In my current tune, car shifts great, firm but not neck snapping. I still have all the gears' torque management enabled and the tables for each gear have anywhere from 150-250 ft/lbs of reduction.
How many people have turned this off entirely? I have an inquiry out to my trans builder but figured I would ask here.
Yeah, I disable the upshift torque managements. I set to None.
I'm a bit confused: under Auto TCC, Upshift, 1-2 tab, Torque Reduction 1-2, REDUCE the values to increase shift firmness, correct?Originally Posted by 06300CSRT8
My trans builder chimed in and stated his 8 second jeep was faster with SOME torque management still left in versus none at all.
hemi426 - I am talking about in Trans>Torque Management>Upshift 1-2 table.
Is it significantly harder on the transmission after disabling this or do they seem to take it fine? I know with certain GM transmissions I've read to keep at least 50% of the transmission torque management to keep from destroying the transmission.
For a stock trans you really shouldn't mess with it at all except for some of the minor torque management changes you can make on the engine side.
I am discussing a fully built transmission, rated for 1000whp+, that is the only situation going lower than stock (or Mopar TCM/Jeep) settings where this could be considered. The Kevlar clutches and additional clutches added to built transmissions can basically do whatever you tell them to with enough pressure. But based on the intricate valve body design and time it take to complete each gear shift, you become limited mechanically pretty quick to just how fast you can get the trans to complete a full gear shift. I am guessing these guys found removing SOME but not all torque management helped them command an ultimately FASTER shift start to finish, which is way more important than just a head banging shift.
I have tuned a few GM trannys with torque management completely disabled, they have all been going years and years with no issues. My personal truck with a 4l80e is completely disabled, and now my 2010 hemi as of a few days ago is completely disabled. (all upshift I'm talking). IMO its not that hard on the transmission as long as your shift time isn't supper aggressive, I like firm but not tire chirping bang shifts. If you think about it all pre electronic transmissions had no torque management and they were fine.
My Hemi hardly feels any different than before, (it had a superchips tune it it before set to "firm"). I read that file and the allowed torque for a shift was set pretty high to achieve a firm shift, I liked how it shifted for the most part and all I did was turn torque management off now and it still feels about the same, maybe a touch firmer at part throttle. Under WOT it shift firm/hard but its not chirping the tires so I don't think its going to break anything, I also don't drive it like that very often.
I know I started this thread with the hopes to find folks not using torque management, but not on the basis of what GM guys have done, glad you are having success on your 2010 Hemi, that is informative for sure.
I guess after further research I have found that on high horsepower setups (1,000+ crank) and without the absolute highest level of a built NAG1, you wont hurt the trans by turning it off but you wont necessarily go any faster. There are mechanical limits of the NAG1 in the clutch design and valving that benefit from some slight torque reduction to get the shortest shift speed. NAG1's are very different than GMs in their basic mechanical design.
I am tackling this monster now. We are adding more torque management on the 3-4 shift as this is my problem area. The shifts are neck snapping and tend to break the input shaft. So we are reducing some of the line pressure and adding some more torque management. Fingers crossed.
'07 MSRT8 426- 4.2 KB- Paramount Super Pro-1000HP club-
On the subject of torque management you have to look at it two different ways. The first is that all transmissions will hold way more torque when nothing is slipping. Fluid temp at the frictions stay low, there is no need for exotic clutches, steels, clearances, bigger shafts and gears ect. Manufacturers are not building these things to shift under power anymore. So by inducing a derate during the shift they get a huge durability benefit by not forcing the transmission to try to drag down an engine running at wot/peak rpm with a couple of paper disks.
The second thing to consider is electronic transmissions set rpm goals for the shafts to complete a shift. When you induce a shift the tcm logic is trying to match shaft speeds to it's next calculated ratio and it takes longer with the engine running berserk. When the next clutch applies, it is braking the engine rpm, trying to get the input speed down. If engine rpm is reduced through torque management the shaft speeds can be matched much faster and the shift completed quicker. I've had much luck with applying more aggressive torque management to get a faster shift.
But there are always those looking for a firmer shift to chirp tires or chase a few hundredths at the track due to the flywheel effect, thinking a transmission that kicks you in the back is faster.
Level 3 Master Chrysler/Jeep/Dodge/Ram technician
20 years experience
Yes and no.
The clutches are slipping during the 'torque phase' and 'speed phase' of the shift. During a heavily loaded upshift the torque phase will happen first. In this phase, the outgoing (release) clutch is slowly released, and the oncoming (apply) clutch is slipped to handle the torque, but slipping to hold the old gear ratio. For RFE, the release clutch is just vented (solenoid turned off) and the apply clutch is PWM controlled to hold constant gear ratio. Then comes the speed phase. At this point, the engine is still at the old RPM but the transmission has finished the torque handoff. the PWM duty cycle of the apply clutch is increased to pull the engine speed down to the new gear ratio. Due to the inertia of the engine, the engine produces more torque than it had previously (from inertia of decelerating the engine!). This torque has to go somewhere.
Option 1:
If the Apply clutch is ramped up to decelerate the engine before the Release clutched is fully vented, the two clutches will overlap. In this scenario, the two clutches will fight and the extra torque from the engine will go into heating both clutches. This is bad for the clutches, but the rest of the transmission is fine.
Option 2:
If we ignore the torque from acceleration, it will be passed through the transmission to the driveline as a bump. Depending on how fast the apply clutch is ramped up (the target turbine acceleration for the shift), this bump may be huge, may break traction on the rear wheels in a 1->2 shift, and may break or stress driveline parts since the torque can well exceed the normal engine output torque. This can be a benefit in high gears, as long as you don't break traction, but in low gears it's useless and stressful on all of the components.
Option 3:
If we slow down the shift (ramp up the PWM duty cycle slower), the magnitude of torque will go down, so you might not feel it. The apply clutch is still slipping for the duration of the shift, and will heat up, but can handle it for a short period of time.
Option 4:
The engine reduces its torque to match the torque which is gained from engine acceleration. In this case, the torque going into the transmission is the same as it will be at the end of the shift, no stress on components, and the shift can be completed more quickly with less heating of the apply clutch.
The RFE transmission has hydraulic accumulators on all of the clutch circuits which limit the speed of the shift, but the 8HP does not. Try driving an 8HP Ram 1500 in tow/haul mode to feel an incredibly fast but bumpless shift. The 8HP requests a very large torque reduction from the engine, so it can complete the speed change very quickly without the driver feeling it.
During the entire duration of the shift, the transmission is handling the full engine power while slipping. The torque reduction combats the extra torque from engine acceleration only and will always make the shift faster. There is also an engine-side limit to how much torque reduction you can request. I would request as much of it as you can, to speed up the shift as much as possible.
Great info, your last point is EXACTLY why there is actually a benefit to be gained by using stronger and more grip clutches, you can command LESS engine torque reduction and allow more to be handled by the slipping clutches. This will ALWAYS be a faster vehicle (NOT a faster shift, read carefully) than more engine torque reduction, at least in the RFE. If you take it to an extreme and were to measure the time a full gear change takes with zero torque applied, and then add back torque until that shift time starts to increase, you will arrive at say X amount of torque, which results in Y acceleration. Having better clutches, that X amount of torque would be higher in the same exercise, and would result in more power getting to the pavement while the mechanical end of the shift is at play, which would result in a faster Y acceleration.
There is acceleration to be gained even with an identical shift time.
In fact I have measured this, at an extreme. Last season I had a HORRIBLE shift flare on the 3-4 shift. Basically I would tap the shifter at 5600rpms (normal shift rpm is 7,000), rpms would flare to nearly 6600rpms, hold there until the engine and turbine matched speeds, then make a very sloppy, clutch slipping shift into 4th.
Guess what...Gforce accelerometer log showed more acceleration during that long ass slipping clutch shift than after it was fixed with a very nice tight shift that started at 6700 and completed before 6900rpms.
What was the cause? Bricked TCM that was commanding ZERO engine torque reduction, my 800whp+ setup was pushing right through the poor clutches. So in the end, zero engine torque reduction, a TERRIBLY LONG shift, roasted clutches, was a faster setup than a torque reduced engine with a nice tight trans. Go figure.....
Sorta. I'm not entirely following.
The speed of the entire shift is due to 3 phases:
-Fill - The time it takes to fill the apply clutch volume until it touches (during this phase nothing is slipping at all, but it is a delay from when you initiate the shift)
-Torque - The time it takes to hand off torque from the release clutch to the apply clutch while maintaining the old gear ratio. In RFE this time is set mechanically by the releasing clutch accumulator volume and is not affected by calibrations. The release clutch is not slipping (much) and the apply clutch is slipping to maintain the old gear ratio.
-Speed - The time it takes to change the speed of the engine to match the new gear ratio. This is set by the RPM which must be changed and the target acceleration rate. The acceleration rate is the primary parameter to tweak during this shift. During this time the apply clutch is slipping.
Normally you only notice/feel the third phase, so you might consider that time alone as the duration of the shift.
During the speed phase, the apply clutch is PWMed to hold a target acceleration. Increasing the friction capacity of this clutch (more friction plates, higher grip plates, etc.) would just make the TCM/PCM lower the pressure applied to hold the same acceleration rate. The extra torque from acceleration of the engine will be passed through (at the new torque ratio) to the driveline. In higher gears this can be fine, but in the 1->2 shift this can break the tires loose if you target too much acceleration with no torque reduction from the engine.
The NAG1 is a bit different than the RFE on the tuning side. We have full control of the pressure, acceleration, fill times, ramp and overlap times, as well as adaptations. We can easily install higher friction clutches, input the new clutch power handling values (there is a spot), lower the time allowed for the phases of each shift, and the TCM will speed up the process and we don't have to worry about frying the clutch packs. On top of that, we can speed up the release rate of the brake clutches so power comes on quicker and harder in the next gear.
I was also discussing this in the context of a well setup drag car with either slicks or sticky drag radials, that if you can launch the car without spinning likely the 1-2 shift can handle almost full torque.
Not to hijack the thread with NAG's and RFE's, but I can tell you guys that playing around with torque management on my '16 Scat Pack with an 8HP...it was HORRIBLE. Obviously there is no tuning for the trans itself, but you can turn off auto trans TQ management (use SPARK, use FSO, use ETC). I went down the road and did a launch got into 3rd and pulled over and turned it back on and flashed my car on the side of the road. When it shifted into 2nd I wasn't sure if the tires were spinning or the trans was slipping because the RPM's came down so slow and there was no "feel" of an actual trans shift. Once I shifted into 3rd and it did the same, I knew it wasn't wheel spin. Just the over-all feel of it was bad, I'm happy with how the 8-speed shifts stock I was just out experimenting and it seems to be more harm than good...on an 8-speed trans anyway.
Option 4:
The engine reduces its torque to match the torque which is gained from engine acceleration. In this case, the torque going into the transmission is the same as it will be at the end of the shift, no stress on components, and the shift can be completed more quickly with less heating of the apply clutch.
If I understand this correctly that means if the engine makes 500nm at redline and after you shift it?ll make 600nm then you should command 400nm of reduction?
Not sure if you are talking about 8HP transmission. If yes:
- Torque reduction does not work like this... Torque reduction request is purely active to stress the least possible the shifting elements.
- Depending on engine reaction to torque reduction, gear step on upshift and engine RPM, a torque reduction value has to be input to further extend transmission lifetime
- Too much torque reduction would cause a "interruption feeling"
- Too little torque reduction would unnecessarily stress the transmission components
Thanks.
DodgeBoy.
Can you turn it off? Yes. It is recommended to do it? Definitely not...
My actual platform is the bmw gen 2 dct. I figured this philosophy could be universal. I understand the basics as you listed but I?m looking for the actual formula. I can?t tel if he meant if the car gains 100nm on the shift if you reduce the engine power by 100nm or if you reduce the engine power to 100nm
Are reduction values based on engine torque at shift rpm and the gear ratio spread?
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