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From: Brent Regan <brent@regandesigns.com>
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Subject: Re: L-IV Choice of Engine
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Market forces require that, to be successful and survive, consumer 
products must be designed to satisfy a selection of requirements imposed 
by the consumer. Over time and competition, natural selection refines 
the design so that it is either better optimized and competes or it 
falls into the dustbin of history.

Engines, while simple in concept, are spectacularly diverse in 
implementation. When you think "engine" think "mammal" and then imagine 
all the different species of mammals. Most all are successfully 
reproducing. Each is optimized for a particular set of conditions that 
allows them to dominate in a specific niche. The same is true for 
engines. Every mass produced engine is optimized for a specific set of 
requirements and no two requirement sets are the same.  Taking an engine 
from one application and inserting it in another results, de facto, in a 
sub optimal situation. You could couple the 350 Hp diesel engine from my 
truck to a weed whacker and it would indeed whack weeds but the 
portability requirement would not be met.

Aircraft engines are designed with the primary requirements of  light 
weight, low speed, high continuos percentage power, high reliability and 
a narrow power band. Think "Draft Horse".

Automotive engines are designed for low cost, high speed, low emissions, 
high peak power and  wide torque range. Think "Cheetah".

What would happen if you hitched four Cheetas to your plow?

Modern automobile engines have benefited in billions of dollars in 
development with the ONLY goal of making them more attractive to 
automobile buyers. The corollary is that all that effort  has been 
expended to make automobile engines that deliberately do not directly 
satisfy the requirements of aircraft.

The landscape is littered, both figuratively and literally, with well 
meaning, would be aircraft engine designers who share a common inability 
to learn from history.  Perhaps driven by the false assumption that 
desirable automobile engine characteristics can be selectively 
transplanted into an aircraft with the simple transposition of hardware. 
The problem, of course is that all the "not desirable" for aircraft 
characteristics are part of the bargain. Eating the brains of your enemy 
won't give you their wisdom but it may give you Mad Cow disease.

People who know enough to design an aircraft engine are wise enough not to.

Brent Regan