so you have in 'crank' degrees:
11 @ 2200 rpm mechanical

and 24 @12" vaccuum

for a grand total of 35 at cruise if 2200 rpm....

there's more in there, somewhere...
what are your shift points for the truck? what is your idle, cruise and WOT vaccuum readings...

off the bat: you could try more initial (technically 30 minus 11 = 19 would be OK, but if the vacuum gauge gets 'peaky' or rattle sets in...back off...BUT you also have to contend with 50 minus 24 = 26 minus 11 = 15...)

Try the initial at 14 or 15 and see what happens...you're still under the typical performance numbers... if it's hard to crank over, plan B comes into formulation...

-D.Idiot

Ian a previous post I quoted from the service manual

Centrifugal Advance:
1.5 deg to 3.5 deg @ 650 RPM
2.0 deg to 4.0 deg @ 900 RPM
3.5 deg to 5.5 deg @ 2200 RPM

Vacuum Advance:
1.5 deg to 6.5 deg @ 7 in. vacuum
10.0 deg to 12.0 deg @ 12 in. vacuum

I just noticed it says Distributor degrees @ Distributor RPM.
With 12 deg BTDC Initial Timing

Does that mean
12 deg @ 650 RPM
15 deg to 19 deg @ 1300 RPM
16 deg to 20 deg @ 1800 RPM
19 deg to 23 deg @ 4400 RPM

In crank degrees? With the vacuum advance added at cruise.
My idle vacuum number is 20 in. vacuum. That must make it fully advanced at idle. So with vacuum attached to distributor. I would get 24 deg advanced?

bwhitejr

_________________
'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

Yep you got it right except for the vacuum advance at idle.....


The vacuum port is just above the throttle plate and doesn't get any vacuum until the throttle starts to open. i.e. no vacuum advance at idle.

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

I think the advance is cumulative and which case it would be:

12 deg @ 650 RPM
15 to 19 degs @ 1300 RPM
19 to 27 degs @ 1800 RPM
26 to 38 degs @ 4400 RPM

This seems to match the "smog curve" of the 1970's.

Have I got this right. I am trying to figure out what to do about my distributor curve. Right now, I have no vacuum advance hooked up because it pulls the advance so far it fires on the next cylinder!

_________________
'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

you were right the first time......


The centrifugal advance specs are total (plus initial) for a given rpm.

vacuum is added to centrifugal.


See

http://www.slantsix.org/forum/viewtopic.php?t=13264


where I went thru curving a distributor........

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Many Thanks emsvitil!

It looks like you have done some very extensive work. Great job!
It will take a day or two to digest it.

In the meantime, I am looking at the recurve springs from Mopar (P2932675). They appear almost identical except that one has a loop that is 90 deg rotated. I thought you were supposed to leave the original light spring and replace the heavy spring with one of these in the recurve spring kit. Since they are almost identical do you replace the two springs in your distributor with the ones in the kit?

bwhitejr

_________________
'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

You're welcome.

I think the recurve springs are for setups with more mods and higher stall converters than trying to get a good curve on a mainly stock setup.

I ended up making my own springs to get what I wanted......

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Mine is not exactly stock. I am running (allegedly 9.69:1), ported and polished 390 cfm carb and an admitedly mild cam with moderate lift.
It is a truck and weighs 4800 GVWR so I guess the distibutor curve is pretty flat.

bwhitejr

_________________
'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

Does anyone have the centrifugal and vacuum timing data for the MP Performance distributor (P3690788)? I assume it may have come with the instructions for installation.

bwhitejr

_________________
'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

Centrifugal advance "curve" is actually a straight line: All the advance gets dumped-in all at once, because this distributor has only one lightweight spring.

The vacuum advance is adjustable.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

SSDan,

Do you have any numbers? Like when does it kick-in and what is the maximum advance and the RPM it reaches it?
Would it be better to experiment with centrifugal advance springs and vacuum on a stock 3874876 then buy a P3690788?

bwhitejr

_________________
'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

it's been posted on one of the "advance" posts...

Specs are easy:

10BTDC initial mandatory
20 deg. mech. advance "all in by 1200"...your timing will bounce badly at anything less than 1000 rpm (like +/- 6 degrees on the timing light)

20 degrees of vac. adv...you dial it in with the allen wrench as to when it's to come in...(I think the one I played with was something like 12 or 14")...

this is a "drag only" distributor...

I use a small block med. spring for 'car' street use to modify this curve to become:

10 initial
20 degrees mech advance "all in" by 2300 rpm (picked by shift and 'cruise' rpm)...



Before recurving I get two of the same distributors, so I have a benchmark/stock one to get me to work (and I know runs)...then I do the swaps to the other one...

One of the posts has the 'slot' welding measurements if you end up with one of those pesky early 70's 15R governors (set @ no initial and 30 degrees of mechanical advance)...


-D.Idiot

I wrapped some wire around/thru the outside of the opening to limit the travel on the centrifugal slot.......

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

If the specifications from the FSM are :
Does that mean I really have a 6.5R governor? It would be hard to tell since the larger distributor spring may be limiting the total amount of advance. From what I have seen in the forums, I was expecting my truck to have a 15R or even a 11.5R governor. Can anyone tell me what they have in their stock trucks?

bwhitejr

_________________
'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

Looks like you have a 5.5R in there (23-12)/2

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes