Old wives tales of leaning:

Old wives tales of leaning:× EGT rises indefinitely with leaning× Highest EGT shows leanest cylinder× Hottest CHT is leanest cylinder× Running LOP causes high CHT× Running LOP will damage valves× Running LOP will increase cylinder

wear× “Gas is cheaper than engine overhaul”

• Cessna 414

• Engines at same power !

• Ball is centered.

• What is going on?

75 ROP 50 LOP

What might lead to detonation?

• Operation of any cylinder in “The Red Box”• Inadequate baffling, Bird nests• High power at low airspeed (poor cooling)• Fouled fuel injector• Incorrect magneto timing• Bad fuel• Bad spark plug acting as a glow plug• Intake manifold leaks?• No enrichment at full throttle?

The Red Box

THE RED BOX defined:

•At and below about 60% power, there is no red box. Put the mixture wherever feels right.

•At ~ 65% power, avoid 100ºF ROP to Peak. •At ~ 70%, avoid 125ºF ROP to 25ºF LOP. •At ~ 75%, avoid 180ºF ROP to 40ºF LOP. •At ~ 80%, avoid 200ºF ROP to 60ºF LOP.

A Catch to LOP Ops

• The spread between EGT peaks will be excessive without tuned injectors (or with a carbureted engine), and the engine will run rough LOP.

• Avoidance of roughness comes from tuning the injectors so they all peak within 0.5 gph

•What can you do with a carbureted engine?

25 LOP

113 LOP

HP difference with

Some Details• As you lean, the first cylinder to peak is the leanest, the last to peak is the richest.

• If cruising ROP, you lean by the leanest cylinder, but

• If cruising LOP, you lean by the richest cylinder- because you are on the other side of the Red Box.

• And you need an engine analyzer to show you where all this is happening!

SOME BASICS

•Absolute EGT numbers are inexact and of little value – but degrees relative to the peak EGT are extremely important in defining landmarks in combustion for each cylinder.

•CHTs are important of themselves

• Running ROP or LOP are valid choices, but most pilots running ROP are not running far enough ROP, and are in the “Red Box”.

When ROP When LOP

•Lean by leanest cylinder Lean by richest cylinder

•Air flow determines power Fuel flow determines power

•Extra fuel retards combustion Extra air retards combust

•Carbon monoxide plentiful Minimal CO

•Not most fuel efficient Fuel efficient at 20-30 LOP

•Engine dirty Oil and engine stay cleaner

•Engine runs hot Engine runs cooler

When LOP:

Fuel flow determines power

–Engines with 7.5:1 compression put out 12.7 hp per GPH

–Engines with 8.5:1 compression put out 13.9 hp per GPH

What does an engine analyzer do?

• Shows EGT and CHT of each cylinder in real time• Records that data every 6 seconds for later download

and review• Presents EGT and CHT with rising bars as well as

numbers• Lean find function shows richest and leanest cylinder as

mixture is brought back• Alarms can be set, like:

– Any CHT above 380F.– Excessive cooling rate– Any EGT above 1600F

Great airspeed Max manifold pressure

Low fuel flow

It’s WOTLOPSOP!