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ignition maping


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I was going to keep this under wraps till Runswick Bay but i think im going to need a little help to get the microsquirt running in time. the install is going ok (crosses fingers as i think about cutting the teeth on the trigger wheel), what i need is some pointers on writing an ignition map so ive got some chance of it starting & being drivable in a fairly short time. The vac advance on the dizzy has split so it's currently disconnected & running at 12 deg at idle & its made a noticeable improvement to the upper rev range but less to the lower.
So how do i transfer this to a micorsquirt map? ive seen people talk about using higher resolution lower in the rev but what & where should i use & how do you work out the vac advance? All advice, suggestions & pointers welcome.

here's the spec (from Haynes)
max revs 7k
ignition timing at idle speed vac connected
manual      5deg btdc
triomatic   12deg btdc

centrifugal advance (decelerating vac disconnected)
rpm        deg
1k       0-1
2k       12-17
3k       20-24
4k       27-31

vac advance (max)
manual   13 to 17 deg at 225mm (8.9in) [30.1kpa]
triomatic  4 to 8 deg at 275mm (10.1in) [36.9kpa]


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ok im not too concerned aboiut getting extra advace dialed in yet ill be compleatley happy just for some pointers on how to start entering the data in to a table ive had ago on MS best guess (attached) but i dont know how good/safe it is i dont like the way the vac comes in higher than the original set up was at full advance.
i thought a basic dizzy spec would be a good place to start.

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You've got a reasonable amount of information about the standard distributor so should be able to get a good start point.  Manufacturers curves are usually as good as you'll get for a standard engine.  You should also be able to use the upper end of each tolerance band as the electronic system is alot more accurate and consistent.

Can't see your table - you'll need to do a print screen and save it as a Jpeg.

Start with the top line - full throttle / 100kPa.  Put in 5º (ass. manual) in the 600 & 750 rpm bins then 5º + 1º @ 1000rpm, 5º  + 17º @ 2k and so on.  You could repeat that right the way down the table for all MAP bins - which would be the same as running with the vac advance disconnected and a serious waste of potential.

You don't have many data points for the vac advance so you'll have to assume that it produces a fairly linear action ie 17º @ 30 kPa, 8.5º @ 60kPa and so on.
So for the 60kPa line you'd be 5º + 8.5º @ 600 & 750 rpm, 5º + 1º + 8.5º @ 1000rpm, 5º  + 17º + 8.5º @ 2k and so on.  I have been known to make up and Excel spreadsheet to do the whole table but probably no quicker than manual in the end!

When tuning on the road you'll probably find that you can't better the factory figures for full throttle but you'll probably be able to add more advance at part throttle, especially low to mid-range, which helps throttle response and fuel economy.  You can also fiddle around with idle numbers and maybe increase the numbers a bit for the 600rpm line to give a bit of anti-stall and idle stabilisation.  If your idle is near 600 anyway, change the bin number to 500 rpm other wise it may hunt.



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Hello Nick,

"You don't have many data points for the vac advance "

The trouble being that the vacuum advance is variable depending on load and speed. If you don't want to run vacuum advance then I would imagine you will need a throttle position sensor to compensate.


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The Megasquirt will be getting an engine load signal either from manifold vacuum or throttle position sensor.  Manifold vacuum far better in this case and comparable to the mechanical vac advance.

The minimal data points I was referring to was for the mechanical vac advance capsule ie "manual   13 to 17 deg at 225mm (8.9in) [30.1kpa]"
hence the need assume that it has a fairly linear action and use that to calculate what it advance it gives over a range of vacuum values.

do you actually have a manual or Triomatic?  Probably best sticking with the figures for the correct one to begin with?



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the microsquirt is going on a manual so ill use that as a starting point, at some point in the future ill add tps with the throttle bodies, but for now its map only. I just need to get some time in the workshop to get the wiring loom finished, the trigger wheel teeth cut & the lc1 fitted, then we can see how good the map is.


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