vacuum advance
June 2nd, 2017, 05:29 AM
#3
Moderator
Join Date: Jul 2007
Location: Edmond, OK
Posts: 16,465
Ported, not manifold.
This is something that is up in the air just as much as what oil and filter to run. Check out this thread for more info:
https://classicoldsmobile.com/forums...m-advance.html
This is something that is up in the air just as much as what oil and filter to run. Check out this thread for more info:
https://classicoldsmobile.com/forums...m-advance.html
June 2nd, 2017, 08:02 AM
#4
Old(s) Fart
Join Date: Mar 2007
Location: Northern VA
Posts: 48,229
These cars came from the factory using ported vacuum to operate the vacuum advance. Of course, this means that there is NO vacuum advance at idle or small throttle openings. The factory initial timing spec accounts for this.
There are two problems with this. First, even with the gasoline available whe these cars were new, the lack of vacuum advance at idle could cause overheating under hot, low speed conditions such as idling in traffic. As a result, Olds often used a thermal vacuum switch that would reroute the vacuum advance to straight manifold vacuum if the engine started to overheat. If you choose to retain the use of ported vacuum for your vacuum advance, you really should be sure the TVS is hooked up to preclude overheating.
Of course, the second and more important issue is that today's ethanol-laced gasoline pretty much negates the factory ignition settings from the 1960s. Ethanol effectively makes the inlet mixture more lean that if you were using straight gasoline, and this also causes overheating. The lower octane rating of today's gasolines makes the car more prone to pinging. In both cases, you need to vary from the factory timing settings. If you plan to do this anyway, I strongly recommend you convert to straight manifold vacuum and avoid the TVS issue.
There are two problems with this. First, even with the gasoline available whe these cars were new, the lack of vacuum advance at idle could cause overheating under hot, low speed conditions such as idling in traffic. As a result, Olds often used a thermal vacuum switch that would reroute the vacuum advance to straight manifold vacuum if the engine started to overheat. If you choose to retain the use of ported vacuum for your vacuum advance, you really should be sure the TVS is hooked up to preclude overheating.
Of course, the second and more important issue is that today's ethanol-laced gasoline pretty much negates the factory ignition settings from the 1960s. Ethanol effectively makes the inlet mixture more lean that if you were using straight gasoline, and this also causes overheating. The lower octane rating of today's gasolines makes the car more prone to pinging. In both cases, you need to vary from the factory timing settings. If you plan to do this anyway, I strongly recommend you convert to straight manifold vacuum and avoid the TVS issue.
June 2nd, 2017, 12:25 PM
#5
CH3NO2 LEARN IT BURN IT
Join Date: Jul 2010
Location: Land of Taxes
Posts: 5,011
The compromise I have been using for years is manifold vac with an adjustable travel(not rate) advance canister. This allows you to dial up the initial a bit and have vac adv. at idle but only a limit of 8-10-12* This provides great throttle response hot or cold. If you hear it popping out of the exhaust pipes back the vac advance down and or the base. This formula has yielded great results for me. Of course, I do not run Ethanol in any of my carbureted machinery.
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