Message-ID: <3AED63CE.6E8A7E09@regandesigns.com>
Date: Mon, 30 Apr 2001 08:08:30 -0500
From: Brent Regan <Brent@regandesigns.com>
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To: Lancair List <lancair.list@olsusa.com>
Subject: Re: running lean of peak
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When thinking about ROP vs LOP remember a few things.

There is no such thing as a 6 cylinder engine, only 6 - one cylinder engines
that are working together, eating at the same table and excreting in the
same toilet. Each cylinder has a slightly different personality.

Smooth engine operation is achieved when each cylinder receives the exact
same amount of fuel and air, is ignited at the same crank angle and is
mechanically balanced.

If you accept that balancing fuel flow is a good idea (Gami) then you must
also accept that balancing air flow is also a good idea as a balanced
mixture is the ultimate objective.

TSIO-550s "feature" tuned induction. The primary benefit of which seems to
be marketing. If you were tasked with dividing an airflow into 6 equal
parts, the resulting system would not resemble the 550's configuration. Gami
recognizes this and "fits" flow nozzles to cylinders. If the fuel flow is
not balanced but the engine EGTs ARE then either induction, exhaust or
ignition are not equal between cylinders.

As you lean an engine several things happen. Peak power happens between 150
and 50 degrees ROP. Stoichimetric mixture and peak EGT do not occur at the
same time but are close to one another. As as you cross stoichimetric
mixture, hydrocarbon (HC) emissions are on their way down and nitric oxide
(NOx) and carbon monoxide (CO) are on their way up. Further leaning causes
combustion to become unstable, resulting in misfire.

Two cylinders with the same EGT are not necessarily making the same power
(same BMEP). Timing and charge volume variances can skew the peak.

Every combustion event has been effected by the one that came before it.
Cycle to cycle variances are amplified by lean mixtures (unstable
combustion).

Every engine is different. Variances in engines result in variances in
results and therefore variances in opinions. It is impossible for two pilots
to compare their experiences with two different engines and draw any
meaningful conclusions (other than the other guy is wrong).

IMHO, running LOP is a good idea IF you are at low power settings. Above
about 65% power it becomes a less good idea, at 75 % a bad idea and 80 % and
above, a very bad idea.

Regards,
Brent Regan

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