Anyone else striving for better MPGs by adding HPs?

[jamesqf]

Originally Posted by Lonesome Trail

By your logic Car A is using less fuel because it's a small engine making more power per displacement, hence is more 'efficient' because of that ratio, correct?

Maybe. Trouble is, you're using a very simplistic model of something that's quite complicated. The power produced by an engine isn't anywhere near as simple as a fixed ratio of X fuel in produces Y hp. It depends on all sorts of factors like valve timing and the speed with which the valves can open & close, internal friction, and much more. That's why each type of engine has its own BSFC map, which shows efficiency under various conditions.

The bottom line is that while it's possible for a larger engine to get better fuel economy than a smaller one under particular conditions, you pretty well have to deliberately seek out those conditions by e.g. looking at the BSFC maps for both, and choosing to run the larger engine at its best point, and the smaller one at its worst.

[Fat Charlie]

Welcome to this type of fun driving!

It's not so much that larger, more powerful engines can be more efficient, it's that larger, more powerful engines take less of a hit on efficiency when they enter inefficient conditions.

On level ground in a line of cars doing 65, my Fit can do over 50 mpg. Let all the other cars pull off and throw in a hill, I'm suddenly getting 25. Yes, my mileage was cut in half because my puny little 1.5 actually had to do some work on its own. But it's wrong to overlook the real numbers: my Fit at its worst is right at the Mustangs' averages and still beats the hell out of the F-150. What good is it to not drop all that much mpg on an uphill when the cost is bad overall mpg?

Let's turn it around: a big, strong engine gets overall what a puny Fit gets uphill. The underpowered car then increases its mpg the moment the hill slackens, and keeps getting higher mpg until the next hill. So while my little car's uphill mpg is pathetically below its average, it's average over 50k miles is 45 mpg.

I know, the (completely legitimate) response is... Fun. We're actually big fans of acceleration here, and pushing every part of the car's envelope- not a lot of granny drivers at this site. The biggest technique is Driving Without Brakes (DWB), but Pulse And Glide (P&G) is the first to start with. DWB's premise is that it's stupid to accelerate towards the stop sign, but carrying it much farther than that is not for the faint of heart. P&G's philosophy is that hard acceleration means less time spent burning gas and more time spent at cruising speed. I know where you're coming from- I was driving a Legacy GT, burning it up 40+ miles each way and getting 20-22 mpg doing it. Then I stumbled in here and did some reading. My next tank was over 28 mpg. I didn't leave earlier (daycare opens when it opens, you don't get points for being there early) and I didn't get to work later. Same Bat Times, same Bat Roads, more efficient methods of putting power to the pavement. In a car where a 400 mile tank was a myth, in the 92 tanks I logged since coming here my average tank distance was 449.8 miles.

But increase the power- you're right in wanting an engine that produces power more efficiently. You can even use it for tearing things up and get better mileage at the same time, or do one then the other. And have fun. Just know that it's you, not the car, that gets the mileage- but an engine that produces more power more efficiently lets you do all sorts of fun stuff!

[Frank Lee]

I'm planning on losing weight by implementing the all-I-can-eat pizza, chips, burgers, and beer diet.

[jamesqf]

Originally Posted by Frank Lee

I'm planning on losing weight by implementing the all-I-can-eat pizza, chips, burgers, and beer diet.

You know, that actually might work for me, 'cause I have a real limited tolerance for pizza & beer, so "all-I-can-eat" before revulsion sets in isn't all that much.

[wdb]

Originally Posted by Lonesome Trail

I've always been a fan of fuel economy comes with a better controlled right foot (or left for the Euro folks)

Uhm, what?

[Vman455]

Originally Posted by wdb

Uhm, what?

Those damn Englandians with their left-foot throttle.

[Fat Charlie]

I traded vehicles with a British patrol one afternoon, and my other guy's driver was scared of their manual- so I got to drive for one afternoon that year! Shifting with my left hand was strange, but the pedals were right where my feet looked for them.

I even found an old pic- Fat Charlie in the desert, taking an afternoon off from helping found ISIS!

[Frank Lee]

Originally Posted by jamesqf

You know, that actually might work for me, 'cause I have a real limited tolerance for pizza & beer, so "all-I-can-eat" before revulsion sets in isn't all that much.

Right, because you live in Opposite World, where everything and every result is the opposite of that gotten by the rest of us.

[jamesqf]

Originally Posted by Frank Lee

...every result is the opposite of that gotten by the rest of us.

Well, I don't know just who you're counting as "the rest of us", but I do know a number of people (besides myself) who seldom if ever drink lots of beer or eat regularly pizza.

[Ecky]

It's possible to improve economy by improving the efficiency of an engine, but you end up fighting some other things. Let's say that you optimize your valve timing so that you have a lower BSFC at cruising speed, AND more torque. Suddenly, your throttle plate needs to be closed more, which in turn hurts BSFC - probably not as much as you gained through improving efficiency, but you have to pair greater power with taller gearing, or your throttle plate is going to fight you.

Food for thought: Why does Chevy shut off 4 cylinders in the Corvette, if decreasing power does not save fuel?

Hypermiling the C7 - Taking the 2014 Chevy Corvette on a Fuel-Economy Run

The C7 coupe takes all the fuel economy advantages of the C6 and stretches them. For instance, the C6's 436-hp LS3 6.2-liter V-8 engine was rich in low-end torque, so it didn't need to turn very fast to sustain speed, but it lacked some of the fuel-saving tech we have now. The C7's new 460-hp LT1 version of the same-size V-8 has the new tricks, including variable valve timing, direct fuel injection, and a cylinder deactivation system that has the engine firing only four cylinders under light loads.

Plus, where the sixth gear in the C6's six-speed manual transmission was a 0.50:1 overdrive, the seventh gear in the C7's manual transmission is an even deeper 0.42:1 overdrive. And the low rolling resistance Michelin Pilot Super Sport run-flat tires that the C7 wears are more advanced than the C6's Goodyears.

^ Cut the engine in half and add an extra gear on top, and you're saving fuel, mostly because you're keeping the throttle plate as close to wide open as possible while driving on the highway, and reducing the amount of air the engine has to pump.

...So I filled up the new Corvette; it took only 3.34 gallons to refuel the C7 after the trip. That's a stunning 37.3 mpg over that course...

~

Honda's idea with the Insight was to downsize from a 4 cylinder to a 3 and gear it like a V8 (or taller), with an electric motor to add power on demand, and it works:



Close to 130mpg @ 35mph




Close to 120mpg @ 44mph




Close to 100mpg @ 62mph