280zx dizzy, too much timing advance. How to make it not hurt my engine?

[kcpope]

Fired up my Z build for the first time today. I’m trying to get my timing set right. I have a 280zx dizzy, D6K80-03. E12-80 module. I rebuilt it and it functions properly, including the vacuum advance.

See attached chart.

According to the attached chart, this dizzy will put my engine in the red “danger zone” with a total advance of 55. Didn’t know this when I bought it 🤦🏼‍♂️ 

Help me understand how I can make this dizzy safe for my engine.

 Option 1: Do I run it without vacuum advance? Set timing at idle to 8. Mechanical advance adds 17 for a total of 35. That said, I’ve heard not running vacuum advance yields poor performance for anything other than engines that run constantly at wide open throttle.

Option 2: Do I set timing at idle to 0. Mechanical advance adds 17, vacuum advance adds 30, total advance of 37. I’m pretty sure performance would suffer here too, probably off the line performance because the timing is starting at 0.

Option 3: is there a way to limit the vacuum advance to keep it in the safe zone? I did rebuild the dizzy, so I am familiar with the internals.

I’d appreciate some ideas here. Or maybe this attached chart has me more alarmed than I need to be??
 

Really hoping I can salvage this dizzy, because the electronic ignition is a nice upgrade.

[kcpope]

Well, after doing more digging, I have a tentative plan.

For the time being, I’ll disconnect the vacuum advance and run 18 static + 17 mechanical for a total of 35, which is a safe performance setting. Not ideal for mpg while cruising, but not the end of the world for now.

Then as time permits, I’ll follow the instructions in this thread and attempt to modify my vacuum advance canister to limit its range of motion to 15 degrees (instead of 30).

18 static + 17 mechanical + 15 vacuum advance = 50 total, which is supposedly fine for these engines at cruising speeds.

Feel free to chime in with anything else you might suggest. Thanks

 

[dutchzcarguy]

1 hour ago, kcpope said:

Feel free to chime in with anything else you might suggest.

Hi, Maybe take a look into a service manual of the 280zx, i know there are special books about the engine and ignition and also a special about the whole injection and ignition maintenance/dial inn..

Edited August 24, 2024 by dutchzcarguy

[Zed Head]

I would measure what really happens rather than hope the table is correct, before taking any actions.  You can set the timing to zero, to stay on the indicator, or use a dial-back timing light.  Connect the vacuum advance to intake vacuum at idle and get the vacuum advance number.  Disconnect the vacuum advance and rev it up to get the centrifugal.

The TB vacuum advance hose is ported vacuum and only works when the throttle blade is off-idle.

[kcpope]

3 hours ago, Zed Head said:

I would measure what really happens rather than hope the table is correct, before taking any actions.  You can set the timing to zero, to stay on the indicator, or use a dial-back timing light.  Connect the vacuum advance to intake vacuum at idle and get the vacuum advance number.  Disconnect the vacuum advance and rev it up to get the centrifugal.

The TB vacuum advance hose is ported vacuum and only works when the throttle blade is off-idle.

Good idea, I’ll do that.

Guess I plugged all those intake manifold ports a little prematurely…

Is there a port that is more ideal than others for this, or just any of them located on the balance tube?

Lastly, approximately what RPM will yield max vacuum advance for testing purposes, maybe 1500 or so? Or will idle RPM of 800 be fine?

I’ll report back with my findings.

[cgsheen1]

Max vacuum will be at deceleration - idle second highest. Under load vacuum will diminish and cruise vacuum will be kinda middle of the MAP range (Manifold Absolute Pressure). Except at Idle, MAP is always changing and LOWERS when you have your foot in it. I think your assumption that advance might hit 55 degrees is likely unfounded. When the mechanical advance is highest, vacuum advance is nominal. When vacuum advance is highest, mechanical advance is non-existent (except on deceleration perhaps where advance is not likely to be a problem).

I'm going by what I see on my MAP gauge - correct me if I'm wrong. BTW - my MAP gauge goes BOTH ways...

Oh, and I don't think Zed Head wasn't talking about vacuum ports on the balance tube - he was talking about the port on the carb near the throttle body...

 

Edited August 24, 2024 by cgsheen1

[kickstand80]

You may have hard starting issues with that much initial advance setting. I would set the timing at 0­° and hook up the vacuum advance to manifold vacuum port (not ported). If you have never done any research on ported vs manifold vacuum source for your vacuum advance now is the time. I won't steer you either direction. BTW your vacuum advance canister is adjustable. You have to remove the clay plug to get to the screw(s), then adjust it with the engine running and using a mityvac pump to activate your vacuum advance and adjust it down if you have to. 

Have you run the engine and actually checked to see how much vacuum advance you are really getting by hooking it up to manifold vacuum and keeping the idle rpm under the mechanical activation point?

Edited August 24, 2024 by kickstand80

[Captain Obvious]

7 hours ago, cgsheen1 said:

I don't think Zed Head wasn't talking about vacuum ports on the balance tube

Actually I think that's exactly what Zed Head was talking about.

Just like what kickstand suggested:

3 hours ago, kickstand80 said:

run the engine and actually checked to see how much vacuum advance you are really getting by hooking it up to manifold vacuum and keeping the idle rpm under the mechanical activation point?

 

[kcpope]

Ok, as suggested, im going to set initial timing at 0. Then I’m going to hook up vacuum advance to manifold vacuum. Two questions…

1. Idle RPM of 800 will be low enough to NOT engage mechanical advance, correct?

2. See pic below. I assume this temporary port will be fine to use as my manifold vacuum port?

 

Edited August 26, 2024 by kcpope

[kickstand80]

YES AND YES