Brad Parlee asked "Does the old tach adjust for dwell?"
I'll leave that particular answer to the tach experts, however I do have
some interesting tales about "dwell".
Back in the mid 60's my new Porsche 911S ate spark plugs for lunch. On
the road everything was great, but around twoen I couldn't get more than
10,000 miles before they would foul-out. The usual response was "buy
Bosch platinum point plugs". They were about 10 times more than a normal
plug, and lasted 15,000 miles. Not such good economics. I changed to the
NGK "copper slug" unit that adjusts for heat range, over a limited
range. The correct selection cured many of the problems.
Getting on to dwell, I purchased a "Delta" capacitive discharge ignition
system from the Colorado manufacturer (first in the country). This
significantly increased the plug life. One of it's features was to
reduce the point current to nearly nothing. No great arc across the
points every time it opened. The great touted advantage was that the
points would never wear out. This was the truth, but not the whole
truth. While the points didn't wear, I still had to adjust them just as
often because the dwell would get unsatisfactory, from dwell meter.
Turns out Bosch was pretty clever. They had carefully chosen the point
acuating block, that rides the distributor cam, to wear down at the same
rate that the points were being eroded. That kept the gap, and dwell,
more constant until replacement time. Now, with point erosion at zero,
the block still wore, requiring more frequent dwell adjustment. The
moral here is "you can't win". The era of mechanical points was
short-lived, as most cars combine electronic sensors with high energy
systems. The "dwell" on these is electronic, set by design, and doesn't
If you are converting the points to the new magnetic, or optical point
systems, dwell issues go away, but I did not have luck with a Bosch
Porsche Tach and an electronic ignition.
Steve Laifman < One first kiss, >
B9472289 < one first love, and >
< one first win, is all >
< you get in this life. >
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