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mapping between advance curve models
https://slantsix.org/forum/viewtopic.php?t=36813		 Page 1 of 2
Author:  gmader [ Fri Aug 21, 2009 9:22 pm ]
Post subject:  mapping between advance curve models
Hi all,

Any ideas on how to map between advance curve models? In this example the two axis define RPM and advance. What I need help with is figuring how to map this to a model, where vacuum and RPM are the XY axes, with advance being the Z axis, such as in this example

Image

To complicate this, a regular distributor uses carb ported vacuum, not manifold absolute pressure. How much difference do you think there is between these vacuum sources? I would like to use the carb hookup until I get a new manifold and throttle body installed.

Any thoughts?
Thanks,
Greg
Author:  gmader [ Sat Aug 22, 2009 7:56 am ]
Post subject: 
I may have answered my own question to some extent. I found this spreadsheet to calculate 3D mappings for Megasquirt 'n Spark Extra here.

Here is an example. Take a look, and tell me if you think it makes sense for a basic slant.

<img src="http://lh6.ggpht.com/_NUfKs-Dy9aI/SpAGHsIL53I/AAAAAAAAAnA/yU4s1X_W9pI/s800/slant%20spark%20analysis.PNG">
Author:  emsvitil [ Sat Aug 22, 2009 3:44 pm ]
Post subject: 
That's really really tiny..........

Got a larger version?
Author:  gmader [ Sat Aug 22, 2009 3:46 pm ]
Post subject: 
Can you see this link?
http://picasaweb.google.com/lh/photo/a0 ... directlink
Author:  emsvitil [ Sat Aug 22, 2009 3:52 pm ]
Post subject: 
The link works, just have to hit download when you're there.......

I think that's what you want.
Author:  gmader [ Sat Aug 22, 2009 3:55 pm ]
Post subject: 
Any thing from your research that I could do better? I tried this ignition map, and it seemed really lazy, and didn't want to pull hard.
Author:  emsvitil [ Sat Aug 22, 2009 4:11 pm ]
Post subject: 
I'd get the power curve the way I want, then add in the vacuum........

Is that showing your centrifugal and vacuum settings?
Author:  gmader [ Sat Aug 22, 2009 4:15 pm ]
Post subject: 
Yes. Centrifugal is the upper chart, Vacuum is the middle, and total is the bottom chart.
Author:  emsvitil [ Sat Aug 22, 2009 4:23 pm ]
Post subject: 
Only 16 degrees of centrifugal, all in at 2000.........

I would think 18-20, all in at 2800-3200.................
Author:  gmader [ Sat Aug 22, 2009 5:12 pm ]
Post subject: 
Here is an all mechanical(centrifugal) spark curve. I am starting at 12 degrees static(initial timing).Take a look
Author:  emsvitil [ Sat Aug 22, 2009 8:19 pm ]
Post subject: 
I'd determine the centrifugal like I did for my test series..........

(a bit easier just plugging the numbers in)


Then once you have the centrifugal where you want it, start adding in the vacuum....
Author:  gmader [ Sat Aug 22, 2009 9:02 pm ]
Post subject: 
Your suggestion makes a lot of sense. I tried the mechanical advance only map, and it seems a lot snappier.

Thanks for the hint.
Author:  gmader [ Sun Aug 23, 2009 12:57 pm ]
Post subject:  Good start
After replacing one bad plug wire, I am in pretty good shape. Right now, I am doing an all mechanical/centrifugal map, and the car is really snappy and responsive. No signs of ping/knocking, and I think I can play around with more advance.

<img src="http://lh5.ggpht.com/_NUfKs-Dy9aI/SpCJGsJCZzI/AAAAAAAAAng/ndjeFqCk2-U/s800/spark2.PNG" />

Is there a max limit, not related to knocking? Has anybody found that if you advance too much that you start to lose power?

Thanks,

Greg
Author:  emsvitil [ Sun Aug 23, 2009 2:09 pm ]
Post subject: 
Yes, advancing too far can lose power...........

But without a dyno, knocking is a easy rule of thumb.


Usually you find the limit, then back off 1-2 degrees.........


With the map, you also have the ability to be non-linear........

So if it just knocks at a certain small rpm range, you can back off the timing just there.....
Author:  emsvitil [ Sun Aug 23, 2009 4:06 pm ]
Post subject: 
I thought of a way to find the best curve..........

It would be easier with a manual tranny, but the idea still will work......

With manual, rolling start in 2nd, automatic rolling start in 1st.


You need a tach (or know mph vs rpm) and a stop watch.


Start building the ignition curve at low rpms... (back off if knock detected)

Setup a curve that is all in at 1500 rpm.

Do a rolling start, and use stop watch to determine the time it takes to get from 1000 rpm to 1500 rpm.

Do it several times to get consistent results.

Adjust max advance at 1500 rpm until you get your lowest time.

When you figure that out, you have the curve from idle to 1500 rpm.

Now add to the curve by having by advancing the max advance at 2000 rpm. (leaving 1500 rpm and below as is).

Test / adjust for best time by adjusting the curve from 1500 to 2000.
(might be easier to time 1000 to 2000)

When you have that, do 2500 rpm....

And so on. (you can pick your rpm intervals)
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