1/2 speed. Just use the corrected crank rpm for the crank so you can use your tachometer or dial back gun for the engine speed. Don't forget that it is stated for distributor degrees as well, not crank.

Now, with that said,

Advance @ Distributor degrees @ distributor RPM is the way the advance sections read in the '74 FSM.
8.0°-10.5°@800
11.5°-14°@2000
Centrifugal
0.5°-4.0°@550
Vacuum
0.5°-2.5°@7"HG
7°-10°@11.5"HG

Base timing is stated as Crank degrees, vac advance disconnected, engine warmed up, at curb idle which should be on the sticker under the hood. I'll toss a WAG at 800 rpm. Spec says 2-1/2° ±2°

:D

CJ
Author:  Fab64 [ Sat Nov 09, 2013 11:46 am ]
Post subject: 
CJ,

Many thanks for the 1974 specs, and also for clearing up my misconception about the rpms (duh!). I don't normally think of this stuff as applying to a distributor machine, but I guess that would make more sense. Too bad I don't have access to one, as it would make the re-curving process much easier.

Roger
Author:  Aggressive Ted [ Wed Nov 13, 2013 2:38 pm ]
Post subject: 
My fender sticker says check it a 750 rpm, but with a cleaned up system I run 10 degrees at 750 rpm with the 15L long throw distributor and some tight springs to keep the mechanical to 20 degrees at 3000 rpm for a 30 total (initial plus mechanical) then add another 24 degrees from the VC-208 can for a 54 to 55 degree total as the springs stretch and the can kicks into overdrive around 15" of vacuum.
Author:  DusterIdiot [ Wed Nov 13, 2013 8:37 pm ]
Post subject:  And...
Points curves and EI curves are like apples and turnips...the points distributor mechanism has heavy springs and a slightly lazy curve because a fast advance would cause the points to bounce and cause a misfire as the plate moved.

Remanufactured could be anything, you may have asked for a 1974 but the guts could be anything (1975 Truck, 1973 car, 1978 Aspen Super Six)...make sure to note what you have when you pull it apart...if it has a 15L governor it's a 1973-1975...if you got lucky and it's a late model with an 11 or 9 governor, then you got a good core to work with. (more initial and limited mech advance = better timing for stock or performance cars).

-D.Idiot
Author:  Fab64 [ Wed Nov 13, 2013 11:25 pm ]
Post subject: 
Thanks for the additional replies. Here are some pics of the inside of my re-manufactured distributor:

Image

Image

It appears to have the 15L governor. Are you saying that the 11 or 9 would be more desirable? I'm not really interested in performance so much as I am in getting better gas mileage.

Roger
Author:  DusterIdiot [ Thu Nov 14, 2013 5:22 am ]
Post subject:  Yep...
Quote:
Are you saying that the 11 or 9 would be more desirable? I'm not really interested in performance so much as I am in getting better gas mileage.
Yes the shorter slot governor allows you to run more initial and limit the mech.advance...which gives even the low compression stocker a leg up on better timing and increases it's performance (which also means possibility for better mileage). That one will work fine for starters but be on the look out for a late distributor for modification and install later...

Also note that if it's a reman the vacc. adv. pod is a generic 20 degree at the crank, that doesn't allow for adjustments so your are stuck with it "as-is", the OEM 1973-1974 had a can with the arm stamped 8.5x (17 crank degrees) and is adjustable.

-D.Idiot
Author:  Fab64 [ Thu Nov 14, 2013 7:35 am ]
Post subject: 
DI,

I don't remember what vacuum can came with this distributor, but I've added a VC-208, stamped 11 on the arm. So it is now adjustable up to 22 degrees.

Roger
Author:  DusterIdiot [ Thu Nov 14, 2013 7:22 pm ]
Post subject:  Err...no...
Quote:
So it is now adjustable up to 22 degrees.
vacc. cans don't adjust "up to" anything, they will adjust so it comes on at a certain vacc. reading, and partial at a certain lower vacc. reading... typically you get a window for max. advance from like 15-12"Hg...depending on how many turns it has. note that unless you got a old stock Vc-208 be careful turning the adjuster out, the new chinese SMP cans (Red box) can unbolt from the diaphragm and become junk...

-D.Idiot
Author:  Fab64 [ Thu Nov 14, 2013 9:36 pm ]
Post subject: 
Quote:
Quote:
So it is now adjustable up to 22 degrees.


vacc. cans don't adjust "up to" anything, they will adjust so it comes on at a certain vacc. reading, and partial at a certain lower vacc. reading... typically you get a window for max. advance from like 15-12"Hg...depending on how many turns it has.
No, I only meant it would provide more vacuum advance than the other unit you had mentioned.
Quote:
note that unless you got a old stock Vc-208 be careful turning the adjuster out, the new chinese SMP cans (Red box) can unbolt from the diaphragm and become junk...
Thanks for the warning. I bought this one two years ago - it's SMP red box, but it says "Made in USA" on the outside - hopefully, that's true. Btw, this one was already turned out 6.5 turns when I took it out of the box - is that normal? I take it there's no stop or any indication when one has reached the maximum travel? How many turns out is the maximum?
Author:  DusterIdiot [ Thu Nov 14, 2013 10:13 pm ]
Post subject:  Ouch...
Quote:
this one was already turned out 6.5 turns when I took it out of the box - is that normal? I take it there's no stop or any indication when one has reached the maximum travel? How many turns out is the maximum?
Typically I get them with 3 turns to full seated in from the factory, I have not seen any gains on these after 5 turns out from seated (it just acts like it's 5 turns out from seated...or the adjuster comes out...).

One of the other problems we've seen recently is quality control, so hopefully yours is a good one (in one case I had a can for a points distributor which should have been 9.5x...it ended up at 4x all the way out...

Good luck on the recurve and tuning. Remember there is a close relation to fuel and spark...so as you adjust your timing, you may also need to change the settings on your carb.

-D.Idiot
Author:  Fab64 [ Fri Nov 15, 2013 7:59 am ]
Post subject: 
Great, I appreciate the info. I'm still working on obtaining baseline readings (at various in. hg. vs various turns in/out) with this vacuum can. I received one of BigSlant6Fan's kits yesterday, and hope to get to the actual re-curve this weekend. I may be back with more questions.

Roger
Author:  DusterIdiot [ Fri Nov 15, 2013 5:31 pm ]
Post subject:  Yep...
Quote:
I'm still working on obtaining baseline readings (at various in. hg. vs various turns in/out) with this vacuum can.
Since I have a distributor machine, I have a "spellbook" that charts the typical ranges for the common cans I use. I think I typically dial that can to about 2 turns out for the daily driver...if it's too much too often, you'll drop that can for a VC-239.

Good luck.

-D.Idiot
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