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Discussion Starter · #1 ·
So I just got a 123 Ignition Tune distributor, and it makes adjusting timing a lot easier since I can just plug a USB cable into it and program a curve and rev limit with a computer. I was wondering if you guys could chime in with suggestions for an optimal curve. Right now I have it set up like this:

0 RPM - 9 degrees BTDC
1000 RPM - 10 degrees BTDC
1400 RPM - 10 degrees BTDC
2300 RPM - 14.6 degrees BTDC
3500 RPM - 26 degrees BTDC
5000 RPM - 33 degrees BTDC
Rev limit: 7000 RPM
 

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1000 RPM = 10 BTDC
1700 RPM = 18 BTDC
3000 RPM = 33 BTDC (no further advance beyond this)

It's going to vary some depending on cam overlap -- more overlap wants less advance curve and more initial timing, but the above is a good starting point for stock or near stock engines.
 

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What are you doing with the MAP signal to the distributor? Those are good settings for wide open or large throttle openings. You can probably benefit from more advance at lower throttle openings (lower MAP values). The less dense fuel mix at lower map values takes longer to burn those benefits form a little more advance. It won't make more peak horsepower; but, may improve response and fuel economy. I recall that Kertwerks posted the advance curves someplace that he was using with his Megasquirt conversions. He is working on B20Es; but, it would be a good place to start. Perhaps you can find it or PM him and he may share it with you.
 

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Does the 123 distributor not have a MAP port or are you just not using it? I was under the impression that all the 123 distributors had the MAP sensor.

As I recall, the B18B does not have a vacuum servo on the distributor; but, the B20B as supplied by the factory, at least on the later versions has the same servo arrangement as the B20E. That said, your engine should run OK with no MAP based ignition advance.
 

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Discussion Starter · #7 ·
It has a MAP port but my intake manifold doesn't have anywhere to hook up a hose. My car originally had a B18 which the previous owner swapped for a B20, but I think he kept the B18 distributor because my mechanical distributor didn't have a vacuum hookup. My understanding anyway was that the B20B didn't have vacuum advance, only vacuum retard.
 

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My understanding anyway was that the B20B didn't have vacuum advance, only vacuum retard.
Sort of correct. The vacuum servo on the B20B and B20E definitely retards the ignition with increasing vacuum. However, on the B20E the port is right at the throttle plate so the vacuum signal that the distributor is getting is not necessarily the same as the MAP signal. I am not sure why they did it that way. I don't know how the B20B is set up.

I don't know your manifold set up. If it has a common plenum you could tap a port into the common plenum area to get a manifold pressure signal that you could use with the distributor. This would allow you to fiddle with mixing in some MAP based advance or retard if you so desired to see how it altered performance. Or, you could just leave it as is if you are happy with it.
 

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I installed a Black Box programmable ignition timing module to my car.

http://www.cbperformance.com/ProductDetails.asp?ProductCode=2013

The table I started out with looks something like this. Have made some tweaks since then but only minor changes to the idle area and going to 6500rpm



Whether you decide to go with a MAP connection or not, I would recommend putting a little more timing below you idle speed, and a little less above it. It creates a more stable idle. Adding MAP timing really improved part throttle response and gave me a few extra MPG.
 

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Discussion Starter · #10 ·
I didn't bother with MAP because first, my manifold doesn't seem to have any vacuum ports and second, from reading around it seemed like many people were saying that MAP readings can sometimes be detrimental to performance, and right now I'm more concerned about giving my car some extra oomph than about fuel economy - maybe eventually that will change though.
 

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I know nothing about the 123 ignition. But I'll try to shed some light on a couple of things.

There were distributors with vacuum advance and some with vacuum retard.

The vacuum hose hookup just next to the throttle plate is called ported vacuum. There's little or no vacuum until the throttle is opened.

If you need straight manifold vacuum a trip to the parts store should find you a T fitting of some sort to go in the PVC line. If you don't have PVC there should be a plug you can pull and put an adapter in for it.
 

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I didn't bother with MAP because first, my manifold doesn't seem to have any vacuum ports and second, from reading around it seemed like many people were saying that MAP readings can sometimes be detrimental to performance, and right now I'm more concerned about giving my car some extra oomph than about fuel economy - maybe eventually that will change though.
The table that carbonmike supplied has a high throttle opening curve that is very close to what Phil suggested (slightly more low RPM and slightly less high RPM advance). The advance provided by the MAP signal generally improves performance and throttle response at part throttle openings where you spend most of your time unless you are a drag racer.

Including MAP based advance could be detrimental if it is done incorrectly. Notwithstanding your absence of a port (a drill, tap and some NPT fittings can fix that) the biggest problem might be getting an appropriate MAP signal. The raw MAP signal on my B20E which has a fairly large common plenum is definitely not steady. At idle and lower RPMs you have no problem seeing the individual intake valve openings on the signal. The Megasquirt seems to do an admirable job of filtering the signal to give a representative steady MAP value. If there is no reasonable common plenum or you had a short stubby manifold, getting a representative MAP signal might be a nightmare (there is a reason why the dudes with ITBs use throttle switches rather than MAP sensors).

If you are uncomfortable with integrating a MAP signal into the distributor at present, the straight engine speed based advance curve that Phil suggested will work just fine. At some point in the future, if you want to explore enhancing your part throttle response, adding a MAP signal is something you can investigate. Your choice.
 

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Discussion Starter · #13 · (Edited)
My manifold looks like this, minus the vacuum port:



I did notice while looking around it last night that it does seem to have an opening on the side of it, but there's a bung in it that is very well seized. Also, isn't that behind the butterfly valve? Wouldn't there be a significant amount of vacuum there even at idle?
 

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If you were going to utilize MAP based timing adjustments similar to the table posted by carbonmike, you would want the MAP port to be located where it is exposed to full vacuum at idle. Carbonmike's curves are pretty much set up that at any fixed engine speed, advance increases with lower manifold pressure / increasing vacuum except for the bits that he notes. That would be pretty much what people think of as 'conventional' vacuum advance.

My B20E with the negative governor control uses the ported vacuum described by bobbyz. I have never hooked up a gauge to it to figure out how the vacuum signal changes with throttle opening. It is not necessarily intuitive and I am not sure what Volvo's objective was in using this arrangement. I know that one of the results of the ported vacuum on the B20E is that if you use the throttle plate rather than the aux air valve to adjust idle speed, it has the potential to screw up your idle advance. On the B20B with the separate throttle plate and slide on the SU carbs, it is not clear to me where you would get a ported vacuum line. My knowledge of the SU is minimal; however, with the throttle plate 'behind' the slide I don't think a port right at the throttle plate will work.

My intention is to ultimately ditch the whole negative advance vacuum governor thing on my B20E and implement a more 'conventional' ignition timing arrangement in Megasquirt using a table similar to what bobbyz posted. I will use the MAP signal in Megaquirt which is ported off of the main part of the intake manifold. From the photo you posted, I assume that the nipple in the center of the manifold is for the crankcase ventilation system? If so, then bobbyz's suggestion that you could buy a T, install it in the opening and have the PCV and MAP run off of the same point is probably a good starting point. It would allow you to hook up the MAP signal to the distributor and do some testing to determine whether there is a material up side to providing MAP based timing. In the long term, if you decided to keep the MAP signal, connecting the MAP signal to the same port as the PCV might not be a good long term solution. Pressure fluctuations in the manifold might end up with PCV fumes working their way down to the MAP sensor in the distributor which may not be sensor friendly. The center location is as good as any on the manifold, but, you might want to tap a new port at 90 dg radially and a couple of centimeters to the side of the existing PCV port.
 

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Discussion Starter · #15 ·
The pic I posted is not of my manifold. Mine looks like that but does not have the nipple in the middle. I just have one of those little air filters on my oil cap so no PCV is vented to the intake.

My manifold has no nipples or vacuum ports anywhere. There is a bung at one end that is proper seized and also a non standard shape so I can't even find a tool to try and unscrew it (it just has a square indent).
 
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