It never even crossed my mind to weld the inside so I’m late cluing in here. I guess it would cause the initial advance to be slower. Is it significant? I have no idea.
Dumping the FBO timing advance plate.
- Thread starter TrailBeast
- Start date
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Mattax
Just the facts, ma'am
Let me repost some factory timing curves. Initial timing and rpm, plus the advance information (maximum and minimums from the shop manuals). Notice the curves all have a similar characteristic. Fast advance from idle to 1400 rpm or so, then slower advance to 4000 rpm.
1973 318, slow idle at 750 rpm.
1968 318 auto and manual transmisson and IIRC manual transmission with Clean Air Package.
1967 273 Hi-Performance Federal, and Manual trans with Clean Air Package (California).
1967 Hi Performance 440 49 state, and automatic with CAP.
Another thing to note is the high performance engines with 4 bbls have better combustion and efficiency in the higher rpms. They don't need as much spark lead at higher rpms as their 2 bbl brethren. Air fuel is more dense, more compression, and the flame grows faster.
Black line shows what happens to the advance curve when we shorten the slots on the inner side.
Now they are pretty much like the '67 non-CAP timing curve.
Maybe it starts advancing at little higher rpm, but that can easily be adjusted by reducing the initial spring tension.
Of course you have to know what you're starting with.
The heavy spring plays a slightly different trick on the tach drive race distributor.
These have no vacuum advance, and they were more focused on easy restart than quality idle. Things were a little different back then.
Brown line is my measurements on a Sun Machine with Sun's converter (fairly slow electronic box)
Blue is the advance curve in the MP tech bulletin.
This distributor does not retard - even with a slow electronic box.
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