Ignition Only

[Axel Rietschin]

----- Original Message -----
From: "Axel Rietschin" <Axel_Rietschin at compuserve.com>
> From: "Bruce Plecan" <nacelp at bright.net>
> > The worst example of this is a turbo motor where you might be running
17d
> of
> > timing.   With too high of overlap cam this can be a major problem.
>
> You don't want radical cams on turbo engines. What you need actually is a
> very reasonable cam that works well at low rpm, before your turbo starts
to
> blow and where your engine is sluggish because of the low compression
ratio.

Oh, I almost forgot! On a turbo engine at high rpm, the backpressure in the
exhaust manifold is roughly equal or even slightly higher than the boost
pressure in the inlet manifold, if the turbine and turbine housing are sized
ideally. The "normal" case on most engines, however, is that the housing is
sized for good response and offers some flow restriction at high engine
speed. Even when the housing is perfect, the turbine wheel starts to become
much of an obstacle at some point. Still with me? If yes, you probably
realized that no fresh gases will be drawn inside the cylinder before the
piston reaches at least TDC, at which point the wasted spark is long gone
unless you have no advance at all. What gets ignited, then? The unburnt HCs?

When you'll begin experimenting with your ALS, you will discover that the
(fully prepared, warmed up and compressed) mixture simply don't ignite at
all with more than 40 or 50 degrees of retard (ATDC) or so, simply because
the pressure is too low and decreasing rapidly.

--Axel



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