I can see how this would be true for manual transmissions, but I think that an auto tranny on a gasser may be a different story.

This, just because the automatic holds gears longer before upshifting, hence more engine revolutions to produce the same number of tire revolutions, and worse MPG overall.

Yet another reason to get a manual trans in your gasser put-around cars Then you get superior mpg my short shifting your gasser while giving it a little more throttle. Remember, the whole secret to mpg is to get into your tallest useable gear using as little fuel as possible to get there.

I've got my eye on that new "fart can" Honda Fit-- looks like a PERFECT car for what I'd want in a little gasser!

jmo

 

Lmao It's funny cause that's already my brother(20 years old this year, I am only 17). And he has his little wail tail, cat back exhaust, sound system, few electronics for the engine, and bought a turbo from somebody that's sitting in the shop. Funny thing is that I'v installed everything for him, and will be later down the road as well But I have warned him that in a few years I will meet up with him at an intersection with his little rice burner, and me in my nice Cummins, and obviously I'll have to beat him in a race

Dinner

 

Hohn - I've had my rice-a-roni for almost 4 years now. It's a 1.8L manual transmission. I did a lazy low speed cruise to my parents house one weekend (275 miles one way, and running real slow only cost me 30 minutes). I averaged 44 mpg! I would rather have a Jetta TDI, but overall, including the original purchase price, my total operating cost is less than a manual trans TDI that can get 50+ mpg. But I'd still rather have the TDI ... but oh well.

My "around town" (which is more rural than most) I usually get 37.5 mpg or so. I shoot for 500 miles on a 13.1 gallon tank. I usually squeeze in about 14 gallons though.

I'd like to know more about this "accelerate briskly" with a gasser, pumping losses, yada yada yada. I've heard this before, but can't understand what pumping losses this is referring to. Plus, how do I know just how "brisk" brisk is? I might over brisk-it and loose efficiency. So since the beginning of my driving career, I have always accelerated gently for mileage. And it seems to work. I'm thinking accelerating "briskly" would be more ... difficult to achieve good fuel mileage. Becuase I don't think I'll know the level of "briskness" to achieve.

As for my truck, I run it gently too. But according to the info on here, that's the way to get good mileage with a diesel. And I do get good fuel mileage. I use every trick in the book, like leaving a gap (I think of it as a momentum buffer) approaching RED traffic lights ... in hopes it will go green before I get there or have to slow/stop for it, and I can roll through in 4th or 5th gear, and ease back up into 6th. I can get 20+ mpg "around town" (more rural than most), 21+ cruising a 70 mph on interstate, and 13.25 mpg towing my enclosed trailer loaded (65 mph). So my truck is doing fantabulous IMHO.

Nice thread.

 

When a gasser's throttle plate is closed, intake manifold vacuum is high. It takes work to produce this vacuum. The engine produces this work on the intake stroke of each cylinder, but work requires fuel.

The theory behind brisk acceleration is that the throttle plate is more open and manifold vacuum is reduced during brisk acceleration; therefore, the work the engine does as a vacuum pump is reduced.

Think about the example I cited - how are gassers set up for economical cruising? Super-tall final drive ratios produce wider throttle openings and lower engine RPM at cruising speed. The wider throttle openings reduce manifold vacuum (thus reducing pumping losses - the work the engine must do to pull the vacuum) and the tall gearing reduces engine RPM (thus reducing frictional losses).

Rusty

 

Mine does the best if I drive easy up to the speed limit instead of gettin there quicker.

Eric

 

i've never heard it as Rusty described it, but sounds like he is right

i've just heard,
if you spend 5 minutes getting up to speed - 5 minutes outside efficient op range.

if you get up to speed in 1 minute - that's only 1 minute in inefficient range,

so you cut your time spent in inefficient operating ranges by 75%

and like someone said, the car is designed to cruise efficiently - NOT accelerate efficiently.

in my gasser pickup, i could gain 2mpg around town by using the cruise EVERYTIME i was in moving traffic, anytime i was over 35mph, i used the cruise buttons to go up or down in speed.

that was when i was more rural though (not worried by other drivers)
did that over several tanks - very repeatable, i use an excel spreadsheet to do my mpg.

got 17 around town in 06, and 18.49 on 80mph trip yesterday

 

Basically, whether gas or diesel, an engine will deliver best fuel economy when you maximize it's operation at or near it's peak BSFC, in the drivetrain configuration that has the least parasitic losses, at the speed which minimizes aerodynamic drag.


p.s. Brake Specific Fuel Consumption

 

if I understand correctly.... you accelerate briskly, then back off throttle.
22-24, what percentage highway to city? you've got two CTD listed. auto or 5sp to achieve 22-24mpg?

 

Rusty - Thanks for the explanation. I've tried to imagine what pumping losses it was that was being referred to before. This is what I imagined it was, but your explanation made it a lot more clear for me.

In actuality, I think this applied well to my dad's old '92 gasser Chevy 1/2 ton. That truck had like a 3.2X rear end or something. It would turn very low rpm in OD. I took it on a long trip one time, and empty I got like 23 mpg with it (5.7L 2WD SB). I ran 65 - 70 mph.

But my Corolla is a different animal. I don't think it works the same. I swear, it feels like when I am cruising 65 - 70 mph, that the throttle plate is being purposely held open. That thing coasts like no other car I've driven. And its a 5 speed manual. Let me explain why I think the throttle plate is being held open.

On my way to work, there is a stretch where I'm running 70 mph. I come up to a traffic light that I have to turn left at onto a 55 mph road. Usually the light is green and there is very little traffic. I would have to guess that about 0.3 to 0.4 miles from the traffic light I cancel cruise and let it coast all the way to the traffic light. It usually requires just a wee bit of brakes near the traffic light, because the car coasts so well.

But, when I first cancel the coast, the car barely slows down for about 4 seconds. Then after about 4 seconds I feel something from the engine that adds braking to the engine. It feels like about 5% of what an exhaust brake might do. In my mind, it feels like the computer closes the throttle plate after so many seconds of 0% throttle, and that's the added engine braking I'm feeling. Its still coasts very well though. Do you think the Japs have programmed the throttle plate to stay open to reduce pumping losses and increase fuel economy? I was thinking it may have a tendency to lean out with the plate open, but with computer controlled fuel injection, maybe a lean condition could be compromised?

As for fuel mileage ... when I drive, I'm trying every trick in the book for maximum fuel mileage. I don't consider a) time at in-efficiency, b) throttle plates, or c) short shifting (at least not extreme short shifting). I think about "The Area Under the Curve." Meaning - You take a line chart. The LH vertical axis is 'Fuel Consumption Rate,' and the bottom horizontal axis is, 'Time.'

If you had a computer graph this out, the area under the curve would be fuel consumed. Basically it's my opinion that accelerating more than briskly, results in more area under the curve. I do things while I'm driving to reduce the area under the curve. Sure would be interesting to have a gage that indications a % of throttle plate opening. Hmmm....

 

Well, if I wanted to go to a city it would be about 75 miles...

 

If I wanted to go to a real city, it's about 115 miles (Birmingham). Montgomery is more like a really large church parking lot. (Not that there's anything wrong with church. )

- JyRO

 

JYRO - does your Corolla have variable valve timing?

 

I'd say it does. It's an '04 model. It's got all the engine acronyms, I get them all mixed up. But it seems like its VVTL-i or some such a thing. I'm looking it up.

 

Maybe the Variable Valve Timing w/Intelligence changes the pump-loss characteristics of the engine when the TPS senses you lifting your foot.

 

When I first got my truck (April 06) I researched this topic extensively. I first tried very gentle acceloration for 800 miles inner city driving, then checked the average mpg using the trucks computer. I then repeated the same experiment (800 miles inner city driving) but did the calculations on my own. Next I did 800 miles (inner city driving) with brisk acceloration and then backing off the throttle and checked the trucks computer for mpg. Again I repeated the brisk accel for 800 miles and did the calculations on my own.

While my calculations showed a slight difference in mpg from the computer, either way I showed a consistant gain of about 1.8 mpg by using gentle acceloration. I think it is due to the fact that, at least in my town, There just isn't enough time to take advantage of the cruising mpg when you let off the gas before you have to slow down for the next light. Then it is brisk acceleration all over again.

My truck at the time was a 100% stock 2001 Dodge with a canopy. It was running on standard, nonsynthetic fluids. It was running on 99% biodiesel, however. Biodiesel does lower your mpg a couple of ticks, but if you remove total mpg from the equation, think the difference in mpg would be the same reguardless of fuel. Anyone want to give it a try?