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Brockster
Posts: 9
Joined: Wed Apr 08, 2009 12:06 pm
Location: Australia

I have just finished putting MJLJ on a V6 buick and have been looking at various ignition maps. I have noticed big difference in load bin numbers. I know how to change the numbers but how do I tell what numbers to put in?
Is it take it for a drive with a laptop and read the load guage for high and low?
If this has already been discussed can someone point me in the direction please?

Brock

Alex B
Posts: 163
Joined: Sat Aug 09, 2008 10:32 am
Location: Hegra, Norway
Best starting point is to find info about the dizzy that is used. There should be data around about its characteristics regarding vacuum- and mechanical advance; and don't forget static advance, very important for the base settings. Once you have these characteristics you can start to build your advance map.

Starting point is static advance at idle. The advance line is horizontal up to the rpm where mechanical advance starts to kick in. Then it slopes up until it has reached its max advance, where it goes horizontal again. The slope doesn't have to be a straight line, it can have extra angles. Changing angles should be a map point for rpm. The values found for mechanical advance apply as start line at ambient pressure, in other words, at full throttle. When you know max vacuum advance you add this up to the sum of mechanical and static advance in order to calculate max total advance.

There are a few topics around with Excel sheets that can be used for calculations of the advance, they are helpful, though conversion of vacuum advance to KPa can be a bit tricky.

Alex

Brockster
Posts: 9
Joined: Wed Apr 08, 2009 12:06 pm
Location: Australia
Thanks for the reply Alex. The engine was originally efi with a digital style ignition. I have converted it back to carby
and it never run a distributor. I have a vacuum guage and can get some numbers from that. Do I convert these to KPA and spread these numbers through the load bins?
I am getting 20 inches at idle and hopefully today I can get some more numbers. I have found the base map and have tweeked that a bit to see if I can get rid of some of the detonation.

Thanks
Brock

Alex B
Posts: 163
Joined: Sat Aug 09, 2008 10:32 am
Location: Hegra, Norway
Hi Brockster,

Driving around and measure vacuum is certainly a way to go if you can't find maps that have been used in the EFI setup. It may work with evenly spread load cells between let's say 20 and 100KPa, can't find a reason why it shouldn't. Little need to go lower than 20KPa, you'll never get a complete vacuum.

Alex

Brockster
Posts: 9
Joined: Wed Apr 08, 2009 12:06 pm
Location: Australia
Went driving with a vacuum gauge to get some idle and WOT readings then using one of the handy spreadsheets on here to through develop a curve. Testing is going well. Have some issues with my manifold and unequal fueling but the ignition system is great.

Brock