Hello Everyone, I am looking for some help with some where to set my 123ignition centrifugal curve and MAP curves.

I have a 280zx block with N42 head that has upgraded cam. I am running Z Therapy Carbs. i was hoping to get some number that are a good starting point. 

Here is where mine is and it runs pretty smooth.  It's kind of on the mild side.  The engine is an F54/P79 mild cam(stage 2) shaved head with lightened pistons(Datsun Spirit stage 2)running FAST EFI.  All we get here is 92 octane.  It's right at 10:1 compression ratio.  Seems to be a bit happier with non ethanol.

 

You could match a curve from a 240Z.  Should get you in the ball park.  The curves are in the FSM.  Pick an early one, they later ones are emissions focused.

Here's 1972.  Don't forget that distributor speed is 1/2 crankshaft speed.  And, therefore, the degrees are double also.  e.g. 9 distributor degrees = 18 crankshaft degrees.  You'll want to study up on the vacuum and MAP readings also.  It takes a little bit of thinking.

The curves are for the two types of engines and their distributors that were offered in 1972.  It's detailed in the chapter.

Here's 1973.  If you just get close to these you'll probably be fine, for starters.  1973 was starting to lean toward emissions goals.  I haven't really compared the changes to the early curves so can't say if they're significant.  Edit -actually you can see that they delayed the advance in 1973.  Retarded timing is cleaner than advanced.  So the 72 curves probably add a little bit more mid-range power, I'd guess.  That's the tradeoff.

Edited August 19, 20222 yr by Zed Head

Here's a good conversion tool for converting mm hg (millimeters of mercury) to pressure.  Manifold absolute pressure (MAP) is the pressure inside the manifold.  So it is kind of the inverse of vacuum readings.   A high pressure number will need low ignition timing advance, whereas a high vacuum number will need a high ignition advance.

Anyway, for the purpose of creating a MAP map you can just take the points on the Nissan curves and convert them to pressure.  Convert the mm-Hg to whatever unit your 123 is set for.  I think that there are two settings, metric and imperial maybe.  Not sure.

Pick a curve, convert the numbers to make a new table to match what 123 software needs, plug the numbers in.

https://www.onlineconversion.com/pressure.htm

 

p.s.  I had to wake up some sleeping (deeply) brain cells to get in to this.  No guarantees that it's correct but I think it's close.  Feel free to correct anything.

I left something out in the post above.  It's confusing.  The MAP reading is the pressure left over in the manifold after vacuum is pulled.  So, to make a new table of MAP pressure readings from a vacuum reading table, you have to subtract the vacuum reading from absolute pressure.   We all live under approximately 14.7 psi all the time.  760 mm Hg.  100 KPa.

123ignition's web site actually has a tutorial on it.  But if you read too much of it the subject gets even more confusing.  It's basically physics class stuff.

https://123ignition.com/support/create-curve-tutorial/

"

Regarding the vacuum curve, this is a little bit more complex. 123ignition works with absolute vacuum in stead of relative vacuum. The advantage of absolute vacuum is, it works also when you drive the car on high altitudes. In case of relative vacuum, you have to adjust the ignition manually. The values in the original Bosch graph are given in mmHg, 123ignition works with kPa. First we convert the values to kPa and crankshaft degrees instead of distributor degrees. You can type in Google: 80 mmHg to kPa

• 0 deg @ 11 kPa
• 10 deg @ 27 kPa

Now we have to convert the relative values to absolute values. Atmospheric vacuum at see level is 100 kPa. So 100 kPa is our base point. Al values below 100 kPa is vacuum all values above 100 kPa is pressure. in this case we have a vacuum curve, so our result will be:

• 0 deg @ 100 – 11 kPa = 89 kPa
• 10 deg @ 100 – 27 kPa = 73 kPa"

You know you've got it right when you successfully use the Earth's gravitational field to sling yourself to Sirius.

On 8/18/2022 at 9:35 PM, Reptoid Overlords said:

Here is where mine is and it runs pretty smooth.  It's kind of on the mild side.  The engine is an F54/P79 mild cam(stage 2) shaved head with lightened pistons(Datsun Spirit stage 2)running FAST EFI.  All we get here is 92 octane.  It's right at 10:1 compression ratio.  Seems to be a bit happier with non ethanol.

 

You can only manage 28 degrees total ? That seems quite low even for 10:1 and 92 octane . Serious amount of power left on the table . 

I want to say that around 35 degrees it starts pinging? I think I went with 28 as a safe number, but I can't recall my logic now to be honest. 

7 hours ago, madkaw said:

You can only manage 28 degrees total ? That seems quite low even for 10:1 and 92 octane . Serious amount of power left on the table . 

Since I'm on vacation from work with nothing better to do, I toyed around with some higher numbers.  I seem to remember you working with these and assume you know more than me haha.  You're right, I was missing out on a bit more power.  A pretty noticeable difference.  I'm not sure how I got that it was pinging once I 1st installed it over a year ago.   The engine was still braking in and maybe i dialed it down to be on the safe side, and old age setting in made me forget to try more advance?  Who knows.  Anyway, for the sake of the OP's research, here are my new curve settings:

We had a thread conversation a while ago about how 34 degrees seems to be the optimum mechanical advance limit across a wide range of engines.  I posted some dyno run videos and maybe some other links.  Not sure why, I think it has something to do with just the nature of the piston movement (you can cover a lot of degrees near the top with very little piston motion) and the basic design of most older engines.

Anyway, if you browse around the internet you'll see 34 degrees a lot.

There's also a thread out there, either on this forum or Hybridz where a guy was setting timing by ear, expecting to hear some knocking when he was "maximized" but he never did and ended up leaving power behind because he was over-advanced.  He discovered it later when he did some dyno tuning.

Also, something I've noticed in these types of conversations - the focus tends to be on "maximum power" which you'll only see at wide open throttle, high RPM.  Most of us never use that area.  I think that getting the vacuum advance dialed in will have more affect on driveablity.  And, probably, the RPM at which maximum mechanical advance is "all-in" as they say, whether it's 28 or 36.  Like if you compare the 72 and 73 curves above you'll see that 72 is "all-in" about 800 crankshaft RPM sooner than 73.  2000 versus 2800.

They used to make machines specifically for setting distributor curves.  You can spend a lot of time on it.

https://www.ctci.org/sun-distributor-machine-the-ultimate-tool/