From: tgardner@athena.mit.edu (Timothy J Gardner)
Subject: Re: Why is US engine technology so retrograde?
Organization: Massachusetts Institute of Technology
Date: Fri, 8 Jan 1993 17:07:51 GMT

In article <lkpk2eINNeo4@exodus.Eng.Sun.COM> tut@cairo.Eng.Sun.COM (Bill "Bill" Tuthill) writes:
>Could someone please describe the technology tradeoffs between
>large-displacement (mostly US) engines, and multi-valve engines
>with smaller displacement?  I'm wondering whether US technology
>is just behind, or whether I'm missing something.

The US manufacturers have always sought to maximize profits by holding onto
old technology as long as possible.  That way they can avoid tooling and
R&D costs associated with new technology.  The old large-displacement engines
soldier on by virtue of advanced engine management systems that help them
to be almost as efficient as newer engines.  When they do break down and build
a new engine (e.g. Ford modular),  US manufacturers are world class in the 
newer technology.        

>For example, consider the best-selling US car, the Ford Taurus.
>The base model has a 3 liter V6 engine with overhead valves; I
>believe this is called a pushrod engine.  This engine produces
>140 HP and 160 ft.lbs. torque.  By contrast, the BMW 325i engine
>displaces only 2.5 liters, yet produces 189 HP and 181 ft.lbs. of
>torque.  And the engine in the Acura Integra displaces only 1.8
>liters, yet produces the same 140 HP as the Taurus engine (less
>torque though, at 126).

Smaller engines have torque and power peaks at higher rpm, in general.  US
drivers tend not to like that.  As a result of learning to shift in my 
childhood on a Yamaha YZ80 dirtbike, the first thing I hear when I drive 
friends' cars is "What are you doing to my engine?"  Of course, the American
style of driving comes from the history of owning cars with large displacement 
engines with prodigious low-end torque.  

>I've heard that a double overhead cam requires less tuning than
>a pushrod or single overhead cam, because of greater rotational
>efficiency.  Is the main reason for larger displacement to produce
>greater torque with similar fuel consumption?

I'm not sure what rotational efficiency is, but your conclusion sounds 
reasonable.  The real economic reasons for the large displacement engines, 
however, is that fuel is cheap and it's a manufacturing artifact.    

>When Ford needed a DOHC engine for the Taurus SHO, they just had
>Yamaha build it.  I know Saturn produces some very nice SOHC and
>DOHC engines, but GM doesn't seem to use these anywhere else in its
>product line.  And Chrysler still produces mostly pushrod engines.

Ford, GM, and Chrysler are moving as slowly as they can in converting to OHC
technology.  GM makes the Northstar 4.6l V-8, the 3.4l Twin Dual Cam V-6, the
Quad4, the Saturn 1.9l fours, the small ohc four from Brazil, plus the LT5 V-8
via Mercury Marine and Lotus, for sale in the US, plus many Opel engines in 
Europe. Ford sells the modular series engines, sohc and dohc 4.6l V-8's for 
now, but with a 4.0l V-8, V-6 and I-4 coming soon.  Chrysler put the new sohc 
24 valve V-6 in the LH cars, and has a high performance dohc head for the 2.2l
turbo four.  I don't count the engines sourced from other manufacturers. 
They're getting there.        

Tim Gardner