Anyone else striving for better MPGs by adding HPs?
 

Just curious, feel like a black sheep with my lists of car modifications, lol.

I've always been a fan of fuel economy comes with a better controlled right foot (or left for the Euro folks) and though it's labeled me a granny driver, it also makes for more money I can buy Dr Pepper with when I fill up the tank.

That said, the engineer in me (software engineer for Intel for almost a decade before striking out on my own) is all about numbers, and the mechanic is all about power and efficiency, so for me achieving better volumetric efficiency (HP per L or CC) naturally goes hand in foot with better economy. Yes you can argue that more power requires more fuel, however that's only when the engine is producing that peak power output. The rest of the time a more efficient engine is just droning along, AND because it is more efficient in terms of power production you are producing more energy to the wheels and less to the exhaust and atmosphere at the same 'load' you had before (Newton's Laws).

Ergo, a more efficient engine of same displacement makes more power AND 'can' achieve better economy, assuming the same driving environment. Having your cake and eating it too.

Anyone else thinking along the same lines?

Only if it's a turbodiesel.

https://i.memecaptain.com/gend_images/WuQaTQ.jpg

Well, your explanation makes sense to me, but probably the only consensus here is that I am not an expert. However, I wonder if increasing the horsepower and maintaining speed with lower RPMs would necessarily equate to the engine being more fuel efficient.

I was a substitute teacher out in Queen Creek and San Tan Valley before joining the Army in 2008. My sister lived out there and we called the whole area Queen Creek before it officially became San Tan.

I just remember trying to find new schools for the first time and intersections were missing street signs. That is my main association with Queen Creek, although I wonder if that was the unincorporated portion.

I once stopped at the Filiberto's and had never seen orange salsa. I loved it!

Welcome to the site!

I would think more power would let you shift earlier and have lower rpms which would improve mpg but I'm not an engineer so I don't really know.

LOL, yeah I'm not a non-believer, more of a sideways thinker...

Queen Creek is huge now, have our own Harkins, WalMart and everything! Even pass through 2 counties, Maricopa and Pinal (I'm on the Maricopa side near Sossaman and San Tan Blvd, still rural though)

I just let the results speak for themselves. It's pretty amazing the looks I get when folks see my little notebooks of fuel numbers (I keep a log for tax purposes, small business owners FTW!) It freaks people out that my lopey cam Fox Body pulls pretty consistent 21-23 depending on if I get stuck in traffic, but I always point this out to folks: When I'm on the freeway and am going up the hills (we have overpasses every mile, it's fabulous for fuel economy) I just sort of imagine my throttle increasing a hair and the car maintains speed just fine. Every 'econo' car I've owned with a stock 4 banger required rolling into the throttle to maintain speed. Same scenario, similar vehicles in terms of weight, aerodynamics, speeds, but the big 'thirsty' engines don't have to work as hard to accomplish the same tasks as the little thrifty engines.

There was an episode of Top Gear where they raced a Prius and a BMW around their track for a bit, the BMW was chasing the Prius which the Stig was driving as hard as he could. They compared fuel economy numbers at the end of the race, and the BMW M-Series got twice the fuel economy as the Prius...

Blasphemy? Maybe. Different driving situations? Absolutely. Just like if you put the same cars in rush hour stop and go for an hour with the a/c running on a 100 degree day, the Prius obviously would get waayyy better fuel economy because it gets to sit there in electric a LOT of the time while the BMW idles away. All depends on how you drive, where you drive, etc.

Very true mostly, lol. If the potential power under the curve is increased via increased engine efficiency, all else being equal, then engine 'load' is decreased vs the less efficient engine and it doesn't have to burn the added fuel (ie convert one form of energy into another) to accomplish the same results, in your scenario achieving 15HP to maintain speed, with no change in RPM.

Absolutely the new tiny turbo motors are amazing, but so are the variable valve timed NA motors, such as my '12 GT. It makes more power than my 5.0L pushrod Fox Body, weighs more, and gets better fuel economy despite the fact that the engines have the 'same' displacement, 5.0L and 8 cylinders. The new Coyote engine is freakishly efficient with it's DOHC and variable cam timing vs the dinosaur pushrod engine, and as such in the same scenarios it's able to accomplish the same tasks while using less fuel (same 91 octane).

Pretty amazing stuff, physics

Easily explained: they lied. It's TV, so if they don't get the results they want, they fake it, as with the exploding gas tanks: NBC Admits It Rigged Crash, Settles GM Suit - latimes And since "Top Gear" is all about performance cars, they're pretty well known for lying about anything that has to do with fuel economy or non-IC engined cars.

^^^That, and...

...you misremember--they claimed 14mpg for the Prius and 16mpg for the BMW. And the BMW was drafting the Prius for the duration of the "test."

Also, a flaw in your reasoning here; gas engines are less efficient at smaller throttle openings. That 4 banger that has to "roll into the throttle" to go up an incline does so at a lower BSFC (i.e. less fuel consumed per power unit produced), and, assuming the same weight, aerodynamic load, etc., and consequently same power produced, the car with the larger engine that seems to do less work to produce the same power to go up the same hill, actually consumes more fuel to do so because the BSFC is higher. This Autospeed article explains the concept; the crux of it being:

"For example, anything that allows you to keep the throttle open wider and the revs lower (like changing up to a tall gear and then holding it) will reduce fuel consumption because BSFC will be improved."

Modding the engine to produce more power at a smaller throttle opening without changing the gearing does the opposite.

Hi Vman, do you have some numbers to back up this statement? It's pretty much opposite what my tuner and Torque Pro tools have told me, plus the old pencil and paper method.

Let's run your example another way...

You're climbing a hill, it requires 'x' amount of energy to maintain speed.

Car A is a 4 banger with typical 4 banger torque band with a curve and peak around 4k RPM, Car B is an efficient V8 with flat torque curve and peak around say 2500RPM as is very common in today's engines.

For sake of argument both cars are geared the same, same size tires, etc.

Now both cars hit the hill at the same time, and to maintain speed Car A must really open the throttle to achieve enough power production to climb the hill, Car B cracks its throttle.

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?

However! To achieve this type of efficiency the engine is 'working' harder. When the throttle blade opens to allow in more air, you have to have more fuel added at the same time to make things work, air alone can't produce 'energy' from an engine. To see this in real life hook up your tuner or scanner device and set to watch your injector pulse width, short term fuel plan, etc.

Or if you're analog another fun tool is a vacuum gauge. Your 4 banger with the throttle open is drawing much less vacuum than the V8 with cracked throttle. You can argue that means the 4 banger is more efficient based on the above statement, OR you can also realize that on all vehicles with vacuum regulated fuel systems your fuel pressure regulator is now opened wide allowing 40psi to the injectors, which are also pumping at say 85% duty cycle in order to meet the power requirements of this hill, vs Car B which isn't working hard, still drawing good vacuum, fuel pressure is lower, injector duration is lower, etc.

Making sense so far? The problem with the efficiency models the way you describe is they look good on paper, but tend to sink in real life. When you look at the numbers in terms of how the engines are functioning, all the non-black and white perfect physics variables that are going into making Car A much more complicated than 'HP per L' efficiency...

To use another example that's really going to mess with your head, aerodynamics. Why does reducing drag improve fuel economy rather than improve it? According to your statement above (new Car A and Car B are now the same cars except Car B has some aero mods) Car A should get better fuel economy because the engine is working harder to maintain the same speed due to increased drag on the vehicle, requiring more power to stay at speed. Higher power requirements means the engine's throttle is open more, means that engine is more 'efficient' as it is producing more power than Car B's engine that is working less hard to maintain speed as the vehicle is more slippery and doesn't require the same energy to overcome drag.

Ruh roh...

Yep that's right, in real life the more slippery version, Car B, gets better fuel economy than Car A even though its engine is 'less efficient' than Car A's as it is producing less power to keep the car moving at the same speed.

Same thing with the Top Gear episode everyone poo-poo'd because it's obviously against popular edict here, let's change the scenario one more time but keeping with their test ideas:

You have 2 trucks pulling say 8,000lbs of trailer. Truck A has the smaller gas engine option, truck B has the bigger gas engine (no diesel here to complicate things). Which truck will get better fuel economy? All else is equal, rigs are essentially the same weight, same aerodynamics, same gearing, etc.

Truck A has to work really hard to get its load moving vs Truck B because it has less power under the curve, which according to your logic means Truck A is getting better fuel economy because it's throttle is wide open and is making more power per L vs the bigger engine Truck B which is just loafing along. Truck A has to work really hard to KEEP its load moving at highway speed vs Truck B, same reasons as above.

Which truck is going to have the better fuel economy? The more 'efficient' Truck A, efficient because it's making more power per L to move its load, or Truck B which I argue is the one that's really more 'efficient' because the engine isn't working nearly as hard, ergo the engine is in fact burning less fuel per L displacement because it has much more power under the curve and you don't need to open the throttle as wide to achieve the same power output as Truck A required to achieve the same end results.

Head hurt yet? I need some caffeine, and my chickens are getting hungry...

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.

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!

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.

Uhm, what?

Those damn Englandians with their left-foot throttle.:D

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!

http://ecomodder.com/forum/attachmen...6&d=1463965258

Right, because you live in Opposite World, where everything and 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.

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

^ 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.

~

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:

http://i.imgur.com/oD8VpKx.jpg

Close to 130mpg @ 35mph


http://i.imgur.com/cNa3MWL.jpg

Close to 120mpg @ 44mph


http://i.imgur.com/MY8DxtV.jpg

Close to 100mpg @ 62mph

Let's revisit Car A and Car B going up the same hill. Let's hold all atmospheric conditions the same. Both Car A and Car B are maintaining the same speed up that hill, they hit the same pavement going up that hill, and the same driver takes each car alternately up that hill.

Let's also assume, for the sake of argument, that everything else about Car A and Car B are identical. They have identical bodies, identical trim levels, identical gearing, identical tire and wheel sizes, identical liquid capacities, have identical weight distribution, consume the same amount of electricity (identical alternator loading), an identical amount of drivetrain wear, and they both weigh the same.

If nothing else, Car B with the V8 will have a larger intake manifold vacuum than Car A with the 4-banger. Remember, Car A has a completely opened throttle, and Car B has it's throttle cracked open.

Generating an intake manifold vacuum requires work, and to generate a larger vacuum, a greater amount of work must be expended. Work requires gasoline in either Car A or Car B, so Car B requires more gasoline simply to push Car B up the same hill as Car A, everything else being identical.

Sorry about my late entry - I just found this thread.

Lonesome Trail, welcome aboard from a fellow Mustang owner and Coyote owner and Arizona resident.

In my experience, the old hot-rodding trick to increase available power to the wheels by under-driving the accessories does result in better fuel economy. It results in more power available to the wheels throughout the entire operating RPM range.

Last May, I installed an ASP under-drive crankshaft pulley on the 4.0 liter Cologne V-6 in my '07 Mustang. It under-drives the accessories (particularly, the water pump and power steering pump) by 25%. It gave me close to 1 MPG, according to my fuel log.

Most people don't believe that I can get over 32 MPG with a 4 liter Mustang.:thumbup:

Re post #22
 

DWL (driving with load) is driving with the highest possible Vacuum reading posable aka the best mpg per load.
There are many examples of this. The real world trumps the paper this time.
As to personal experience.
When I installed a MSD 6 Digital ignition system (from a stock HEI) and a RPM Air gap Edelbrock intake (from a stock aluminum) . my vacum went up 2"from 15"mg to 17 at idle (625rpm engine liked 425rpm but the alt. quit below 600rpm and the 800 stall tork converter would not allow a stock750-800rpm idle) and I saw an improvement in mpg of 2.5. (From 7.5 allday every day. to 9.5-14mpgdepending on how I drove.)
This was a 6000lbs tall (24"under the frame) off-road capable 4x4 that was also used to pull a 16,000lbs 5th wheel
More of the right kind of power = more efficiency = better mpg..
Gumby Stay Flexible .

I have a question. Take a Ford 4.6 and a 5.4. IIRC the 5.4 is a stroked 4.6. How would they compare, mpg wise with the same set-up? Then, how would they compare if the 5.4 had a taller rear end? Just thinking.

I am going to just about triple the horsepower and double the torque on my suburban. Be interesting to see what it does to the fuel economy.

Uhhhh.... No.

Oh, okay. I'm sure that must be the case. You sure showed me. And everyone who ever put in a taller final drive. And all the car manufacturers who invested in production variable cylinder technology.

Tell you what. Explain why the MDS 5.7L Chrysler Hemi gets better gas mileage than a non-MDS 5.7L Chrysler Hemi, between a 2005 Dodge Ram 1500 pickup truck with RWD and a 5.7L non-MDS engine and the 545RFE transmission, and the 2006 Dodge Ram 1500 pickup truck with RWD and a 5.7L MDS engine and the 545RFE transmission. The 2006 had an EPA rating that was 1 MPG better than the 2005 (city and highway and combined). No other significant changes were made to this truck from 2005 to 2006, so they both weighed the same, and both had the same aero.

2005 Ram -> https://www.fueleconomy.gov/feg/noframes/21104.shtml

2006 Ram -> https://www.fueleconomy.gov/feg/noframes/22186.shtml

So... you were able to idle all over the place while driving? You didn't touch your gas pedal once while driving? I'd hate to have been stuck behind you.

I think the confusion is coming from somebody here equating higher idle vacuum with higher efficiency.

Fuel economy by swapping in a taller rear end can be roughly guessed at by the rule-of-thumb that a percentage change in gear ratio will give you about half that percentage change in fuel economy. For instance, going from 3.92 to 3.64 (which is a 7% change) should give roughly a 3.5% increase in fuel economy.

Don't know about the change in displacement, though. Couldn't even venture a guess on that one.

There seems to be some confusion here. Usable power gains and improved economy can be seen from:

-Reducing parasitic loads
-Increasing compression
-Fundamental combustion chamber redesign, for higher efficiency (e.g. longer stroke*)
-Weight reduction
-Aerodynamic drag reduction
-LRR tires

*Longer stroke may actually reduce peak power if you need to reduce redline RPM

However, many methods of adding usable horsepower have the opposite effect and will reduce economy, all else being equal, such as:

-Running rich
-Adding more displacement
-Higher RPM / shorter gearing
-Forced induction (on non-diesel)
-Cold air intake

Many modifications that improve economy, do so at the expense of power, such as:

-Smaller displacement (cylinder deactivation, smaller block, etc.)
-Cam regrind
-Warm air intake
-Running lean
-Taller gearing


So, it really depends on which approach you're going to take.

This post really ought to be a sticky, all by itself.

https://youtu.be/MBYVZLRyQjk
On my 79 Chevrolet the vac gage acted like an mpg meter It got so as I could predict the mpg based on what the # of inmg vac had ben doing for the last 2 hrs . Hold it down at 7inmg you got 7mpg (85-90mph) holdit up at 14 inmg and you got 14mph (55-70mph). Get behind a truck and watch it pick up 3-5inmg. Pulling a grade I'd try to maintain 7.5inmg because my Edelbrock carburetor had the 7inmg enrichment springs.
Z---
As a side note when I put the MSD in I was able to switch from premium to bace grade . This improved my bottom dollar by 20-40cents per ga.+ a healthy bump on the amount of fuel consumption .
So bottom line. Proformance parts sold to hard core racers ,installed in place of stock parts, helped my cost of operations aka economy. By improving the efficiency of my approximately 400hp 350ci.
Attachment 20148
Working my truck at Tuttle Creek Off Road Park in Kansas
Gumby Stay Flexible

Ideally you wouldn't run lean or or have a warm air intake at wide open throttle, but this is how a lot of people set up their machines.

[wandering the forums looking for a thread to comment in...]

I'd point to the HotVWs Mileage Motor magazine series. Based on work by John Karcey, an AA Fuel engine builder, for his Karmann Ghia as documented in VW [Trends or Greats](, I forget) and available at CB Performance; and developed over 8 installments by Bruce Simurda.

The plan involves a stroker crank and high reciprocating mass. Stock pistons and cylinders means better cooling and the 1/4" stroke pulls the torque curve downward. A Freeway Flyer transaxle, electronic ignition, low friction lubricant, &etc.

Karcey used a 50lb Jaguar pulley (prolly a little slow off the line :)), I forget what HVWs used; but the motor sitting on my bench has a Gene Berg 8lb crank pulley (and his Type IV cooler upgrade and a spin on oil filter).

HVW's test vehicle started at 28mpg and their goal was to crack 40mpg. They got to 39.99999ohIgive up. And this was with no aerodynamic mods to speak of (IOW Herrod Helper). Karcey claimed 50mpg in his Ghia in the 1970s.

I think a lot of it is in the build quality. Did you know VW racers drill holes in the tops of their pistons to go faster? True story.

Edit: Fixing a typo, but what about this: Entire engine assemblies can be dipped in liquid nitrogen. Apparently it doesn't affect rubber seals and such. Individual part machine better after treatment so maybe it's best to re-crystallize the metal grains and then machine to tighter tolerances before assembly.

All I know is that my brake rotors are holding up great. Some claim 3—4 times the part life. But it doubled the cost of the stock part. So maybe you could assemble an engine too loose or too tight, freeze it to -273°F and have the various alloys settle in together before you fire it up.

I'm not sure. It's a mixed bag. Aircraft powerplants get torn down and rebuilt based on engine hours with no debate.

I believe there are watercooled V-6 aircraft rated engines. Do you have any example?

2500hp AA fuel engines have a fairly short life span. So do Bug engines rebuilt in the carport with Harbor Freight tools.

Possibly a level playing field is motorcycles; they come in air- water- varieties. Here's a water-cooled Vespa:

http://vintagestyle.eu/img/cms/2016/2016-05-30/014.jpg
http://blog.vintagestyle.eu/ten-inch-terror-meet-the-vespa-husqvarna/

Without a doubt watercooleds live longer. Due to the smaller operating temperature "bandwidth" and greater heat rejection capability, they can be (are) built to tighter tolerance and run leaner to boot.

But running lean is what kills the #3 exhaust valve. Oh, wait...

You can troll me all you want about 'watercooled's better', but i was hoping someone would comment on the square bore/stroke ratio, high reciprocating mass strategy which yields in the test case, better mpg and added hp.

The Beetle starts out over-square; the 1/4" stroke just brings it closer to square. The theory being a square bore/stroke has the least surface area, to retain the heat of combustion.

The low end torque possibly compensates for the long-legged transaxle.

How do you think the high reciprocating mass helps?

IMHO most of the action of combustion takes place early on; perhaps whether an engine is square or not is of little consequence, or less consequence than simply what the stroke is because the stroke defines what the piston speed will be and from what I can tell optimal piston speed is 1000-1200 ft/mn. Of course with a longer stroke you get your 1000-1200 at a lower rpm with all the good things that brings.

Perhaps the high rotating mass is helping with lug-a-bility- short shifts, tall gears, and whatnot. Spool it up and it can get moving with those long legs without stalling

I agree with the conclusion. But surely the most action is taking place 90° after TDC, when the lever arm on the crank throw is at a maximum?

https://www.google.com/search?q=air+vs+water+offroad

Scanning the result here suggests that the advantage goes to water-cooling creeping in traffic or over boulder-sized rocks.

Old racing Porsches started with air-cooled cylinders and water-cooled heads. Some interesting discussion here:

http://rennlist.com/forums/996-forum/202717-what-technical-innovation-led-to-porsche-going-to-water-cooled-engines-on-996-a.html

*noise reduction
*Four valves per cylinder for emissions reasons doesn't leave room for cooling fins
*air-cooling is really just oil cooling anyway
*...and, yes; of course, longevity.

I'm late to th party i was going to say diesel water cooled.
Working for KAP I found a sorce for turn-key 454cuin 350hpfor 2500usd in Grant's Pass ,Oregon. From a co Named Welcome to Hellgate Jetboat Excusions.
They do a complete r&r for a new carb to oil pan including all boltons, at a 5000hr interval. There insurance company requires them to flow FAA power plant rebuild or replace interval. Its cheape(and easier) to buy a turn-key FAA approved than to rebuild.
Gumby Stay Flexible

That's interesting—a V8 powered jet boat that follows aircraft regulation?