Are Moper FSM Distributor Specifications Complete?

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dibbons

dibbons

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Seems like too little mechanical/centrifugal advance, unless the Factory Service Manual specifications don't show true total advance.

1972 Factory Service Manual
340 Distributor #3656278

Centrifugal advance listed as:
1 to 5 degrees @ 650 rpm
12 to 14 degrees @ 1050 rpm
11.5 to 13.5 @ 2400 rpm

2.5 BTC +/- 2.5 degrees idle

Adding 13.5 plus 2.5 = only 16 degrees total
(or am I adding this up wrong and it should be: 5 plus 14 plus 13.5?)

Taking into account 34-35 degrees total centrifugal is universally accepted for a small block Mopar, it seems the factory was way off (16 degrees total), or the full centrifugal advance is not listed under specifications. Which is it? Thank you.

72 distributor.jpg
 
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Great info for reference, horrible specs for anything that you want to run properly!
 
brian6pac said:
That dist advance x2 for crank
Click to expand...

EXACTLY. This is known as "distributor degrees" Many distributors are stamped with the no. right on the mechanism.

If you have an unknown, or are trying to rework the slots, I think it was Crackedback posted this dimension chart

Dimensions for Mopar distributor slots, in DISTRIBUTOR degrees

Modifying advance slots
degrees / slot size
6.............. .340
7................355
8................375
9................390
10...............405
11.5 ...........420
12...............435
13...............445
14...............460
15...............475
16...............490
17...............505
18...............520
 
dibbons said:
Seems like too little mechanical/centrifugal advance, unless the Factory Service Manual specifications don't show true total advance.

1972 Factory Service Manual
340 Distributor #3656278

Centrifugal advance listed as:
1 to 5 degrees @ 650 rpm
12 to 14 degrees @ 1050 rpm
11.5 to 13.5 @ 2400 rpm

2.5 BTC +/- 2.5 degrees idle

Adding 13.5 plus 2.5 = only 16 degrees total
(or am I adding this up wrong and it should be: 5 plus 14 plus 13.5?)

Taking into account 34-35 degrees total centrifugal is universally accepted for a small block Mopar, it seems the factory was way off (16 degrees total), or the full centrifugal advance is not listed under specifications. Which is it? Thank you.

View attachment 1715135158
Click to expand...
Yes as brian6pac wrote. except idle speed is in the back of the fuel chapter.
 
Bear in mind that ANYTHING built in 68 or later went down that long, downhill road of emissions requirements, and got worse and worse every year.......slower and slower advance curves, longer and longer so initial timing could be rolled back "in some cases" AFTER TDC, and in the case of CA, this started in 66

If you want some idea of "how it was" look up the high performance hemi/ 440 specs in 66-67 shop manual
 
The big difference in CAP vs non-CAP is timing at idle speed; then they made up for it with the primary advance curve. I posted a comparison a few ago. Later they started changing the curves more as just posted by 67Dart273.

One downside of retarding the initial timing, especially when coupled with running leaner as they did, was increased engine temperatures at idle. That was somewhat addressed with idle solenoid so the throttle would close more when the engine was shut off. Other workarounds and changes to the concept were added over time to address overheating in traffic. Nowadays, the fuel in some locations (and times of year) is such that even fully stock engines sometimes have issues at idle/off idle with this setup. Its not about the octane - its about the fuel's distillation curve. I have no idea what your fuel is like - just something to be aware of if it comes up.

Since you're showing an magnetic pickup distributor for '72, I have to assume that is CAP spec'd and may be different than the 49 state version for that year. So those to can be compared too if your curious, and depending on what your goal is.
 
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Funny, the other night I graphed the '67 440 A134 Hi Performance with single point distributor along with the CAP A134 curve. The CAP may have been dual point - if anyone really cares I'll look it up.

blob.png

Both curves are maximums - I forgot to update the legend.
 
You probably also want more base advance. There is another post going which discusses it. They said the factory set initial close to TDC, which is too late. The purpose was to increase exhaust heat for emissions reasons.
 
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