Civvy Distributor Timing

[george walker]

Just remember the vac pump needs manifold vac. too.

[moosejr]

There are volumes that could be written into the theory behind vacuum advance and where to connect it. The standard is that it should go to ported vacuum, with base timing set while it is disconnected. Keep in mind that there is more to it than just how much advance and when. You start looking at valve timing, then you get into the engineering of the camshaft itself. But truly, what it all really comes down to, is than an in-line six cylinder with a carburetor and single runner intake and exhaust is never going to be efficient by today's modern standards, .. so do whatever makes it run best for you, in your climate, etc.

[brute4c]

I guess I dont see how much advantage, or disadvantage, there is to having it "on" at idle as opposed to coming on at just off idle and beyond.

[moosejr]

Keep in mind that you have to look at your performance across the board, ...The tuning process sets your base timing WITHOUT vacuum advance. If you set the timing with vacuum on you lose what you would gain with the vacuum advance, making it useless. Also keep in mind that at Wide Open Throttle, you have virtually no manifold vacuum, so at that point you are relying on mechanical advance.

[moosejr]

Keep in mind that you have to look at your performance across the board, ...The tuning process sets your base timing WITHOUT vacuum advance. If you set the timing with vacuum on you lose what you would gain with the vacuum advance, making it useless. Also keep in mind that at Wide Open Throttle, you have virtually no manifold vacuum, so at that point you are relying on mechanical advance. Also, when you adjust the idle mixture, you want the throttle plates closed, to if your running manifold vacuum to the vacuum advance, it would throw off your mixture adjustment, what I have run across is that running manifold vacuum was that my power peaked at a lower RPM, and I also started getting detonation, however that was not on a 230, . . and your results may be different. FWIW

[amphi]

There are volumes that could be written into the theory behind vacuum advance and where to connect it.

Agreed – I read volumes trying to understand why and when ported came into existence. There is a lot of misinformation published on the Internet. Some even believe ported increases vacuum and advance is in a linear fashion as the throttle opens from closed to full.

The standard is that it should go to ported vacuum, with base timing set while it is disconnected.

I'm not convinced it "should" go there but I do agree most use ported if available. The result is slightly retarded timing at idle making for an incomplete burn. This is a good thing if your engine uses an air-injection emission system because it aids the combustion of the hydrocarbons in the exhaust gas stream. Again this is at idle only.

But truly, what it all really comes down to, is than an in-line six cylinder with a carburetor and single runner intake and exhaust is never going to be efficient by today's modern standards, .. so do whatever makes it run best for you, in your climate, etc

Agreed – Go with whatever works for you because truly it is not a big deal either way.

I guess I dont see how much advantage, or disadvantage, there is to having it "on" at idle as opposed to coming on at just off idle and beyond.

Oh so true

And yes moosejr – once you open the throttle significantly it is all over anyhow.

I have lots of old iron around here designed for leaded fuel. This stuff seldom, if ever, sees the road. I run premium gas and have the timing slightly retarded to minimize piston rock (pinging) under heavy load. This is true for my M715 with the 12v civilian distributor.