Fw: FW: Electronic timing advance

[Bruce Plecan]

I got an off list mail, that I think warrants being commented on list.
Depending on you level of expertise you will find this interesting or
boring, and the "target" reader is the new guy.

I will acknowledge that a small light car is somewhat different
then a large american v-8 sedan.
  But, not since for the obvious reasons.  Look at the bore to
stroke, and rod lenght to stroke ratios of say in my example of
the X1/9.  They are great.  Look at how much valve diameter they
stuff into the cylinder head.  With roughly the same cam specs
my X was at >100/Liter, and my SBC is 320ish for 355, 10+%
better,  and by current standards ancient.  With these basic differences in
design, really show what a marvel EFI, since
without getting your hands wet, you can tune as necessary,
between these extremes, without having to spend years dinking
with Air Correction Jets, and emulsion tube volumes/wells..

>
>Ya, but this is a very light car where the load might not have been as
>high, and the engine reved to such a high RPM that loads were again not
>so high.

If you look at when a rod most often fails.  For those that don't know
it's after the intake valve is opening, and as the rod is moving away
from TDC.  It's in tension at this time, and while the crank is pulling it
down, the intake air tract volume is acting against this movement.
So as the rpm build these loads get much larger.   This pulling the
rod apart aspect IMHO is what makes S/T charged engines so
great.  Bearing maintance increases due to the power output, but
breaking rods min, and you don't have to spin the begibbers out
of it to make power.

Your example of nailling it in 3rd argues against this however.
>If we were talking about a large american car with a V8 couldn't the
>situation have been different.

Every engine is different.  Even say two twin engines.  If you noticed in
my last post I specifically mention using what I have, and then adjusting as
nessecary.  If I don't have a vacuum advance I'm not going to reengineer the
dissy to add it.  I will play for hours with dissy
spring weights, to get the right curve for what I have, and all the while
work with the carb to get the fuel right.
   What is kind of funny is on some of the tuner chips they just think
in terms of centri/vac curves rather than what you can do with the numbers
(just something to chew on)..

  Tuning/timing, is all about heat.  Making as much as you can, OR
NEED.
  At WOT you want to make lots of heat but not exceed the termal limits of
the engines components.
  During cruise you want to make just enough heat/energy to move
the car, with the min amount of fuel.

Now with the above said, you can readily see that the the combustion
chamber dictates what it's going to need to get the above done.
Bruce