Thread: MSD Success
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fredmeister fredmeister is offline
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Join Date: Oct 2002
Location: Baltimore, MD, USA
Posts: 2,232
Originally Posted by JFairman View Post
Your curve sounds good but I don't know your timing at idle.

You can modify the origonal distributor to make a a similar curve without spending a dime if the vacuum pots are working right.

To do it you bend the advance limiting tabs you wired the advance weights too inwards about 1/8" to limit total advance and then advance the static timing to about 8-10 degress BTDC at idle.
Check that and the entire advance curve with a dial back timing light to see where it is after doing this if you try it. Then readjust the advance limiting tabs if needed. You can do that without taking the distributor apart, just pry off the little stamped steel oval cover plate on the side and carefully bend the taps one way or the other with a flat blade screwdriver using it like a little pry bar. Then press the cover plate back in it's hole.

Now the total centrifical advance curve is limited but vacuum advance, vacuum retard, and boost retard all still work.
Only problem is centrifical advance will start too early and you'll have part throttle medium speed acceleration detonation before boost starts building and retarding timing because static timing is advanced around 10 degrees so you install either heavier advance weight springs if you can find some that fit right or drill holes in the advance weights to lighten them and delay the centrifical advance curve.
You can always remove the advance weights and braze some brass rod into the holes filling them up with brass if you lighten them too much so go slowly in steps with that.

The MSD 6al2 is better since you can program all you want but the way I described doesn't cost anything, works, and improves low speed drivability and gas milage too.
Timing at idle is 12 degrees BTDC. Full total advance is 34 degrees under vacuum.

I have created a bunch of tables in excel which enables me to superimpose the charts at each running condition and see the total timing at discrete manifold pressure and rpm conditions.

Its nice being able to tailor these curves electronically and not rely on the mechanical pots and weights to function perfectly in all conditions. It only takes a slight failure for a small amount of time and the engine is toast...there is too much chance for corrosion to build up inside the dizzy and freeze up the advance machanism to risk it with the turbo under high boost.

1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"

Last edited by fredmeister; 12-10-2012 at 06:24 AM..
Old 12-10-2012, 06:18 AM
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