taa442

I read a post about vacuum advance some time a go that explained the differance between ported and full time vacuum.The post said you could use an echlin vc-1810 advance can if your engine vacuum was below 15hg.I went too napa and this one was not available. I did look up in there catalog and found similar ones.Anyone know about this? Thanks,Tim

BangScreech4-4-2

Yeah, I'm not too keen on them. I got one from Accel and it hasn't been too effective. Besides, I think you're kind of confusing issues. If I read you correctly, you're experiencing low manifold vacuum, right? If so, then an adjustable VA can isn't going to solve your problem -- those are strictly for modifying the amount of vacuum advance in the distributor.


I think what you're looking for is a vacuum storage reservoir. Try Summit Racing or similar -- they have a bunch of them.

Fun71

I would say use one with similar specs. Measure how much vacuum your engine makes, then find an advance can in the NAPA book that meets your criteria.


I found the info below in a quick search. The VC-180 gives full advance at 8" vacuum - is yours that low?

http://www.vetteclub.org/warehouse/t...acuum-text.txt
Basic rule for vacuum can selection:

THE VACUUM ADVANCE CONTROL SHOULD PROVIDE FULL ADVANCE AT NOT LESS THAN 2" LESS THAN PREVAILING IDLE VACUUM
AT NORMAL IDLE SPEED WITH APPROXIMATELY 24-32 DEGREES TOTAL IDLE TIMING.

One of the following three NAPA/Echlin vacuum cans should be appropriate for all OE engines,
including those converted from ported to full time vacuum advance, using the above rule.
Vacuum cans for modified engines (such as non-OE cams that alter idle vacuum) can be selected using the basic rule.

VC680 (stamped "B1") 0@8". 16@16"
VC1765 (stamped "B20") 0@6", 16@12"
VC1810 (stamped "B28") 0@4", 16@8"

oldcutlass

You also need to base your vacuum advance amount on what your total timing is and how much more advance your timing needs.

taa442

Thanks for the replies.Thats the info I was looking for.Tim

oldcutlass

Towards the end of this link, it lists pn's for vac adv canisters:
http://www.lbfun.com/warehouse/tech_...ance_Specs.pdf

don71

I found that link to be a very informative article that I haven't seen yet. Thanks. Having a little trouble to save to "favorites". It printed out ok.

oldcutlass

When you open the link click on the favorites tab and then click on add to favorites.

don71

Thanks for trying to help, but that doesn't work for me.......and it's not a big deal.

I'd rather have it on paper.

Good luck to the folks that might have vacuum advance questions.

Octania

"If you choose to run straight manifold vacuum to your vacuum advance in order to gain the
additional timing advance at idle, you must select a vacuum advance control unit that pulls in all of the advance at a vacuum level 2” below (numerically less than) the manifold vacuum present at idle"

was found near the start of the article.

Also, you young whippersnappers please read and digest this:

"Ported vacuum advance is an emission control technique to increase EGT, which promotes oxidation reaction in the exhaust, but it also increases operating temperatures, increases the tendency to detonate and run-on at shutdown, and increases fuel consumption. With a handful of exceptions, all GM pre-emission engines equipped with vacuum advance used full time manifold vacuum.

If your experience... does not go back to pre-emission engines, then all you've ever seen is
ported vacuum advance on emission controlled engines."

Fun71

I disconnect the vacuum advance to help my car through emissions testing (yes, a '71 gets tested here in Phoenix, and yes, I was shown how much the emissions go down on an exhaust gas analyzer with the vacuum advance disconnected) and the coolant temp goes up quite a bit (~20º) in the 20-30 minutes or so it takes me to get through the test. As soon as I leave the facility, I pull around the corner and reconnect the vacuum advance to manifold vacuum and the temp goes down within a few minutes.