Re: ign curves



Yvan wrote:
Nedavno Mrcheerful napisa:

The vac advance doesn't occur at idle, so an idle figure is typically
a few degrees BTDC, 8 degrees would be very common.

I am about to set it up that way. I measured vacuum, and at no load
(car stationary) vacuum kicks in at ~1200rpm and maxes out at ~1400
rpm

At BMW 1602 in my example that would give ~40 deg advance at 1500 rpm!
Way too much I think. And what I have looks like factory repair
manual.


I have run racing engines at 36 degrees at idle !!

That rarely runs at idle :-)

If you go for an idle of 8 degrees and a full advance of 40 you won't
be far out for a start.


I looked at few ignition maps, and most of them stay below 40 (32-37)
at full load. I read somewhere that petrol today does not tolerate
high advance.



Push the advance a far as seems to give extra power without
pinking/melting plugs

I did not hear my engine pinking, but I am afraid to push it to far, I
am not sure I can recognize pinking (I can hear it on my Fiat at high
load at low speed).

I guess I'll have to test, it seems that I can not find ignition curve
anywhere on the net (I contacted BOSCH bout got no reply).

autodata has info about the mbar of suction, but I don't know if you have a
way to add that on (ie a calibrated vacuum sensor).

The figure you want to aim at is the mechanical advance figure, which in
your case is a minimum of 8 degrees at idle and max of 40 or so at 4500, if
it is mappable then add in the 30 at 3000 figure,

the vac advance does not occur under load, it will only occur when the
throttle is eased back, (the extra vacuum advance will then give cleaner
running and more economy.)

you may well have a non loaded timing of close to 40 degrees at 2000, but on
the move and accellerating that would drop back to 25


.

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