EPA - Cars LESS Fuel Efficient Than In The 80s!

The EPA has released its fuel economy numbers for 2005 vehicles (although it appears that the release was delayed until after the energy bill passed, proving that Washington can make a political issue out of simple math). Industry-wide, fuel economy increased 0.2 MPG from last year to 21 MPG. Go team! Oh, but that’s still 1.4 MPG less than the peak reached in 1987, a year in which carburetors were still standard equipment on some vehicles and vehicle styling was still inspired more by rectangular masonry objects than small candy confections. Honda topped the rankings with an average of 25.1 MPG, while Toyota came in a distant second 23.5 MPG. Ford had the worst average of any company in the report at 19.5 MPG.

From autoblog.com

 

I saw that same statistic announced on ABC news. They just left it hanging out there without comment or any kind of in-depth report as to why fuel economy is so abysmal today. At first I was a little shocked but after I thought about my coworker's constant complaints about the horrid gas mileage for her Jeep, I wasn't really that surprised after all.

(She pays $400 a month for gas. I pay $100 a month for gas. We take the same route and drive the same distance (give or take 5 miles) to work. Oh yeah, I drive a 15 year old Camry. I expect my numbers to improve when I get my Prius.)

 

Back in the 70s, I used to own a 2-cylinder Honda microcar (600 Coupe). It had terrible acceleration, but I could get about 50 mpg on the highway. Now I drive a Prius which has much better acceleration, and I typically get highway mileage in the low 50s with the A/C running.

There have been great improvements in automotive technology, unfortunately most US car buyers are more obsessed with power than economy. So who is really to blame, the US car manufacturers who are building the types of cars people want to buy, or the consumers with their "go fast" mentality?

 

There is a real reason that fuel economy is lower now than in the 80's, the carburetor. It cannot meet any CARB or other emissions standards, all cars are now fuel injected. If you look at some of the older cars that had carbs, they were easily getting 30 MPG or more. Emissions standards are so high that fuel management systems and related parts have killed fuel economy. Another factor to consider is you can only get so much out of a drop of gasoline. To get the proper burn for complete combustion, the air to fuel ration must be 17:1, no higher, no lower. If you lean it down, you get beyond the 17:1 ratio, emissions go up. Carbs could easily get it above 17:1, run a lean burn carb and you get very good fuel economy, your emissions suck, but great gas mileage.

 

You're so hopelessly misinformed it's scary. Other than cost and simplicity, carburetion has no advantages over fuel injection. Ignoring all of the efficiency and emissions advantages of FI, there's still the obvious advantage of being able to run much higher compression ratios with FI compared to carburetion.

The reason avg. fuel economy is lower now compared to the 80s is that cars now are heavier and much more powerful. Back in the '80s 0-60 in under 10 seconds was considered adequate. Today only the very slowest cars can't break 10 seconds 0-60.

The only emission standard that is having a significant impact on fuel economy is SULEV, specifically by requiring movement of catalytic converters closer to the exhaust manifold and affecting exhaust flow (recent tech column question in R&T pretty much asked this exact question).

 

The car manufacturers are responding to consumers. They're producing the one thing that the consumer is willing to pay more for: horsepower.

 

Sorry, you're both wrong.

Carburetors have a couple big disadvantages compared to fuel injection.

1. Carbs are much more restrictive than fuel injection setup, which limits horsepower, this requiring a larger engine. A larger, less restrictive carb, will not atomize/mix the air/fuel as well leading to higher emissions at low air flow rates.

2. Carbs have very poor control over the amount of fuel mixed with the air compared to fuel injection systems, which accurately measure air flowing in to the engine, adjust fuel injector duty cycles as appropriate for conditions and then also adjust the ratio further based on feedback from oxygen sensors in the exhaust. Modern FI systems keep track of how it's had to historically adjust FI duty cycle to meet the targeted air/fuel ratios so that it hits the desired air/fuel ratio targets with even more accuracy.

The only reason you can run more compression with FI than with a carb is because a FI system is so much better at controlling the air/fuel mixture as well as being able to produce a very evenly mixed air/fuel mixture. If you're not able to control the air/fuel mixture or if you have pockets of mixture with high or low amounts of fuel, the tendency to detonate/ping goes up a significant amount which will eventually lead to engine damage depending on how bad it is.

The air/fuel ratio that (almost) all cars run at today under normal operating conditions is approximately 14.7/1 (stoich), not 17/1.

The reason that cars run at stoich is because it is the leanest air/fuel ratio that burns cleanly. If you lean the air/fuel ratio out more than that, power will go down slightly, but NOx emissions (the stuff that leads to smog) skyrocket.

Not to mention that running lean can also cause your catalytic converter to overheat reducing it's lifespan.

The Honda Insight was able to run air/fuel mixtures leaner than stoich because it has a special, very expensive catalytic converter which traps NOx emissions and then would burn them off when the car ran rich for a little bit.

Because diesels don't use a throttle body and regulate power output by varying the amount of fuel injected, they also run a wide range of air/fuel mixtures, but this is also why diesels have only recently been cleaned up enough to meet federal emissions standards by being fitted with either a NOx trap (like the Insight) or Urea injection. Commonly, a reduction in compression ratio is also used to help reduce NOx emissions, but of course, this reduces fuel economy a side-effect.

So yes, modern emissions requirements have definitely caused cars to burn more fuel than they would otherwise. I would fully expect that you could get another 10-20% fuel economy out of a car that did not have emissions requirements to worry about with just ECU tuning.

Also, modern catalytic converters flow so well that they do not provide for much of a restriction under most loads, even when they are closely coupled to the exhaust ports to encourage quick warmup. In fact, if you completely removed them, you would not see a significant increase in fuel economy, may a couple percent at the most. You might see an increase in peak power output, but that's it.

Sorry for the long reply, but it's a pet peeve of mine when someone berates someone for misinformation when the information they provide is not much better.

 

I stand by my statement that the reduction in fuel economy compared to the '80s is due to cars being heavier and more powerful. Also, my statement that current emission standards are not significantly impacting fuel economy is partially based on the following correspondence which appeared in a recent issue of R&T.

 

I did not (and still do not) question that portion of your post.

Please read R&T's response again.

They clearly state that the close coupled cat reduces peak power by about 10%. Which I do not disagree with. But they do not say anywhere that the cat also reduces fuel economy by 10% and in fact, only make very vague references to efficiency and instead concentrate on the power aspect along with throttle response.

Which is what I expect from a publisher like R&T, who has historically been an entity enthralled with the love and joy of driving vehicles and not a group which concentrates on improving fuel economy.

So I'll say it again: In order to keep emissions low (in particular, NOx emissions), you must keep air/fuel ratios within a very tight range, meaning 14.7/1 or slightly richer. This has a significant affect on fuel economy, because you could significantly lean out the air/fuel ratio in most light load situations and open the throttle body slightly, make the same power but do it more efficiently - at the expense of NOx emissions.

The Prius (and other cars using the Atkinson cycle) work around this by holding the intake valve open longer and allowing the engine to spit air back out the intake valves, thus reducing the amount of air sucked in to the engine and allowing wider throttle body angles which improves efficiency because the throttle body when nearly closed presents large pumping losses to the engine (it's not easy to suck air past a nearly closed metal plate). The Atkinson cycle has the drawback of significantly reduced peak power output, but this can be somewhat alleviated by using variable valve timing.

Another approach which was popular in the 80s to reduce pumping losses and NOx emissions was EGR (Exhaust Gas Recirculation). By recirculating air in to the cylinders from the exhaust (which will have just about all the oxygen burnt off) you also reduce the amount of fresh air required while still being able to maintain 14.7/1 air fuel ratios, thus allowing wider throttle openings and an reduction in pumping losses.

Recently EGR has seen an upsurge in popularity as automakers look for any way possible to improve fuel economy without affecting peak power output.

 

I understand that but 20% improved fuel economy from reduced pumping losses due to a slightly wider throttle opening seems very optimistic.

 

I said 10-20%, which is what Mitsubishi has proven possible.

From: Lean burn - Wikipedia, the free encyclopedia

 

Per Light-Duty Automotive Technology and Fuel Economy Trends: 1975 Through 2007 - Executive Summary | Cars and Light Trucks | US EPA peak US gas mileage was in 1987.

Minicars? I don't See No Stinking Minicars - Column/Csaba Csere - The Steering Column/C/D Staff/Columns/Features/Car and Driver - Car And Driver
also has some info that many might not be aware of/noticed.

 

Boy,

1973 average fuel economy was 13mpg and but 2007 it was about 20mpg. In 1987 it was 22mpg average. Note that over the same period that average fuel economy was going up the 0 to 60 times were really dropping! 1987 had going for it was less vehicle weight (not many light duty trucks yet) and lower hp.

Modern fuel injection and computer controls ARE GREAT. The draw back has been that the U.S. auto manufactures have been using the technology gains to get more horse power and faster cars (and JUST meeting the CAFE standards) rather than improving fuel economy. The only time fuel economy sells cars is during periods of gas price shock.

 

Funny how only some car manufacturers respond to the other thing consumers are willing to pay more for: fuel economy.

Speaking of fuel economy... My 1986 Mitsubishi Mirage regularly got 40 to 45mpg. Sure, it was a small car, a stick shift, and no A/C, but still... That, and the VW Rabbit were staple vehicles amongst my young adult friends who didn't have a lot of money but needed to get around.

 

I don't remember MPG on my first car (1987), but I do remember it had a 15 gallon tank and gas was 99 cents a gallon. It cost me less than $15 to fill up my car. I usually got a free drive-in car wash with a fill up too.

Ah, those were the days....

 

I think as far as gas prices are concerned we are now paying about the same percent of disposable income per gallon as we did in the early 1960's. The big difference is that the very cheap gas of the 70's and 80's made it possible for people to move out of the cities away from there jobs and into the new suburbs. So, miles REQUIRED to drive by 'our' current life styles does consume large amounts of gasoline.

My dad used to sell gas for 8 gallons for a dollar. Sounds cheap but the 1940's dollar is not the same thing as the 2007 dollar.