There is a lot of info out there about the various vacuum advance units used on the GM window style distributors used post 1957 but almost none for the early 50s Delcos. It seems like most of the Delco Remy 49-55 V8 distributors like the Olds, Pontiac, Cad, Studebaker and maybe some other makes use similar appearing vac canisters. There are different part numbers that appear similar so maybe they had different springs inside or internal stops for different applications. Does anyone have info on these? A list of part numbers and what vac they reach full advance at would be nice when building an engine with a performance cam. Were there ever any adjustable units available for the pre window cap Delcos? I've done some digging around and haven't seen any. I may take a junk one apart to see how they are set up inside.
I doubt you'll find one that's adjustable. Most of the factory service manuals for the older cars have the specs for the advance unit, and some have the part number for it, but usually you need a combination of the factory service manual and the factory parts books to figure it out. Not many folks have those books. If you can find an old Standard Motor Products catalog and buyers guide it might be a big help, though. I think my oldest is from the early 90s, and most of that stuff was obsolete by then.
If you hunt down old literature for this, I'd try to find a distributor machine's specifications book. I'd guess a handy reference for part numbers and specs would be part of the setup.
That was one of the beautiful things about the old Sun Engine Analyzer consoles from years ago. Aside from the scope they usually had a big metal file box attached to the side of the roll-around cabinet. Inside were tune-up specs printed out full page on card stock like used on a manila folder. Each year, make and model had its own sheet to easily find every tune-up spec needed for what ever vehicle you had plugged into the scope. Ignition timing and advance, idle speed(s), cranking compression, vacuum advance, plug gap, firing order, plug wire location in the cap, distributor rotation, voltage regulator settings and tons of other information that lots of folks ignored. And all the variations for different engine, trans, and carburetor combinations. Tuning up a '54 Hudson Hornet with a 308? Here's your specs. '62 Rambler with a flathead 6? No problem. A '67 Checker Marathon with a Chevy 283? Here you go! The tune-up spec cards would be just about as valuable as the scope itself.
Thanks! I sent a message to a friend who has a bunch of old parts catalogs from when she worked at a parts store. I'll see how far back her books go. I think some of my old Motor manuals have some specs. Tonight I'll look. It'd be interesting to take apart a stock early vac can and also a window cap adjustable one to see how they change spring preload inside.
This is not what you want, but it might help someone else searching here. Later model info and description. https://www.crankshaftcoalition.com/wiki/images/e/e4/Vacuum_Advance_Specs.pdf
Here's a cutaway of a can. Ignore the retard function, and you can see the front spring tension is adjusted. No need to hack up old parts.
I'm thinking that the blue Motor Manuals from that time frame had the vacuum advance specs listed on the tune up section. Back in the day when there was a specific vacuum advance on the shelf for each level of engine that was offered = 283 2 barrel truck engine, 283 powerglide 2 barrel 283 power pack 4 barrel. There was a different part number for one for each engine and now you get one for that model of Chevy distributor that is expected to work on all.
It was already labeled that way, had to use the same term. It was the only good image I found quickly, and had to save it and upload already. Guess I should have edited it. Just trying to save a part from destructive curiosity. We've all been there, right?
Be aware that due to the age of the early style advance cans that many of them have bad diaphragms now. It's getting harder to find a good usable one...
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