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cs
08-01-2010, 10:34 PM
I've been noticing that there is a direct relationship to torque and gas mileage. I could be wrong, but it does appear that this is the case. Based on the cars I've driven over the last few years is that a car with more torque has more contestant gas mileage, not necessarily better but more contestant.

First example is a car with great torque, the RX-7. On the highway it averaged 22 mpg and in town it was 21 mpg. Pretty even numbers.

The next was the Ford Taurus. It was a fairly torque car with the V6. In town it would average somewhere around 23 mpg and on the interstate it was more like 28 mpg and even sometimes 30 mpg.

The next car is my Mitsubishi Mirage. This car has a small 4 banger and not that much torque. If you do a lot of in town driving you will get around 22-24 mpg. Mix in a little of highway driving and that number jumps to 28-30 mpg. On the highway it will consistently average 38 mpg.

From these results I see that more torque translates to mpg's that are closer together regardless of how you drive. As the torque decrees driving conditions play more into gas mileage. As you can see with my last example with a low torque car mileage can vary as much as 16 mpg depending on how the car is driven.

Chad

ChaseKenyon
08-02-2010, 01:27 AM
Best way to get torque over the broadest RPM range is forced induction.

Turbos rely on the exhaust gases so are functioning best when the rpms and load are a max or close to it. But it is virtually free horsepower and torque. the problem being that it is hard to control and has a small operation range of RPM for it's efficiency. Thats why all the trucking and even the MB cars have extra gears so they can stay in the sweet spot as to the RPM. As long as you are willing to shift a 5x5x4 tranny and keep the engine in it's narrow 2650 to 3275 RPM range you get maximum distence per fuel gallon or pound as used in trucking ind busing world.

I have owned and put four MB diesel cars through well over 2,300,000 miles on diesel and pure veggie oil. Based on that and my regular usage of the 40 ft long 40,000 lbs GVW Prevost "camper" and it 's 8V71 Detroit 2 cycle monster v8 diesel I am way to familiar with the trade offs between torque and HP. Even though non turbo to compensate for altitude my bus is set up for mountain travel with a very rare Allison 5 speed full lockup CRD close ratio tranny. She down shifts faster and harder than the late GM Allison and Ford Diesel towing specials with the exhaust brake option.,


To put it bluntly my 2.2 liter 5 cylinder super turboed ex Ice racer Audi 5000 CS turbo QT Avant factory over size turbo special, with about 250 BHP at max boost, in real world gets about 15 mpg around town and only 24 mpg on the highway.

My Jaguar 4.0- V8 Supercharged VDP averages overall 19.5. Around town it drops to 16.5. on the Highway it gets just under 25 about 24.977 mpg


The Audi weighs about 3300 lbs empty. The jag Weighs about 4000 according to the owners manual. The Jags TORQUE CURVE is virtually flat from 1400 rpm to 6700 rpm at around 450 FT lbs. The best the Audi can get is about 300 from 4200 to 5400 Rpm.

So In the real world of hills and freeways, interstates and fast winding state highways in the mountains which gets the better mileage the EPA rated 25 avg or the Jag at 19 avg? My average with Jag in day to day operation has been about 19.5 mpg. The Audi under the same use can only give me 16.o mpg. with the Daughter living here and her PT CRuiser in the fleet for the wife to take to work at the DOT The jag use is back up to 40 mph average from 29 mph average. That puts the avg mpg back up to 22.7 overall. I designed many robotic "drivers" for EPA test sites. In reality the Jag kicks my Audi's but no matter what the EPA says. 227 Ft lbs TQ (for 1000 rpm) and 3300 lbs,,,, or 415 Ft lbs TQ (from 1400 to 6400, almost 5000 rpm of 90% plus of max torque at full throttle) and 4000 lbs of vehicle..


Road runner/ dodge 6 packs and and such in 1969 could repeatedly take the street Hemis on the drag strip with almost 100 extra ft lbs of torque. especially with a contest automatic to auto trans fight. Now on the street where things usually went significantly past the 1/4 mile at about 135 mph the much greater BHP of the Hemi would show it's winning Royal Flush poker hand. Reality from an ex asst. service manager at a dodge plymouth, Chrysler dealer. On the drag strip the 440 six pack with torqueflite was king. On the other hand the 426 Hemi 4 speed was the king on the street.

The real world vs the gov't world.:arg:arg


And I built a lot of the systems they (epa and the car companies) are still using.

ChaseKenyon
08-02-2010, 01:33 AM
The real world vs the gov't world.:arg:arg


And I built a lot of the systems they are still using.

Another interesting note. The Audi is not listed for towing and has a factory tow rating of 000.00 lbs.

The jag right in the regular owners manual is rated to tow 4200 lbs with trailer brakes, 2000 without.

cs
08-02-2010, 08:08 AM
From what I can tell, based on above, is that the stronger car is more consetant on the gas mileage, maybe not better, just less change from one driving condition to the other.

Chad

John E Hardiman
08-02-2010, 10:54 AM
Here is a way to look at it.
Torque is proportional to stroke and so is displacement.
Hp is torque x rpm.
Fuel consumption is a fixed rate (idle) + a factor proportional to displacement x rpm. The fixed rate is higher for non- fuel injected engines.

Given the same piston diameter, a larger displacement engine has more torque and therfore more HP for the same RPM. This allows the engine to run at a lower rpm accross the power band, thereby having less change in the overall fuel consumption. Our '91 Chrysler Le Baron ragtop has a FI 3.0L V-6 that idles at 700 rpm, yet has enough torque to push the car at 70 mph at 2000 rpm (0.77 final drive on the 5 speed). On the other hand, our '83 AMC Jeep Wagoneer with a 360 2 BBL gets 7 GPH, regardless of speed or mode.

OconeePirate
08-02-2010, 11:12 AM
A lot of the same things that make cars go faster also, if you keep your foot off the loud pedal, will also increase overall fuel economy. Like Carroll Shelby is quoted as saying, "Horsepower sells cars, torque wins races."

On the consistency thing, my '72 Sedan deVille with the four hundred seventy two cubic inch engine, I had to write it out because it was that awesome of a construct, got 13 miles to the gallon. Period. Did not matter what kind of driving I was doing. My TR6 got about 17 mpg in "spirited" driving but could manage close to 25 mpg during calm highway driving. My Comet seems to average around 20 mpg.

Out of those three cars, all 1972 tech (the Comet is a '63 but it has an engine from a '72 Maverick in it), the Cadillac would have to be considered the most efficient. The Cadillac was right at 20 feet long, weighed 2 1/2 tons, would rather comfortably seat 6 people, and carry their luggage.

yzer
08-02-2010, 11:34 AM
Torque is a wonderful thing. I agree with ChaseKenyon that forced induction is the most economical way to have it.

My little 2003 Subaru WRX is my second turbocharged car. This one has a 2.0 liter four-banger engine that will deliver a peak 209 ft/lbs. torque and 230 peak HP. Typical mixed driving is 24-26 MPG. Long distance freeway cruising in overdrive with cruise control is 28 MPG. "Spirited" twisty road driving on a lonely mountain highway might get me 12 MPG. Turbos eat fuel and produce a lot of power but the choice to open that waste gate is up to the driver. No boost and the WRX is just another economical AWD four-banger.

By comparison: the engine in my boat is a 1947 Chrysler Crown Marine M-7. This L-head six is 250 CI with a single barrel updraft carburetor. It is rated at 215 HP and will produce 200 ft/lbs torque at 700 RPM. It weighs 800 lbs and gets about 4.5 GPH.

Bluecometk
08-02-2010, 12:23 PM
yzer, Your 2.0 WRX is actually a watered down 2.0L. It is known as a TLEV emission class engine. It needs to be wound tight to get the torque that it advertises.
Basically an emission compromise in both economy and cleanliness.
The WRX 2.0L in Japan and other countries puts down 280T and 280HP.We got ripped off!!

The 2009 and later 2.5L WRX has 250HP and gets 3mpg overall better mileage.

As a side note the 2002 WRX only put down 227HP because they couldn’t get the 230HP numbers from every engine consistently and still meet the requirements.



Bluecometk

yzer
08-02-2010, 12:38 PM
Yes, the JDM WRX had a lot of advantages but it also cost more than the US model. I'm still pretty happy with the car. You need a little more than 3,000 RPM to get quick response from the turbo. The US 2.0L redlines at 7K but the power band starts to fall off around 5.7K or somewhere near there.

Remember marketing for the 2002-2003 US WRX? 0 to 60 MPH in 5.3 seconds? You can do that with a +5K RPM launch and hitting 60 MPH in second gear. Not the best thing to do on a regular basis.

Captain Blight
08-02-2010, 12:41 PM
Well, it's not just peak torque but how flat the curve is and how soon it comes in. One of the things that make the various 6-cylinder BMWs such a joy to drive is the silky smooveness of a lot of grunt way down low. My '90 325iX would not be considered an agricultural implement by any means, but I was once able to make use of its abundant torque and all-wheel drive to pull a series of lilac stumps (not that it made a difference to them, I have no idea what it takes to kill a lilac). In my experience, I've come to prefer torque coming in right off idle over screaming lightswitch high-end power. And all else being equal, the engine with the flatter torque curve will lead an easier life (you won't feel the need to wind it real tight) and probably give good long service.

yzer
08-02-2010, 12:54 PM
Generally speaking, I'll agree with that preference for low-end torque. However, the pocket rockets can have a decent service life with good maintenance. My previous turbo car was the 1990 Mitsubishi Eclipse GS. That was another 2.0L turbo. The original turbocharger was replaced at 190K miles. I figured it had another 75K miles left on the lower end bearings before I sold it with 270K miles on the odometer.

cs
08-02-2010, 01:15 PM
Here is a way to look at it.
Torque is proportional to stroke and so is displacement.
Hp is torque x rpm.
Fuel consumption is a fixed rate (idle) + a factor proportional to displacement x rpm. The fixed rate is higher for non- fuel injected engines.

Given the same piston diameter, a larger displacement engine has more torque and therfore more HP for the same RPM. This allows the engine to run at a lower rpm accross the power band, thereby having less change in the overall fuel consumption. Our '91 Chrysler Le Baron ragtop has a FI 3.0L V-6 that idles at 700 rpm, yet has enough torque to push the car at 70 mph at 2000 rpm (0.77 final drive on the 5 speed). On the other hand, our '83 AMC Jeep Wagoneer with a 360 2 BBL gets 7 GPH, regardless of speed or mode.


This is what I was talking about and right along with what I was thinking was happening. Higher torque motors have to work less and thus less variance.

Chad