electronic distributors

[Todd Knighton]

gofast at ix.netcom.com wrote:
> 
> I've been
> told that BMW piston ratings were optimistic - BMW 9.5:1 is more like real-
> world 8.8:1, so I should be OK with 93 octane. So, thanks for all the octane
> enhancer stuff, but thats probably not the problem.

	The compression ratio is usually described for an average throughout
the service life of the vehicle.  For example, the 1989-1994 911
carrera's are quoted as having 11.3/1 compression ratio, when they
actually have 10.8/1 new.  But after milling the heads for clean up
during rebuilds to the service limit puts you at or above the 11.3/1
rating.

> 
> If I set the advance to 38 degs max, lets say, then I will not be able to
> idle well, as the mixture, set by the computer, is too rich. I thus need to
> retard the timing more at idle. The short of it is I need to change my
> distributor curve, and, possibly, my ECU as well. The best solution, I'm
> told, is to use the entire FI system from a 79 528i. A used FI system will
> probably set me back $400-600.
> 

	Does this car have a flapper type air flow meter, if so you can fool
the thing with a small bypass around the air flow meter to get the thing
to idle correctly.  then, by using the idle micro switch to activate a
solenoid, you can then disable the bypass at anything other than idle.
	If this condition only occurs at idle, or does it occur at all low flow
regions?  If so leave the bypass open all the time.  At high flows, the
bypass will be negligible and leave the a/f unaffected.



> Another alternative is to get someone to recurve my current distb's advance.
> Bob McElroy mentions this. Does anyone know/recommend where I can get this
> done? I live in Stamford, CT.

	Most hot rod shops sell springs for recurving the distributors. 
Changing the mechanical limits of it is just a matter of bending the
stop tabs in or out to change the motion of the weights.

> 
> I have access to a 79/80/81 BMW 528i electronic distributor. Can I make/buy
> a control unit for it that will advance timing with rpms?

	MSD sells a neat unit that you lock up the advance weights and control
the advance from this little cockpit mountable gadget that will adjust
advance vs. rpm's.

Todd Knighton
Protomotive Engineering