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How much power can the stock tranny handle before slippage occurs?
My technician who was formerly with Renntech says that the 722.6 tranny is much stronger than the 722.9 and to hold off on the tranny upgrades. Doing the Renntech R2 package which brings TQ up to 900lbs.
Last edited by slowdiver; Jul 14, 2017 at 02:01 PM.
How much power can the stock tranny handle before slippage occurs?
My technician who was formerly with Renntech says that the 722.6 tranny is much stronger than the 722.9 and to hold off on the tranny upgrades. Doing the Renntech R2 package which brings TQ up to 900lbs.
I am very interested in this as well. I just got the R2 package from Renntech minus the airbox. My torque is limited to 1150Nm. I hate to have unused torque, so I consider upgrading the transmission as well. But I have two further questions concerning this
1.) What about the rest of the car - axels, engine, diff, flexible disc - can all these components really hold up to the punishment
2.) I enjoy my car at very high speeds on the autobahn, but will more torque really help? I heard that MKB had slippage on the rear tires above 250 km/h with their world record SL65 BS, they run more than 1250Nm. I can hardly believe the tires really spin at theses speeds. I never saw the funny yellow light above 180 km/h on my car, and I only have 275 tires
I would like to use every bit of torque the car has, but will I really notice it or just torture the car more?
the poster comments roughly translated: "Only above speeds of 260km/h you can put the hammer down without any worries, we still had wheelspin at full throttle at 240km/h on street tires."
Keep in mind, 1300Nm and I guess the traction is not great on the sl due to the low weight over the rear axle.
How much power can the stock tranny handle before slippage occurs?
My technician who was formerly with Renntech says that the 722.6 tranny is much stronger than the 722.9 and to hold off on the tranny upgrades. Doing the Renntech R2 package which brings TQ up to 900lbs.
You'll be toeing the line on the very upper limits of those clutches.
I say run the oem until you can't. You won't damage anything else (except maybe the converter) and it won't cost you extra to replace a worn trans than it would to replace a perfectly operating one.
You'll most likely see a long 2-3 shift under heavy pedal as the first sign it's going.
I talked to 4 big German tuning companies today about ecu tuning, unfortunately everyone tells a slightly different story. Maybe someone could explain what is true and what is not.
To get more torque than 1000Nm through the transmission, there seem to be two options:
1) just remove the ecu torque limits and fake the torque values so that the transmission thinks everything is fine. This solution seems to be not so clean because the tcu does not have the correct holding pressures which are necessary for the actual torque.
2) remove the torque limits on both, ecu and tcu. Now you are able to use the real torque values and can adapt the transmission holding pressures accordingly. I was told that when adapting these pressures properly, the limits of a stock transmission are immense, it will be able to hold 1250Nm all day long. This seems hard to believe.
Could anyone who has some knowledge/experience in this regard tell me whether this information is correct or not?
My transmission failed a couple of years ago, and I did a lot of research before rebuilding it. This is going from memory, because it didn't affect the physical rebuild process.
The clutches and brakes are controlled by a cascade of valves that apply variable fluid pressure to each piston. The valves are cycled opened and closed quickly, and the pressure is modulated by adjusting the valve pulse repetition or duration. The actuations aren't performed digitally ( like on or off) - the TCU has the option to vary the pressure applied and adjust the timing of each shift to achieve smooth changing. That's the real driver for electronic control - so the clutches and brakes are automatically adjusted.
That means the actuation pressure for each piston is one of the parameters controlled by the TCU, and I believe tuners take advantage of the opportunity to bump up the pressure.
Indeed, I suspect Mercedes do as well. There are many different gear and clutch configurations, depending on the torque rating of the tranny, but the "upgraded" transmission on all the V8K and V12TT cars actually uses the same clutch configuration as the lesser V8 transmissions, where you'd expect them to use more. Therefore I suspect that the high capacity units operate at higher pressure anyway. Certainly, some of their clutches are longer, which allows thicker frictions and pressure plates, which probably allow the use of higher pressures.
I don't like talk about things where I don't have direct experience, so I won't regurgitate what I read as fact, but I BELIEVE that it is possible to increase the torque capacity by increasing piston pressure under software control. I'm just not positive about it. I don't think it's a method that tuners will necessarily be willing to discuss.
They would probably rather you thought that they were making expensive hardware modifications in order to increase torque capacity, rather than changing a few numbers in the software.
If they were going to make to some hardware changes, it would probably be along the lines of adding an extra pair of friction and steel plates to some of the clutch packs, because the 1000Nm units do have extra space. I did some measurements and sums at the time - I'll see if I can dig them out.
I was mooting the idea of a DIY transmission upgrade, but never went ahead, and never needed it with "just" a Eurocharge tune.
Nick
Last edited by Welwynnick; Jul 28, 2017 at 01:28 PM.
My transmission failed a couple of years ago, and I did a lot of research before rebuilding it. This is going from memory, because it didn't affect the physical rebuild process.
The clutches and brakes are controlled by a cascade of valves that apply variable fluid pressure to each piston. The valves are cycled opened and closed quickly, and the pressure is modulated by adjusting the valve pulse repetition or duration. The actuations aren't performed digitally ( like on or off) - the TCU has the option to vary the pressure applied and adjust the timing of each shift to achieve smooth changing. That's the real driver for electronic control - so the clutches and brakes are automatically adjusted.
That means the actuation pressure for each piston is one of the parameters controlled by the TCU, and I believe tuners take advantage of the opportunity to bump up the pressure.
Indeed, I suspect Mercedes do as well. There are many different gear and clutch configurations, depending on the torque rating of the tranny, but the "upgraded" transmission on all the V8K and V12TT cars actually uses the same clutch configuration as the lesser V8 transmissions, where you'd expect them to use more. Therefore I suspect that the high capacity units operate at higher pressure anyway. Certainly, some of their clutches are longer, which allows thicker frictions and pressure plates, which probably allow the use of higher pressures.
I don't like talk about things where I don't have direct experience, so I won't regurgitate what I read as fact, but I BELIEVE that it is possible to increase the torque capacity by increasing piston pressure under software control. I'm just not positive about it. I don't think it's a method that tuners will necessarily be willing to discuss.
They would probably rather you thought that they were making expensive hardware modifications in order to increase torque capacity, rather than changing a few numbers in the software.
If they were going to make to some hardware changes, it would probably be along the lines of adding an extra pair of friction and steel plates to some of the clutch packs, because the 1000Nm units do have extra space. I did some measurements and sums at the time - I'll see if I can dig them out.
I was mooting the idea of a DIY transmission upgrade, but never went ahead, and never needed it with "just" a Eurocharge tune.
Nick
Nick, as always, thank you very much for your long answer.
Concerning hardware modifications, this really doesn't seem to be necessary. As I said, I heard that 1200Nm and more is doable for the transmission without extensive ware - on a stock transmission by just adapting the valve pressure.
But the thing that bothers me is that many tuners say that an ecu tune only is not a clean solution because you have to manipulate the torque values to make the transmission use all the torque. For example:
I want 1200Nm to be put through. I program my ecu in a way that it sends the tcu a torque value of only 1000Nm so that it won't limit the torque. The disadvantage is that the valve pressure is not adapted accordingly (which would require a tcu tune). So you are running a valve pressure that is always too low which leads to wear and excessive heat.
Does this make sense to you? This is how it was explained to me and it sounds plausible.
Last edited by black-series; Jul 28, 2017 at 03:31 PM.
Yes, I believe you would certainly need to have a TCU tune as well.
There's been occasional discussion of this, and those that had an ECU tune, then followed with a TCU tune later, were very enthusiastic about what the TCU tune added.
Hate to barge into to this with a question, but today I was trying to dyno my SL600 Eurocharge ECU, stock TCU, and cold air intakes. We couldn't keep the trans from downshifting from 4th even in dyno mode.
So we tried to roll into fourth, getting up to a high enough speed it wouldn't kick down...floored it and the car redlined in less than 2 seconds...dyno didn't even have time to pick up a #......so the car has 55K miles....do I have a bad trans or gear....or could this be the lack of a TCU tune causing issues.
Sorry for the hijack, but this bothered me today, thanks
It was in S.....I will take the blame on this one, too used to driving manual transmission Corvettes(ZR-1).....what about the "slip", any thoughts of the engine shooting to redline?
Could those who ran 1200Nm or more on a stock transmission of a 65 AMG share their experience (only tcu tune, no hardware upgrades)? Is the transmission able to hold the torque successfully without any compromise? How about durability?
There are many different opinions on this topic, so I would very much appreciate a real life experience because this is the only thing that counts in the end.
Yes, I believe you would certainly need to have a TCU tune as well.
There's been occasional discussion of this, and those that had an ECU tune, then followed with a TCU tune later, were very enthusiastic about what the TCU tune added.
Nick
Renntech Stage 2 includes the TCU tune and I have been very happy so far. I also upgraded the Torque Converter and my Technician believes I am now running somewhere around 1,000 LBs TQ. I have not experienced any tranny slippage thus far, but it has not been very long (under 1K miles). Thank God for the 355 Pirelli on back. Installing the Weistec Methanol Kit shortly and suspect this will add more power as well, so I will definitely be testing the upper limits of the stock 722.6 tranny.
New conductor plate
my tranny threw a code, so my tech pulled my valve body and cleaned it. He suspected I needed a new conductor plate and that is exactly what the issue was. I now have much smoother shifts. Apparently this is a common issue with the 722.6
I am not entirely sure whether you intended to post your last comment in this thread or whether you wanted to reply to my transmission problem thread. If the latter is the case, I already changed the conductor plate in my transmission without any success, the problem still remains unsolved.
Maybe I can convince you to check my last post in the thread check engine light - transmission problem
As I explained in my last post, the transmission is in perfect condition, no signs of wear whatsoever. I was about to pay 3000 Euros for a full revision and got a call back from the company telling me there is absolutely no point in changing anything except of two clutches.
Putting a new transmission in at that point would be like taking a sledgehammer to crack a nut.
My car is back in the shop due to jolting upshifts from 2nd through 4th gear. It doesn't happen all of the time. The TCU isn't throwing any codes and we believe the tranny is mechanically sound. Our current guess is that the TCU has to be reflashed due to the high stall Torque Converter. We have a call with Renntech tomorrow to get their feedback. Any thoughts on what could be the issue?
Long story short, my technician re-installed the OEM torque converter and the tranny is now shifting perfectly. We believe there was something faulty with the aftermarket torque converter. My technician continues to say that the 722.6 is an incredibly strong tranny that can handle all of the additional power. Starting to research down pipes now.
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