Let's talk fuel economy on automatic cars...

On my mother's old Golf Mk.3, the "sport" mode was utterly useless anyway. It just shifted up later - but if you floored it in "economy" mode, the auto box did so, too.
 
In layman's terms, it's like a clutch made of fluid (autos don't have clutches). Mechanical part linked to engine pushes fluid, fluid pushes other mechanical part, drive shaft moves. When the drive shaft is being prevented from moving (brakes), the fluid is pushed around by the engine without moving the other bits.

This is why you can't spin an automatic's wheels. It's like trying to move a rock that's underwater without actually touching it with your fingers. Not very effective. So, lots of torque loss. As a result, you need more gas or revs, which uses more fuel. All there is to it. Although, the tech is getting better supposedly. The torque converter is also where the auto's "creep" comes from. It's a by-product, and I'm sure the engineer who realized this probably thought that it would be a nuisance.

Driving an automatic for fuel mileage is just the same as a manual. Accelerate gradually (not slow, just gradual and smooth), try to use as little neutral throttle as possible once up to speed, get into top gear as quickly as possible. If you have a manually shiftable auto, use that and shift earlier than it normally does in D. Some higher-end autos in the 90s even had all four or five gears available manually.

Shifting into neutral at the light probably doesn't do anything, but it can't hurt. Which one offers lower revs?

Um, not quite true. You can spin the wheels on an automatic. In fact, most drag cars are automatics, and we all know they can do burnouts.

You also forgot the torque multiplication effect of a torque converter, which is one benefit that an automatic has getting off the line as well as in rock crawling.

The strategy for best fuel economy on an overdrive/lockup automatic like the one in the OP's ovloV is to get to your cruising speed quickly, and set your cruising speed high enough that you're in top gear with the torque converter locked. At that point, you are almost as fuel efficient as a manual in top gear; the crankshaft, torque converter, gearset and driveshaft are all locked together and there's no slip in the system.
 
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Um, not quite true. You can spin the wheels on an automatic. In fact, most drag cars are automatics, and we all know they can do burnouts.

You also forgot the torque multiplication effect of a torque converter, which is one benefit that an automatic has getting off the line as well as in rock crawling.

I can't spin the wheels in a Honda auto. I can spin the wheels with a Honda manual, even without revving the nuts off it and dumping the clutch. Therefore, I know there is much torque loss in automatic cars. I'm sure if the car had enough power, like a Koeniggsegg, then it could spin the wheels.

Also, a drag racing car is not a road car.

I don't know anything about torque multiplication. I don't see how an automatic is handy when getting off the line...
 
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I can't spin the wheels in a Honda auto. I can spin the wheels with a Honda manual, even without revving the nuts off it and dumping the clutch. Therefore, I know there is much torque loss in automatic cars. I'm sure if the car had enough power, like a Koeniggsegg, then it could spin the wheels.

That has less to do with the automatic and more to do with the gearing. Automatics often have different axle ratios.

Also, I don't know what non-TCS Honda automatic you can't spin the front wheels with. Even back in the 90s, you could spin up the front wheels on the 4 cylinder Accord EX with an automatic.

Also, here's a 150hp Cougar that weighs the earth. It has an automatic. Hey, look!

[youtube]g4P2W8sxdS0[/youtube]

Also, a drag racing car is not a road car.

Really?

[youtube]bHny3w5FSCg[/youtube]

[youtube]upTxxtM69HA[/youtube]

[youtube]W3WhA7CPK9A[/youtube]



I don't know anything about torque multiplication. I don't see how an automatic is handy when getting off the line...

It's obvious that you don't know anything about it. Kindly educate yourself:
http://en.wikipedia.org/wiki/Torque_converter#Efficiency_and_torque_multiplication

Automatics have many failings, but come on...
 
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While drag racing transmissions from Lenco etc are automatics, they have little to do with any gearbox found in a ordinary automobile.
 
The drag cars I am referring to are using actual production or production-based automatics, like the GM TH400, or the TH700R4 or the Ford AOD. That Cougar I linked is bone stock and has its original Ford AOD transmission, for example.

The vast majority of the weekend-warrior or street/strip drag cars (the kind people drive to the track, race, then drive home followed by driving it to work during the week sometimes) are automatics. The problem with a manual on launch is that unless you want to roast your clutch on the launch, you aren't going to get into your peak powerband right away, whereas you can set your automatic to do so so that it is point and shoot instead of "feather and slip".
 
I've heard that you can race-prep an ordinary automatic by modifying the valves so you can control them manually (can't find a good expression of what I mean). If you run a stock autobox in a drag race, shouldnt it loose some time compared to a manual once up to speed in shifting because of it's inherent sluggishness? Maybe not enough to offset the advantage it gets on launch though...
 
You are correct, though usually one does not modify the valve body - one replaces the valve body with one intended for manual shifting of the gearset, a "manual valvebody." I have one for the 700R4 I put in my Series III, but am undecided if I want to put it in.

Now we're talking about generalities, as a lot depends on driver, car, which gearbox, etc., etc., but assuming all else is equal, the automatic cars tend to be quicker in the quarter mile drag than the manual cars. Most of the benefit is in the launch, as you surmised - the automatic cars, properly set up, just launch and leave, whereas the manual car may just sit there and spin its wheels looking for traction. In addition, if you select the proper torque converter stall speed for your engine (or the factory did it for you), your engine will get into its powerband faster than the manual car's once you both hook up (get traction) and get moving. It will also tend to stay there as the TC will slip to try to bring the revs up to its stall speed.

Automatics are also less likely to shatter driveshafts or halfshafts on launch due to the buffering effect of the torque converter.

Where the stock automatic falls on its face is the shift timing, which the factory will sometimes make a total screwup of for various reasons, and shift speeds as well as the shift programming. This is why "shift kits" are so popular for automatics - the user can tailor the shift points as well as some of the shift programming and shift speeds. Automatics also have higher parasitic loss (as many here have pointed out), but that is outweighed by the advantages listed above - and if you install a shift kit, you can get your otherwise stock automatic to shift gears faster than any human can shift a manual.
 
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Also, I don't know what non-TCS Honda automatic you can't spin the front wheels with. Even back in the 90s, you could spin up the front wheels on the 4 cylinder Accord EX with an automatic.
Truth. I can get at least one wheel spinning on my little Honda (94 Accord EX, 2.2 I4) with little to no effort. And it's an auto.
 
Truth. I can get at least one wheel spinning on my little Honda (94 Accord EX, 2.2 I4) with little to no effort. And it's an auto.

I'm thinking the poster's inability to spin wheels on an automatic Honda is less a factor of the car and more a factor of the poster's, um, "mad skillz."
 
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Adding to what Spectre said about shift kits.

My El Camino had a shift kit, where as my friends Malibu (basically the same car) didn't. His auto box was very slow to shift and would tend to draw out a shift over a period of weeks, where as my El Camino (especially at full throttle) had almost violently fast shifts. 1-2 full throttle shift was my favorite thing in the world. Even the 2-3 (being a 3 speed auto) was quite head snapping.
 
so spectre I have a question.... If automatics with shift kits kick A$$ then why is manual transmissions so much more popular in the racing world?
 
so spectre I have a question.... If automatics with shift kits kick A$$ then why is manual transmissions so much more popular in the racing world?

Because automatics aren't linked to the human brain and have the nagging ability to shift gears at the wrong time.

Autos are the generally preferred transmission for drag racing though, as they can be made to shift quickly and efficiently while accelerating, and they don't miss gears. You really won't see a manual in a competitive drag racer.
 
Because automatics aren't linked to the human brain and have the nagging ability to shift gears at the wrong time.

Autos are the generally preferred transmission for drag racing though, as they can be made to shift quickly and efficiently while accelerating, and they don't miss gears. You really won't see a manual in a competitive drag racer.

Exactly so, which is why I said that automatics have lots of problems, but on launch or while rock crawling is not one of them. Criticize the automatic transmission on the faults it does have, not some imaginary deficiency.
 
Here I was all set to go out and show that an automatic can handle huge burnouts, exhibit the effectiveness of a properly set up automatic in straight line acceleration, the way the shift kit kicks, etc etc etc ... and my water pump up and quits. I thought it was "More money, more problems.", not "No money, more problems!" :lol:
 
I'm thinking the poster's inability to spin wheels on an automatic Honda is less a factor of the car and more a factor of the poster's, um, "mad skillz."

Because flooring the throttle is so hard. :rolleyes:

Jesus, can you blame a guy for going off his experience? I don't read wikipedia all day... does a Civic or an Accord made recently have TC?
 
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Because flooring the throttle is so hard. :rolleyes:

Jesus, can you blame a guy for going off his experience? I don't read wikipedia all day... does a Civic or an Accord made recently have TC?

Yeah, for almost a decade now - optional or later standard. As with most cars these days.
 
Yeah, for almost a decade now - optional or later standard. As with most cars these days.

Weird, cause I've had an Accord past the traction limit and I never noticed it bog down or anything.

That explains that then.
 
is it good or bad to switch to Neutral when waiting at a stoplight?{/quote]
I only shift into Neutral when at the lights in hot weather, i found it helps to keep my transmission fluid cooler, other than that no real need to. Just remember to change back to drive before taking off again :lol:

- if, like me, you have a car with two settings for the gearbox (Economy and Sport) - does it really make a difference in the fuel consumption.
I drive in economy, i found sport/performance mode to hold gears for to long before upshiting for everyday driving.

Assuming that one keeps his driving style, is it better keep the car in the same gear longer or is it better to shift through all the gears when accelerating. I can reach 50mph in 2nd if I'm in Sport mode. In Economy that will be achieved in third.
Engines have a certain spot in the rev rangewhere you'll get the best economy, aim to keep the engine in that band as much as possible.

Also, is it better to accelerate quickly until you achieve your desired cruising speed, or is it better to accelerate slowly and take your time to reach your cruising speed?
I accelerate what is kinda slow for my car, but quick enough to stay with the flow of traffic. Idealy i try to accelerate between 2000 - 2500rpms (optimal economy band).

That's my 2c worth
 
I find coasting in Neutral is bullocks. Apparently most modern engines use no fuel at all under engine breaking (i.e. in gear and connected to the driveline), due to the inertia of the driveline keeping the engine running without any extra fuel (Or something like that, probably explaining it wrong). My instant fuel meter on my 530i agrees with me. Coast in D with engine breaking down a hill and it'll be sitting on 0L/100km (My car also automatically downshifts to keep a constant speed while coasting down a hill). Shift into neutral and it shows about 5-6L/100km, indicating that it's using fuel to keep the engine running.

That said, you do get a bit more roll out of neutral due to the fact that you don't have the friction of your driveline slowing you down, so the car is free to roll without any other forces being applied on it.

Someone else back me up on this, but I've also heard that coasting in Neutral is bad for your torque converter. Apparently it puts stress on it or something and can fry gearboxes.

@MadCat360 I can get my 3sp Automatic god-damn-Nissan-Bluebird to spin the wheels off the line. You're just not trying hard enough :p Don't ever floor an LS1 Commodore in first (4sp auto) without traction control on. It's scary...

I whole heatedly agree with Spectre on the subject of slushboxes spinning wheels. Pretty much any burnout car over here use automatics. Hell, my brother's mate has a Ford Falcon Burnout Wagon with a big block that runs a 3sp auto. That got 1st place in a burnout competition on the weekend. That bastard spins all gears..
 
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