why are manual transmissions so much faster accelerating

[iwantanewcomputer]

it seems like allowing a computer to choose the optimal time to shift and mechanically shifting faster, spending less time in between gears, as i assume an auto would be able to do, shoud give better acceleration

 

[Bassyhead]

It's not just the type of transmission, the differences between auto and manual can be more than the shifting capabilities. Manuals typically have more gears and different gear ratios than autos which will influence performance ratings.

 

[CycloWizard]

Bassyhead hit it right on the money. Imagine that there is some curve that exactly defines maximum acceleration. You can always better approximate that curve with five lines than four lines. Each line is representative of the acceleration in one gear. Since a manual transmission typically has five gears and an automatic has only four, the manual approaches the optimal acceleration curve.

 

[Cattlegod]

i would put my money is that you can get a MUCH better shot off of the line with a manual.

 

[Gibsons]

Don't manuals also weigh less? if so, is it enough to make a difference?

 

[iwantanewcomputer]

i know that manuals have 5 gears, but why not make a racecar that automatically shifts have 5? and i don't think manuals weigh much less compared to the weight of the car

 

[silverpig]

I think a lot of it is there is more control over when you shift with a manual than an auto. The auto in a porsche is probably not tuned purely for racing, but rather incorporates a lot of smoothness + drivability + fuel economy in when it was designed to shift. Think about it, do you shift at the same rpms when you're racing a 0-60 as you do when you're going to get groceries?

 

[The Boston Dangler]

Manual transmissions are at least 10%, sometimes as much as 20%, more efficient at transfering power to the wheels than an automatic. The reason for this is the fundamental difference between the two.

Manuals use a clutch, basically a pad, to engage the motor's flywheel. This is done by surface to surface friction. If you're not careful, you can stall the motor, or you can "smoke" the clutch. Gearshifting is done by physically engaging and disengaging each gear, through solid linkages (mostly US and older foreign, plus some very high perfomance trannies) or cables (almost any recent car). The only exception I know of is the Neon, it uses the same torque converter on both models.

Automatics use a torque converter to grab onto the engine. A chamber is filled with transmission fluid. There's a "fan" on the motor side, attached to the crank. There's another fan on the tranny side. The engine's fan spins up, and the fluid's pressure spins the tranny input. This is the reason an automatic-equipped car will "creep" forward. In the past few years, manufacturers have produced what's called a "lock-up" torque converter. This improves efficiency at constant speed by not allowing any slip between the motor and tranny, but it's good only for cruising. Also, an automatic's gears are shifted differently. Hydraulic pressure engages clutch-packs in the center of each forward gear (reverse is first gear backwards), letting them grab onto a common shaft. Or there could be planetary gears, which are so complicated I'm not even gonna go there. But it's the same principle. Gearshifting is usually done through a hybrid of electronic and mechanical computer. Before the 80's, it was entirely a mechanical computer! Instead of electricity, it functions with fluid pressure and valves. By installing a shift kit, you change the flow settings, essentially reprogramming the mechanical computer. By the way, the SR-71 Blackbird is the world's fastest mechanical puter.

The losses are the result of the entirely hydraulic nature of the automatic.

So, you have a car with push-button shifting, and you think you're Michael Schumacher? Wrong. So-called "manumatics" are just an automatic with buttons that let you "ask" for a gear. There is still a torque converter, and the car WILL NOT let you do something that causes destruction of the motor or tranny. The real deal starts at about $150,000.

 

[MrDudeMan]

Originally posted by: The Boston Dangler
Manual transmissions are at least 10%, sometimes as much as 20%, more efficient at transfering power to the wheels than an automatic. The reason for this is the fundamental difference between the two.

Manuals use a clutch, basically a pad, to engage the motor's flywheel. This is done by surface to surface friction. If you're not careful, you can stall the motor, or you can "smoke" the clutch. Gearshifting is done by physically engaging and disengaging each gear, through solid linkages (mostly US and older foreign, plus some very high perfomance trannies) or cables (almost any recent car). The only exception I know of is the Neon, it uses the same torque converter on both models.

Automatics use a torque converter to grab onto the engine. A chamber is filled with transmission fluid. There's a "fan" on the motor side, attached to the crank. There's another fan on the tranny side. The engine's fan spins up, and the fluid's pressure spins the tranny input. This is the reason an automatic-equipped car will "creep" forward. In the past few years, manufacturers have produced what's called a "lock-up" torque converter. This improves efficiency at constant speed by not allowing any slip between the motor and tranny, but it's good only for cruising. Also, an automatic's gears are shifted differently. Hydraulic pressure engages clutch-packs in the center of each forward gear (reverse is first gear backwards), letting them grab onto a common shaft. Or there could be planetary gears, which are so complicated I'm not even gonna go there. But it's the same principle. Gearshifting is usually done through a hybrid of electronic and mechanical computer. Before the 80's, it was entirely a mechanical computer! Instead of electricity, it functions with fluid pressure and valves. By installing a shift kit, you change the flow settings, essentially reprogramming the mechanical computer. By the way, the SR-71 Blackbird is the world's fastest mechanical puter.

The losses are the result of the entirely hydraulic nature of the automatic.

So, you have a car with push-button shifting, and you think you're Michael Schumacher? Wrong. So-called "manumatics" are just an automatic with buttons that let you "ask" for a gear. There is still a torque converter, and the car WILL NOT let you do something that causes destruction of the motor or tranny. The real deal starts at about $150,000.

good post :thumbsup:

 

[Bassyhead]

Also I would like to note that some of the things that were previously noted as improving the performance of a manual over an auto also help its fuel economy better. Like CycloWizard said, a manual better approximates the acceleration curve, therefore the engine will be running in a more optimized fuel consumption pattern. Also, like The Boston Dangler mentioned, the presence of a torque converter in an auto introduces losses as they're not 100% efficient. Thats why they usually "lock" when the vehicle reaches a certain speed after accelerating. Clutches in manuals are either engaged or disengaged (hopefully), so there's no losses incurred while you're accelerating.

 

[Mark R]

So-called "manumatics" are just an automatic with buttons that let you "ask" for a gear. There is still a torque converter, and the car WILL NOT let you do something that causes destruction of the motor or tranny.

There's an increasing number of 'semi-automatic' transmissions that do work just like a manual. A proper clutch, and individually selected gears. E.g. Audi's DSG

There is a computer controlled hydraulically operated clutch. When you're stopped it disengages, and then engages once you accelerate to pull off. The gears are also selected in a similar way to a manual - although the linkages are moved by hydraulic actuators. There are a couple of subtle differences - there are 2 seperate gear sets - one for the odd gears, one for the even gears. This allows the 'next' gear to be preselected, before the transmission needs to change. A seperate selector clutch then transfers drive from one gear set to the other to make the change.

Some variants of these transmissions can out accelerate and get better economy than the fully manual equivalent. However, the real big difference is getting rid of the torque converter - these sap power like crazy.

 

[seiyafan]

One of the many reasons is that in auto tran gears are upshifted by the speed you reach and that's tuned for better mileage.

 

[dwcal]

Originally posted by: The Boston Dangler
So, you have a car with push-button shifting, and you think you're Michael Schumacher? Wrong. So-called "manumatics" are just an automatic with buttons that let you "ask" for a gear. There is still a torque converter, and the car WILL NOT let you do something that causes destruction of the motor or tranny. The real deal starts at about $150,000.

You're right about the torque converter. Most of the difference is power loss from slip in the torque converter. The higher weight of the automatic (usually about 100lbs) is a smaller part of it. Also, automatic used to have fewer gear ratios, but that's not true any more.

I wouldn't say it costs $150,000, though. Audi and BMW both have models around $40,000 with the semi-automatic transmissions. Audi's DSG is more advanced than the BMW SMG because of the dual clutches that Mark R describes.

 

[tishoo]

Originally posted by: The Boston Dangler
So, you have a car with push-button shifting, and you think you're Michael Schumacher? Wrong. So-called "manumatics" are just an automatic with buttons that let you "ask" for a gear. There is still a torque converter, and the car WILL NOT let you do something that causes destruction of the motor or tranny. The real deal starts at about $150,000.

Excellent post, and important points, Boston Dangler!

Although true computer-shifted manuals are out on the (is it called DSG?) gearboxes on Audi's A3, and more Audis and VWs. Still wouldn't convince me to buy one, but the tech is pretty cool!

True manual for me until my left knee gives out - no compromise. Unless true SMG or F1 shifters enter my affordability range

<edit> Oops, I wasn't the first to mention DSG - that's what happens when you speed-scroll. Anyway - fun discussion and good topic.

 

[Peter]

The torque converter is what's ruining your 0-60, since it just doesn't "bite" when you're trying to get off the starting line - nowhere near revving the engine to max and letting go of the clutch pedal. Past that, the auto box will still eat more of the engine power because it is made of more and heavier components.

So even with the same number of gears, you don't stand a chance.

Automatically operated manual gearboxes are out there, and have been for ages. Remember the Citroen DS in 1955? It had a standard 4-gear box and clutch, hydraulically operated. Today, the technology is making its comeback, mainly in small cars where fitting a true auto box would be inefficient.

 

[makken]

Originally posted by: The Boston Dangler
Manual transmissions are at least 10%, sometimes as much as 20%, more efficient at transfering power to the wheels than an automatic. The reason for this is the fundamental difference between the two.

Manuals use a clutch, basically a pad, to engage the motor's flywheel. This is done by surface to surface friction. If you're not careful, you can stall the motor, or you can "smoke" the clutch. Gearshifting is done by physically engaging and disengaging each gear, through solid linkages (mostly US and older foreign, plus some very high perfomance trannies) or cables (almost any recent car). The only exception I know of is the Neon, it uses the same torque converter on both models.

Automatics use a torque converter to grab onto the engine. A chamber is filled with transmission fluid. There's a "fan" on the motor side, attached to the crank. There's another fan on the tranny side. The engine's fan spins up, and the fluid's pressure spins the tranny input. This is the reason an automatic-equipped car will "creep" forward. In the past few years, manufacturers have produced what's called a "lock-up" torque converter. This improves efficiency at constant speed by not allowing any slip between the motor and tranny, but it's good only for cruising. Also, an automatic's gears are shifted differently. Hydraulic pressure engages clutch-packs in the center of each forward gear (reverse is first gear backwards), letting them grab onto a common shaft. Or there could be planetary gears, which are so complicated I'm not even gonna go there. But it's the same principle. Gearshifting is usually done through a hybrid of electronic and mechanical computer. Before the 80's, it was entirely a mechanical computer! Instead of electricity, it functions with fluid pressure and valves. By installing a shift kit, you change the flow settings, essentially reprogramming the mechanical computer. By the way, the SR-71 Blackbird is the world's fastest mechanical puter.

The losses are the result of the entirely hydraulic nature of the automatic.

So, you have a car with push-button shifting, and you think you're Michael Schumacher? Wrong. So-called "manumatics" are just an automatic with buttons that let you "ask" for a gear. There is still a torque converter, and the car WILL NOT let you do something that causes destruction of the motor or tranny. The real deal starts at about $150,000.

hit the nail on the head.
I'll just add that the power loss in auto's is a percentage, not a constant amount.

for the so called "Manumatics," there are generally 2 different types.

Systems like the Lexus Speed-shift, Porsche Tiptronic, Mercedes E-Shift, or BMW Steptronic, are in fact automatics that just allow you to pick a gear.

The other type are generally called "Sequentials," after motorcycle transmissions I believe, and the fact that you cannot skip gears. These systems, the most prodominant of which are the BMW SMG, Audi DSG, and Ferrari F1 gearbox, are basically manual transmissions with hydrolic systems to operate the clutch for you (oversimplified view).

check out www.howstuffworks.com for a lot more info

 

[CrispyFried]

Automatics definately waste power, just note the fact that all automatics have transmision coolers and feel how hot they get after a hard run..

 

[The Boston Dangler]

thanks

 

[johnnqq]

gear ratios+ lose power through the torque converter. yes, autos could engage the clutch faster, but it won't know the best time when you take a turn around the track. top fuel cars have pure auto trannys

 

[camotec]

Yeah not only what Johnnqq said but also alot of the fastest drag cars of today have auto transmissions not all are automatic as such though, people (rigoli brothers fastest WRX in the world) have used a stock subaru 4 speed auto and tightened it up for quicker shifts and insted of letting a computer decide when to shift they have a series of buttons they use to shift with, allowing them to have the quick change of an auto with no clutch but to also have the quick response and knowhow of when to shift.

The performance gap is decreasing as the Autos Trans gets smarter.
In Australia alot of the performance cars with manuals come with 6 gears to give better gear ratios for acceleration but alot of new autos are coming out with 5 speed trannies

Cheers
Ben

 

[makken]

5 speed auto's have been out for a while
6 speed auto's have been out for a few years
7 speed auto's just came out last year i believe?

I doubt, at least for passenger cars, that manual transmissions will ever grow beyond 6 speeds. the H pattern just gets too confusion past that point.

The same doesn't apply for the sequentials though; BMW's SMG3 system has 7 forward gears

 

[rivan]

Good thread. I'd always been curious just how lossy torque converters could be. Looks like google time to see what I find.

 

[camotec]

Originally posted by: makken
5 speed auto's have been out for a while
6 speed auto's have been out for a few years
7 speed auto's just came out last year i believe?

I doubt, at least for passenger cars, that manual transmissions will ever grow beyond 6 speeds. the H pattern just gets too confusion past that point.

The same doesn't apply for the sequentials though; BMW's SMG3 system has 7 forward gears

Where in the world are you?
I guess australian cars are behind a bit, i am sure the imported euro cars have more auto gears.

Cheers
Ben

 

[BigfootsMonk]

Here's my 2 cents,

More gears does not necessarily mean faster acceleration. Its a matter of gear ratios. Better calculated gear ratios means better acceleration from x mph to y mph. More gears will result in higher top end, but then aerodynamics will come into play. ex: Evo VII?

Automatics does not always shift when u hit a certain speed. Try flooring an auto and not flooring an auto. You will find out it shifts differently.

Clutches are somwhat of a torque converter also but without the hydraulic fluid. It doesn't always totally engage or disengage the engine. ex: gas braking on a hill

 

[makken]

Originally posted by: camotec

Originally posted by: makken
5 speed auto's have been out for a while
6 speed auto's have been out for a few years
7 speed auto's just came out last year i believe?

I doubt, at least for passenger cars, that manual transmissions will ever grow beyond 6 speeds. the H pattern just gets too confusion past that point.

The same doesn't apply for the sequentials though; BMW's SMG3 system has 7 forward gears

Where in the world are you?
I guess australian cars are behind a bit, i am sure the imported euro cars have more auto gears.

Cheers
Ben

??? USA, california?
5-spd is pretty much the standard for auto's now; even new economy cars (eg honda civic) have 5spd auto's.
http://automobiles.honda.com/models/spe....asp?ModelName=Civic+Coupe&Category=DX

6-spd auto's are widespread through the higher luxury models--AFAIK all of BMW series cars (except for the Z and X series) use 6spd auto's
http://autos.msn.com/research/compare/d...74&v=m11614&v=m11477&v=m11498&v=m11527

7-spd was just introduced with the Mercedes SLK not so long ago:
http://www.mbusa.com/brand/container.js...de=SLK350&class=06_SLK&spec=0&menu=3_0