Design Approaches for Max Efficiency-- Who is Winning?

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Back in 2008, gas spiked to $4.50/gallon and the feds were about to raise EPA CAFE MPG numbers, so all the car makers were setting strategy. Mazda & Toyota said "no turbos", GM & Ford said TDI, etc., hybrids sprinkled around the product line-ups. Which strategy has paid off?

Goal: Measure powertrain efficiency to see what progress is being made, and which approach is best.

Formula: (hp/170) x (MPG/28) x (weight/3274)
...It adjusts for weight & power differences, normalized on the Equinox 1.5T numbers.

Notes: C-Max has a low ground clearance advantage, and the RAV4 Hybrid is disadvantaged by AWD friction.
All others are FWD for comparison purposes. 2018 models except the QX50 is 2019.
All jelly bean shaped CUVs of similar mass & size. Wheel & tire sizes are similar, all 17" to 19", ignoring those diffs, but you can see the QX50's massive 19" wheels actually mean it's powertrain is even better than the number suggests.

C-Max Hybrid (188/170) x (40/28) x (3640/3274) = 1.8 (low ground clearance, port, NA)
QX50 (264/170) x (27/28) x (3810/3274) = 1.7 (VC+Turbo+DI+portI)
RAV4 Hybrid (194/170) x (32/28) x (3924/3274) = 1.6 (AWD, portI, NA)
Mazda CX5 (187/170) x (28/28) x (3527/3274) = 1.2 (Skyactiv NA, cyl deactivate)
CRV (190/170) x (30/28) x (3307/3274) = 1.2 (TDI)
Escape (179/170) x (26/28) x (3576/3274) = 1.1 (TDI)
Equinox (170/170) x (28/28) x (3274/3274) = 1.0 (TDI)
RAV4 (176/170) x (26/28) x (3455/3274) = 1.0 (portI, NA)

I've heard Mazda is adding a supercharger to some '19 Skyactiv engines, which should advance that design approach in efficiency.
Nissan (Infiniti)'s design approach is in Hybrid territory, very good.
If you factor in "driving impressions", people don't like turbo-lag in TDI engines.

Conclusion: Hard to beat hybrids, yet, gotta say, the VC+turbo+DI+portI Nissan approach is awesome, no batteries required to get very high efficiency. GM & Ford need improvement, & Toyota needs to jump on the bandwagon to keep up in powertrain efficiency for their non-hybrid models.
For mostly city driving: Hybrids rule.
For mostly highway or mixed driving: Infiniti's VC Turbo engines are king. If they offer a downsized version in their cheaper car lines, it will reduce power but MPG will be way up there. So far, the '19 Altima VC-Turbo coming out still keeps the high HP 2.0L and still manages 29 MPG combined EPA, so a 1.5L version of it could get 35 MPG combined EPA or so in the future.
 
I rent cars on a weekly basis and drive quite a few miles. Mostly in the North East. These are my results with my driving style, same roads, same times, generally between Teterboro NJ, White Plains, NY, Burlington, VT and Milford PA. YMMV.

2018 Toyota Camry achieves 32 MPG (unrefined, noisy and cheap feeling, a little unevenness under accel, and not up to past standards of NVH)
2018 Mazda 6, 30 on reg, 31 on premium
2018 Accord 1.5L 30 on regular (did not try premium)
2018 Chrysler 300 V6, 27mpg
2017 Ford Fusion hybrid 40mpg, but driving to achieve MPG, otherwise in the mid 30's.
Prius 45mpg, any year
2018 F150 2.7L 23MPG
2018 Altima 27MPG
2018 Corolla 32MPG
2017 Impala 26MPG
2016 Q50 27MPG (turbo)
2018 Subaru Crosstrek 29MPG
2018 Mustang 2.3L EB, 25MPG (don't like the car at all, get the V8)

I guess my conclusion is that Toyota seems to have the best efficiency in conventional cars, and the Prius is hard to beat for all out MPG. The Camry is pretty powerful too. But it's a bit on the "wonky" side in the power delivery department. Nothing, nothing, nothing as the pedal is depressed, followed by good accel. Takes a bit to get used to. Not unlike other cars placed in "ECO" mode.
 
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Accord Hybrid:

(212/170)(47/28)(3519/3274)=2.25?

All of this with a very simple PI NA 2 liter, a couple of motors and a single speed reduction gearbox engaged with an electromagnetic clutch?
Seems too simple to be real.

Have I got something wrong here?

For the record, the Accord is now at 44.5 mpg after ~400 miles from new, about 250 of which were fast highway where fuel economy is not at its best, maybe 42 mpg.
 
The reason I posted my MPG is that EPA numbers do not reflect my use. A quick look on www.fueleconomy.gov also shows that most drivers get fairly close to my numbers.

I'd love to try an Accord hybrid. I'd be shocked if I achieved 44+ MPG in one. As that's what I get in the latest Prius.
 
The formula basically works. Higher MPG, with higher weights, and higher HP, all compared to others, is what counts in energy conversion efficiency & usable power.

The main "job" of a vehicle is to convert chemical energy to kinetic energy as efficiently as possible. .....

It somewhat fails since CdxA (drag) is not considered since I was originally just comparing jelly bean shaped, blunt boxes to each other. The Accord partly does better due to better aero (boat tail), yet it does run the engine closer to optimally, at around 75% torque load @ ~2,000 RPM; the more it does that, the greater the energy conversion efficiency.
Originally Posted by Cujet
The reason I posted my MPG is that EPA numbers do not reflect my use. A quick look on www.fueleconomy.gov also shows that most drivers get fairly close to my numbers. I'd love to try an Accord hybrid. I'd be shocked if I achieved 44+ MPG in one. As that's what I get in the latest Prius.
MPG in real life is all over the place. That's why the EPA numbers are important, since its for a mix of driving to compare car A to car B, apples to apples. It gets the variation of driving cycles out of the comparison. ( For example, real-world driver 'Sam' drives easy, at 50 mph a lot, and he reports 35 MPG in his Equinox, while 'Bill' drives city type cycles, stop-n-go, and he says the Equinox is awfull, getting only 24 MPG. )
 
I'd pick Toyota with the 18 and 19 Camry Hybrid. The 18 LE my parents have drives great, 50mpg in city or highway. Have driven the non hybrid variant, the hybrid is just better. More responsive acceleration, especially in sport mode. Near instant. As mentioned above, the gas only version has a lag that is unfortunate. The SE adds a firmer suspension that I really like, but takes a hit on MPG.

Nice quiet cabin, no weird Prius styling and its just an overall really nice car. In fact, purchased my 18 SE hybrid today, so a bit biased I suppose.
 
Originally Posted by xBa380
I'd pick Toyota with the 18 and 19 Camry Hybrid. The 18 LE my parents have drives great, 50mpg in city or highway. Have driven the non hybrid variant, the hybrid is just better. More responsive acceleration, especially in sport mode. Near instant. As mentioned above, the gas only version has a lag that is unfortunate. The SE adds a firmer suspension that I really like, but takes a hit on MPG.
Nice quiet cabin, no weird Prius styling and its just an overall really nice car. In fact, purchased my 18 {Camry} SE hybrid today, so a bit biased I suppose.
Congrats on the buy! I just read some reviews on the latest version of the Camry Hybrid, and, holy cow, they have improved it. You got the Li-ion battery one, which is more efficient than the NiMH battery one (who's using NiMH batteries anymore?!.. Toy is!) .... Its efficiency is an engineering achievement. I'm not sure it will quite unseat the Honda Accord Hybrid as my favorite, mainly due to its simpler design approach, but the Camry Hyb does beat the Accord Hyb on MPG. They both mostly beat my C-Max, except I kinda like its boxy shape & hatch.

Only problem I see is that the Accord, Camry, & Fusion hybrids are cars, not small boxy CUVs, or even SUVs/PUs, like most people buy these days. (Ask Ford, who is giving up on the sedan market in the U.S., announced lately.)
Those sedans do very well on my crude algorithm since sedan aero drag is less with those nice tapered boat tails and low ground clearance. Proof: The RAV4, also a Toyota, does nowhere near as well as the Camry on efficiency.
 
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It's hard to beat a conventional manual if it offers suitable ratios and is intelligently operated. I would've bought a conventional manual-transmission "economy" car again instead of the Prius, IF one had been available with suitable ratios, and with as good a balance of aerodynamics and cargo space as the Prius offers. None was.
 
The formula does not work. It favors heavy and powerful vehicles. Do you think the Hellcat is the pinnacle of fuel efficient technology?
 
Originally Posted by brages
The formula does not work. It favors heavy and powerful vehicles. Do you think the Hellcat is the pinnacle of fuel efficient technology?


Engine efficiency is energy in vs energy out and the efficiency improves with size. The most efficient engines are also the largest, usually found in those huge cargo ships.

Fuel economy alone is not a measure of efficiency.
 
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True, large engines can be significantly more efficient.

I suppose a passenger bus could be considered amazingly efficient by many measures. Interior volume, passenger room, passenger MPG, etc.

In many ways size can help overall efficiency, above and beyond the efficiency gain due to the large size of the engine.

So, I guess I go back to BSFC and thermal efficiency of comparable class engines. And to overall MPG of a vehicle. Hybrids simply seem to be the more effective choice in many ways.

My Cessna 177RG aircraft gets 17MPG in normal cruise (about 165MPH) and peaks at 25MPG as an absolute maximum (at about 125MPH) . The clunky old Lycoming engine is very efficient, relatively close to a Prius or 2018 Camry in thermal efficiency.
 
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Originally Posted by Cujet
True, large engines can be significantly more efficient.

I suppose a passenger bus could be considered amazingly efficient by many measures. Interior volume, passenger room, passenger MPG, etc.

In many ways size can help overall efficiency, above and beyond the efficiency gain due to the large size of the engine.

So, I guess I go back to BSFC and thermal efficiency of comparable class engines. And to overall MPG of a vehicle. Hybrids simply seem to be the more effective choice in many ways.

My Cessna 177RG aircraft gets 17MPG in normal cruise (about 165MPH) and peaks at 25MPG as an absolute maximum (at about 125MPH) . The clunky old Lycoming engine is very efficient, relatively close to a Prius or 2018 Camry in thermal efficiency.

In a car you can gain a bit of mileage by doing the pulse and glide thing, even leaving the engine idling for the glide. Does this work with a plane using altitude? I guess if you have a variable pitch prop you could glide pretty good at quite a low rpm? Then go WO for max thermal efficiency and climb to keep your speed down, and then burn off the altitude with low power glide?
 
Strategies only work if your company is setup to deliver them.

Toyota already has a hybrid setup that's bullet proof, and can rapidly port over to the entire lineup.
Nissan already has a design in the work for EV, so they keep going forward.
Ford has eco-boost and aluminum frame.
Mazda has no huge investment, so they "tune" an existing design and throw in more expensive parts, instead of high fixed cost R&D (before HCCI is ready).
Honda with turbo.

If you try to force them to copy each other's strategy they will fail, and go out of businesses.
 
Originally Posted by PandaBear

Mazda has no huge investment, so they "tune" an existing design and throw in more expensive parts, instead of high fixed cost R&D (before HCCI is ready).


Seems a pretty unfair characterization of Mazda who have developed a new engine for each generation of vehicle since the 70's with among the least carryover engine series of any automaker, despite many of the older engines remaining in production (there was nothing wrong with them). And honestly, not one of them could be considerded bad. Many of them were ahead of the curve, like the K-series V6, and Skyactivs. If you go a step further and apply 'new engine releases' to a ratio of R&D-to-revenue, I'd bet they have almost anyone beat in that regard.

An example, they could have kept the older F-series engines going (1.8L-2.2L equivalent to Toyota S-series), but instead had to "improve" weight and friction and shrink packaging, so they created the FS/FP engines, for just 1991-2001 years, after which they began using the MZR which they also designed. Conversly, Toyota had been using the S-series engine since January 1980, and "tuned" and fiddled with it until 2002. And it was a headgasket eating sludge monster that needed special attention, right to the bitter end. Facts.

I have a HUGE amount of respect for the Mazda engineers (which seem loyal to the company and vice-versa), and know intimately how underrated their hardware is. Plus also have to give a serious nod to their total lack of reliance (if not outright ineptitude) on PR and marketing- I don't know anyone that does it worse. They don't seem to spend very much on marketing and it certainly shows
 
Originally Posted by Cujet
True, large engines can be significantly more efficient. I suppose a passenger bus could be considered amazingly efficient by many measures. Interior volume, passenger room, passenger MPG, etc.
Trains, buses, all efficient for what they do. ....The formula I originally used is really only good when comparing vehicles of similar sized engines and vehicle weight. LIke buses and even the Hellcat, they can score very high since they produce a lot of peak power while still being able to be efficient at much lower engine loads, where the fuel economy tests are done. Yes the formula is really bad at going outside of a specific general size, aero shape, & vehicle configuration. I use it to find out what small, boxy, jelly-bean shaped CUV in the 3500 lb size class really has the most efficient powertrain.

After all, you wouldn't usually cross-shop a Hellcat with a CRV, right? That formula is for comparison within a class.
 
Originally Posted by oil_film_movies
The formula I originally used is really only good when comparing vehicles of similar sized engines and vehicle weight.


If you are comparing equivalent vehicles, just look at mpg, then.

The formula is intended to normalize for differences in weight and power, but it ends up favoring vehicles within a segment with greater peak power and greater weight.

Suppose you compared two models of the same car, where the only difference is, one has a larger engine. For example, a 2012 Rav4 with V6 compared to the I4. The V6 has 50% more horsepower at a 15% penalty in mpg (these numbers are fairly typical). So the V6 comes out looking much better via "the formula". But that hardly means it's better fuel-saving technology. The technology in this example is basically the same, it's just got more peak power.

Likewise, simply adding weight to a vehicle makes it a better performer according to "the formula" since adding weight - like adding hp - doesn't affect mpg in a 1:1 ratio.
 
Originally Posted by brages
Likewise, simply adding weight to a vehicle makes it a better performer according to "the formula" since adding weight - like adding hp - doesn't affect mpg in a 1:1 ratio.
Let's say 2 vehicles have identical peak hp & MPG too. The heavier of the two gets a better score here because it gets the same MPG as the lighter one, revealing that its got a better powertrain efficiency. Simple as that. The "1:1 ratio" comment doesn't apply to a simple ranking formula.
Again: You score higher if you move MORE weight, at MORE MPG, with MORE power: Energy conversion efficiency.
Take each attribute: weight, hp, and MPG, and score them using this simple algorithm to get a ranking. Thats why you can't think 1:1, or 1.3459873 : 2.304005, or whatever. Its just a ranking.

This isolates whats really going on in the powertrain, since weight and peak power variables are accounted for in the ranking results.

Cost $$$ is another variable you could add in. For example, when originally I decided on a 2018 Equinox 1.5T a year ago, I looked at the Hyundai Tucson (cheapest version), and was surprised how poorly it did in MPG for its weight and power output (formula uses those).
'18 Hyundai Tucson: (164/170)x(3300/3274)x(26/28) = 0.9, using a DI 2.0L, no turbo, but you can get a base model for $20k with a great warranty, so we should weight it in there I guess...

C-Max Hybrid (188/170) x (40/28) x (3640/3274) = 1.8 (low ground clearance, port, NA)
QX50 (264/170) x (27/28) x (3810/3274) = 1.7 (VC+Turbo+DI+portI)
RAV4 Hybrid (194/170) x (32/28) x (3924/3274) = 1.6 (AWD, portI, NA)
Mazda CX5 (187/170) x (28/28) x (3527/3274) = 1.2 (Skyactiv NA, cyl deactivate)
CRV (190/170) x (30/28) x (3307/3274) = 1.2 (TDI)
Escape (179/170) x (26/28) x (3576/3274) = 1.1 (TDI)
Rogue: (170/170)x(3454/3274)x(29/28) = 1.1, (portI, NA, CVT gets the credit)
Equinox (170/170) x (28/28) x (3274/3274) = 1.0 (TDI)
RAV4 (176/170) x (26/28) x (3455/3274) = 1.0 (portI, NA)
Tucson: (175/170)x(3369/3274)x(27/28) = 1.0, (TDI)
Tucson: (164/170)x(3300/3274)x(26/28) = 0.9, using a DI 2.0L, not great but cheaper.

Surprising how Rogue beats other TDI high tech with port injection & a CVT, thats one way to get efficiency. No DI soot either.
 
Well, the Subaru Forester, which has a better AWD system than anything you've listed looks like this:

(177/170)(28/28)(3440/3274)=1.1

The first real-world full tank of the Accord Hybrid looks like this:

(212/170)(46.8/28)(3519/3274)=2.3
 
Subaru Forester's powertrain efficiency is almost tops, and they are doing it without a turbo on a down-sized engine. A 2.5L DI (2019 model is DI) with CVT looks like it beats the downsized-turbo approaches, and the Skyactiv tech too. Only hybrids & VC-turbo exceed it, for more cost, its important to say.

The 2018 Subaru Forester is AWD, and the others above are 2WD (for comparison purposes) so the Subaru powertrain efficiency is even better than the 1.1 score suggests.
So the AWD Forester gets the same MPG as a 2WD Equinox, has slightly more peak power, & the Subie uses a 2.5L NA port injection engine (no turbo lag) to do that? Not bad. I'm giving the Subie's CVT the credit for powertrain efficiency gains here. And, you can get a base 2018 Forester for $22k.

2019 Forester adds DI to the 2.5L, which adds power and MPG. 2019: (182/170)(29/28)(3449/3274)=1.2
 
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