Questions (mostly ignition)

[Bill Lewis]

While trying to decide what approach is best for my project, I've been
wondering about a few things...

1) Just how sensitive is the ignition timing?  Can you tell a difference
   between 1 or 2 degrees?  What about 1/2 a degree?

2) I've always thought the whole idea of spark advance was to give the mixture
   time to get really burning.  And that the idea of advance in degrees BTDC
   was an artifact of the distributor - what you really wanted was time BTDC.
   
   Why do centrifugal advance curves typically max out well below the redline?
   Do we really want the ignition point in terms of crankshaft degrees, or
   would it be better in terms of time?

3) Many modern micro controlled engines have discarded the distributor entirely
   in favor of multiple dual-output coils.  In a dual-coil system, aren't
   the extra sparks in the exhaust-intake overlap period dangerous on a engine
   with radical cam timing?  Why does the current Porsche 911 use still use
   a distributor?

4) Do Bosch Motronic systems that take pulses off the flywheel ring gear count
   these pulses and trigger events at a particular tooth number?  Are these
   pulses used to get a better idea of the engines acceleration?  A 911 has a
   130 tooth ring gear.  That's a little less than 3 degrees per tooth.
   Do they use a software PLL to synthesize 'extra' teeth?

5) When the knock sensor kicks in, how much do factory systems typically
   back off the timing?

6) What is a good minimum RPM for a system?  i.e. what is cranking speed?

7) After you decide you need a particular size injector, say 21 lbs., how do
   you go about finding a part number or source for it?

7) What size injectors are used in the Chevy 305 and 350 Tuned Port systems?

Thanks for any consideration.../Bill

-- 
Bill Lewis - wrl at access.digex.net