Economy cars and horsepower.

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OneEyeJack

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Would economy cars get better gas mileage with smaller less powerful engines. Do current economy cars really need as much power as they currently have?

Yesterday I was driving down the freeway at 3AM doing about 80mph in my 4Runner and a Yaris which as I understand it is a very basic no frills transportation device blew by me going at least 100mph, maybe more. Evidently it has a bit more power than needed to supply the needs of basic transportation. Does this extra power lead to a driving style that allows the use of more power which means more gasoline that may not really be necessary for the commute to work and back or a trip to the grocery store?
 
It is rather simple why a car is able to go 100MPH etc.

A vehicle needs excess power to accelerate in a tolerable/safe manner, climb steep grades at upper elevation at highway speed, and carry full loads.

However majority of time on relatively flat roads it needs very little of what the engine is capable of hence able to go 100MPH. Also 85MPH is speed limit in some states so that magic 100MPH is not that much more speed. The Yaris is marketed across the globe and is an everyday car for many markets not considered a penalty box.

I found it laughable that you were potentially speeding at 80MPH and bothered by a "lessor" car doing 100 MPH
smile.gif
 
I've long said that no car NEEDS more than about 130-140 hp. I base that on a half million miles of use of MB diesels down to as low as 67 hp. I can cruise fine in my 67 hp, 3400lb 240D. That includes merging and accelerating, which some think demands a v6 "for safety".

It's also why hybrid and turbos are great. A little extra when needed, less the rest of the time, and perhaps none when stopped.

Nothing says the poor Yaris was at WOT ridiculously raucous.
 
Originally Posted By: JHZR2
I've long said that no car NEEDS more than about 130-140 hp. I base that on a half million miles of use of MB diesels down to as low as 67 hp. I can cruise fine in my 67 hp, 3400lb 240D. That includes merging and accelerating, which some think demands a v6 "for safety".

It's also why hybrid and turbos are great. A little extra when needed, less the rest of the time, and perhaps none when stopped.

Nothing says the poor Yaris was at WOT ridiculously raucous.


The 240D has something that makes up for low HP rating, ample torque at low rpm due to diesel engine. Not exactly valid to state 67HP as reasonable # without that major tid bit....

The idea of V6 required is not as valid in most folks minds given sales pretty low in top selling vehicles when an option. 4 cylinders have come a long way offering incredible MPG with power curves at great starting prices($20k). Hybrid/turbo stuff is still pricey.
 
There does come a point where not enough power causes MPG to go down, mostly because you have the run at higher RPMs to do everthing. It is the reason my WS6 pulls down 26 to 28 MPG on the highway. 70 mph at 1800 rpm, I don't have to even leave sixth gear on some of the larger hills.
 
I had a one ton car with a 1.3 63 horse engine. 5 speeds, topped out between 80-90mph. Plenty for everyday needs and it just lets tou study traffic flow to merge, instead of flooring it at the last second, as I have seen done- which can stink.

Pretty fun car to throw around...no power steering, 13" wheels- they do not make em like they used to.
 
My 1975 Vega with 98 HP would go 105 MPH, which was faster than my friend's '83 VW GTI. That really irked him something awful. It would accelerate and handle better than my Vega, but I could outrun him on top end. Cars need more power to accelerate to highway speeds than they need to maintain those speeds.
 
Originally Posted By: ARCOgraphite
Remember 100 horse power is actually the power of 100 horses. Imagine hitching up 100 horses to your Chevette
smile.gif



But those 100 horses would never get your Chevette up to 100 MPH! But 100 HP would.

CAUTION! NERD ALERT! ENGINEERING HISTORICAL REFERENCE BELOW!
James Watt created the original definition of a Horsepower by measuring the speed and the force that a draft horse could apply to a turnstile that was turning a pump moving water out of a coal mine. The horse could maintain 180 pounds of push on the turnstile while traveling at 181 feet per minute. Multiplying the force and speed gave a quantity of 32580 foot*pounds/minute, which Watt rounded to 33,000 and called it 1 Horsepower. This was how he rated his steam engines in order to give an idea of how quickly they could work in comparison to horses.
 
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To propel a Yaris at say, 65 mph probably only take about 25 hp. So if you were willing to live with very slow accelleration, then yes, a 25 hp motor might do. And of course you mileage would be better just due to lighter weight and using the engine in it;s sweet spot.
 
Originally Posted By: madRiver
It is rather simple why a car is able to go 100MPH etc.

A vehicle needs excess power to accelerate in a tolerable/safe manner, climb steep grades at upper elevation at highway speed, and carry full loads.

However majority of time on relatively flat roads it needs very little of what the engine is capable of hence able to go 100MPH. Also 85MPH is speed limit in some states so that magic 100MPH is not that much more speed. The Yaris is marketed across the globe and is an everyday car for many markets not considered a penalty box.

I found it laughable that you were potentially speeding at 80MPH and bothered by a "lessor" car doing 100 MPH
smile.gif


Ego, ego.
 
Originally Posted By: KrisZ
Does your 4Runner really need a V8 in it?


Well, maybe but remember it's not a high horsepower motor, only 285hp with 325 ft-lbs of torque. I tow a utility trailer weighing from 2K to 5K off road, up and down some steep hills and on soft and rutted roads in the desert, plus a horse trailer and a travel trailer. About 20-40% of the driving time is towing something or other. The 4Runner works hard for its living unlike some other sport utility vehicles and pickups.

My daily driver Honda has 76 horse power and I get around just fine. The cruising speed on the freeway is the flow of traffic which around here is anything from 70-80mph and the Honda keeps up with no trouble at all.
 
Originally Posted By: philipp10
To propel a Yaris at say, 65 mph probably only take about 25 hp.
Sounds to be about the right figure. I've heard its 20 hp to 40 hp to keep a 'typical' car going at 60 mph, accounting for the differences in drag coefficient and rolling resistance creates the spread of course.
Originally Posted By: philipp10
So if you were willing to live with very slow accelleration, then yes, a 25 hp motor might do. And of course you mileage would be better just due to lighter weight and using the engine in it's sweet spot.

You couldn't do much of a hill, and the engine's sweet spot is not at the max power high rpm point, its actually at peak torque where cylinder filling is maxed out, occurring at a lower rpm than near redline max power.

That Yaris (106 hp max) was probably doing 90 hp just to maintain 100 mph since wind drag goes up with the square of the speed.
 
The vehicle price means nothing, weight and gearing determine torque needs.

Horsepower is only a function of torque but you didnt specify an average RPM.
 
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