Can anyone explain to me why some high stall converters have a dip or drop in RPM’s just after they hit their stall speed and also a pause in acceleration just before continuing to climb the RPM’s and accelerating? I’m talking about a WOT take off from a dig while still in first gear. With all things being equal and the stalls being the same, on acceleration from a dead stop, one converter will have the RPM’s climb quickly, stall or grab, then keep climbing and
pulling. The other converter’s RPM’s will climb quickly, grab but pull down the RPM’s and the acceleration will pause, then continue climbing the RPM’s. Even if they stall the same, it seems the second converter slows the car down. Could it be the STR is not proper for the set up? How can this be avoided? I’ve seen this in even 4000 stall converters. I thought high stalls removed dead spots or rpm dips like that. Any info?

 

Let me ask you...
What do you know about the way in which a 3-Element Torque-Converter, or a Lock-up Torque-Converter functions?
Do you know what is occurring as the Engine RPM starts to increase...
and then as the vehicle starts to move?

 

Yeah, I have a very good theoretical understanding. A rough idea. I just don’t have physical practical hands on experience. The crankshaft, flex plate, TC housing, hub, and impeller all spin together. Engine drives the impeller. The impeller pumps fluid. The faster the engine spins, the more fluid is pumped. The impeller takes in fluid from the center and ejects is out from the edges via centrifugal force. The impeller drives the turbine by forcing fluid to strike its outer edges. The turbine is connected to the transmission input shaft. The fluid exits the turbine via the center towards the center of the impeller intake. However, the fluid is flowing in a reverse rotation to the impeller. The stator redirects the fluid in the right direction that is the same as the impeller. The stator is locked via sprag. The physical size of the converter can be reduced to increase stall. Impeller fun angle can be changed forward or backwards. Backwards to increase stall,
reduce efficiency, and increase leverage on the fluid for more torque multiplication. Forward pitch to decrease stall, increase efficiency,
at the loss of multiplication. The stator acts as a fixed point to cause leverage against the inner impeller vanes and speeds up the fluid entering the impeller causing multiplication. Vane size, amount, overlap, angle, shape, and window size can be used to manipulate STR, stall, and efficiency. The space between the impeller, stator, and turbine, can be used to manipulate stall. A stator with many curved blades at a flatter angles that overlap reduce window area and really turn the fluid may increase multiplication, increase stall, but be inefficient. Less vanes, steeper angles, straighter vanes, no overlap, may reduce stall, reduce STR, but increase efficiency. The part I have trouble with is the transition. the coupling. When the stator, fluid, impeller, and turbine all spin together. I’m not worried about lock up. I can picture it all in my head. I just have ZERO physical real world experience. No torque converter shop, no cutaways, no racing experience, no comparing them back to back in cars. I know some converters “grab the engine hard” and pull the RPM’s down some don’t and have smooth transitions. I’m just not sure which combo does that or why the heck you would even want that? I want to be able to buy what I need and not have to go through 5 converters to find the right one. Which converters transition smoothly and not pull the motor down hard like that. Also, I’m what situations would you need the converter to do that? That pause in acceleration seems annoying.

Thanks

 

What is your setup? N/A? Power adder? If it’s N/A I completely get what you’re saying and agree. I run a FTI converter and I am N/A and it stalls and keeps climbing. None of what your second converter is doing. Best converter I’ve ever bought.

 

Awesome! What FTI converter you running? Part number? Stall? Hard hit? Soft hit? High or low STR?

I have an FTI 0086 unit, just not installed yet.

28 inch tires, 373 gears, cam only

thanks

 

This is not my video. I found it on youtube. I don’t know the set up or the totality of what’s going on, but this is what I’m talking about.

What is going on at 6 seconds? Like everything pauses. At least the RPM’s don’t dip here, they only pause. Acceleration stops climbing for a second.

 

Here is another. These are not too bad. Acceleration does not seem affected on this one.

 

This one is pretty bad. Not one of our cars but u get the idea....

 

PRNDL think i have been emailing you back and forth about this as well. Don't get engine RPM slope(rate of change) confused with vehicle acceleration they are separate and behave in their own unique ways. With a g-meter installed this can be viewed quite easily. The small dip(or short flat spot in RPM graph) is the converter and motor "stale-mating" if you will as they pull the drive shaft to catch up to engine RPM. After the drive shaft catches up to the motor and converter, RPM and acceleration will behave in a similar fashion, but not prior.

Dalton

 

I think you have a very good understanding of how a stall works mechanically. I think, however, you are not thinking of whats going on in those scenarios. I have many many pull videos like this on my truck and my car. So let me explain whats going on. Say the stall is 4000 (flashing) like the first video probably is. He's stalling it up below the stall (you have to keep in mind even those the stall is 4000, the convertor isnt 100% free wheeling or slipping to the 4000...so it will move the vehicle) he lets of the brake, the vehicle starts accelerating in the "looser" part of the stalls rpm range, and by the time it couples up, the car is moving a few mph and rpm is about 4500....now...Imagine a standard trans launch. You slip the clutch...car starts moving and then you finish letting off the clutch...its likely to bog a little bit if the rpm isnt high enough.

 

Watching this video It looks like the car spun and grabbed. that is why the speed climbs and dips as well before continuing to climb.

 

This is a perfect example of the dip doing as it should. Watch the speed climb rather quickly at first as the conv and engine pull the drive shaft to the engine. then acceleration slows as the drive shaft up to the engine and converter.

 

Thanks for clearing it up Dalton. Makes sense. I just don’t have the practical experience.

 

That makes perfect sense! Awesome.

 

This makes perfect sense! That’s for your help and time.

I like car theory. Especially performance theory. Plus it seems I was overthinking things. Thanks for all your time gentlemen.

 

i never thought of wheel slip. I was thinking it was mismatched parts. I was trying to avoid issues. Great info.

 

I corrected a typo

 

Thanks man