Ignition timing on my NAPZ Engine / 85 KC 720

[720inOlyWa]

When I put my engine back together, I set the timing at 5 degrees- maybe a pudgy five- and it ran fine. I set it there because that’s where it was in the photo in the Haynes guide. I have a thousand miles on it now and I have been trying to smooth it out in transition from idle, so playing around with the timing seemed appropriate. 

 

This time, I consulted the back cover of my official Nissan shop manual and it said between 3 and 2 degrees BTDC. So I set it there. It runs great- and maybe picks up from idle a bit better, I’m not sure. But the pinging under load is now evident. The manual says retard it a degree or two if this happens, so I will. That will put me right back to about 5 degrees again.

 

I am sure that five degrees is fine. I am not worried about it.  I was just curious about the discrepancy. Is timing an approximate thing when it comes to production cars like my little 720 King Cab?

[MikeRL411]

Most likely the pinging is due to the lower actual Octane ratings of gasoline as compared to 30 years ago.  Seasonal dilution with Ethanol also contributes to differing ignition.

[720inOlyWa]

You may be right. However, when I squinted my tired old eyes ad read the fine print again, it said: “3 degrees, plus or minus 2 degrees”, which can easily put me back at five degrees, right?  Ooops. sorry. I don’t have a problem after all!

[datzenmike]

If you are at 3 degrees retarding it 2 degrees goes down to one. Advance means more or + timing. Retard means backward or - less timing.

 

The NAPS are very tolerant of too much advance, they don't ping much but they don't give the best power either. The correct timing is 3 degrees + or - 2 degrees (that's +5 down to +1 degrees BTDC) to allow for different grades of gas, temperature, humidity, altitude and temperatures. All of which affects the timing.

[NissanEgg]

Well, what would you recommend on a Z20S with Z24 dizzy, a Weber 32/36DGEV, 4-1 header and full 2" mandrel bent exhaust,  and Nissan Motorsports camshaft?  I run it at 7* and it seems fine.  If I set it to 5* or less it suffers alot in the midrange and up top.

[datzenmike]

Single or dual plugs??? Single will always need more advance than dual plugs.

 

If it runs strong at 7 then seven it is.

[NissanEgg]

Dual plugs.  Haven't tried going any higher as I am afraid it might ping.

[xsdg]

The Z20 has a knock sensor, doesn't it?

[datzenmike]

Ah ah ah I didn't catch that. The Z20 may run a different advance, I'll check when I get home. Otherwise follow the timing recomended on the under hood emissions sticker.

 

Yes the Z20 does indeed have a knock sensor and ignition retard.