How to get the blackbox to mimick the old distributor?

ewout · Post by **ewout** » Fri Apr 20, 2007 2:37 pm

Hello!

I'm new here. I've just bought, recieved, assembled an talked to the Megajolt blackbox and all seems fine so far.

I have nearly all EDIS components and a triggerwheel to install on my van. It's a 1983 Ford Transit with the well known 2l pinto engine, although it's running on low compression 8,2:1.

I don't worry about the installation in the vehicle, that's clear to me, as far as I can judge the installation instructions.

What is unclear to me is how to get the blackbox to act like the old distributor. I do have all the theoretical data about the mechanical- and vacuumadvance, but how do I convert this into something the blackbox can work with?

Please could someone enlighten me?

Thanks a lot! Ewout - the Netherlands

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Ford Transit 1983cc ohc pinto low compression engine 8.2&#58;1 compressionratio.

Centrifugal advance			Vacuum advance
revolutions		advance		Vacuum in mm Hg	Vacuum in kPa	advance
1200 and lower		-1.0 to +1.0	70 and lower	9.3		0
1400			-1.0 to +3.0	75		10		-1.0 to +0.5
2000			 5.0 to  9.0	100		13.3		-1.0 to +2.0
3000			14.5 to 19.5	110		14.7		-1.0 to +5.0
4000			24.5 to 30.0	150		20		 9.4 to 15.4 
4800 and higher		32.5 to 36.5	190 and higher	25.3		16.0 to 22.0

1. Vacuum between 9.3 to 25.3 kPa
2. Max advance is 22deg at 25.3 kPa
3. Basic static timing is 6deg BTDC

MAP&#58;	100 - 9.3 = 90.7 kPa
	100 - 10 = 90 kPa
	100 - 13.3 = 86.7 kPa
	100 - 14.7 = 85.3 kPa
	100 - 20 = 80 kPa
	100 - 25.3 = 74.7 kPa

	800	1200	1400	2000	3000	4000	4800	5800
90.7	
90
86.7
85.3
80
74.7

Post by **brentp** » Sat Apr 21, 2007 9:04 am

Hi,

It seem you might have a few options:

- You can start with the built in ignition map and start tuning from there
- You can look under the Ignition Map library and see if someone contributed a Ignition Map that might match your engine configuration

Starting with the default MAP or one of the contributed maps you can take your distributor curve and see how close it matches the current ignition configuration. you can then make small adjustments based on that analysis. The 3D tuning view might help you 'visualize' the igniton map.

Often, the old distributor curve may not be the best for what you are seeking- perhaps you want more power in a certain rev range- you may want to experiment with your tune and in the process, learn more, and then hopefully give us some feedback on your work!

Best regards,

MartinM · Post by **MartinM** » Sat Apr 21, 2007 8:45 pm

Good question! - and very hard to answer using the layout capabilities of posted replies!

I don't see how the centrifugal and vacuum advances can be a range at a specific rpm or pressure unless it indicates a tolerance - in which case, just take the averages...

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Centrifugal advance         			Vacuum advance
revolutions      	advance      		Vacuum in mm Hg   	Vacuum in kPa   advance
1200 and lower      0   				70 and lower   		9.3      		0
1400         		1	   				75      			10      		0
2000          		7					100      			13.3      		1
3000         		17					110      			14.7      		2
4000         		27					150      			20       		12
4800 and higher     34					190 and higher   	25.3      		19

Then I think you need to aim for a map that looks like this...well nothing like this, but you get the idea....

Code: Select all

                 1200    1400     2000   3000    4000    4800
74.7	                 x         x          x         x         x         x	
80	                  x         x          x         x         x         x	
85.3	                 x         x          x         x         x         x	
86.7	                 x         x          x         x         x         x	
90                        x         x          x         x         x         x	
90.7	                 x         x          x         x         x         x

- note the convention that lower absolute pressures are towards the top of the map

So remember that total advance and any rpm and pressure = centrifugal advance at that rpm + vacuum advance at that pressure + static advance

In simple terms therefore, and not doing all the work for you.....(!)
...you need to have a centrifugal advance map...with columns from 1200 to 4800 (with the 4 intermediate rpm points) and rows from 74.7 to 90.7 (with the 4 intermediate pressure points) with all rows the same, with the centrifugal figures above
...you need to have a MAP advance map...with columns from 1200 to 4800 (with the 4 intermediate rpm points) and rows from 74.7 to 90.7 (with the 4 intermediate pressure points) with all columns the same, with the vacuum advance figures above
...you need to have a static advance map...with columns from 1200 to 4800 (with the 4 intermediate rpm points) and rows from 74.7 to 90.7 (with the 4 intermediate pressure points) with all points the same, and set to 6 (the static advance)

Then......just add together all the values at the corresponding points in all the maps to give the overall map

This gives you a 3D map with 6 rpm bins, one for each column and 6 advance bins, one for each row ie a 6x6 map.

Of course the MJLJ has a 10x10 map so all you need to do is convert 6x6 into 10x10 .., but I'll leave you to work out how best to do that, probably by suitable insertion of interpolated values.

Does that make any sense at all????

Post by **brentp** » Sat Apr 21, 2007 9:55 pm

Taking this a bit further- Directly mapping a distributor RPM curve (centrifugal advance) with the load curve (vacuum advance) will result in a simplified Ignition map in the MJLJ- a good starting point, as was pointed out.

Since distributor advance mechanism (the ones I'm familiar with) have centrifugal advance curves that operate independently from the vacuum advance mechanism, you end up with an RPM curve that is further modified, independent of RPM, by the vacuum advance actuator.

So, in other words, you have a map that varies advance across the RPM axis, and is separately modified across the load axis.

I think your data was hard to read because it seems you have the centrifugal map and vacuum map side-by-side. This might be more clear... is it correct?

Code: Select all

Centrifugal advance			                
revolutions		            advance		    
1200 and lower		        -1.0 to +1.0	
1400			            -1.0 to +3.0	
2000			            5.0 to  9.0	    
3000			            14.5 to 19.5	
4000			            24.5 to 30.0	
4800 and higher		        32.5 to 36.5	


Vacuum advance
Vacuum in mm Hg	    Vacuum in kPa	advance
70 and lower	          9.3		            0
75		               10		        -1.0 to +0.5
100		             13.3		      -1.0 to +2.0
110		             14.7		      -1.0 to +5.0
150		             20		                9.4 to 15.4 
190 and higher	       25.3	         	  16.0 to 22.0


1. Vacuum between 9.3 to 25.3 kPa
2. Max advance is 22deg at 25.3 kPa
3. Basic static timing is 6deg BTDC

You would also 'rail' the advance values for areas of the map where you might end up calculating the advance values outside of a realistic range.

starting map for RPM (centrifugal) curve (with static advance built in), to illustrate Martin's points

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1200    1400     2000   3000    4000    4800
6         7          13       23       33       40	
6         7          13       23       33       40	
6         7          13       23       33       40	
6         7          13       23       33       40	
6         7          13       23       33       40	
6         7          13       23       33       40

As you will see, the computer will be able to create 'curves' that are difficult, if not impossible to create using mechanical techniques. You could do something nonsensical as well as tune your engine beyond what the simple distributor will be able to do.

So using this map will be a good starting point for getting your engine running well, but realize you can take it much further from here- you have fine control over ignition advance!

I'm thinking this would be great material for the how-to section. Thanks for the contributions!

Regards,

ewout · Post by **ewout** » Sun Apr 22, 2007 2:01 pm

Oh dear, these answers are better than I've hopes for! It is certainly not my intention to have someone else do the work, I just needed to be guided into the right direction!

My English is not my native language, so it'll take a while to understand what you have come up with! It is correct that there are two tables, a centrifugal advance curve and a vacuum advance curve. Ie. the first is a function of rpm, the second of pressure.

I'll come back to this later when I fully understand your comments and have started this jig-saw puzzle. Thanks so much for now!

Ewout

MartinM · Post by **MartinM** » Sun Apr 22, 2007 2:35 pm

Well, three tables actually....

The first is the rpm advance table ie imagine you have disconnected the vacuum advance pipe, so you only get the advance caused by the centrifugal weights rotating the base plate - so every row is the same ie advance is independent of pressure

The second is the centrifugal advance table ie imagine you have disconnected the centrifugal weights, so you only get the advance caused by the vacuum pulling the base plate around - so every column is the same ie advance is independent of rpm

...and the third table is the static advance table that has 6 in every cell

And the total table is the sum of all the values at each corresponding point across all the tables.

Post by **brentp** » Sun Apr 22, 2007 5:35 pm

Very well put. I could see a javascript application, or a tool in the configuration software that could generate a map for you after asking some questions.

Brent

ewout · Post by **ewout** » Sun Apr 22, 2007 7:50 pm

Quick one in between: why are the advance numbers ranged? Ie. from -1 to +1 for a specific rpm, or 16 to 22 on a certain load. Could this be to check the old distributor's state? So, it's okay if it scores somewhere in that range?

For tha actual map making, do I just take the average of that range to start with?

Because static advance is always the same, I didn't consider it a table, but ofcourse it is one!

Thanks! Ewout

fikus01 · Post by **fikus01** » Sun Apr 22, 2007 10:23 pm

i think they give tolerances to which the engine will stil run ok because as a manufacturer they will only give a rough setup to each engine as oppose to setting it up perfectly as u will eventually do with the megajolt! that is bad english i know but its late!

MartinM · Post by **MartinM** » Mon Apr 23, 2007 8:57 am

If the variations are there just because of tolerances due the mechanical nature of the centrifugal and vacuum advances in the distributor, then given their magnitudes, that's a powerful case for any distributor-less ignition system.

When I've been in rolling road sessions with a MJLJ, power output changes caused by moving the ignition by 1 degree are pretty small, but you can usually see the difference when moving by 2 degrees.

ewout · Post by **ewout** » Mon Apr 23, 2007 9:26 pm

MartinM wrote:Does that make any sense at all????

Yes it does. I think I understand it. The final map is a total of 3 maps. I'm not sure whether I did it correctly, but here is the first trial. Did I fill in the advance correctly for the given vacuum advance, or should it be upside down?

And final map

If this looks correct, then I will make the bigger 10x10 map.

Thanks for any advice! Ewout

MartinM · Post by **MartinM** » Tue Apr 24, 2007 3:04 pm

Looks perfect to me...

...and its very comforting that applying the "3 map technique" ((c)MJM 2007) using the original data results in a final map which subjectively looks fine, both in the directions that the advance increases (more rpm = more advance, more vacuum = more advance) and the actual values from 6 to 58

Well done! Report back if it actually works in practice...

ewout · Post by **ewout** » Tue Apr 24, 2007 5:05 pm

MartinM wrote:Looks perfect to me...

Report back if it actually works in practice...

Okay, thanks for reviewing it! This means I have to speed up installing the hardware!

I will definitively report back everything experienced!

Ewout

m j · Post by **m j** » Sun May 27, 2007 4:43 am

looks to me like the MAP table is the centrifigal, and the centrifigal is the MAP table
mislabeled or am I wrong?

MartinM · Post by **MartinM** » Sun May 27, 2007 6:13 am

m j wrote:looks to me like the MAP table is the centrifigal, and the centrifigal is the MAP table
mislabeled or am I wrong?

You're correct - they appear to be wrongly labelled. I never noticed that last time

The final map is OK though...