2D mapping

[westfield]

Hi

The racing series I run in will only allow control of advance based on engine speed. Can anyone tell me if there is a problem with using MJLJ with a 2D map? Presumably the TPS version would be needed with a fixed resistance instead of the TPS or just the wire connecting the two terminals?

Thanks

Tony

[MartinM]

Use a TPS unit, connect pin 9 to earth.

To make sure there's no problems, it's best to put the same advance values in every row on the map - i.e. different advance for each rpm bin, same advance values (at each rpm) for each load bin

eg
10, 12, 14, 16, 18, 22, 24, 26, 28, 30
10, 12, 14, 16, 18, 22, 24, 26, 28, 30
10, 12, 14, 16, 18, 22, 24, 26, 28, 30
10, 12, 14, 16, 18, 22, 24, 26, 28, 30
10, 12, 14, 16, 18, 22, 24, 26, 28, 30
10, 12, 14, 16, 18, 22, 24, 26, 28, 30
10, 12, 14, 16, 18, 22, 24, 26, 28, 30
10, 12, 14, 16, 18, 22, 24, 26, 28, 30
10, 12, 14, 16, 18, 22, 24, 26, 28, 30
10, 12, 14, 16, 18, 22, 24, 26, 28, 30

PS don't use this map - I made it up!!

[rbalmford]

I'm running mine in 2D at the moment as I haven't yet installed the TPS. I've left the TPS input unconnected, but then written a custom 'load axis calibration' table with a load value of 95 for each ADC value (just use a text editor and create a file with 256 lines of '95'). When running, it then uses the bottom line of the map irrespective of ADC value (as they are all mapped to a load value of 95). Also, when cranking it will use the top left cell, so you can put a low cranking advance there if desired, which it will use when rpm<457. Above this rpm, it will use the bottom line of the map. Works fine on my Xflow (in a Westfield).

Rich.

[david jenkins]

Hi

The racing series I run in will only allow control of advance based on engine speed. Can anyone tell me if there is a problem with using MJLJ with a 2D map?

That's a very odd rule! Even the standard mechanical distributor found on most older engines uses both engine speed and vacuum (engine load) to set the ignition, even if it doesn't do it very well.

I used a 2D MJ map for a while, until I was ready to go 3D. If your interpretation of the rules is correct, you may have to put a resistor across the TPS input, but then I'd guess that you'll have to persuade a scrutineer that you won't change it back! Get him to put an official seal on the plug, or something.

Good luck!
David

[MartinM]

That's a very odd rule! Even the standard mechanical distributor found on most older engines uses both engine speed and vacuum (engine load) to set the ignition, even if it doesn't do it very well.

...you may have to put a resistor across the TPS input, but then I'd guess that you'll have to persuade a scrutineer that you won't change it back! Get him to put an official seal on the plug, or something.

Good luck!
David

IIRC most racing engines with a dizzy (and competition dizzys) don't have the vacuum advance plumbed in anyway since the engines tend to operate at high rpm and/or full throttle where the vacuum is very small and the dizzy isn't able to take it into account (mechanical stiction etc) anyway.

As regards the average scrutineer, unless you're going to show product specs and wiring diagrams (and he/she understands them!), then they will have to take your word for it. If anything, my suggestion of just connecting pin 9 to a solid earth would be preferable as it's easier to mark with paint etc.

[MartinM]

...and if it's easy to see you don't have a TPS fitted at the carb end or pedal end (or a vacuum pipe to a MAP MJLJ), then that's also a pretty good indication that you are only running 2D...

[brentp]

Hmmmm.

With a 10 position rotary switch, the appropriate resistors and dual maps enabled you could have 20 switchable 2D maps!!

[MartinM]

...or use the 10 position switch and set the rows to eg

10,10,10,10,10,10,10,10,10,10
12,12,12,12,12,12,12,12,12,12
14,14,14,14,14,14,14,14,14,14
16,16,16,16,16,16,16,16,16,16

etc

...there's got to be something around a given incline, gear and/or rpm and switch-selecting the different rows to derive the best advance to put into a final map - I just can't get my head around what though...