[Gmecm] TBI Swap - Iron Duke Tech IV

[bcroe at juno.com]

Just to see what's possible, I did some measurements 
on a V8 HEI, mechanical advance.  I believe these would 
apply also to a 4 cylinder/electronic advance.  

The rotor overlaps the plug wire post by about 19 degrees 
of rotation.  That's 38 degrees at the crank.  So if the 
maximum crank advance minus the minimum crank 
does not exceed 38 degrees, its possible (by rotor 
phasing) to have the rotor overlap the post for any 
advance.  The typical way to achieve the desired 
phasing if needed, is to move the pickup coil angle.  
Then of course the HEI has to be rotated the other 
way to get timing back on the mark.  

The posts are pretty far apart on a 4 cylinder.  It would 
also be possible to widen the rotor tip or the posts to 
increase total overlap angle.  Phasing is less of a 
problem with a mechanical HEI, because the rpm 
advance moves the rotor without changing the phase; 
only the vacuum changes it.  Bruce Roe
___
19 Feb 2006 Andrew Gibson <andrewsharyn at yahoo.com> writes:
> >Timing should never be restricted by the physical 
> >constraints of the rotor/terminal relationship.  A little 
> >rotor phasing can fix that.  Bruce Roe
>   Rotor phasing is an issue with a distributor. If you look at the 
> spark tables in a DIS vs Distributor setup you can see the 
> limitations. At no load cruise you want a lot of adavance and at WOT 
> high rpms you want very little to none. Just the physical design of 
> the distributor cap prevents major changes from no advance to full 
> advance or the spark will jump to the previous tower.