Talk me into buying a automatic XJ (not a flame fest!)

[TheAlmightySam]

Wheeled a 5-speed (not an XJ, but a 5-speed nonetheless) for a couple years, and then found my way into my AW4-equipped XJ. Wouldn't go back.

No clutch to burn up, no clutch pedal to have to press, and I can keep both hands on the wheel at all times. Love my automatic.

 

[rockwerks]

You guys do realize that you are quoting a drop out from MIT?

your MIT's dyno graph results are faulty:

http://www.converter.com/whatsnew_dynamometer.htm



http://www.encyclopedia.com/doc/1G1-141705055.html]

http://www.tciauto.com/Products/TechInfo/torque_converters_explained.pdf

http://www.truckinweb.com/brandpages/ford/0102tr_drag_racing_traction_tips/

Now let’s jump into transmissions. Automatic transmissions are now the typical choice for most street performance cars, because they offer a smooth application of power compared to a manual transmission. The torque converter is an interesting and often misunderstood piece of equipment. It also is a torque multiplier for the initial movement of the car. At maximum stall, a stock converter will multiply engine torque by a factor of between 1.9 and 2.2:1. This means that just as you nail the throttle at, let’s say, 3,000 rpm with a small-block making 400 lb-ft of torque, the converter will push roughly 800 lb-ft of torque through the transmission input shaft for the first few feet the car moves. This torque multiplication decreases rapidly as the car >> gains speed so that by the 60-foot mark, torque multiplication has virtually disappeared.

http://www.chevyhiperformance.com/techarticles/68560_acceleration_basics_info/

I could not be happier with how this swap turned out. I love not shifting. Around town, it is nice to be able to have a cell phone in one hand and a soda in the other and not spill the chicken nuggets in my lap because I had to shift. Traffic still sucks, but now I don’t have to work out the left leg nearly as much.

Off-road, it’s even better. I usually don’t have to get over 1,000 RPM on the trail. The combination of the low-end torque of the engine and the low stall torque converter makes my rig crawl very well. This is one of the common misconceptions about automatics. With a 3.06:1 first gear, 2.72:1 low range, and 4.10’s in the axles, I have a mechanical crawl ratio of 34.13:1.

The thing that most people don’t think about is the torque converter, which can hydraulically multiply torque by as much as a factor of 2. If you bring this into the equation, this brings the crawl ratio down to a slow 68.25:1. This is great for crawling and climbing, but not low enough for me for two reasons. The engine braking when descending is not great - acceptable, but not as good as my manual. The other problem is cruising on the highway. With the .70:1 overdrive, 4.10’s and 35’s, my engine is only turning 1650 RPM at 60 MPH, which is below the power band. These two issues have me seriously looking at 4.88’s. 4.88’s will allow better crawling off-road and put the Jeep into the power band at highway speeds.

http://www.rockcrawler.com/techreports/aa_autoswap_yj/index.asp

the average torque convertor has a stall of 2100 rpm and rated around 2.2:1 multiplication.

For the crawler it basically doubles your crawl ratio over a manual at idle RPM's and the multiplication decreases as engine RPM's catch up to the speed of the convertor stator.

http://www.bmracing.com/noflash/tech/torque.html

quote from B&M engineer:

What does a Torque Converter Do?
At the most basic level, a torque converter connects the engine to the automatic transmission, much like a clutch connects an engine to a manual transmission. The converter housing bolts onto the motor's flexplate (also known as the flywheel), and the housing spins right along with the motor. On the output side, the torque converter's turbine is attached to the transmission's input shaft. Inside the torque converter is a stator assembly. It redirects fluid flow, resulting in torque multiplication and torque multiplication is what allows a converter to provide better low-speed acceleration. Most torque converters today will multiply torque by a ratio of at least 2 to 1. For example, if your motor is making 250 lbs.-ft. of torque and your converter is multiplying it by a factor of two, then the transmission will see 500 lbs.-ft. of torque. This can improve a car or truck's acceleration capability substantially. NASA defines a torque converter as a device for changing the torque speed or mechanical advantage between an input shaft and an output shaft. The goal for automotive enthusiasts, clearly, is to gain a mechanical advantage. The torque converter also serves another extremely important function in a car or truck. A vehicle's engine must be able to connect and disconnect from the differential, so the car or truck can stop moving (i.e., turning the drive wheels) while the engine is still running and the transmission is in gear. In the case of an automatic transmission, it is the torque converter that performs this connect/disconnect function (again, like a clutch in a manual transmission). By slipping internally, the torque converter allows the car to idle while it's in gear.

 

[heyjpark1]

No, no, no, no, no. LOL. You are still misunderstanding the effects of force multiplication. But it doesn't matter, I'm never going to be able to show you that you are wrong, even after showing you every graph in the world.

Sigh...!!!1

 

[heyjpark1]

You guys do realize that you are quoting a drop out from MIT?

your MIT's dyno graph results are faulty:

http://www.converter.com/whatsnew_dynamometer.htm

quote]

BTW, the MIT students charts had nothing to do with a dynamometer.

 

[rockwerks]

No, no, no, no, no. LOL. You are still misunderstanding the effects of force multiplication. But it doesn't matter, I'm never going to be able to show you that you are wrong, even after showing you every graph in the world.

Sigh...!!!1

not just me you will have to change the view of the entire world, including physics and ASE master mechanics.

 

[Darky]

Torque converters multiply torque the same as slipping a clutch, at least, that's how I understand it to work. The difference is that the converter is designed for that and isn't going to smell like skunk and then burn out like a clutch. A clutch gives a much more direct and therefore efficient connection. I learned to drive and wheel in stickshifts, from my first car a 94 Geo Tracker to a 92 Trooper and then a 90 Samurai. I got pretty good workin the clutch off-road with the Tracker and Trooper (Samurai was a $500 pile and I didn't trust it since it could barely handle pavement) and loved being able to abort a hill climb instantly upon losing traction. Just pop in the clutch and roll back down. My Cherokee is the first auto-equipped vehicle I've ever owned and I love it. The clutch burned out in the Tracker, was way out of alignment in the Samurai and I don't know what happened to the Trooper, but the whole tranny grenaded. The Cherokee I've owned for over 3 years now, and the only thing to require me to go near my tranny was "rebuilding" the neutral safety switch. Which would I pick? DD, I'd actually go for a stick since its more fun, but off-road I think I've been won over to the auto side. Its just so nice to not have to worry about how much clutch slippage to allow or how quickly to let it out when trying to ease up and over something. I know there're those who say, no one has a stick that's properly geared for off-road, but that actually works in the advantage of the auto. Proper gearing isn't quite as important which is nice when you're poor like me and can't afford to spend money on new gears any time soon.

 

[heyjpark1]

I agree that for wheeling, I would much rather have an auto. I disagree that, as Rockwerks thinks, automatic transmissions are more fuel efficient or somehow magically multiply torque or horsepower or whatever else he thinks, despite the rest of the real world.

 

[jfox21]

ok while i believe all the stuff about torque multiplication and whatnot, it still doesnt change the fact that a manual is more efficient. The torque converter is a fluid filled housing. that fluid causes friction. an automatic car will lose more power to the wheels than a manual due to parasitic losses caused by friction.

put simply. . . if you dyno an engine with a manual, the horsepower to the wheels will be 5-10% higher than that exact same engine hooked up to an automatic. end of story

 

[rockwerks]

ok while i believe all the stuff about torque multiplication and whatnot, it still doesnt change the fact that a manual is more efficient. The torque converter is a fluid filled housing. that fluid causes friction. an automatic car will lose more power to the wheels than a manual due to parasitic losses caused by friction.

put simply. . . if you dyno an engine with a manual, the horsepower to the wheels will be 5-10% higher than that exact same engine hooked up to an automatic. end of story

wrong again, read the articles I posted here. autos of 30 years ago where bad, now many strip cars are going to autos because of the quicker off the line than a manual (torque multiplication), more power to the ground.

You know why loaders and backhoes all use autos now (more efficient at low speeds)

the next generation of autos will make manual trans totally obsolete

 

[vetteboy]

not just me you will have to change the view of the entire world, including physics and ASE master mechanics.

No, you're just misunderstanding the situation.

A torque converter will absolutely multiply torque. At the expense of output speed and overall efficiency.

It does not add any additional horsepower to your drivetrain, and there is a very well-defined relationship between horsepower, torque, and RPM. You don't magically get more power because you've got this fluid filled donut between the motor and transmission.

What you do get is an effective torque multiplier resulting from the speed differential between the rotor and stator on the converter. It's as if I were able to leave the line with my t-case in low range and gradually shift it back to high range as the car began moving.

If a torque converter actually added any power to the drivetrain, then all our worldwide energy problems would be solved.

edit: FWIW, the manual transmission became obsolete a long time ago. There just happen to be a few of us out there that prefer to have control over different aspects of the vehicle...plus there's the vast majority of the European population too.

 

[98XJSport]

I don't know if standards have become obsolete, it depends on the auto transmission's capability and setup.

Example: My car is available with a 6 speed standard or an auto. With auto the car runs a 17 second 1/4 mile. With the 6-speed it is capable of low 15's sometimes high 14's. All is the same other than tranny.

Moral of the story- Some autos suck, some don't. Overall the XJ auto has been pretty good to most here, it selects gears well for offroad applications, whereas most "SUV" trannys these days are set up for highway/city driving and rare offroad excursions.

 

[rockwerks]

No, you're just misunderstanding the situation.

A torque converter will absolutely multiply torque. At the expense of output speed and overall efficiency.

It does not add any additional horsepower to your drivetrain, and there is a very well-defined relationship between horsepower, torque, and RPM. You don't magically get more power because you've got this fluid filled donut between the motor and transmission.

What you do get is an effective torque multiplier resulting from the speed differential between the rotor and stator on the converter. It's as if I were able to leave the line with my t-case in low range and gradually shift it back to high range as the car began moving.

If a torque converter actually added any power to the drivetrain, then all our worldwide energy problems would be solved.

edit: FWIW, the manual transmission became obsolete a long time ago. There just happen to be a few of us out there that prefer to have control over different aspects of the vehicle...plus there's the vast majority of the European population too.

Like I said I guess all those articles from the professionals are also wrong.

Besides the MIT paper Id like to see one of you guys post a real article that takes your position

 

[vetteboy]

Like I said I guess all those articles from the professionals are also wrong.

Besides the MIT paper Id like to see one of you guys post a real article that takes your position

Actually, I would say the burden of proof is on you, because not a single link or quote you posted goes against what I said.

I think the bigger issue here is that you don't understand the difference between horsepower and torque.

 

[rockwerks]

exepts from papers above

f your car has an automatic transmission, it has an additional torque multiplier above and beyond the trans and the differential gears. It's called the torque converter because it is a fluid coupling that disengages the engine from the transmission at idle so you can pull to a stop or shift gears without stalling the engine. The torque converter is actually a misnomer -- it should be called the torque multiplier because it doesn't simply provide a one-to-one connection to the transmission like a clutch does with a manual transmission.

A torque converter will multiply engine torque on takeoff. This torque multiplication factor remains in effect until the vehicle speed catches up with engine speed. A purpose-built high-performance torque converter can multiply torque even more, as much as 2-1/2 times. OEM torque converters can vary greatly in the amount of torque multiplication and stall speed. Replacing your stock torque converter with a high-performance torque converter can decrease quarter-mile times by 0.4 to 0.6 seconds with no other changes. Installing a high-performance torque converter should be the first step in any performance upgrade program.

Most torque converters today will multiply torque by a ratio of at least 2 to 1. For example, if your motor is making 250 lbs.-ft. of torque and your converter is multiplying it by a factor of two, then the transmission will see 500 lbs.-ft. of torque. This can improve a car or truck's acceleration capability substantially.

I guess these dont support my conclusion?

 

[vetteboy]

*sigh*

One more time. The difference between horsepower and torque.

I'm not arguing that they don't provide an effective multiplication of torque. They absolutely do. It does not add any additional power to the drivetrain, and in fact results in an overall loss of power due to a drop in efficiency when operating in stall mode. While the butt-o-meter says that an automatic may be faster off the line, this does not equate to "automatics are more efficient". It's faster because the fluid coupling allows the motor to operate at a higher RPM (and thus higher output) during launch.

Like I said before, the only reason for this conversation not making sense is if you don't know what the true definition of power is compared to torque.

 

[98XJSport]

Which have lower (deeper) r+p gears, 5 speed xjs or auto xjs?

 

[vetteboy]

4.0L 5-speeds came with 3.07s, autos with 3.55.

 

[98XJSport]

So that would mean if they were to have the same take off torque, the 5 speed must have a lower first than an auto would...

Don't mind me, simply trying to straighten my own thinking out.

Sounds like all of this is like axle gearing, deeper gears multiply the torque but have no effect on the power the engine is producing - hence why a dyno pull would be taken in the overall gear setup that is closest to 1:1.

 

[rockwerks]

4.0L 5-speeds came with 3.07s, autos with 3.55.

My converted auto MJ with 3:07's still launches and crawls better than the MJ with the 5 speed.......gearing has little effect if any. The 3:54 gears only come into effect at highway speeds to increase fuel economy

 

[rockwerks]

So that would mean if they were to have the same take off torque, the 5 speed must have a lower first than an auto would...

Don't mind me, simply trying to straighten my own thinking out.

Sounds like all of this is like axle gearing, deeper gears multiply the torque but have no effect on the power the engine is producing - hence why a dyno pull would be taken in the overall gear setup that is closest to 1:1.

A Typical dyno does not SEE the torque multiplication and dismisses it

the torque converter does work like a 2:1 gearbox in front of the tranny

and the drivetrain does see the power, but as engine speeds catch up to torque converter speed the torque multiplication diminishes. So at 2100 RPM typically the trans sees 1:1 torque