Why is LOP (lean of peak) controversial?

One thing no one has mentioned is LOP may not be possible with
carbureted engines. The flows to each cylinder just aren't consistent
enough to make it work. Also you really need CHT and EGT guage on each
cylinder to do it right. The problem with LOP, isn't running LOP, its
that you are running peak and THINKING you are running LOP. The same
could be said of running rich of peak too. Running AT peak is really
only a problem at higher power settings. So most of this LOP stuff is
really for turbocharged fuel injected engines. I said MOST. Some people
with just fuel injection use LOP and a FEW at least claim to use it
with carburetion.

LOP works, but I think you have to really know what you are doing and
have the right equipment. But if you are running at 65% power or below,
it doesn't hurt to try it, no matter what sort of equipment you have
(unless of course you dont even have a mixture knob :-))

Thomas Borchert wrote:
Andrew,

So...what am I missing?


The inertia of the pilot population, myths, misinformation, engine
manufacturer's law departments - all factors. "Show me the numbers" is
the old trick to silence the LOP opponents. They can't.

I take it you are familiar with John Deakin's columns on the topic and
engine management in general at avweb.com?

--
Thomas Borchert (EDDH)

Doug wrote:
: One thing no one has mentioned is LOP may not be possible with
: carbureted engines. The flows to each cylinder just aren't consistent
: enough to make it work. Also you really need CHT and EGT guage on each
: cylinder to do it right. The problem with LOP, isn't running LOP, its
: that you are running peak and THINKING you are running LOP. The same
: could be said of running rich of peak too. Running AT peak is really
: only a problem at higher power settings. So most of this LOP stuff is
: really for turbocharged fuel injected engines. I said MOST. Some people
: with just fuel injection use LOP and a FEW at least claim to use it
: with carburetion.

: LOP works, but I think you have to really know what you are doing and
: have the right equipment. But if you are running at 65% power or below,
: it doesn't hurt to try it, no matter what sort of equipment you have
: (unless of course you dont even have a mixture knob :-))

I guess that's what I was trying to say. I'm assuming that most people
reading the thread know that carb'd engines (particularly 6's) generally have too poor
fuel/air distribution between the cylinders to run LOP.

I do know that I am running about half of my cylinders slightly LOP and about
half AT peak. Although the EGT is higher than LOP, the CHT is *lower*, and thus
should have cooler exhaust valves (or at least about the same). That's also why I
tend to limit myself to 65-70% at most. A little safety margin. Besides for my bird
(PA-28), the airframe doesn't buy much speed increase from 65-75% on a 180hp engine.
It's not worth the extra fuel burn for the additional 5 mph or so.

Again, the *at peak* operating condition is mentioned in one of the Lycoming
publications as the "best economy cruise" setting and is considered acceptable.

-Cory

--

************************************************** ***********************
* Cory Papenfuss, Ph.D., PPSEL-IA *
* Electrical Engineering *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

On 28 Sep 2006 07:58:18 -0700, "Doug"
wrote:

One thing no one has mentioned is LOP may not be possible with
carbureted engines. The flows to each cylinder just aren't consistent
enough to make it work.

This may not be a problem if you're flying with autogas. I've noticed
in my Warrior that leaning too much causes roughness and missing when
flying with 100LL. I'm sure that everyone else has noticed the same
thing. When running on autogas, you can lean aggressively and the
engine continues to run smoothly. I've wondered what causes the
difference, and how much I can take advantage of it without proper
instrumentation. I've read that generally you can lean as aggressively
you want as long as you're below 75% power.

I've wondered if the smoothness might be due to cleaner plugs, but
100LL causes lean roughness even with new plugs. I've also wondered if
those ads that the oil companies used to run about their gasolines
making your car's engine run smoother due to better fuel distribution
suggest an explanation of the difference. I've suspected that this
might explain it. If true, it might be another reason to get the
autogas STC--better fuel economy.

RK Henry

: This may not be a problem if you're flying with autogas. I've noticed
: in my Warrior that leaning too much causes roughness and missing when
: flying with 100LL. I'm sure that everyone else has noticed the same
: thing. When running on autogas, you can lean aggressively and the
: engine continues to run smoothly. I've wondered what causes the
: difference, and how much I can take advantage of it without proper
: instrumentation. I've read that generally you can lean as aggressively
: you want as long as you're below 75% power.

... *and* 400 degrees CHT.

: I've wondered if the smoothness might be due to cleaner plugs, but
: 100LL causes lean roughness even with new plugs. I've also wondered if
: those ads that the oil companies used to run about their gasolines
: making your car's engine run smoother due to better fuel distribution
: suggest an explanation of the difference. I've suspected that this
: might explain it. If true, it might be another reason to get the
: autogas STC--better fuel economy.

I haven't really noticed much different in mine whether running autogas or
100LL. One possible reason could be vapor pressure. I bought the vapor pressure
tester along with my autogas STC just so I could check for vapor-lock in the summer.
The 100LL has a slightly lower volatility than the autogas, at least here. If to
autogas vaporizes better and easier, it could do it sooner out of the carb jet and
make for a better distribution.

-Cory

--

************************************************** ***********************
* Cory Papenfuss, Ph.D., PPSEL-IA *
* Electrical Engineering *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Doug,

You're right about carb'd engines. However, I still think it is vital
to understand the basic principles of how the engine works, carb'd or
not. And "leaner=hotter" or "richer=better" is simply wrong.

The problem with LOP, isn't running LOP, its
that you are running peak and THINKING you are running LOP.


Not if you are below 75 percent power. Then the problem pretty much
goes away.

--
Thomas Borchert (EDDH)