alcazar

iTrader: (2)

generally slower accelerating than their manual counterparts?

My bro in law has an auto box Jag and reckons it changes gear faster than a person could, so why is it slightly slower?

Alcazar

davegtt

Because the gearbox sapps quite alot of the HP to drive it.

Jaybird-UK

they dont have conventional gears as such, rather a torque converter which is not as efficient as a manual gear box.

That said, some cars now have automatic clutches which is slightly different as it changes a 'normal' manual box.

NACRO

Of course with the advent of fancy twin clutch robotised manuals like the DSG the HP advantage of a manual doesn't apply.
That's one of the reasons your average driver is quicker in one of these. I bet there have been quite a number of 'faster' cars humiliated by relatively low power VAG group cars due to the seamless, repeatable ease of shifts. Every start would be like a perfect max attack run on a dragstrip if the driver so wished.

NotoriousREV

Autoboxes traditionally use fewer gears than manual and are taller geared. They are also set up to shift smoothly in most cases so tend to slur between gears. Finally they also use a low stall rate for economy and smoothness (in essence, at what revs is drive applied). Try sticking your car in second, launching at 2200rpm and changing gear slowly and smoothly. You'll be as fast as most standard autoboxes.

With a higher stall converter, shift kit and a low ratio final drive you could end up quicker than a manual. Ask 90% of drag racers

PeteBrant

CVT is the answer

NotoriousREV

Theoretically you could create a highly tuned engine with a very narrow powerband and use CVT to ensure the engine is kept in that range.

I imagine a Scooby flat 4 with a turbo the size of your head and a CVT box set up to keep the engine around 8000rpm. You'd probably snap all the rubber bands though

PeteBrant

Frank Williams says if F1 would allow it he would go for CVT in a heartbeat

NACRO

Apart from the one time in a hundred you fluff a change (if you're an average driver that is)

I'm willing to bet that forced out of their comfort zones and making very fast changes the error rate would be considerably higher than that.

fivetide

iTrader: (1)

Does depend what car you are in too. The auto Supras for example are faster 1/4 mile than the manuals.

5t.

Beef

No they're not - what they are is more consistent, you're always going to get a good launch.

[Davey]

Regular Torque Converter based autos are slow and drain power low down, but out on the motorway they are geared so highly it makes sense my Omega is geared to something stupid like 260mph.. it would need several 1000 horse power to get there but it means at motorway cruising speeds its barely ticking over

fivetide

iTrader: (1)

ok go ask on mkiv supra forum. in other news fastest FTO in the UK is also an auto.

5t.

[Davey]

An FTO that actually made it to the track without breaking down? WOW!

NotoriousREV

Changing gear without lifting off is good for boost, saves vital 10ths otherwise spent spooling back up to pressure.

noobyscooby

Far too noisy.

noobyscooby

Got a hire VW Passat 2.0 TDi with 6 speed auto box - amazing in sport mode how quickly it puts on 2000 rpm before the next gear change and so on straight up to 100 mph. Sh*it in other ways but fine for daliy motorway commute.

Shark Man

Turbo Diesels are as fast or faster than their manual counterparts: because of their narrow powerband and high amount of low rpm torque, they suit autoboxes far better.

Autos also suit Turbo Petrol engines as the turbo stays on full boost between full throttle gearchanges. Whereas it will momentarily lag between gearchanges on a manual car.

Inherantly the big problem is that most auto boxes have very tall gearing, so lesser powered n/a petrol engines therfore end up being sluggish and slur away as the torque converter saps the power as it tries to overcome the tall gearing before it can get into its optimum powerband (for example; Jag XJS V12 will do 60mph in 1st and 120mph in 2nd gear a manual conversion will knock 2secs off the 0-60 time, also a 528 BMW will do 75mph in 2nd and 5th will do 1500rpm at 80mph ), thus they end up being slower, sluggish and more thristy on fuel at slower speeds

However, once the engine is in its optimum powerband things even out. Also an autobox will match a manual on fuel consumption after the torque converter locks up (usually cruising about 50mph+ ).

CVT autos on paper are the cream of the crop; The engine can run at its peak output and the gearbox will adjust gearing to suit. But alas, they never adjust fast enough and lag behind so loads of revs and no go, and the clutch unit grabs too much in traffic making the thing guzzle fuel with a vengence, also pulling away from standstill can be like pulling away in 3rd gear. As the slipper clutch doesn't allow enough slip to overcome the over-tall intial gearing. But once up and running, they go quite well.

SMG is as fast as a manual counterpart, but it isn't really a "true" auto; Its an automated manual box; Using eletro-hydraulic clutch and gear actuators. In the gearbox, it basically does what your left hand and left foot would do. Whereas conventional autos use a variety of brake bands and clutches to select each gear which compomises of planetry gears, whilst CVT is just a clutch and a belt.

CrisPDuk

Automatic transmissions work well on cars with big wide torque bands, like yank V8s for instance. They can also be made to shift as quickly and brutally as a manual, the key is the fluid in the torque converter

paulwrxboro

wasent the fastest scooby 1/4 mile an auto ?

Shark Man

Fluid does help, but upping line pressure and fitting better clutches helps even more:

My landy has a Borg warner 35 autobox taken out of a Rover P5. When I rebuilt it, I changed some of the springs in the valve block which modulates the line and shift pressures, and used uprated clutch packs. Which now make the shifts really firm, whereas before it was very slushy. Dextron III fluid was the finishing touch.

It's only used for offroading, where autos really do work well.

Pumpkin

An auto box is about twice as heavy as a manual box.

Klaatu

I had a S2 Landrover with V8 and BW35 g/b, was great to drive. Also converted a LR 90 4 pot, 5 sp manual to V8, 4 sp auto, which worked really well.

I have a Subaru Impreza with auto (As I could not find a good manual, and the wife can't drive a manual) it is geared very tall, around town driving consumption is horrendus, but on the highway, it's good. It's way better than the VW Golf I had before anyway.

Shark Man

Errr, completely incorrect! The difference in weight with most is certainly nowhere near as twice the weight! Some are lighter!

The weight is completely hit on miss based on the application. The only heavy bits in them is the gearset, clutch housings and the torque convertor. Everything else is usually aluminium alloy.

For example the impreza 6 speed manual 'box is heavier than the 4 speed auto. The BW65 and TH400 fitted to many old Jaguars are no heaveir than the Moss manual counterparts. The later Getrag manual is a heavy lump.

And the BW35 weighs nothing...can be lifted single handed with fluid, bell housing torque-convertor and flexplate! Now try lifting a LT77 manual with the bellhousing, flywheel and clutch on your own!

Diesel

I've been learning about these gearboxes a lot at the mo (how to increase its life by changing the oil and filter on a 'sealed for life' BMW gearbox is a hot topic on my other forum)!

Def works well on my 530D that produces mountains of torque at 2000rpm, but wouldnt suit a Honda VTEC!

They have come a long way since my fathers 3 speed rover P1.

D

Klaatu

The 4HP22 g/b behind a V8 in a L/R 90 was awesome offroad. It was a "nuts and bots" job apart from the engine mountings.

But I know there are many modifications one can apply to a "slushbox" to make it very nippy indeed. The stall speed of the t/c can be raised, as well as clutch and valve pack modifications. I also recall, from many moons, a specialist said that the BW65 valve pack can be modified to "lock up" in 2nd for bump starting etc.

r32

Like some one said, the VAG DSG system is quicker than a manual change .....

NACRO

That would have been me and the auto versions of the cars are quicker than the manuals. They also feature launch control.

YouTube - DSG vs 6spd manual