In a message dated 9/13/02 9:07:38 AM Eastern Daylight Time, Davgil@aol.com
writes:
<< This analyzer appears to be
technology consistent with a 25 year old vehicle, so I am curious as to
what,
if anything, the dwell angle in this case means. >>
Dwell angle is the ( dwell) time the points are closed. Think of a
distributor as having 360* of rotation and the low spots on the shaft as the
measured angle.
The dwell angle can be altered by adjusting point gap. Using dwell angle
makes points adjustment much more accurate because you are reading a meter
rather than pulling a feeler gauge 60's and 70's GM cars had a door on the
distributor cap that accessed a screw. This screw allowed point adjustment
while the engine was running. It also allowed proper tuning without any
tools sans a 1/8 allen key. This was accomplished by turning the key until
the engine stalled, then turning in the opposite direction X turns. The
engine would stall when the point gap was zero, the screw pitch and arm
length were consistent so X turns gave Y dwell.
4 cylinder engines have large dwell angles with 6 cylinders having less and
8's even less. To increase dwell ( and coil saturation since the power stays
on longer) on a straight point system move towards a smaller gap as this
allows the points to stay closed longer. The problem here is with small
gaps, arching becomes a problem and point life is shortened.
High performance 8 cylinder engines generally used a dual point system. ( two
sets of points in parallel) This allows a greater effective dwell time while
retaining normal point gaps.
This is all accomplished by having the points slightly out of sync of each
other. One set is the "make" set and the other is the "break" set.
On a electronic system, dwell is preprogrammed and not changeable ( there
may be a very old ( 60's) system or two without pre set dwell, check your
manual) Some systems 74 up GM HEI had dwell that changed with engine speed
from what I recall.
Harold
/// triumphs@autox.team.net mailing list
/// or try http://www.team.net/cgi-bin/majorcool
/// Archives at http://www.team.net/archive
|