V6 v V8 v Diesel

[DocMT]

I am no physics expert...so, i won't contest your formula and reasoning. I wonder how EPA calculates EPA for highway. And in all cases, highway mileage of a V8 vehicle vs. a V6 of the same vehicle, the V6 always win.

Vehicles are driven over identical driving patterns by professional drivers in controlled laboratory conditions on a dynamometer, which is like a treadmill for cars. The conditions that occur during driving, such as wind drag and inertia are accounted for on the dynamometer. There are two types of tests that are conducted: city and highway tests.

The city test is approximately 11 miles long and simulates a stop and go trip with an average speed of about 20 miles per hour (mph). The trip lasts 31 minutes and has 23 stops. About 18 percent of the time is spent idling (as in waiting for traffic lights). A short freeway driving segment is included in the test. The engine is initially started after being parked overnight.

The highway simulates a 10 mile trip with an average speed of 48 mph. The vehicle is started "hot" and there is very little idling and no stops.

Source: Fuel Economy - On-road Vehicles and Engines | Cars and Light Trucks | US - EPA

 

[Quentin]

I think this is the source of your confusion. First of all, you're not packing "extra energy", you are carrying extra weight. Two completely different things. Secondly, as you said, if the vehicle identical, then it has the same frontal area & aerodynamics, so that extra weight is a penalty for fuel efficiency, even if you're talking about 100% highway cruising.

If you took any vehicle over a controlled test loop (and you can design whatever test loop you want) and then repeated the same test in the same vehicle, only with 500 extra pounds of ballast in it, I can 100% guarantee you that your fuel economy will decline when you have that extra 500 pounds on board. It doesn't take a degree in engineering to understand the fundamentals here...

You keep jumping into absolutes. I'm just saying that the penalty isn't as bad on a pure highway driving situation as some people think it is. City, hell yeah, extra weight destroys your mpg. Highway... eh, marginal difference, IMO. Things in motion tend to stay in motion unless acted upon by an outside force.

And yes, a heavier car at the same speed as a lighter one has more energy. Would you rather get hit by a baseball going 50mph or a car? If it is "only carrying extra weight", you should be just fine walking into traffic. Weight doesn't kill you. Speed doesn't kill you. Energy does.

Anyway, I'm done here. There are way more variables in the equation comparing a GX to a 4Runner to even bother arguing why it gets the mpg it gets.

 

[M1911]

Actually, Honda has a wonderful 4-cyl diesel in Europe that gets excellent mileage and does not need this urea stuff. It was destined to come to the US via Acura TSX in 2010...but the plan was deleted because of rising diesel prices over here. There was some rumor that the Honda diesel got canned over here because it would not meet EPA stricter diesel standards.

For me, i just want the damn center diff back in the Trail...screw the V8!

Euro NOX limits are about 1/10 of the US limits. So most Euro diesels won't meet US limits without additional, expensive development.

 

[M1911]

You keep jumping into absolutes. I'm just saying that the penalty isn't as bad on a pure highway driving situation as some people think it is. City, hell yeah, extra weight destroys your mpg. Highway... eh, marginal difference, IMO. Things in motion tend to stay in motion unless acted upon by an outside force.

Sorry, but cars are ALWAYS being acted upon by an outside force. They are ALWAYS being acted upon by aerodynamic drag. They are ALWAYS being acted upon by friction between the tires and the road.

Furthermore, roads are not flat or straight. When you go uphill, that requires added force. Then you waste that potential energy by braking as you go downhill. When you go around a corner, you get more friction due to scrubbing of the tires.

All things being equal, a heavier car or truck always uses more energy than a lighter vehicle. There simply is no doubt about that.

Idealized physics models about the behavior of solid bodies in vacuum have limited applicability to cars and trucks on real roads traveling through air.

 

[DocMT]

You keep jumping into absolutes. I'm just saying that the penalty isn't as bad on a pure highway driving situation as some people think it is. City, hell yeah, extra weight destroys your mpg. Highway... eh, marginal difference, IMO.

Think about that. You can disprove what you're saying here simply by comparing both the city & highway EPA ratings on the same vehicle with a V6 & V8 engines. Take the 4th gen 4Runner for example. The difference in city fuel economy for the V6 vs the V8 is the same as the difference in highway fuel economy for the V6 vs the V8. So much for your theory.

And yes, a heavier car at the same speed as a lighter one has more energy. Would you rather get hit by a baseball going 50mph or a car? If it is "only carrying extra weight", you should be just fine walking into traffic. Weight doesn't kill you. Speed doesn't kill you. Energy does.

Sure, energy in a crash isn't even debatable. A heavier vehicle will carry more energy into a collision. However, we're not talking about a crash. We're talking about overcoming aerodynamic drag...and in that situation carrying extra weight in NEVER beneficial. How can you fail to see that cutting through the air and colliding into a brick wall are apples and oranges?

Anyway, I'm done here. There are way more variables in the equation comparing a GX to a 4Runner to even bother arguing why it gets the mpg it gets.

 

[Quentin]

M - Of course, drag is acting on the vehicle. It acts the same on both vehicles. The only delta is the mass that results in different inertia. The car doesn't instantly stop when you let off the gas, does it?

Doc - Air has mass. Aero boils down to basic mechanical physics. It is a bunch of itty, bitty crashes.

Oh right, I said I was finished arguing.

:banana:

 

[truckmike26]

Walk away? I don't think many people would be interested in racing a 4Runner against a GX. And there was no such conflict when the 4Runner had the same V8 as the Lexus during the 4th gen run.

Besides, not many people cross shop a 4Runner and a GX. Two very different demographics.

Say you owned a car company. And you charged a premium for your premium line of vehicles. To the automotive press, what sort of spin would you put on the fact that your premium model is slower/less efficient than the cheaper model?

The last GX was a Prado and weighed "only" 300 lbs. more (vs. 500 lbs. more with the current model) and had a substantially different overall profile.

 

[DocMT]

Doc - Air has mass. Aero boils down to basic mechanical physics. It is a bunch of itty, bitty crashes.

Oh right, I said I was finished arguing.

:banana:

Yeah, almost as much mass as a brick wall, right? LOL, give it up. You're on the losing end of the debate and there's no digging yourself out of the hole you've made.

So explain to me again why the V6 & V8 4Runners have the same fuel economy difference in their city and highway figures. Amazing how you just ignored the most relevant fact... Your theory is in the toilet right there.

 

[DocMT]

Say you owned a car company. And you charged a premium for your premium line of vehicles. To the automotive press, what sort of spin would you put on the fact that your premium model is slower/less efficient than the cheaper model?

The last GX was a Prado and weighed "only" 300 lbs. more (vs. 500 lbs. more with the current model) and had a substantially different overall profile.

Yeah, okay...but we're talking about SUVs here. Truck-based SUVs. Not many people care about acceleration figures or comparing those figures against other similar vehicles. That's why you rarely see manufacturers touting accleration figures in vehicles like these. Sporty cars? Sure. Truck-based SUVs? Not at all...

 

[DocMT]

From consumer reports. 4runner right, GX left. Sorry, the V8's numbers are way too close to the V6. It's not enough to sway "smart" consumers from the V8. I think you will see it in the 4Runner as an option. Gas prices are also variable and they will come back down. How many people are going to consider the JGC due to the added towing capacity? And for those of us who drive in the mountains, the V8's torque is far superior. My sister's 2011 4R cannot touch her husband's 2005 4R with the V8 going up a steep slope in the mountains. And for towing in the mountains forget about it. The V8 has its place which is why the Jeep still offers it. Even if they make a Platinum model 4R and offer the V8 only in the top of the line model that would give those of us who need the power an option.

Don't hold your breath waiting for the V8 to return in the 5th gen because it probably isn't going to happen. Gas prices are way up and are predicted to go even higher. $5/gal isn't out of the question. And Toyota knows that V8 sales would suffer big time as gas prices continue to rise.

Your Grand Cherokee comparison is fair, but you have to remember that Jeep has been offering a V8 in the Grand Cherokee since about forever. Toyota only offered a V8 in the 4th gen 4Runner, never before it and not after it. So it doesn't surprise me that Jeep still offers a V8 because they've always offered it.

As for your sister's 4Runner.....that's funny. What exactly do you mean when you say it "can't touch" her husband's V8 4Runner? Do they drag race up mountains or something? Surely your sister's V6 4Runner can get up the same mountain as her husband's 4Runner.

 

[Koz]

I said it before and I’ll say it again, if the 5th gen had the 4.6 with the 6 speed it will get BETTER mileage then the V6 with the 5 speed. The problem is, once a buyer hears V8 (with today’s gas prices) they will get worried.

Koz

 

[Thai]

I said it before and I’ll say it again, if the 5th gen had the 4.6 with the 6 speed it will get BETTER mileage then the V6 with the 5 speed. The problem is, once a buyer hears V8 (with today’s gas prices) they will get worried.

Koz

But, Koz, if Toyota put in a 6-speed in the hypothetical V8 model, then wouldn't it also put in the 6-speed in the V6 too?? If so, then wouldn't your advantage disappear?

The other issue is that the GX uses premium gas vs. regular for the 4runner. So, you have to add that cost too.

In addition, even though it is just 2 mpg difference, this difference is still quite significant. If you were to drive 100 miles:

GX (at 17 mpg) uses 5.9 gallons after 100 miles

4runner (at 19 mpg) uses 5.2 gallons

Difference of 0.7 gallons.

Another example: Corolla does 35 mpg on the highway vs. my Prius at 48 mpg:

Corolla 2.8 gallons

Prius 2.08 gallons

Difference is 0.7 gallons.

So, to put it in perspective, the GX's 2 mpg penalty vs. a 4runner is like going from a 35 mpg to a 48 mpg car...it is a big jump in fuel cost! MPGs are deceptive that way...a 2 mpg difference (17 vs. 19) is equivalent to a 13 mpg different (35 vs. 48). This is why a few folks want EPA to change MPGs to GPM (gallons per mile) measuring stick.

 

[Quentin]

Yeah, almost as much mass as a brick wall, right? LOL, give it up. You're on the losing end of the debate and there's no digging yourself out of the hole you've made.

So explain to me again why the V6 & V8 4Runners have the same fuel economy difference in their city and highway figures. Amazing how you just ignored the most relevant fact... Your theory is in the toilet right there.

You honestly expect 200lbs difference to show up in fuel economy ratings of 4300lb and 4500lb vehicles? The V8 limited is 5% heavier than the V6 limited. The difference between the GX and 4Runner is closer to 600lbs (SR5... don't know what the weight is of the Limited and can't be bothered to look it up). That is a 13% heavier.

There is no need to dig because I'm basing my thoughts on the total energy equation and the forces that are acting upon the vehicle. I agree that the heavier vehicle has more rolling resistance, but once you are up to speed, that difference is negligible when compared to drag considering that a normal rolling resistance coefficient is on the order of 0.01. For example, an SR5 4Runner has about 46lbs force of rolling resistance. A GX has around 52lbs. 6lbs difference is pretty small when talking about over 250lbs of drag that the 4Runner sees at 60mph (and 340lbs at 70mph).* When you look at city driving, rolling resistance is a much larger portion of the total drag (due to aero drag being a function of the square of velocity).


* Using 37 sq ft as frontal area, 0.36 as drag coeff, and 18.6psf as dynamic pressure at 60mph, 25.3psf at 70mph

 

[DocMT]

You honestly expect 200lbs difference to show up in fuel economy ratings of 4300lb and 4500lb vehicles? The V8 limited is 5% heavier than the V6 limited. The difference between the GX and 4Runner is closer to 600lbs (SR5... don't know what the weight is of the Limited and can't be bothered to look it up). That is a 13% heavier.

There is no need to dig because I'm basing my thoughts on the total energy equation and the forces that are acting upon the vehicle. I agree that the heavier vehicle has more rolling resistance, but once you are up to speed, that difference is negligible when compared to drag considering that a normal rolling resistance coefficient is on the order of 0.01. For example, an SR5 4Runner has about 46lbs force of rolling resistance. A GX has around 52lbs. 6lbs difference is pretty small when talking about over 250lbs of drag that the 4Runner sees at 60mph (and 340lbs at 70mph).* When you look at city driving, rolling resistance is a much larger portion of the total drag (due to aero drag being a function of the square of velocity).


* Using 37 sq ft as frontal area, 0.36 as drag coeff, and 18.6psf as dynamic pressure at 60mph, 25.3psf at 70mph

I'm done debating this with you. It doesn't matter how many people tell you that you're wrong, you'll just keep going and going and going. So go ahead and believe whatever you want. When you're done, take a look at the EPA fuel economy ratings and then try to convince yourself again. LOL

 

[DocMT]

I said it before and I’ll say it again, if the 5th gen had the 4.6 with the 6 speed it will get BETTER mileage then the V6 with the 5 speed. The problem is, once a buyer hears V8 (with today’s gas prices) they will get worried.

Koz

Even if that is true, you're doing an apples & orange comparison. A 6 speed will always have an advantage over a 5 speed, even when it's behind a V8 engine.

 

[Quentin]

I'm done debating this with you. It doesn't matter how many people tell you that you're wrong, you'll just keep going and going and going. So go ahead and believe whatever you want. When you're done, take a look at the EPA fuel economy ratings and then try to convince yourself again. LOL

Running the aero and rolling resistance drag numbers says my theory is pretty sound. Comparing the EPA numbers of two vehicles that, while similar in weight, have a V6 versus a V8 and the V6 being a part time 4WD while the V8 is full time leaves too many variables to say what has the biggest impact to fuel economy ratings.

 

[DocMT]

Running the aero and rolling resistance drag numbers says my theory is pretty sound. Comparing the EPA numbers of two vehicles that, while similar in weight, have a V6 versus a V8 and the V6 being a part time 4WD while the V8 is full time leaves too many variables to say what has the biggest impact to fuel economy ratings.

You just don't give up, do you? LOL

Want more proof? Look at the figures that Thai posted. Throw out the 4wd numbers since you brought up the full time vs part time discrepancy between the V6 & V8 4Runners. Instead, look at the 2wd numbers. Now notice that the V6 4Runner is rated exactly 1 MPG higher in the city cycle compared to the V8 in the city cycle. But on the highway...drumroll please.... the V6 is rated exactly 2 MPG higher (or, 100% more if you want to look at it in percentages) than the V8 4Runner. So again, your theory just dropped right into the toilet. If anything, this goes 100% against your silly theory.

But if you want to keep thinking you're correct, feel free. It really doesn't matter at this point.

 

[aspade]

The EPA test is crap. Their highway test is done on a treadmill at an average of 48 mph. Even the new "high speed" highway test for 2008 still averages 48 mph - it has more stops.

Real highway driving at 75-80 is drag dominated and all the weak driveline tricks for a good EPA score don't do much of anything.

Which is why when CR put the trucks on a genuine highway the "22 mpg" 4R showed zero improvment over the "20 mpg" GX.

 

[Quentin]

You just don't give up, do you? LOL

Want more proof? Look at the figures that Thai posted. Throw out the 4wd numbers since you brought up the full time vs part time discrepancy between the V6 & V8 4Runners. Instead, look at the 2wd numbers. Now notice that the V6 4Runner is rated exactly 1 MPG higher in the city cycle compared to the V8 in the city cycle. But on the highway...drumroll please.... the V6 is rated exactly 2 MPG higher (or, 100% more if you want to look at it in percentages) than the V8 4Runner. So again, your theory just dropped right into the toilet. If anything, this goes 100% against your silly theory.

But if you want to keep thinking you're correct, feel free. It really doesn't matter at this point.

They have different engines. And that only results in a 5% difference in curb weight. Show me two V6 4Runners with a decent difference in weight that directly relates to a substantial difference in fuel economy while running a relatively steady state pattern. I'm just saying that weight isn't a big deal in those conditions. Show me a part of that overall energy equation that says that weight is a substantial portion of the overall energy loss and I'll gladly concede.

Aspade - I agree. The EPA test is getting pretty useless. So many companies are out there are setting their cars up for the test and not what returns better real world numbers. CR found exactly that cars with similar power, size, weight (OMG!!!) got similar gas mileage versus the EPA test that showed some substantially better than others.

 

[Thai]

The EPA test is crap. Their highway test is done on a treadmill at an average of 48 mph. Even the new "high speed" highway test for 2008 still averages 48 mph - it has more stops.

Real highway driving at 75-80 is drag dominated and all the weak driveline tricks for a good EPA score don't do much of anything.

Which is why when CR put the trucks on a genuine highway the "22 mpg" 4R showed zero improvment over the "20 mpg" GX.

Actually, i disagree. EPA is pretty accurate, esp. their 2008+ numbers...even at TRUE highway speeds. Sure, there are drivers that fall outside the EPA numbers, but that is because these drivers either drive like grandmas or drive like bank robbers. But, for the average driver, the new EPA rating is very accurate.

Why do i take CR numbers with a grain of salt? Easy. They do NOT test all the vehicles on the same day with the same driver. So, you have to take into account many variables, including different driver, different season, different weather, etc.. So, unless CR does a comparison of a 4runner and a GX on THE SAME DAY BY THE SAME DRIVER, their numbers are just only slightly better than two members on this forum arguing about mpgs! In other words, nearly useless for comparison and for this argument.

EPA, on the other hand, offers a scientific way to compare two vehicles without having to account for driver's skill, weather, elevation, etc.. So, unlike CR, EPA rating is perfect for comparison b/w any two vehicles, whether it be a Corolla vs. a Land Cruiser or 4runner V8 vs. 4runner V6 or 4runner V6 vs. GX460, etc..