From: eliot@stalfos.engr.washington.edu (eliot)
Newsgroups: rec.autos
Subject: Re: Why is US engine technology so retrograde?
Date: 8 Jan 1993 02:24:37 GMT
Organization: clearer than blir
NNTP-Posting-Host: stalfos.engr.washington.edu

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.

Two major factors to consider:  taxes and gas prices.

In many european and asian countries, you pay taxes based on the
capacity of your engine.  italy and singapore comes to mind.  i think
one of our singaporean netters can enlighten us more.  how would you
like to pay one dollar of tax for every c.c. of engine displacement?
that would put mustang 5.0's out to pasture real quick.  i'm pretty
sure japan also has some kind of taxation based on engine size.

so small engines with high outputs have an advantage in terms
of being cheaper for the owner and that obviously translates
into bigger sales.

as for gas prices, the cliche is that bigger engines consume more gas,
but this is not a hard and fast rule.  a high revving, high strung 4
banger can be more thirsty than a lazy v6 with lots of low end and
tall gearing.  but generally speaking, the larger the combustion
chamber, the greater the potential for consumption, so for those
countries with high gas prices, smaller, more efficient engines turn
out to be cheaper to operate.

>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).

the one true measure of engine efficiency is hardly ever mentioned
anywhere.  it is called bmep or brake mean effective pressure.  this
number is independent of rpms or size and measures how effectively the
engine combustion pushes the piston down.  i don't know the exact
definition of bmep, perhaps some ME types can explain further.
comparing max. power and torque outputs is only partially helpful in
making conclusions because there are so many ways to produce output.
i.e. either a flat lazy "curve" or a peaky one.

for america where people generally drive 55-65 and where engines
typically run mostly below 3000 it is not optimal to produce tons of
power at 8000 rpm and none at 2000.  i think that the american engines
tend to emphasize low end and mid range more, which inevitably leads
to more modest max. power numbers.  another reason not to place too
much emphasis on numbers.  the high powered, high strung car will be
better at the race track in the hands of a skilled driver, but its
characteristics will be far less useful for the grocery shopper who
wants a slushbox.

a 3 liter V6 that produces 140 bhp will require far less effort from
the driver to extract those 140 horses than a 1.8 4 banger that
produces the same amount.  that is the bottom line, and the advantage
of cubic inches;  something that numbers unfortunately do not convey.

>Is the main reason for larger displacement to produce
>greater torque with similar fuel consumption?

see above.

>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.

I think that SOHC and DOHC are not necessary for low revving engines.
they are superior only if you have an engine that is constantly high
revving, so i wouldn't necessarily bash the american car makers for
not being exclusively SOHC or DOHC.  Mostly I think that it is simply
not fashionable to be pushrod, just as it is starting to become
unfashionable to have "only" 2 valves per cylinder, never mind that it
offers better low end than a 4 valve.

that said, i have not seen anything from the american makers (nor the
japanese, for that matter) resembling the audi s4 engine, where a
computer managed wastegate is used to produce max. torque at 2000 rpm,
eliminate turbo lag, while at the same time having enough lung power
to rev to 7200 rpm and have a specific output of over 100 bhp/liter.  now
that is a truly high tech piece of engineering.


eliot

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