Automatic Transmissions vs Manual :-)
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This is a discussion on Automatic Transmissions vs Manual :-) within the Transmission & AWD forums, part of the Tech & Modifying & General Repairs category; So my friend and I have been having a friendly debate about which type of major transmission is stronger. It ...

  1. #1
    Wrinklechops

    Automatic Transmissions vs Manual :-)

    So my friend and I have been having a friendly debate about which type of major transmission is stronger. It has sparked my interest and made me want to learn which is stronger/more reliable/can handle abuse. Considering all the applications of both major types of transmissions and talking to a few mechanic friends of mine, the general consensus is that manual transmissions are stronger as a general rule of thumb.

    Now, I have heard that the Subaru 4EAT transmission can handle more power than say, my 05 WRX manual transmission, but neither can handle what the 6spd in the STi can. Then again, I have also heard that the weaker 5spd transmissions were in the earlier 02 WRXs and that by 05 for example, the transmissions were a little stronger.

    I'd like to see what everyone has to say about this. I understand that with our AWD cars, the transmission can take a brutal beating if you are always launching your car. We don't have the wheel spin that a FWD or RWD car has for example. That translates into the transmission/clutch taking the brunt of the force, right?

    Now, many built drag cars have automatic transmissions (3spd or something) but I interpret this as more of a driver/reaction/speed shifting thing than a measure of strength. Touring cars, Indy cars, NASCAR, etc all use manual transmissions. I assume this is for much better control over acceleration and all the other advantages a manual transmission could have.

    It has been brought up that some heavy duty automatic transmissions applications include firetrucks, dump trucks, tractors, buses, etc. But is has also been brought up that semi trucks use a manual gearbox. I assume a firetruck or other heavy duty application of an automatic transmission is more for the convenience than it is for the strength.

    I understand both types of transmissions have come a long way and can both be very strong, but as a general rule of thumb it seems that automatic transmissions are more prone to failure from overheating (hence the semi truck application of a manual for example) and are much more costly to repair and time consuming.

    I'm not sure what types of automatic transmission equivalents to this would be but I understand one very, very strong type of manual transmission is the dog-engagement box. Without boring everyone who doesn't know about this with a detailed explanation, I will provide a video from PPG themselves to talk about it:




    And so I will open it up for discussion. I am curious what everyone here has to say. And I am sorry if this has already been discussed at length on this forum, but I couldn't find it if it had.

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  3. #2
    Wrinklechops
    Advantages

    * Manual transmissions typically offer better fuel economy than automatics. Increased fuel economy with a properly operated manual transmission vehicle versus an equivalent automatic transmission vehicle can range from 5 % to about 15 % depending on driving conditions and style of driving -- extra urban or urban (highway or city). There are several reasons for this:

    o Mechanical efficiency. The manual transmission couples the engine to the transmission with a rigid clutch instead of a torque converter that introduces significant power losses. The automatic transmission also suffers parasitic losses by driving the high pressure hydraulic pumps required for its operation.

    o Driver control. Certain fuel-saving modes of operation simply do not occur in an automatic transmission vehicle, but are accessible to the manual transmission driver. For example, the manual-transmission vehicle can be accelerated gently, yet with a fully open throttle (accelerator pedal to the floor), by means of shifting early to a higher gear, keeping the engine RPM in a low power band. By contrast, in an automatic transmission, the throttle position serves as the indicator of how fast the driver wishes to accelerate. If the accelerator pedal is floored, the transmission will shift to a lower gear, resulting in high engine RPM and aggressive acceleration. The thermodynamically efficient combination of open throttle and low RPMs is unavailable to the automatic transmission driver. Fuel-efficient acceleration is important to achieving fuel economy in stop-and-go city driving.

    o Fuel cut-off. The torque converter of the automatic transmission is designed for transmitting power from the engine to the wheels. Its ability to transmit power in the reverse direction is limited. During deceleration, if the torque converter's rotation drops beneath its stall speed, the momentum of the car can no longer turn the engine, requiring the engine to be idled. By contrast, a manual transmission, with the clutch engaged, can use the car's momentum to keep the engine turning, in principle, all the way down to zero RPM. This means that there are better opportunities, in a manual car, for the electronic control unit (ECU) to impose deceleration fuel cut-off (DFCO), a fuel-saving mode whereby the fuel injectors are turned off if the throttle is closed (foot off the accelerator pedal) and the engine is being driven by the momentum of the vehicle. Automatics further reduce opportunities for DFCO by shifting to a higher gear when the accelerator pedal is released, causing the RPM to drop.

    * Manual transmissions are still more efficient than belt-driven continuously-variable transmissions.
    * It is generally easier to build a very strong manual transmission than a very strong automatic transmission. Manual transmissions usually have only one clutch, whereas automatics have many clutch packs
    * Manual transmissions are generally significantly lighter than torque-converter automatics.
    * Manual transmissions are typically cheaper to build than automatic transmissions.
    * Manual transmissions generally require less maintenance than automatic transmissions
    * Manual transmissions normally do not require active cooling, because not much power is dissipated as heat through the transmission.

    o The heat issue can be important in certain situations, like climbing long hills in hot weather, particularly if pulling a load. Unless the automatic's torque converter is locked up (which typically only happens in an overdrive gear that would not be engaged when going up a hill) the transmission can overheat. A manual transmission's clutch only generates heat when it slips, which does not happen unless the driver is riding the clutch pedal.

    * A driver has more direct control over the state of the transmission with a manual than an automatic. This control is important to an experienced, knowledgeable driver who knows the correct procedure for executing a driving manoeuver, and wants the machine to realise his or her intentions exactly and instantly. Manual transmissions are particularly advantageous for performance driving or driving on steep and winding roads. Note that this advantage applies equally to manual-automatic transmissions, such as tiptronic.

    o An example: the driver, anticipating a turn, can downshift to the appropriate gear while the steering is still straight, and stay in gear through the turn. This is the correct, safe way to execute a turn. An unanticipated change of gear during a sharp turn can cause skidding if the road is slippery.

    o Another example: when starting, the driver can control how much torque goes to the tires, which is useful for starting on slippery surfaces such as ice, snow or mud. This can be done with clutch finesse, or possibly by starting in second gear instead of first. The driver of an automatic can only put the car into drive, and play with the throttle. The torque converter can easily dump too much torque into the wheels, because when it slips, it acts as an extra low gear, passing through the engine power, reducing the rotations while multiplying torque. An automatic equipped with ESC, however, does not have this disadvantage.

    o Yet another example: passing. When the driver is attempting to pass a slower moving vehicle by making use of a lane with opposite traffic, he or she can select a lower gear for more power at exactly the right moment when conditions are right to begin the manoeuver. Automatics have a delayed reaction time, because the driver can only indicate his intent by pressing the throttle. The skilled manual transmission driver has an advantage of superior finesse and confidence in such situations.

    * Driving a manual requires more involvement from the driver, thereby discouraging some dangerous practices. The manual selection of gears requires the driver to monitor the road and traffic situation, anticipate events and plan a few steps ahead. If the driver's mind wanders from the driving task, the machine will soon end up in an incorrect gear, which will be obvious from excessive or insufficient engine RPM. Related points:

    o It's much more difficult for the driver to fidget in a manual transmission car, for instance by eating, drinking beverages, or talking on a cellular phone without a headset. During gear shifts, two hands are required. One stays on the wheel, and the other operates the gear lever. The hand on the wheel is absolutely required during turns, and tight turns are accompanied by gear changes. If the hand leaves the wheel, the steering will begin to straighten. In general, the more demanding the driving situation, the more difficult it is for the manual driver to do anything but operate the vehicle. The driver of an automatic transmission can engage in distracting activities in any situation, such as sharp turns through intersections or stop-and-go traffic.

    o The driver of a manual transmission car can develop an accurate intuition for how fast the car is traveling, from the sound of the motor and the gear selection. It's easier to observe the lower speed limits like 30 km/h and 50 km/h without glancing at the instrumentation.

    * Cars with manual transmissions can often be started when the battery is dead by pushing the car into motion (or allowing it to roll down a hill) and then engaging the clutch in third or second gear. This is called a push start or commonly, "popping the clutch."

    * Manual transmissions work regardless of the orientation angle of the car with respect to gravity. Automatic transmissions have a fluid reservoir (pan) at the bottom; if the car is tilted too much, the fluid pump can be starved, causing a failure in the hydraulics. This could matter in some extreme off roading circumstances.

    * It is sometimes possible to move a vehicle with a manual transmission just by putting it in gear and cranking the starter. This is useful in an emergency situation where the vehicle will not start, but must be immediately moved (from an intersection or railroad crossing, for example).
    Last edited by Wrinklechops; 07-25-2009 at 04:58 PM.

  4. #3
    Registered User wunderboy987's Avatar
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    hahaha manual all the way of course
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  5. #4
    Wrinklechops
    Quote Originally Posted by wunderboy987 View Post
    hahaha manual all the way of course
    Personal preference or do you have any facts to add to this thread? Not trying to be a jerk just trying to get some discussion over this going

  6. #5
    Registered User wunderboy987's Avatar
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    Quote Originally Posted by Wrinklechops View Post
    Personal preference or do you have any facts to add to this thread? Not trying to be a jerk just trying to get some discussion over this going
    you pretty much said it all im sure. didnt read it all. better gas milage, more control. the list goes on
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  7. #6
    Wrinklechops
    Quote Originally Posted by wunderboy987 View Post
    you pretty much said it all im sure. didnt read it all. better gas milage, more control. the list goes on
    Si.

    And what about strength? That's what the debate started as... trying to see which type of transmission would be better suited to handle high power and abuse. Even if it's just factory i.e. my 5spd vs the 4EAT from Subaru, etc...

  8. #7
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    The transmissions you see in drag cars are automatic for a few reasons. Miss a shift on a 1000 hp car and your tranny might literally explode...or just turn into mush. The time it takes shifting also becomes a much more relevant factor when your shooting into the single digits in the 1320. You can build up, or buy a 3 speed transmission to take more power than the STI tranny ever could. ex For $1000 I could buy a 3 speed from summit racing that was stronger than an STI tranny.

    However the reason you see manuals in non-straight line racing is, like you said, to optimize your use of the powerband. A 3 speed auto would likely get significantly stomped by a 6 speed manual on an autocross course (all other things being equal).

    On our cars (WRX) the stock newer 5 speed, IMHO, will handle the power much better than the stock 4EAT. It may not like you on launches but neither does an auto.

    It is tough to say however, because the ratio of guys with 5mt's that mod their cars, to auto guys, is quite lopsided as production #'s were already lopsided. I would be interested to see how well a 300whp or even a 250whp 4EAT would last under non-ridiculously abusive driving.

    I currently have no dyno proof of the power I'm putting out, I'd humbly guess around 230 to the wheels, and my 4EAT seems to be ok so far. I realize in the future it WILL let go, and I'm planning on swapping in a manual when that happens.

  9. #8
    Wrinklechops
    Quote Originally Posted by xsnapshot View Post
    The transmissions you see in drag cars are automatic for a few reasons. Miss a shift on a 1000 hp car and your tranny might literally explode...or just turn into mush. The time it takes shifting also becomes a much more relevant factor when your shooting into the single digits in the 1320. You can build up, or buy a 3 speed transmission to take more power than the STI tranny ever could. ex For $1000 I could buy a 3 speed from summit racing that was stronger than an STI tranny.

    However the reason you see manuals in non-straight line racing is, like you said, to optimize your use of the powerband. A 3 speed auto would likely get significantly stomped by a 6 speed manual on an autocross course (all other things being equal).

    On our cars (WRX) the stock newer 5 speed, IMHO, will handle the power much better than the stock 4EAT. It may not like you on launches but neither does an auto.

    It is tough to say however, because the ratio of guys with 5mt's that mod their cars, to auto guys, is quite lopsided as production #'s were already lopsided. I would be interested to see how well a 300whp or even a 250whp 4EAT would last under non-ridiculously abusive driving.

    I currently have no dyno proof of the power I'm putting out, I'd humbly guess around 230 to the wheels, and my 4EAT seems to be ok so far. I realize in the future it WILL let go, and I'm planning on swapping in a manual when that happens.

    Thank you for your reply That's interesting about you being uncertain as to how much power your 4EAT can take. My friend was telling me they are good for 400whp? Hmm I don't know. But it's always a good idea to upgrade anyways if you plan on power output levels like that.

    Granted, I understand all stock transmissions will eventually fail if you keep on upgrading your power output with no attention to your transmission whatsoever. I'm sure it's the most neglected and overlooked component for people who like to mod their cars. People probably figure "hey, if it works why upgrade it?" but they soon find out that wear and tear and hard launches will take a toll on their transmission. And that brings us to the discussion of how much power/abuse they can take. Like I mentioned, my friend said that the 4EAT is stronger than my (2005 WRX) 5spd manual transmission. Again, I'm not sure about that and certainly won't be "upgrading" to a 4EAT if/when my 5spd fails. If I had the money, I would obviously look into some PPG gear-sets or a PPG dogbox. Otherwise, maybe some Legacy GT 5spd transmission parts?

    I understand that drag cars have to be automatic almost. Insane power outputs and racing in a straight line. Driver reaction time must be on point or else like you said, your tranny is toast. In any other type of racing application though, it seems very advantageous to have a manual transmission. And I'm quite certain those are built manual transmissions.

    That being said, 2 equally powered cars with a manual transmission and automatic, it seems the manual would be better

  10. #9
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    Quote Originally Posted by Wrinklechops View Post
    Thank you for your reply That's interesting about you being uncertain as to how much power your 4EAT can take. My friend was telling me they are good for 400whp? Hmm I don't know. But it's always a good idea to upgrade anyways if you plan on power output levels like that.

    Granted, I understand all stock transmissions will eventually fail if you keep on upgrading your power output with no attention to your transmission whatsoever. I'm sure it's the most neglected and overlooked component for people who like to mod their cars. People probably figure "hey, if it works why upgrade it?" but they soon find out that wear and tear and hard launches will take a toll on their transmission. And that brings us to the discussion of how much power/abuse they can take. Like I mentioned, my friend said that the 4EAT is stronger than my (2005 WRX) 5spd manual transmission. Again, I'm not sure about that and certainly won't be "upgrading" to a 4EAT if/when my 5spd fails. If I had the money, I would obviously look into some PPG gear-sets or a PPG dogbox. Otherwise, maybe some Legacy GT 5spd transmission parts?

    I understand that drag cars have to be automatic almost. Insane power outputs and racing in a straight line. Driver reaction time must be on point or else like you said, your tranny is toast. In any other type of racing application though, it seems very advantageous to have a manual transmission. And I'm quite certain those are built manual transmissions.

    That being said, 2 equally powered cars with a manual transmission and automatic, it seems the manual would be better
    True indeed! However, the longwithstanding quote on how much power the 4EAT can handle, is a bit misleading.
    A 4EAT can handle 400whp IF:
    Its relatively new (plenty of clutch pack life left)
    The owner religiously changes fluid to a good synthetic.
    The owner installs a transmission cooler
    You purchase a modified Valvebody
    Ideally a better stall converter as well.

    The valvebody will firm up the shifts, and the torque converter will allow for better launches, and will generally be a bit stronger than the stock unit.

    The gears BY THEMSELVES in the automatic are very strong. That's where you hear the strength reports coming from. Guys aren't breaking the actual gears until they are deep into 400whp territory.

    So with 1000 in mods you can have yourself a very strong 4EAT indeed. In that respect i could see it outshining the 5speed.

  11. #10
    Wrinklechops
    Quote Originally Posted by xsnapshot View Post
    True indeed! However, the longwithstanding quote on how much power the 4EAT can handle, is a bit misleading.
    A 4EAT can handle 400whp IF:
    Its relatively new (plenty of clutch pack life left)
    The owner religiously changes fluid to a good synthetic.
    The owner installs a transmission cooler
    You purchase a modified Valvebody
    Ideally a better stall converter as well.

    The valvebody will firm up the shifts, and the torque converter will allow for better launches, and will generally be a bit stronger than the stock unit.

    The gears BY THEMSELVES in the automatic are very strong. That's where you hear the strength reports coming from. Guys aren't breaking the actual gears until they are deep into 400whp territory.

    So with 1000 in mods you can have yourself a very strong 4EAT indeed. In that respect i could see it outshining the 5speed.
    Ah ha, I see the light now!

    Then again, if I had $4000 to throw at my transmission, I could get some insanely bulletproof internals from PPG

    RalliSpec - Gearbox Parts

    Alas, that is obviously not very realistic.


    One thing I thought I might add (if I didn't mention it already) is something I read about the STi's 6spd in all it's glory and superiority....

    >>OILED AND PUMPED

    The 6-speed transmission is lubricated by a trochoidal oil pump mounted at the rear of the unit. The pump has a 4-lobe inner rotor and 5-lobe outer rotor. Gear-driven by the center differential, the rotors force oil to the transmissionís main shaft, pinion shaft and transfer gears at a rate that depends on the center differentialís speed. A regulator and pressure-relief valve maintain oil pressure.

    A pressurized system ensures a constant oil supply to the gearing while minimizing the amount of oil required within the transmission case. The oil level lies underneath most of the gearing, which reduces both friction and oil foaming. Reduced friction improves efficiency and performance, and keeping the oil from foaming helps to maintain oil quality and effectiveness.

    While lubricating the transmission, the oil system also helps to cool it by carrying away heat from the gearing, which enhances durability and reliability.

  12. #11
    Master Baiter EJ257's Avatar
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    Quote Originally Posted by Wrinklechops
    Then again, if I had $4000 to throw at my transmission, I could get some insanely bulletproof internals from PPG
    You're in luck - Andrewtech is running a GB for ~$3K on Nasioc
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    Registered User PurpleMongoose's Avatar
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    You want strength? Manuals are used in all your over-the-road haulers.

    You want control? Show me a racing series that uses automatics...

    Add into the mix that manuals are less complex, therefore less expensive with fewer parts to break, and infinitely more fun, and I think we have a winner.
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    Quote Originally Posted by PurpleMongoose View Post
    You want strength? Manuals are used in all your over-the-road haulers.

    You want control? Show me a racing series that uses automatics...

    Add into the mix that manuals are less complex, therefore less expensive with fewer parts to break, and infinitely more fun, and I think we have a winner.
    This is not so much a strength issue. Its a powerband and fuel economy issue. On a big turbo diesel you want those RPM's in just the right spot. Making a 9-18speed automatic is not feasible. However making an automatic that CAN handle that amount of power is possible, just not a good option for semi's and such.

    I also must take back what i said about our 4EAT's handling 400whp. I guess i just read 400 and thought crank horsepower. Or roughly 300whp with our massive drivetrain loss. Building a 4EAT to reliably take 400whp will require much more than a valvebody and a torque converter.

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    I ordered the same borla exhaust too, and love the way it sounds it also looks very nice. I have people asking me all the time what kind of exhaust it is because it sounds so good. I got mine from borla parts here, borla 11760 and was pleased with the price a delivery time. You should also check craigslist sometimes you can find a used set.

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    Registered User 03subiedude's Avatar
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    my subaru is the first manual ive owned and its o.v. i will only own manuals from here on out... would u like me to list the reasons just scroll down and read,,,,,
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