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Manual or Automatic cars accelerate faster?

  1. Jan 12, 2012 #1
    We have a long debate on which transmission can accelerate faster. My idea is manual and I drive a manual, and I could pass other AT car (same capacity) quite easily. But some say automatic because the auto shift is very short.
    How about your idea?
     
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  3. Jan 12, 2012 #2
    http://en.wikipedia.org/wiki/Manual_transmission

    Race cars use manual transmissions, but its usually a special type. Often manual transmissions are faster because automatics are usually standardized 4 speeds, while 5 and 6 speed manual transmissions are commonly available. If you know what you're doing though its possible to shift faster with a 4 speed manual then automatic.
     
  4. Jan 12, 2012 #3

    alt

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    While I used to prefer manual for the fun of it, in reality, I've found autos to change much faster than you could generally change a stock standad manual.
    I just got a new six speed auto. The changes are so fast they're breathtaking, particularly when gas pedal is floored ..
     
  5. Jan 12, 2012 #4
    Manual transmission cars can accelerate faster because the driver can control when their shifts are made. If you want to accelerate faster than an automatic transmission car you just need to keep your shifts in the power band of your engine, which an automatic transmission will not. The fastest shifting cars you can get have sequential gearboxes, where the shift is automatic, but the driver determines when it happens.
     
  6. Jan 12, 2012 #5
    Even if an auto shifts faster and at the optimal engine rpm range they will still be slower because of the torque converter. Torque converters don't lock up until around 1k rpm or so depending on the model wasting a lot of power on launch.
     
  7. Jan 12, 2012 #6

    Ivan Seeking

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    1000 RPM is ~ at idle.
     
  8. Jan 12, 2012 #7
    This is the heart of the point. Automatic transmissions change up at lower revs because they are designed to do so, primarily to protect the engine. With a manual gearbox you have the option to change up much later, allowing you to accelerate much more aggressively. But it is not particularly good for your engine, or for your fuel consumption.
     
  9. Jan 12, 2012 #8

    Pythagorean

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    Downshifting for a boost seems faster and more personalized in a manual. With an automatic you have to slam the gas pedal all the way in to activate the torque converter.

    But... ultimately depends on the technology. I'm sure there are autotransmissions that can putative me.
     
  10. Jan 12, 2012 #9

    Pythagorean

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    Also, auto correct is annoying
     
  11. Jan 12, 2012 #10

    turbo

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    I have a good friend with a Lenco manual transmission in his drag-racing bracket Duster. He is so reliable in elapsed-time numbers that his competitors call him the "automatic transmission".
     
  12. Jan 12, 2012 #11
    Might not be good for my engine or my mpg, but it's great for getting up to highway speed in time to fit into a gap in traffic.
     
  13. Jan 12, 2012 #12
    Seems like what it comes down to is driving ability. In theory, a manual "can" shift quicker (and appropriately timed) than an automatic (less energy loss), but in reality, most modern automatics are likely far better at shifting than you are. There's a reason Formula 1 cars use a semi-automatic trans.

    Now, most non-sports autos will shift early to promote engine life, so you have to take that into consideration as well. In that sense, manuals likely provide a faster car, more fun to drive.
     
  14. Jan 12, 2012 #13

    OmCheeto

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    One of the fastest cars I ever saw at the drag races when I was a kid was a 427 Yenko Camaro with a 2 speed powerglide automatic transmission.

    My brother owned a '68 Camaro with the powerglide transmission, and it was one of the slowest vehicles I think I've ever been in. (210 hp. Would do 60 mph in first gear!)

    It turns out the Yenko's secret was the high stall torque converter.

    https://www.youtube.com/watch?v=9QmtQ_ueIpA

    But then again, transmissionless vehicles are starting to play the game, so it's only a matter of time before we need to rephrase the question.

    https://www.youtube.com/watch?v=wbi1RhgRrxk
     
  15. Jan 12, 2012 #14

    rhody

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    Anhtho and OM (you gearhead, hehe...),

    Sorry, car acceleration (that I can afford) manual or automatic transmissions are so boring I practically fall asleep while on the gas, and equally unimpressive on the brakes. If you want to have some real fun, try one of these, BMW S1000RR. I have one, and have never performed the track test shown here: 0 - 186 mph in 19.1 seconds, and then 150 mph to 0 in about 9 seconds it is truly amazing. (watch from 30:00 on) You can't buy this kind of performance anywhere for less the mid 6 figures. I have pegged first through third gear a few times, then hard on the brakes, you get the same effect, but top speed is about 36 mph less. The 0 - 150 mph acceleration takes about 9.7 seconds, that is quick for any street vehicle especially one that is exposed to the wind and all the elements. The screaming engine noise from 10k - 14k rpm adds to the effect and fun, on my bike it makes 109 db, so you know it is coming, sets off car alarms too, by mistake of course.

    BMW S 1000 RR: 0 - 300 km/h



    Rhody...
     
    Last edited by a moderator: Sep 25, 2014
  16. Jan 12, 2012 #15
    In the day we called it speed shifting with a manual. It takes some practice not to grind the gears, but if done properly it is definitely the fastest shift.

    Omcheeto was right about the old power glides. They could, or at least some of them could be an advantage because there are only two gears. We used to call them slush pumps.

    This guy comes close to speed shifting but no cigar.

     
    Last edited by a moderator: Sep 25, 2014
  17. Jan 12, 2012 #16

    turbo

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    This was a couple of years back and he was running a G-force tranny, at the time, I believe. He's now running a Lenco 4-speed and is scary-consistent. Consistency is the life-or-death measure for bracket racers. Stay within your dial-in time because if you run too fast, you'll break out and lose your heat. Sucks to have to trailer your car home because you ran too fast.

     
    Last edited by a moderator: Sep 25, 2014
  18. Jan 12, 2012 #17
    Hehe, this reminds me of my Honda Magna V65, 6 gears, 10k RPM red line, I can pull off 100kph (60mph) in first gear. In a way this also sucks, cause when I really put the hammer down when I'm riding I never change gears before I'm up to highway speed (but that doesn't usually hold me back :devil:).
     
  19. Jan 14, 2012 #18

    alt

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    That would make sense. My new six speed auto (the first auto I've had in 25 years) has that, plus a fully auto performance mode - which obviously delays the changes to considerably higher revs. And it's just breathtaking - foot to the floor leaves my head pinned to the headrest .. though I suppose I'm more used to slower (normal) driving.
     
  20. Jan 15, 2012 #19

    rcgldr

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    Depends on the technology involved.

    A fluid clutch acts as a torque multiplier, which helps with launches if traction isn't an issue. However the fluid clutch consumes power, so it's a handicap in higher gears. Some fluid automatics use a mechanical clutch for top gear to avoid this loss and get better gas milage.

    The shift times on an automatic can be made very quick. For "classic" automatic transmissions, a "valve body" which is fluid driven mechanical logic, controls the shift time and when shifts occur. For a passenger car, shifts are made smooth by having two gears partially engaged at the same time with a smooth transition. For a drag racing car, there's no need for smooth shifts, so the overlap period is made very small, and the required rpm to launch is set higher.

    A mechanical clutch is a torque limiter, converting power to heat while it slips. On a high powered car, the limiting factor is tire traction, not engine torque so it doesn't matter. Humans can only shift so fast, but road racing cars can use electoncially programmed no lift sequential shifters, like XTRAC, which can do shifts in 50ms to 30 ms, depending on the gear (rpm drop is a factor), with the driver just toggling butons or a shift switch.

    DCT's (dual clutch transmissions) use two sets of mechancal clutches, one for odd gears, the other for even gears. These also use electronic logic to shift gears. Some of these also include launch control for the mechanical clutch, so the driver never needs to use a clutch pedal.

    Formula 1 doesn't allow DCT's, but they get the equivalent effect by having the clutch and gearbox controlled by the same ECU that controls the engine. Gearshifts involve a short period where both gears are engaged at the same time (the taller gear takes the load on an upshift), and the clutch and fuel are controlled for a smooth shift while rpms quickly change to prevent tire slippage and protect the drive train. There were 1 or 2 years where Formula 1 race cars were fully automatic, including launch control (clutches were used in pit stops).

    Top fuel drag cars only have a single forward gear (plus a reverse), and the clutch is mechanically programmed with springs and weights to try an keep the tires at the limits. The crew has to estimate how much traction there is on a run when programming how much initial torque to use and quickly the clutch increases torque during a run (the cars have downforce, so the torque is increased during the first part of a run until the clutch is fully engaged).

    A Corvette Z06 goes 60 mph in 1st gear, with a top speed of 198 mph in 5th (but it would take 3 to 4 miles to reach that speed). 6th gear is a true overdrive. Some exotic cars are geared even taller. The fastest bikes like a Suzuki Haybusa or Kawasaki ZX14 reach just over 80mph in 1st gear. Top speed is 190+ mph, but there's a speed limiter set to 186 mph (300 kph).
     
    Last edited: Jan 15, 2012
  21. Jan 15, 2012 #20

    Moonbear

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    I'm going to jump in and ask if this is a theoretical question or an applied question? In theory, a manual transmission will accelerate faster, assuming you have no regard for doing anything to protect your engine from abuse. In practical terms, the answer depends upon the driver. I regularly pass dingbats with manual transmissions while driving my automatic transmission, because there are a lot of dingbats who don't know how and when to shift...or run out of hands to shift while they're holding a cell phone in one hand, lighting a cigarette in the other, steering with the third, and shifting with the fourth. I can tell when I'm behind someone with a manual transmission, because there are those points when they take their foot off the gas, slow a bit without braking, hit the clutch, shift, then accelerate again when I'd prefer to drive THROUGH them if I could.
     
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