Jeff77789

Okay first of all I would like to say that I already know how to drive manual and i drive it on a regular basis as well. That being said, I also know how to drive an automatic (obviously)

my question is that what gear configuration is technically better?
the manual transmission has the gears on the input shaft, the output shaft and the counter-shaft and uses synchero rings to shift the gears
the automatic transmission uses a planetary gear system, locking different gears in place to get different gear ratios and directions.

So which gear layout is better? The high end supercars use a hydraulically controlled manual transmission connected to paddle shifters but why not an extremely fast shifting automatic transmission?

Bladecutter

Easy answer:

Manual transmission is better.
Less power loss due to torque convertor full of heavy fluid spinning under load all the time.

BC.

PeteInLongBeach

It depends how you use the car and what your priorities are...

Conventional automatics generally can be somewhat less efficient in power transmission and fuel consumption due to losses through the slipping fluid coupling (torque converter). On the RX-8 automatic, this occurs in gears 1-4. However, the torque converter locks up in 5-6, so no loss during cruising. Also, in the RX-8 application, the automatics are geared much higher in the cruising gears than the manual transmission, so the engine turns much slower when cruising. This results in more fuel efficiency (and less engine wear) during cruising conditions. Also, the automatic has no synchro hubs or clutch to wear out and replace.

For my uses, I do a lot of long distance highway driving, and absolute acceleration performance is not a priority for me, so I prefer the quieter and more fuel efficient automatic RX-8. I also like the fact that I will never need to replace clutches and synchros.

For those who prefer sportier driving with better acceleration, then the manual transmission would be better. But, there are trade-offs....

RIWWP

iTrader: (2)

The flip side of no clutch to replace ($300 to $800) in 90,000 miles is 3 transmission fluid flushes, at $150+ each. Fluid changes between the two are radically different. Just $40 drain and fill for MT, full power flushes for AT.

My personal preference for MT includes the delay of AT being unfavorable. Start accelerating in an AT at even low throttle, and then jump on the brakes. There is a moment of continued acceleration. MT starts decel immediately. In a point of need, i belive this difference can make the difference between hitting or not hitting the car in front of you.

PeteInLongBeach

Whereas Mazda makes no recommendation on ATF changes, the industry standard among manufacturers usually appears to be 60,000 - 100,000 miles (if any is given at all). A professional "power flush" is not needed if multiple refills are done to remove most of the fluid (and this is not needed for cars with torque converter drains). 2 or 3 drains/refills should only cost about 8 quarts of fluid and about an hour of time.

Whereas a fluid-coupled AT (as opposed to a solid-coupled CVT) will have a bit more lag in deceleration than a solid-coupled MT, there is no "continued acceleration" once the throttle is released. I think any difference in this regard is negligible.

Jeff77789

well im sure there will be a lag in acceleration due to the fluid coupling.
i studied the torque converter, and somehow i can never get my head around the fact that one turbine can spin the other one

RIWWP

iTrader: (2)

It would be interesting to get a quantified test...

The AT 3 I'm driving this week (rental) does indeed have a perceptible lag on lifting off the throttle before it starts losing speed. I have to believe it makes a measurable difference in braking, starting from the mental recognition that brakes are needed.

Jeff77789

what about an automatic transmission with a clutch instead of a torque converter?

should be an interesting combo if the clutch was manually operated as well

PeteInLongBeach

Of course, that is the downside to conventional / torque-converter automatics, although it is fairly negligible unless you are using the car for competition.

PeteInLongBeach

That sounds like intake modulation to me, not the transmission. Some cars have a dampening of the throttle return on deceleration for emission purposes, others can malfunction that way. I have never noticed a lag in deceleration on any A/T RX-8 I've driven.

RIWWP

iTrader: (2)

I did some more thinking and watching, and I think it may have a large part to do with the lockup vs no-lock. What I previously described occurs more the higher the gear you are in. I also noticed that if you go from a neutral throttle state to an acceleration state, the RPMs would increase about 800rpm before you would get any acceleration. They would remain "artificially high" until you stopped accelerating, at which point they would drop about 800rpm. Presumably this is the shift from locking, to no lock, back to locking.

For lifting off the throttle from an acceleration state, the engine speed is greater than the driveshaft speed (factoring in gear reductions) for a period of time. This certainly means that even though the engine speed is dropping, it is still providing a greater force forward because it is still faster.