Stall Convertors

[Prove It]

Hi guys, im converting my car from Manual to Auto. Its gonna have a rebuilt 4spd in it but talking to the guy at SA RACE, he started talking about stall convertors. As ya can prob tell I have absolutely no idea how they work or how to use them when its in the car so any info on this would be greatly appreciated.

Cheers guys, Mitch

[ETM]

have a read of this mate.

http://auto.howstuffworks.com/auto-parts/t...e-converter.htm

[JETURBO]

dude use serch I have a thread up on when I got my stally some very good info in it

[Prove It]

Cheers for the link ETM,

Jet link us to your thread mate keen on a read of the "girl stall" lol sorry that's what im told it is hahaha

[aiboart]

An auto box has in fact two transmissions operating in series.

The first transmission is a infinitely variable liquid transmission, the torque convertor.

The second transmission is composed of conventional planetary gears.

The engine feeds into the torque convertor transmission, which in turn feeds into the planetary gear transmission, which then feeds it into the diff and CV's etc.

Power has rectangular 'shape'. On one side of the rectangle is revs, on the other side is torque and the area of the rectangle is power. The purpose of any transmissions, whether liquid or solid (gears), is to keep the area of the rectangle as constant as possible whilst changing the shape of the rectangle. Changing the shape of the rectangle is equivalent to changing the ratio. That's the theory. In reality however, due to frictional losses, the power rectangle always shrinks in area whenever the transmission changes it shape (changes the drive ratio).

So conventional gears convert revs into torque by virtue of its geometry. (In overdrive they convert torque into revs)

A torque convertor behaves exactly the same way, it changes revs into torque. The torque convertor does this by altering fluid flow geometry within the torque convertor.

Conventional gears have fixed ratios, they will always alter the the power rectangle the same way. If you want to vary the ratio you need to change gear, hence you have gears 1, 2, 3, 4... etc.

A torque convertor, a liquid transmission has a trick; it can seamlessly and continuously change (gear) ratio form infinity (at idle) to some maximum value say 80kph.

A torque convertor will allow your engine can stay at say exactly 1,800RPM whilst the car accelerates from 0kph to say 80kph. The thing to note here is that the torque convertor is not a just a fluid coupling, it is not just slipping whilst the engine is at 1800 revs. The torque convertor is actually converting the high revs to high torque at the launch just as if the car was in some exceedingly low gear. After launch and during acceleration the torque convertor is changing the drive ratio in a constant manner just as, if instead of having 6 gears you had thousands of gears. The proof that the convertor is in fact converting revs to torque is why a XR6T Auto stalled up to 1800 RPM will jump off the line and accelerate at a constant rate - a fluid coupling would just slip and generate heat.

A car engine operate in conditions of continually varying speed and continually varying load; an infinitely variable transmission is exceedingly valuable in these circumstances. Having an infinity of ratios continuously changing is much better than having 4,5,6,7 or even 8 gears and having to change between then, even if using a DSG.

So if a torque convertor is a infinite ratio transmission and an infinite ration transmission is so valuable, why do we even bother with gears? There are a few simple answers,

1/ the torque convertor when converting high revs in to high torque waste more energy than the equivalent gear ratio. This is because fluid flow geometry is exceedingly more complex than gear geometry.The wasted energy goes into heating up the auto torque convertor fluid. To use the analogy above, the power rectangle shrinks more for a specific torque convertor ratio than it does for the equivalent gear ratio. If you do a lot of converting, say stalled at the line, you are pumping a lot of heat into the auto fluid...

2/ torque convertors whilst having an infinite ratio (they can operate with the car at 0kph) still have a limited operating range - they can only handle a certain

gap between the input shaft speed and the output shaft speed (the so called stall point). This limited range is why auto boxes have gears in addition to the torque convertor, there is simply not enough range in a reasonably efficient torque convertor to cover all road speeds in a modern car.

3/ the wider the range of the toque convertor, the bigger the stall, the more inefficient it gets. This is essentially due to the fact that the internal friction is a function of the internal fluid speeds. The modern trend is to have smaller and smaller conversion rations (stall points) with more gears in the box.

So, if you fit a wider range torque convertor, I.e. a higher stall convertor, you will be fitting a unit that has a wider range between the speeds of the input shaft and the output shaft.

1/ The wider range will allow your engine to rev higher when the car is stationary, thereby generating more torque at the rear wheels at launch (the convertor converts the extra revs into extra torque). As the internal fluid in the convertor will be moving faster there will be more internal friction at high and hence more transmission loss.

2/ The wider range will also mean that in general you will be driving around at any given road speeds with more engine speed. This will translate to more torque at the wheels, but it will also mean that your engine will be using more fuel.

Hope that helps

Regards,

aa

[Prove It]

LOL that's insane, cheers for that mate that's really helpful.

Just one question though that might be a bit stupid

jus say for instance I was at the strip about to run a quarter mile (in the car ) to stall it up, its just foot brake and acceleration up to what ever revs your stall convertor is then just release the foot brake and off ya go? pretty much a basic way of puttin it??

so confused

[JETURBO]

well yeh and nar

a stock modified will only really stall to the limit with the brake aplied

a custom converter can be flashed to the value say 3k from bare take off

ie my converter acts as normal when I boot it at 20kmh drops back and off u go like a norm auto only get the effect of the stall when from take off

bloosties 3k high stall in hes y will do 20kmh hit the pedal and it will go straight to 3k like droping the clutch then it will blaze the tyres 1,2,3 and crab down the road like your in summernats

[Trough Lolly]

weeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee that would be fun.

[JETURBO]

u dam right its fun

[Prove It]

u dam right its fun

oh ok fair enuf then I reckon the modded convertor would def be the way to go.

I never been to summernats or gazzanats but I dont want to make main north look like a burn out pad LOL