Steve (and all),
One thing that never seems to be considered when changing advance springs is
that it has more of an effect than just how rapidly (or slowly depending on
the springs used) the advance comes in.
Assume if you will that you have 10 degrees of initial advance at idle and say
36 degrees at 2,500 rpm (full advance). If you install weaker springs they can
flex and add advance even at idle. Again assuming you check your timing at
idle with the weaker springs and found that you now had 16 degrees (and likely
pinging too). You then reset your timing back to 10 degress and all seems well
- wrong. The problem is that at full advance you now have only 30 degrees.
The advance weights have slots and at the end of the slot it effectively
becomes a stop. Weaker springs shorten the distance the advance can move in
the slot simply because they are effectively allowing some advance even at
idle (that you must compensate for by resetting the idle advance). I have
made the mistake of using springs so weak that (with point type ignition) the
points spring would counter the weak advance spring and at idle the timing was
very eratic. Additional some springs regardless of tension are longer than
others and effectively create the same problems.
The best thing to do would be to have the distributor set up on a machine. I
am too cheap for that, so when change springs I set the idle advance as
desired then slowly increase the rpm and with the timing light watch the rate
of increase. When it holds I know the total amount and at what rpm. Often with
weaker springs I have to file the slot to get the total advance back up to
where it should be (and if I go too far solder a part of it back up!). This
should all be done with the vacuum advance disconnected by the way.
A lot if it is guesswork and dependent on the temperature and humidity on any
given day. What allowed for good aceleration on a cool, humid day will likely
still ping when it is hot and dry.
I know in your case Steve you added stronger springs to deal with the
pinging. It is probably like an athlete on performance enhancing drugs, you
felt the thrill of a rapid advance from the weaker springs and wonder why you
can't have that power all the time. But, just like the drugs will likely kill
the athlete so would the advance ultimately kill your engine. Remember the SFV
had temps around 110 recently after a very mild Summer and that might have
prompted your spring change too.
Personally I would try some stock springs set at stock setting and see how
they work. Then if there is no pinging try a slightly softer spring. Remember
thought the effect on the initial and total advance. Given todays gas and your
compression ratio thought it is likely a fine line you will be walking. Maybe
wait until October and at least you should be dialed in for the next 6 months.
Tom Witt B9470101
|