Hope to get some help. I am thinking of replacing my Delco disributor with a Pertonix plug and play. I currently have a vacuum advance system on the Deco, which seems not to be working as it should....do I run into any troubles if I simply buy a non vacuum distributor and cap the vacuum at the carb? I have a 250 chevy with a holley 4412 carb...
Distributors are factory set with a performance advance curve and are provided with additional springs for custom advance curves.
Wait. . . What? How is he going to have reduced mileage going from a points type,vacuum advance distributor to an electronic ignition Pertronix distributor? He should see a performance increase if anything.
A pertronix with vac advance is the same price as one without. At least you could plug it off if you don't want to use it. Your 250 will like at least 14* initial plus vac advance to run at it's peak.
Like the others said, run the vacuum advance unit. The aluminum factory delco was a problematic unit with issues etc. Adjust the timing to factory specs without the vac hooked up and then hook the vac up to manifold vacuum. Should add some fuel economy and help cool the engine. Adjust the rpm after the ignition...
Awesome! Thank you for the info. I guess I will be buying the vacuum advance unit and plugging if not needed.
I used an HEI on my 230 in my 65 c10. Had an offy intake, holley 7448 and langdon's headers. Ran it at 14* initial. It would ping a little at 16 so 14 was good. Vac advance hooked to ported. However with the stock intake, no headers, a 1 bbl carb and an hei it didn't like more than 6*. But only vacuum available with the 1bbl was manifold vacuum.
..Listen to Bubba,..A street driven hotrod needs a vacuum advance and needs to be hooked to manifold vacuum..A change was made to ported vacuum in the 70s on smog engines.. Ported vacuum will run the engine hotter to burn off hydro carbons..
As stated above street driven cars run better with vacuum advance. I made all the mistakes then paid attention to whats said here. I changed to a "B26" vacuum advance and hooked it to manifold vacuum. The engine (327) immediately ran smoother. Part throttle acceleration was very smooth and it idles good even with the cam. Don't know about running cooler, doesn't get that hot here. Not checking mileage.
I really do a ppreciate all the valuable info. Is there a different if I hook up to the vaccum port at the carburator or can I attach it to the manifold port? I do have a ofenhauser intake manifold and notice there is a threaded option on the back of it...I am assuming it is for vacuum port?
Took the vacuum advance off my engine long ago and plugged the line. Never noticed any difference in performance or mileage, or heat. Runs a little better at higher rpm's than with the advance. It's nearly all street driving, and no issues.
Maybe you don't understand what the vacuum advance does. Removing the vacuum adv. doesn't improve performance. Ago
Hm, my experience in the past is that manifold vacuum will run hotter than ported vacuum - assuming you set the ignition timing to say 10 deg without the vacuum hooked up, then hook up the vacuum, you will be idling with 20 degrees advance. That gives the flame that much more time to transfer heat into the cylinder wall. I tried hooking it up both ways and see how fast the temp comes up when driving in the morning, it definitely came up faster with manifold advance. It will idle faster and give you more vacuum. I also found that then if you turn down the idle it will be more prone to running rough just because you're running 23" of vacuum, very very thin air at that point. I have a thermal vacuum switch on my thermostat housing that gives me manifold vacuum when cold, then switches to ported around 160F. I found this to work great. I don't even have the fast idle or choke hooked up. The pertronix units are nice BTW, I have used them before and they work well. Just remember they change the timing so you'll have to re-set the ignition timing. Sent from my DROID device using the TJJ mobile app
I think I know what a vacuum advance does, it's as simple as the name; it advances the engine timing based on vacuum, so at high vacuum it's advancing, and under accelration it's basically out of the picture. In a heavy car a vacuum advance is almost a must, but the lighter a car is the less effect a vacuum advance has. A lighter car can easily perform better with just mechanical advance.
This is my personal opinion I tend to disagree with you. I have a light 32 Ford and it really cruises nice with vacuum. On the hi way very little throttle and hi vacuum it gets better mileage. Ago
Check out this thread from a while back. It goes into great detail and explains the theory. See Vacuum advance 101. http://www.jalopyjournal.com/forum/showthread.php?t=740699&highlight=hotrodmyk&page=2
I have fixed three cars by simply moving the vacuum advance from ported to manifold vacuum...By reading the link fully, you may,i say may, you will have a clearer understanding of how a vacuum advance really works...I did
For nearly anything that's street driven, vacuum advance (combined with proper initial and mechanical advance) is the way to go. Easier hot starting, smoother idle, better off-idle driveability, better mileage and less prone to pinging under a load are some of the benefits. Retarded timing can make an engine run hotter, so keeping the timing advanced at the proper time can reduce engine temps. Manifold vacuum usually works best, but it's easy to switch and try ported vacuum as well. Put a vacuum gauge inside your car connected to full manifold vacuum and drive it that way for at least a couple weeks. Watch how your driving style effects the vacuum reading and you'll see how and when your vacuum advance works as well as when the power circuit in the carb comes into play.
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