[Gmecm] HEI conversion & cam sync

[bcroe at juno.com]

20 May 2005  "Carl Rumberger" <perfdyn at cwnet.com> writes:
> > I wouldn't mind hearing how to set "phase" between the
> > rotor and the timing pickup.  

> With EST the rotor phasing isn't fixed. 

Right, it wasn't fixed with a vacuum advance either.  But it 
will cover a larger range with EST, because the mechanical 
at least did not change phase for rpm.

> It should sweep across the cap terminal with timing 
> change. The rotor phasing should be past the cap 
> terminal with the most retarded computer timing signal
> (GM-EST). The rotor phasing should be before the cap 
> terminal with the most advanced computer timing signal 
> (by approximately the same amount that it was past 
> when retarded).

Based on what I said above, phase doesn't care where 
the weights are locked, because the star wheel is already 
locked to the rotor.  Setting the initial 10 deg advance will 
take care of any any variation relative to the shaft.  
 
> You don' t have to have a see through cap to view this. 
> With a timing light, note the retarded and advanced 
> timing points. If you know the approx. spark tables you 
> will be using, you already know these figures (assuming 
> the timing is properly set). Position the crankshaft (static) 
> at the advanced and retarded timing points and see 
> where the rotor points relative to the cap terminal.

OK, with weights locked set initial 10 deg timing with 
engine running, then stop and set the crank angle 
midway between min and max advance.  If the rotor is 
not centered on the cap terminal, I need to modify coil 
angle (what used to be the vacuum advance input).  
What I really want to adjust, is the body of the HEI (and 
cap) while keeping the coil fixed in space, 
so my 10 deg initail is maintained.  

It's going to be hard to keep the coil fixed relative to the 
shaft while moving the body coil angle.  Maybe a better 
procedure is first lock the mechanical advance.  Then 
statically line up the rotator with the cap terminal as 
you said, in the middle of the advance range.  Now run 
the engine (or maybe crank it) and adjust the previous 
vacuum input (coil angle) to get 10 deg advance.

Changing the position of the "star wheel" to the rotor 
mounting surface or changing the position of the cap 
relative to the dist. housing don't sound like practical 
approaches to me.  

> > I have been thinking some more about adding cam
> > sync to the commonly available & very cheap CCC type
> > HEI.  Perhaps just dropping a plug wire through a pickup,
> > with a bit of signal processing, would be the easiest.
> SNIP
> 
> Unless you plan to go sequential EFI or "coil on/near plug" 
> ignition, I don't see any point in knowing cam position/sync.
> 
> Carl Rumberger
> Performance Dynamics
> perfdyn at cwnet.com

My 79 Eldo already is sequential port injection.  I am using 
one of the original HEI reed switches (originally one for 
each batch of 4 injectors) for cam sync, but I want to go 
to a CCC electronic advance HEI instead of the weights.  

Using a timing light inductive pickup might be a quick 
way to get started, thanks.  The circuit will be different to 
get cam sync.  I also have a pickup from the 
old FIR*T system, but you have to pull one end off a wire 
to get it on.  

thanks for helping me think this through

Bruce Roe