Setting 240z timing

[siteunseen]

I found the Excel spreadsheet Walter Moore made.  I have the D6K8-05

10 degrees at idle

17 weights

20 vacuum

47 total @2,500 rpms

Thank you @Walter Moore

D6K8-05

10

17

20

47

2500

27

M

1979

 

[siteunseen]

If the vacuum is unhooked do I still add the 20 into my total? Should it be 47 or 27? 

Or should the vacuum advance be hooked up instead of plugged?  Thanks for any help, I'm confused once again.

[siteunseen]

I think I'll need a vacuum pump to get to 20 off the distributor?  Then I eliminate that from my total. So with a vacuum pump I need to dial back my light to 27?

Sorry to be a pita but the unknown scares me.

[siteunseen]

Can you help me out @Jeff G 78 

[djwarner]

I have a D6K80-03 from a 1979 280ZX AT in my Series I. I found the following specs for it and used it in setting my timing. Doubt it will be significantly different than yours.

Centrifugal advance 0 @ 600 RPM, 8.5 degrees @ 1250 RPM.

Vacuum advance 0 @ 5.9 inches of vacuum, 5 degrees at 9.8 inches of vacuum.

Please remember that vacuum decreases as you open the throttle, so the only time you would see both high rpm and high vacuum is letting your foot of the throttle at high speed. During this period of engine braking, you are at low pressure during the compression stroke and actually need the additional spark advance and won't see a knock.

If you are drawing vacuum from the carb port, check to see what vacuum you are actually drawing at idle. These ports are designed to only port vacuum while decelerating and will read zero at idle. If you are porting vacuum off the manifold, disconnect and plug it when setting the timing.

The timing spec given in the factory manual is for engine off with a test light (not a strobe) directly connected to the points. This is known as static timing. When setting timing with a strobe, there will be a component of centrifugal advance as well as this static timing. If you have vacuum connected, the two advances will confound your readings and idle speed as you set the timing.

To figure the expected timing at your desired idle speed you have to calculate the amount of centrifugal advance at idle. For mine at 750 rpm, it is 150/650 times 8.5 degrees or about 2 degrees. (650 rpm is the difference between no advance and max advance rpms.) If the static timing was 5 degrees at 0 rpm, you should observe 7 degrees at 750 rpm and no vacuum. If you see significant change in idle speed as you adjust your timing, reset your idle speed and then idle mixture and recheck your timing. repeat until your rpm and timing  are on spec and  you have adjusted for best idle mixture.

All that said, the idle timings specs for our cars has varied over the years. As a rule, they are retarded to control pollution rather than to avoid knock. This gives you some room to err on the advance side without risking harm to the engine. While most manuals typically set timing to 10 degrees BTDC at idle, I routinely set mine to 17. This conforms to the earliest non-pollution controlled models.

 

 

Edited July 3, 2016 by djwarner

[siteunseen]

Thank you Mr Warner.  I'll have to read that a few times to wrap my head around it though. 8^)

[Stanley]

Me too. Don't know much except that if the timing isn't on, you're throwing away a bunch of potential speed.

My Z did fine with stock US timing and regular gas and the stock head. With a newer, higher compression head it was pinging so I went to premium (91 in CA) gas, OK. Then got a FSM and a light and put it at 17 deg per book for my new euro distributor. I was burning rubber all over the place and it's an automatic. Pinging badly though so I put it about 10 deg. at 1000 rpm IIRC. So I guess I learned something. Feel like there's more to learn though. Feel like I'm shooting from the hip with this. How much ping is OK? 150K on the engine and I don't want to hurt it; but also don't want the CRX's to beat me. Ran the rock drill in my youth so my ear's not great.

[madkaw]

Cliff,

I think the best of Both  worlds would be to limit the vacuum advance so you can run max total timing WOT.  Meanwhile I would run about 17 initial and disconnect the vacuum while you play around for best power. There are threads somewhere where folks have limited the travel on the rod connecting the vacuum . 

[siteunseen]

So simply put, set the initial to 17 degrees at 750 RPMs.  Since I have 8.5 weights, add 17 for a total of 34 degrees on my dial back light.  At 2,500 RPMs with the light set to 34 I should adjust the distributor until the big notch (TDC) on the pulley lines up with the pointer, 0 degrees.  That would give me total advance of 34.  Drive it and see how it performs?

What should the vacuum pull on the front carb be at 2,500 RPM?  I'll hook my vacuum gauge up and get some numbers and report back.

Thanks guys

[siteunseen]

When my dizzy is spinning with the motor at 2,500 rpms those weights are out?  The vacuum advance should stay unhooked and plugged at high rpms too like setting initial timing at idle?

I'm going to understand this one way or the other!

[madkaw]

Minimum of 2500. 

Yes - disconnect vacuum and set dial back to 34 total . As far as figuring the vacuum on top of that - not sure , but I would say just add in the vacuum advance on top of the 34 at 3000 and see where it stands. In the end Cliff, your motor will tell you if the advance is too much. I bet you will have to either limit the vacuum portion of advance , or just reduce  your timing- period