> I was wondering today about advance curves. I have been told that
>setting the timing to 16 BTDC will give me more power in low rpm's compared
>to 0 BTDC. Why is this exactly?? I have also been told to make sure that
>the total advance is not more than 35 deg. Why is this?? What will happen
>if it is more than this?? It seems that we are striking a balance between
>a high initial advance (at low rpm's, which is good for some reason) and
>not too much advance at high
>rpm's(which is bad for some reason). Does someone have an idea of an
>'ideal' advance curve for our engines and why its ideal?? Some engines,
>turbo engines for example, are actually retarded at higher rpm (I
>believe). Why is this??
> Any enlightenment would be greatly appreciated.
Advance curves were mechanically controlled and related to rpm and vacuum
when our toys were originally built. Since most of us are aware of the
smog and no-smog variations, I won't try to get into that except to say
that those were the days when engines were tuned to get by smog tests not
to run right, so that should give you an idea how interrelated a number
of engine factors can be.
As a general statement (stock or near stock) datsun motors can exhibit
severe detonation with too much total advance under load. This does (not)
interesting things like melt piston tops and other terminal problems.
However, under light load/high vacuum conditions you might see higher
total numbers that 35 degrees. When you nail the throttle, the decrease
in vacuum reduces the advance back to the mechanical only maximum.
Obviously this whole system is complex and subject to all sorts of wear
and adjustment issues. For a very good treatment on Datsun distributors,
as well as other interesting Datsun things, check out Jason Gray's
website <http://home.att.net/~jason510/>.
All of the variations and wear issue make newer all electronic systems
such as the Electromotive crankfire setup very attractive. You set the
initial and total advance with a couple of trimmers (variable resistors)
and there are equally as simple adjustments for the advance curve itself.
No moving parts except the trigger wheel attached to the crank pulley and
spins past a magnetic pickup. Spark is rock stable from 0 RPM to as far
as you want/dare to spin your motor. Not real cheap at around $450 for
the complete system, but not much more expensive than having a
distributor rebuilt, recurved, and then adding something like an MSD
ignition box.
FWIW, Ron
Ronnie Day
rday@airmail.net
ronnie_day@acd.org
___________
The ACL Group
Arlington, Texas
(817) 572-0873
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