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

[vetteboy]

A true dyno doesn't give two craps about gearing, because gearing has nothing to do with power. The only reason gearing could be a factor is because typically with a higher reduction ratio the amount of power loss through the gear system is increased (efficiency goes down).

The only time a torque converter isn't losing power is when it's in lockup mode.

 

[summitlt]

Not to get off topic, but how does a dyno get accurite results without seeing gearing? If you put two cars side by side, one with 2.73 gears and one with 7.17 gears. the one with 7.17's is obviously going to turn the wheel on the dyno a lot better than the one with 2.73 gears.

How does a dyno accurately see that?

 

[vetteboy]

Because it takes a certain amount of power to keep the dyno drum turning at a certain RPM. The dyno measures the speed it's turning and the amount of torque applied to keep it turning at that speed, and calculates horsepower from those two numbers.

Low gears will let the dyno apply more resistance, but it will happen at a slower RPM. Likewise you won't get as much resistance with higher gears, but it will be turning faster.

Horsepower can be found by:

HP = (M * n)/5252

where M is the torque being applied (in ft-lbs) and n is the speed in RPM. Since gearing is all about proportions - twice the reduction equals half the speed, for example - it all cancels out since the torque and speed are next to each other in the equation.

Horsepower is basically a measure of how fast a prime mover (the engine in your car, in this case) can apply a given amount of torque...or how fast a machine can do a given amount of work.

 

[heyjpark1]

*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.

Give up...I've already tried.

 

[rockwerks]

Give up...I've already tried.

Which you should I have found hundreds of articles to support the gain in torque to the drivetrain and have posted such.

You on the other hand have posted none.............HMMMMMMMMMM I wonder why? You find me 4 from professionals like B&M, JET, others and I will admit IM wrong.

 

[x*BIGASSALEX*j]

not to knock off the Auto's but I have a 5 speed and I love it, it actually makes you a better driver, you will learn how to control the vehicle, not saying none of you can drive but it does show you foot control.

Again 5 speed for mem, as for DD or just a weekend thing, maybe an Auto.......


However Im preety good at drinking coffee, sending emails on the blackberry and shifting, what I say BETTER DRIVER.......

 

[vetteboy]

Which you should I have found hundreds of articles to support the gain in torque to the drivetrain and have posted such.

You on the other hand have posted none.............HMMMMMMMMMM I wonder why? You find me 4 from professionals like B&M, JET, others and I will admit IM wrong.

Like I've posted a bunch of times already, yes, there's an effective increase in torque to the rear wheels due to the slip and stall mode in the converter.

What is wrong here is your assinine claim that this makes them more efficient, and that it adds power to the drivetrain.

One more time: look up the difference between power and torque. It will enlighten you.

 

[rockwerks]

Like I've posted a bunch of times already, yes, there's an effective increase in torque to the rear wheels due to the slip and stall mode in the converter.

What is wrong here is your assinine claim that this makes them more efficient, and that it adds power to the drivetrain.

One more time: look up the difference between power and torque. It will enlighten you.

For the millionth time I have and even talked to an engineer at B&M, he said Im right....so where is your supporting info? cant find any?

 

[vetteboy]

In order for your claim to be correct, that a torque converter adds power, it has to be over 100% efficient.

We'll start with Wikipedia.

A torque converter cannot achieve 100 percent coupling efficiency. The classic three element torque converter has an asymptotical efficiency curve that resembles an inverted U: zero efficiency at stall, generally increasing efficiency during the acceleration phase and poor efficiency in the coupling phase. The loss of efficiency as the converter enters the coupling phase is a result of the turbulence and fluid flow interference generated by the stator, and as previously mentioned, is commonly overcome by mounting the stator on a one-way clutch.
...
Generally speaking, there is a trade-off between maximum torque multiplication and efficiency—high stall ratio converters tend to be relatively inefficient below the coupling speed, whereas low stall ratio converters tend to provide less possible torque multiplication.

While torque multiplication increases the torque delivered to the turbine output shaft, it also increases the slippage within the converter, raising the temperature of the fluid and reducing overall efficiency.

From Kennedy's DynoTune:

Stall refers to the maximum speed a the motor can achieve against the converter when the turbine is locked and prevented from rotating. The rpm achieved (stall speed) will be a function of the engine torque and the converter design. In general, the higher the stall, the less efficient the converter is at high speed. So why would you want a high stall converter? To allow the engine to get into the meat of the power band quicker. A converter optimized for drag racing will have a stall speed much higher than a street converter. Allowing the engine to get into the power band quickly more than compensates for the disadvantage of lower efficiency.

And another custom converter company:

http://www.converter.cc/tech_talk/tech_main.htm

With high stall toque ratio converters, there are important trade-offs. What you take at one end you give up on the other. Typically, a torque converter with a very high stall torque ratio, such as 2.0-2.5, will be much less efficient above its rated stall speed. There is a sacrifice in higher rpm efficiency to achieve high stall torque ratios. That lower efficiency translates into less horsepower transmitted to the tires over an RPM range.

The problem with a high stall torque ratio converter is that it is only high while the car is not moving. Maximum stall torque ratio occurs at wide open throttle with no rotation of the transmission input shaft. As the input shaft starts to rotate with vehicle forward movement, the stall torque ratio will become non-existent much sooner than a converter of the same stall, with a lower stall torque ratio. A converter with a stall torque ratio of 2.2 for example, would display that at the starting line, but it would drop off much sooner than a converter with a lower stall torque ratio.

For example: A competitor's converter with a claimed stall torque ratio of 2.5 (red graph line) would typically have an efficiency of around 90% at high RPMs (5,000 plus). That means 300 flywheel horsepower would translate to 270 horsepower at the transmission input-shaft. A Super Yank Converter with a stall torque ratio of 1.6 (green graph line) has efficiency in the 97% range. That means a 300 horsepower engine would transmit 291 horsepower to the transmission input-shaft: A gain of 21 horsepower! For an LS-1 customer dyno sheet showing 97% efficiency press here.

As you can see, the converter with the lower stall torque ratio will multiply torque for a longer period of time than the converter with a higher stall torque ratio. As most of you know, most racing occurs above 3,000 RPMs. That's why the lower stall torque ratio often wins the race.

*Lower stall torque ratio is gentler on the tires at the initial launch, but it will pull harder for the remaining 1,305 ft. of the 1/4 mile. Less races will be lost at the starting line from excessive wheelspin.
Lower stall torque ratio will be more efficient and transmit more torque and horsepower to the tires.

Dig it yet?

Meanwhile, a clutch is ALWAYS 100% efficient when engaged (unless it is slipping), and a few spur or helical gears will be more efficient than fluid losses throughout an automatic transmission.

So to summarize what I'm getting at here:

1. Torque converters DO offer increased torque during stall mode, at the expense of efficiency.
2. Torque converters DO NOT provide increased power to the drivetrain.
3. Manual transmissions, due to the absence of fluid losses that are inherent to a torque converter, won't provide that torque multiplier, but WILL transmit more POWER consistently through the RPM range, thus being more efficient.

Again, figure out your definitions, then ask your guy if a torque converter gives you increased torque or increased power.

Then again, I guess the fact that I'm a certified ME and work with power transmission and motion control on a daily basis means nothing either.

 

[filmxj]

I have both currently and I think it depends on what your priorities are. If you want to tow and if you are concerned with avaliability of parts, and do a lot of technical, vertical wheeling, I would reccomend the auto (rated at 5000 pounds properly equiped).

I like wheeling with the 5-speed though. Seems a little more purist, especially when you get pretty good at pushing all 3 pedals at the same time. Just letting the thing idle over rocks is cool too - no feet on the pedals at all. The 4.0 has enough tourque that if your gearing is right you can just point the wheel and it will do the rest.

I've never really liked the shift points in the AW-4 but you get used to it. Finding transmission mounts for anything but the auto can be tricky. Auto is more reliable in my experience. The pucker factor is a lot less when stuff gets tricky in the auto. Your control over application of power is a lot more better - no fear of rolling backwards off a 3 foot ledge etc.

Just my 2c.

 

[vetteboy]

Finding transmission mounts for anything but the auto can be tricky. Auto is more reliable in my experience.

Pretty much only true for the '89s and earlier that used the Peugot trans. They became pretty standardized once it switched to the AX15.

Rockwerks, get a chance to talk to your B&M guy yet?

 

[rockwerks]

Pretty much only true for the '89s and earlier that used the Peugot trans. They became pretty standardized once it switched to the AX15.

Rockwerks, get a chance to talk to your B&M guy yet?

yep. this is the last Ill post, we seam to be at an impass here. I know Im right and you know you are right: I guess we will need to leave it at that LOL:

I am a lifelong automatic transmission engineer. The 6 mpg you experience going uphill would be 4 mpg with a manual. The torque multiplication improves gas mileage, not lowers it. Manual transmissions are today a waste of money, time and maintainence. Further, the coefficient of drag in a synchromesh transmission more than out weighs the slight fluid slippage found in todays converters. Then there is the question of longevity. The clutch looses.

 

[vetteboy]

Funny, and here I was thinking all along that the laws of physics governed engineering as well.

You wouldn't happen to have an email address for this poet dude, do you? I think he and I could have an interesting chat.