The Stovebolt Site Forums The Shop Area Engine Shop Correct Vaccum Advance

Have you checked the function and range of your vacuum advance lately?

Not easy these days to find the correct vacuum advance for the right engine and year. 235 1962 in this case.
The local parts suppliers don't even carry it, including NAPA.
And every one of the online and catalogue places sells the very same vacuum advance for all 40s-60s 235s, although they had different specs originally.
I got one of those but it only starts advancing the distributor after 9 inches of vacuum pressure.
1960 truck shop manual says should start at 4 inches for my correct distributor.

I have also a PCV system which drops the vacuum considerably, so the vacuum advance hardly engages. Centrifugal advance works OK.

There is only one place online I could find with the correct one - they are backordered for about 3 weeks.

Does anybody know where to find a GM# 1116089 vacuum advance. Listed as 55-57 pass. and 58-59 trucks.

Btw: How much vacuum pressure drop is normal when connecting a PCV system to the manifold compared to no PCV?

I am mostly looking for all the benefits at light load/cruising from a vacuum advanced timing, like better response and mpg.
Another benefit might be the blapper at deceleration in the exhaust pipes should be less or gone, I believe.

Some of them are adjustable. The inlet fitting screws out & you can add or remove shims to adjust the rate of advance & shorten the spacer to get more advance. The pcv system should not effect the vacuum unless they are hooked in the same outlet.

The advance I got right now is not adjustable.
But thanks for the tip - didn't know that.
I might just get an early NOS 50s advance and adjust it to the shop manual specs.

I was wondering about the difference in manifold vacuum pressure with a PCV system and without.
PCV seems like a controlled vacuum leak.
I have the correct valve according to the current manufacturer's reference.
Just wondering what the numbers should really be, as some of the current production replacement parts are only close enough but not original spec.

I think I got a NOS 55-57 pass. and 58-59 trucks advance on the shelf. Still in the original Delco box.

I don´t need it anymore since I switched to a Mallory distributor that don`t needs vacuum.

I go and have a look in the workshop tomorrow if you want me to, let me know.

Frank

That would be nice of you.
I'm looking for one that starts to advance already at 4 inches of vacuum with 10 inches max advance.
I have tested mine with a t-ed vacuum gauge and sucking on it - starts at 9 inches - too late.


I just got back from the parts store and finally found the right PCV valve after 3 tries.
The parts book says Deutsch-PCV118, but that one dropped my vacuum pressure to 4 inches at idle, down from 17 without PCV.
I looked at each metal housing valve in stock and decided on the PCV125 for a 2 liter V6.
It had the loose valve piece inside go in the farthest when held upside down.
Bingo! It measures now 14 inches at idle.
Almost like without PCV, but enough draw to evacuate all the gases.

One down, ?? to go.
It's fun fine tuning this engine and getting the little things right.

For the vac advance unit, try a part number search at Partsvoice , or check out Vapinc . The NOS units seem rather pricey.