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JFairman JFairman is offline
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Join Date: Jul 2006
Location: S. Florida
Posts: 7,289
"MSD 8762 controls the boost and you have modified the distributor ignition curve or did you just modify the slot only?"

I did modify and shorten the centrifical advance curve by bending the vertical steel tabs that stop and limit the centrifical advance weight outer travel inwards about 1/8". I also ground some metal off the sides and outer edges of the centrifical advance weights to make them lighter. Then I polished them to make them pretty and finished looking while equaling their weight even though you can't see them installed. It just makes me feel good.

That has a similar effect as putting in stronger advance weight springs but none are available unless you take apart many BMW and Mercedes mechanical distributors and test the springs... The same diameter housing distributors including points and condensor units including ones that spin the other direction all use the same advance weights, but different springs.
So I made the advance weights lighter to delay the centrifical advance curve a little and then advanced the static timing to 12 to 15* btdc so final centrifical advance is the same as it was stock.

"So your running 35* BTDC @ 4000 RPM and this is only possible with WMI? If so what is the safe limit with out a WMI?"

Yes, but that is only with full vacuum advance and full centrifical advance together and only at steady low load cruise on flat level roads like the interstate in Florida.
WMI is not spraying during steady cruise on flat level roads because there is no boost happening then.
When accelerating timing will stay there until boost starts comeing on.

If you remove the vacuum advance hose during steady no load 4000 rpms then timing is at 26 to 28* btdc just like when in nuetral while you're back there with a timing light on the pulley. It sounds like you may be forgetting about full vacuum advance on top of full centrifical advance. Thats when you have around 35* btdc

Under boost there is no vacuum so there is no vacuum advance but there is always centrifical advance.
The distributors vacuum retard and the MSD 8762 both work at the same time to gradually pull timing back to around 18* btdc when boost comes on. That way vacuum retard is pulling timing back to a safe level.

I set the adjustable pressure switch for the WMI so it starts spraying at .7 bar to help reduce the chance of detonation between .7 and 1.1bar
WMI is overrated by the places that sell it but it helps especially when the mixture in the WMI tank is around 70% methanol and 30% water. It's kinda fun to experiment with it and watch the AFR gauge when it comes on and the 930 intake manifold being a flat plenum with 6 holes leading downwards to the intake ports works good for WMI distribution with little laminar flow wetout and dropout on the manifold walls unlike the Carrera manifold with all it's length and twists and turns.

If I think of it I'll take a picture of my distributor tomorrow and post it so you can get an idea how far it's turned in the lengthened slot. I have a stainless steel washer and nylock on the stud but you'll get an idea.
Old 04-20-2013, 06:17 PM
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