Setting up an initial ignition timing table

[wmahaffey]

I have finished my MSnEDIS unit and am almost ready to try to start my engine. It is a 1994 Lincoln 4.6L 4 cam. When can I obtain good starting values for the fuel and spark tables?

Thanks,

William Mahaffey

[wmahaffey]

Lance,

Thank you so very much.

William

[Scott]

Very interesting! I've never seen anyone attempt to formulate an advance curve.

Just out of curiosity, I plugged the method into a spreadsheet and found some similarity to the rough Seat-O-Pants spark advance tuning that I came up with some time ago.

Here is the file for those who may be interested in modifying it for their own engine combination.
http://planetcampbell.us/IgnitionAdvanceCurveEstimate.sxc (OpenOffice.org file format)

Just enter the appropriate values in the boxes in column C.

[mbohn]

My pappy said, "Son, you're gonna drive me to drinkin..."

[eliotmansfield]

For the benefit of those running Mr Gate's products (and to save you downloading openoffice!) Ive converted Scotts spreadsheet into Excel format and also added the "boosted" calculations.
I'm no excel wiz, but i'm sure there's a way to add the max retard function in also so it never goes over/under a certain amount.

[wmahaffey]

Eliot,

Thank you very much.

William

[kbracing96]

This is realy cool, Thank for your hard work guys

Kyle

[eliotmansfield]

Its handy starting point i think. the figures at the edges are a bit wacked out though, your actual curve would be a roughly diagonal line from the bottom left to top right.

I would try to smooth out and flatline the edges, as you are clearly not going to have -22 advance (retard)

[ronchinoy]

Briliant guys.
Though you lost me when I read this

Below 100 kPa, we add 0.3° per 1 kPa drop. So for example, if our total
spark at 100kPa and 4000 rpm was 36°, the advance at 50 kPa would be:
36° + 0.3° x (100-50) = 51°

I dont see how an engine can run 51° under any conditions.

[benflynn]

I run 52* under vacume and at first my trigger angle was wrong adding another 15*...still ran ok

[Skiericski]

For the benefit of those running Mr Gate's products (and to save you downloading openoffice!) Ive converted Scotts spreadsheet into Excel format and also added the "boosted" calculations.
I'm no excel wiz, but i'm sure there's a way to add the max retard function in also so it never goes over/under a certain amount.

Here's the same xls but modified to keep advance under boost from dropping below a given percentage of 100KPa advance adn also to allow a max advance to be specified. Nothing that's at all difficult to do during transcription, but what the heck.

Edit: Any chance a mod could change the title of this thread to something involving ignition timing? I would have never seen it had it not been linked from another topic...

[kbracing96]

OK I have a question, Is there any way to transfer these values from the spreadsheet to the ignition table quick and easily? I tried cut and past, but that didn't work. Or do you just have to type them all out? Thanks, Kyle

[eliotmansfield]

I think we need lance to move or sticky-ise it.

[Skiericski]

OK I have a question, Is there any way to transfer these values from the spreadsheet to the ignition table quick and easily? I tried cut and past, but that didn't work. Or do you just have to type them all out? Thanks, Kyle

I wondered the same thing. I tried opening a saved advance table in excel, but the values in the saved table aren't the actual advance numbers you see in MegaTune. Can anyone point to the standard format for advance tables? Knowing the format it should be easy to do the transform in excel and copy-paste the values into a saved advance .vex file using notepad.

[djandruczyk]

the values stored in the file are the values in MS units. to convert to
advance you need to divide by 2.84 and then subtract 10 from that total
so:
255 in the vex file = (255/2.84)-10 = 79.78 deg (actually this is deg BTDC)
0 in the vex file = (0/2.84)-10 = -10 deg (Since this is deg BTDC, a
negative number then makes it equal to deg ATDC (without the minus sign)
so a 0 in the vex table is equal to 10deg ATDC.




Dave J. Andruczyk



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Posted by email.

[Skiericski]

Thanks, Dave. That's what I needed to know.

Here's an XLS that gives you a table that you can copy and paste directly into a .vex file opened in NOTEPAD (wordpad didn't work for me as it tries to import it as a table.)

[Ferret]

--- Skiericski <e.aston@utah.edu> wrote:
the values stored in the file are the values in MS units. to convert to
advance you need to divide by 2.84 and then subtract 10 from that total
so:
255 in the vex file = (255/2.84)-10 = 79.78 deg (actually this is deg BTDC)
0 in the vex file = (0/2.84)-10 = -10 deg (Since this is deg BTDC, a
negative number then makes it equal to deg ATDC (without the minus sign)
so a 0 in the vex table is equal to 10deg ATDC.

Is this formula good for all Megasquirt versions (MSnS, EDIS, Extra...) or just for some of them?

Avner.

[Jani Mäki]

I modded Excel list some more, so now you can input your own MAP and RPM values and it calculates spark advance based on those...

[64Vair]

Briliant guys.
Though you lost me when I read this

Below 100 kPa, we add 0.3° per 1 kPa drop. So for example, if our total
spark at 100kPa and 4000 rpm was 36°, the advance at 50 kPa would be:
36° + 0.3° x (100-50) = 51°

I dont see how an engine can run 51° under any conditions.

I have an air cooled motor, (Corvair), with good squish area, (cut out the step from the heads, and the piston comes to within .040 or the squish), I have measured 10.5:1 CR on 5 holes with almost 10.75:1 on the sixth hole. I use Sunoco 260 (94 octane), and have NO detonation problems running 40 degrees under max load, and 57 degrees max under low MAP. I have ALL my advance in by 2400 rpm, and could run MORE advance if I were racing. I drive the car on the street so I have the motor under load at 2000 rpm and need to keep a little timing out to prevent knock. If I were racing, I would not have the engine under load below 3500 rpm, and could probably dial in 3 degrees more timing. Once I have my MS1 3.0 built, I will use that to control my timing and will therefore be able to dial in a little more timing for racing, and keep it as is for street.
Cylinder head preperation has a LOT to do with how much timing you can run. If I had more "open chamber" design, and did not have the squish area I do, all things being equal I would not be able to run as much timing. If I had domed pistons, that were further down the bore, away from the squish area, I would not be able to run as much timing, (This is assuming that the CR remained as it is now, 10.5:1). The table that is posted here should keep you well out of trouble. Always better safe than sorry. Still, if you know how to build motors, and how to take advantage of the squish area offered by wedge heads, you can run possibly a lot more timing. Also, remember that aluminum heads will allow more timing than cast iron ones will.
Tom