Horsepower requirements should be sufficient for safety.
A rational answer to the question of what is sufficient is:
75 mph on steepest allowable superhighway grade at 7500 foot above sea
level elevation at "standard temperature and pressure" with the vehicle
loaded to maximum gross weight.
No more and no less horsepower is indicated for perfectly adequate
performance. More is wasteful, less is unsafe.
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Having more power available is never wasted. The cost of manufacturing an
engine capable of 200 or 250 hp is very much the same. A cam is a cam no
matter where you place the lobes. The fuel consumption on today's cars at
highway cruising speed is even pretty close on engines of that HP range.
I don't want "adequate", I want fast when I want fast. My 234 hp car out
performs my former 185 hp car and gets better mileage. I have not, however,
had the opportunity to see if the rated top speed of 137 is attainable
easily. I've not been past 110 yet.
Not completely true. Take a look at a lot of vehicles that have poor
aerodynamics (every truck,van suvee and JeeP)
the so called fuel savings you theoretically get with the 4 cylinder
when compared to the six, is gone once you try to maintain speed since
the smaller engine rev's more. Same holds true for the six when
compared to the v8's.
Then call on the Goverments and rich ass oil companies to speed up
developement of fuel cells and bio fuels.
You know, I can't count how many times I've been driving up US 395 in
the '80s and early '90s in some POS low horsepower car/truck and "wanted"
to pass some fuckwit driving 45, but wasn't able to because I couldn't
safely summons up the needed horsepower to pull out and overtake said
I recently drove up in my midsize Avalanche (305HP V8, getting the same or
better mileage than under-powered cars and trucks of the '80s) and "wanted"
to pass three times. I did so with no reservations..
Oh, that's right. We're gonna run out of oil by 1998 or 2000 at the latest,
based on projections from the mid 1970's.
Keep in mind, my 1987 Nissan hardbody had a 2.5L I4 engine with around 120
HP and got 16-20 MPG.
My 1995 GMC Jimmy 4x4 had a 4.3L V6 engine with around 190 HP and got 18-22
My 2002 Kia Sedona Minivan had a 3.5L V6 with around 195 HP and got 16-22
My 2006 Chevy Avalanche has a 5.3L V8 with around 305 HP and gets 18-22 MPG.
The higher the price of oil, the more there is.
-to extract at a profit or shall we say economically.
You need to compare similar technologies, that means of the same ERA.
You also need to compare your typical driving environment. Mine is only
about 20% highway, so although my car (as for many) gets very good
highway mileage, it's the urban driving figures I should compare.
It's interesting looking at the new Jeep Cherokee SRT-8, which uses
about twice the fuel of my 3.3L Concorde, both highway and city.
The diesel Cherokee uses about 50% of the fuel the SRT-8 uses and it
isn't a slouch.
Most cases. Take the basic 3800 GM engine that has been around many years.
They've increased both power and fuel mileage over the years. Go back even
more. The mid-50's Chevy had a 232 cu in straight six. With changes in
technology, that same 232 cubic inches performs so much better and uses fuel
much more efficiently.
There is a 4 cylinder with 162 hp that gets 2 mpg more. Not much of a
trade-off for me. In a year of my typical driving (25000 miles, the
difference is 60 gallons. Most people drive half of that, a difference of 30
gallons. Sure, times 50 million cars it makes a difference but I'd rather
conserve more in other areas and enjoy driving.
Yet, in the same model year, the less powerful engine almost always gets
better fuel economy.
Not according to the best science available today.
In my car, a Ford Contour, the 4 cyl 2.0 litre engine gets about 34/24
mpg and V6 2.5 litre engine gets about 30/20 mpg. That's about 10%. In a
year, I would save about 70 gallons of fuel. Over the life of my car, I
would have saved around 800 gallons of fuel and paid less for the car. I
would have saved some in car insurance, but, the savings would probably
be about the same as the cost of the timing belt replacements. And, for
the more powerful engine, I didn't really gain anything.
I don't need the extra power. And, I still would have enjoyed driving.
Saying it over and over doesn't make it true. Go spend a few weeks
researching magazine road tests (don't just use EPA figures, they're
flawed badly). In real world driving, engine in today's cars makes
*very* little difference unless the driver is a consistent lead-foot.
There are even quite a few cases where moving up to the next engine size
will yield better mileage because acceptable performance can be achieved
with a lower (numerical) rear-end ratio, plus the bigger engines often
get an extra gear in the transmission too .
I have a great example.
A former manager of mine lives in Hesperia and works in San Bernardino.
On his daily roundtrip - about thirty miles and 4000 ft elevation change -
he figured he'd do better buying an I4 than a V6.
Well, because of the flat torque of the I4, he ended up with worse gas
mileage over the first year in his new I4 than he had in his old V6.
While your point is valid about anecdoti Jeff, it remains that efficiency is
a function of load and capability. An engine with more torque is going to
work less under the same circumstances than one with less.
I recently drove two identical model cars, but one was a 4 cylinder and one
was a 6 cylinder. Real world mileage experiences of people who own the 4
cylinder versions are no better than those who own the 6's. I could easily
see why when I had a chance to really compare performance. On a stretch of
interstate the 4 cylinder had to rev about 500 RMP higher than the 6, to go
at the same speed. That 4 was other wise quite impressive in terms of its
acceleration, etc. Geared differently to accommodate a poorer torque curve
than the 6, and less horsepower, made it at the very best, no better than
What people here have been saying is that there is real world experience out
there on the street that defies the notion that all things being equal a 4
will always be more efficient than a 6. It's simply not true. There's not
even reason to believe that it should be true.
Just a point about engines in general. The number or cylinders is only one
measure of its characteristics. An Offenhauser 4 cylinder can out perform
any GM V-8 ever made and it gets terrible fuel mileage. Engine performance
is a function of displacement and efficiency and what the engine was
designed to do. High rpm for speed, low rpm for torque, etc.
I know of some 4 cylinder economy cars that can out accelerate vehicles with
8 cylinder engines with superchargers.
Blanket statements that one engine is going to be more economical based on
the number of cylinders is just plain wrong.
Actually, they will work the same, because they are putting the same
amount of power.
Depends on how it is geared and driven.
But we're not quite on the same page. If you have a car that is not
underpowered, it is going to take the same amount of energy to move it
from point A to B. However, if if has significantly more power than it
needs, more than 150 HP for small car like a Honda Civic, then the
mileage will suffer.
Of course, it's not always true. There is no such thing as always.
It takes more energy to turn a bigger engine that a small engine.
Which takes more energy? To turn over big block Ford or the one-cylinder
engine on Dad's old lawn tractor? The big block Ford, of course.
There's more bearing surfaces to have friction, more air/fuel mixture to
compress, a large volume to suck air into.
While it is obvious for a huge engine compared to a small engine, the
same principle holds form a 2.0 Litre 4 cyl engine vs. a 2.5 litre six
cylinder using the same technology.
However, that doesn't mean that the difference is always going to be
huge. The Honda Accord 4 cyl (2.4 litre) only gets about about 2 mpg
more mileage than the 6 cyl (3.5 litre). So while the smaller engine is
more efficient, it is not hugely more efficient.
There are things you can do to make a engine have higher power output,
more all of which get more air or air/fuel mixture into the engine,
like more valves per cylinder, which allows more mixture or air to enter
the cylinder, add a turbocharger or super charger, which also pushes
more air into the cylinder or run the engine at a higher speed, which
does the same thing.
And there are things which increase the efficiency, like storing some of
the mechanical output of the engine as chemical energy (or electrical
energy) which can quickly be converted to mechanical energy via a motor
(hybrid), use Atkinson-cycle engine (like the Toyota Prius), use a
transmission which is geared well (my car has plenty of power to
maintain 70 mph at 2000 RPM, yet the car is geared to run at 3000 RPM,
so the engine seems more responsive), particularly one with an infinite
number of steps between the highest and lowest ratio (continuously
variable transmission, also like the Toyota Prius) and using variable
And, of course, how much mileage one gets is determined by how one drives.
Mike Marlow turned on the Etch-A-Sketch and wrote:
I imagine he would have been just fine in a V6. The point was, moving to a
smaller engine, with less HP/torque, caused him to need to rev the engine
way higher than he would have needed to in the V6 or in an 8.
(For those in southern california, I'm talking about the I-15 Cajon pass.)
I know it freaks me out when I drive my wife's V6 Vue and see the tach go up
to four or six thousand rpm. On my truck, the tach rarely goes over 2000
Really? Take an Accord, or Camry, or Altima -- the 4 almost always
gets better mileage than the V6. Mustang? V6 vs V8, same story.
Only if the 4 is so underpowered it has to work really hard might your
claim be true.
And that is from magazine tests.
Not to anything like the degree they did in years past. Checked the
mileage on a 400-horsepower Corvette lately? Its better than a
4-cylinder Citation would deliver back in the 80s.
The simple fact is that a truly efficient engine only uses as much fuel
as is demanded of it. Whether it is capable of 50 horsepower or 450
horsepower doesn't make all that much difference when its only being
asked to deliver 25 hp.
With today's cars, the shape and weight of the chassis itself is a FAR
bigger factor in fuel economy than engine size.
.... the mileage on a 400-HP Corvette is better than a 4-cylinder Citation
back in the 80s. A truly efficient engine only uses as much fuel as is
demanded of it. Whether it is capable of 50 HP or 450 HP doesn't make
that much difference when its only being asked to deliver 25 HP.
With today's cars, the shape and weight of the chassis itself is a FAR
bigger factor in fuel economy than engine size.
The greatest increases in mileage over the past 30 years have been attained
by making cars smaller to decrease vehicle WEIGHT. Carmakers had to switch
to more costly and more failure-prone FWD in these smaller cars to recapture
the space taken up by the driveshaft tunnel. A lesser but quite important
improvement in mileage was gained by computer controlled fuel mixtures.
Virtually all fuel management mileage improvement has been attained. The only
thing left is cutting more WEIGHT. Smaller displacement engines do not provide
better mileage, except for the contribution of their lower block WEIGHT.
There are no alternate fuels approaching the efficiency of petroleum in dollars
per mile total cost to produce, except for solar power, which is not available in
sufficient quantity, and nuclear power, which is religiously feared and shunned.
The car of the future will be small, small, small.
Rodan. <---- Go ahead; pry my cold dead hands from my '92 Roadmaster.
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