[Gmecm] Running V8 with $A1 DIS code

[Programmer]

I don't drop in much anymore, but....

L4 = 180 crank degrees (DIS with wastespark /2)
L6, V6 = 120 crank degrees for firing event. (DIS with wastespark /2)
V8 = 90 crank degrees for firing event

Camshaft 1/2 speed of crank

L4 = Cam 90 degrees for valve/CR/ignition event
V6 = Cam 60 degrees for valve/CR/ignition event
V8 = Cam 45 degrees for valve/CR/ignition event.

Note that with these timing events the maximum distributor timing allowed ?
L4 = 90 degrees of ignition timing (in theory, guys)
V6 = 60 degrees of ignition
V8 = 45 degrees before firing the next pole.

These are theoretical, as trying to add 45 degrees ona V8 would just fire
the next cylinder at the wrong time...

Too much "initial" advance in EFI, and the entire curve is added--leading
cause of detonation and other issues.

One of the reasons for DIS was to allow for even "more" timing advance in
some cases. Directly looking at the LS1 code (as an example), many V8's have
very high timing values (very low load, mid to high RPM) of as high as 55+
degrees ignition timing--which if in a conventional distributor setting
would fire the next cylinder instead of the one you want to fire !

If the crank trigger has 6 slots on the crank (which every V6 should have),
there is a coil pack "event" every 60 degrees of crankshaft rotation--not
120 at the crank. Remember--DIS has in reality, twice the # of firing
events--power and waste at each cylinder for each crankshaft 360 degrees if
the coil pack is grouped.
 The earlier V6 Cavalier, as an example, had 6 slots on the crankshaft
spaced 60 degrees apart, with a 10 degree offset (#7) slot to determine
which is #1. This additional slot was used for both timing calculations, and
RPM inputs to the ECM/PCM. Hope this is making sense...

Individual coil pack or COP is 120 degrees at the crank for a V6.

Lyndon.


----- Original Message ----- 
From: "David Haggard" <david at newcovenant.com>
To: <gmecm at diy-efi.org>
Sent: Friday, April 15, 2005 5:58 AM
Subject: RE: [Gmecm] Running V8 with $A1 DIS code


> Oops..... Every 60 degrees of CAMshaft rotation. How easy it is get this
stuff mixed up!
>
> While my thought process of how the number is determined is different from
HTH's (IGN REF), the idea is the same. In my mind, it all eventually goes
back to the old-fashioned way of determining when to fire a coil-- a
distributor being turned and timed by the camshaft.
>
> David
>
> > -----Original Message-----
> > From: gmecm-bounces at diy-efi.org
> > [mailto:gmecm-bounces at diy-efi.org] On Behalf Of WopOnTour
> > Sent: Thursday, April 14, 2005 9:38 PM
> > To: gmecm at diy-efi.org
> > Subject: Re: [Gmecm] Running V8 with $A1 DIS code
> >
> > Actually 6cyl DIS fires a coil every 120 degrees, not 60 But
> > I agree with the 45.
> > IIRC reference angle is the #of degrees between the IGN REF
> > voltage state switches. Every 60 degrees on the V6
> > (triggering on every trailing edge or 120 degrees) and on the
> > 8 cyl that would be 45 degrees (triggering every 90
> > degrees)
> > HTH
> > WOT
> >