Coasting?

[naikaidriver]

Originally Posted by wparsons

An automatic has a torque convertor, and will always decouple slightly on deceleration.

That may have been true 10 years ago but not anymore with modern automatics. Many "performance minded" cars that come with automatics come with a locking torque converter (such as the 86) that locks in accordance with vehicle speed. In our case, the TCM locks the converter at speeds in excess of 30mph (Source: 2013 Scion FRS Service Manual).

Toyota has been using this same method extensively in their Lexus line, BMW, Mercedes, Honda, Acura also use similar locking techniques.

Now while locking a torque converter to the output shaft of the impeller gives many of the advantages of a clutch you still have higher rotating resistance due to the presence of transmission fluid, under pressure, within the torque converter.

Perform this experiment with an auto and a manual FRS and you should see that the manual will coast in gear longer than an auto provided your speed is over 30mph. Of course, this experiment is a bit "flawed" all things being equal since there are obvious weight differences between the manual and auto as well as the taller gears of the auto will not send as much rotating drag to the rear wheels from engine compression.

Be careful making broad, blanket statements in front of car nerds.

Oh, and BTW, the presence of a torque converter is not what defines a transmission as an auto or manual.

Scott

[FRiSson]

Originally Posted by SloS13

Some threads on this forum are just retarded as balls.

"Threads are just retarded as balls"

Is this some kind of riff on string theory?

[Mobius357]

I wish my truck would engine brake as well as my car.

[Xdragonxb0i]

Originally Posted by wparsons

An automatic has a torque convertor, and will always decouple slightly on deceleration so they coast further/longer. Most don't lock up except when you're on the gas.

Any computer controlled manual (using a clutch, single or double) is still a manual, even if a computer and hydraulics are doing the work for you and will react like one.



Having more effective engine braking takes even more load off the brakes, so I don't see the issue here?

Something that hasn't been touched on yet is that when under engine braking above idle you're actually burning VERY little (or zero) gas, so it's better for economy to stay on the gas a bit longer then coast in gear letting the engine slow you down than to pop it into neutral and coast for longer.

Im kinda confused, i coast to to slow down and i usually dont even touch the brakes because im letting my cars weight and inertia slow me down to the appropriate speed
Could you elaborate more on engine braking?? its a new term that never heard before

[Gords_zenith]

Originally Posted by Xdragonxb0i

Im kinda confused, i coast to to slow down and i usually dont even touch the brakes because im letting my cars weight and inertia slow me down to the appropriate speed
Could you elaborate more on engine braking?? its a new term that never heard before

Umm not to point this out but I suggest you review the laws of physics. Im a little fuzzy on the actual wording but one of the laws goes something like this "An object in motion, tends to stay in motion" so your statement of using weight and inertia to slow you down is.....what's the word.....dumb? Lol JK but seriously YES engine braking is the biggest factor, as well the rolling resistance of your tires, friction of wheel bearings, brake drag, and don't forget air resistance acting against the car. And I suggest you start by googling "engine braking". Haha good luck

[bcj]

Close throttle. No fuel. Pulling vacuum on the intake stroke (throttle closed right?).
No explody on the power stroke and trying to pull the existing molecules in there farther apart.
Slows down.

Higher compression engines can also pull higher vacuum.

[wparsons]

Originally Posted by naikaidriver

That may have been true 10 years ago but not anymore with modern automatics. Many "performance minded" cars that come with automatics come with a locking torque converter (such as the 86) that locks in accordance with vehicle speed. In our case, the TCM locks the converter at speeds in excess of 30mph (Source: 2013 Scion FRS Service Manual).

I'm 99% for sure the auto FRS I test drove had the usual slight decoupling at even highway speeds. It definitely slipped like a usual auto on a bunch of occasions, but the last auto one I drove was almost 8 months ago. It won't drop right to idle, but it'll drop a noticeable amount of RPM when coasting.

Originally Posted by naikaidriver

Now while locking a torque converter to the output shaft of the impeller gives many of the advantages of a clutch you still have higher rotating resistance due to the presence of transmission fluid, under pressure, within the torque converter.

If it's locked, the fluid is a moot point. You can't get more resistance from rear end to engine than a locked clutch/torque converter. If the torque converter isn't locked then the fluid is buffering the engine resistance to the rear wheels helping it coast further.

Originally Posted by naikaidriver

Perform this experiment with an auto and a manual FRS and you should see that the manual will coast in gear longer than an auto provided your speed is over 30mph. Of course, this experiment is a bit "flawed" all things being equal since there are obvious weight differences between the manual and auto as well as the taller gears of the auto will not send as much rotating drag to the rear wheels from engine compression.

If anything, the taller gears in the auto will make it coast further. If the torque converter is fully locking even when engine braking it would coast the same (assuming equal ratios) as the manual. If you try it in 5th in a manual and 4th in an auto the ratios are pretty close so any significant difference would be from the torque converter.

Originally Posted by naikaidriver

Oh, and BTW, the presence of a torque converter is not what defines a transmission as an auto or manual.

The widely accepted terminology I see lots of places is that an automatic has a torque converter. Anything else (SMG, DSG, PDK, etc) is an automated manual. There's more to it than the torque converter, there's also how the gears work inside the casing, and if it has valvebodies, bands, etc or plain physical gears. The two (torque converter/clutch and gears/bands/etc) go hand in hand though.

Originally Posted by Xdragonxb0i

Im kinda confused, i coast to to slow down and i usually dont even touch the brakes because im letting my cars weight and inertia slow me down to the appropriate speed
Could you elaborate more on engine braking?? its a new term that never heard before

Engine braking is the term used to describe slowing down by "coasting" in gear, using the resistance of the engine wanting to return to idle as a braking force. When you're doing this you'll notice the instant fuel economy will drop to 0L/100km because the engine is kept turning by the driveline and car rolling, not relying purely on burning fuel. If you coast with the clutch in or in neutral you'll see the instant economy is more like 3L/100km depending on your speed. Some cars will totally shut off the injectors under engine braking, some keep some fuel/spark going.

[muffinman]

No one thinks its cause the car has low torque? 6th gear at 70mph in the mt is like 3000rpm. More powerful cars are closer to 2000rpm at that speed in 6th (7th in some porsches). If the car had the power to cruise on most highways at say 2300rpm, without having to downshift to get up every little hill, toyota/subaru would've put a higher 6th gear in.

[Xdragonxb0i]

Okay, I am doing what that is described. I just worded it wrong in my previous post