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10/20/2017 1:01:18 AM
9/22/2017 12:11:25 AM
Posted: 8/23/2005 6:17:06 AM EDT
Is there a tradeoff between HP and fuel economy?

What I am getting at. Take the Nissan Maxima 3.5l V-6

A few years ago, it made about 225 hp. Now, the same engine can make 275+ hp.

Instead of HP, could they have left it at 225 HP and increased the fuel economy?

I lover performance, but I would give up 30-40 hp for an extra 5 mpg about now.

And I can afford the gas prices.

Thanks

TXL
Link Posted: 8/23/2005 6:37:28 AM EDT
Yes, there is, but you may find that increasing engine power actually increases mileage. I have an Olds 98 with the supercharged 3800 engine that produces 240 HP and gets 30 mpg in everyday driving. My Hyundai has a 140 HP 4 cylinder engine and a manual transmission that gets 28 mpg in the same traffic. The 70% increase in power in the Olds means I don't have to work the engine near as hard during acceleration. This is an overly simplistic example, but I have heard similar things about the Chevy Malibu - the 6 cylinder engines got / get better mileage than the 4 cylinder engines.
Link Posted: 8/23/2005 6:40:25 AM EDT
Yes there is a tradeoff with current technology or they would have found a way to build 300hp SUV's with 40mpg...Some are better than others at getting around it Lighter weight cars ...more efficient engines but there are limits to what you can do.

I'm pretty sure the new Maxima engines are bigger than before...They used to be 3.0 liter until the recent model
Link Posted: 8/23/2005 6:43:39 AM EDT
It depends on a couple things. How you make the horsepower and power to weight ratio.

When you make horsepower by RPM it takes more fuel to spin the engine faster. When you make it through displacement it can save fuel, depending the P/W ratio.
That, of course is overly simplified.
Super/turbo charging is a different ballgame.
Link Posted: 8/23/2005 6:49:39 AM EDT
Fuel economy is the ENERGY required to accelerate the vehicle to speed and maintain it.

Power is the rate of change of energy which is just a fancy way of saying acceleration rate, 0-60 times if you need a specific (but transmission and traction also affects this).

But what you feel in acceleration is torque. Not horsepower. Torque is force, rotational force. And force is energy.

So how does this all tie together? Quite easily.

Torque in a gasoline engine is the volumemetric efficiency of the engine. Power is the product of torque and RPM. So if an engine is tuned to have a broad torque curve, the power goes up because the engine can still generate good torque at higher RPMs.

In most cars, engine power needed for highway cruise is less than 15 Hp, including AC. An engine tuned for higher power will not need the extra torque to maintain the speed and will get similar mileage. The engine may be spinning at an RPM where 150 Hp is possible but because it is pulling 16 inches of manifold vacuum, it isn't generating but 15 Hp.

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