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F37, Boost Control, and lockup questions  RSS feed
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subgenius

Joined: 06/08/2009 14:53:04
Messages: 4
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Hello,

I am looking at purchasing either the stage II tune or the "HOT" tune. First, I am wondering, does your tune override (or ignore) signals sent from the TCU to reduce power output / let the transmission slip as is the case with the F37 flash? I am guessing there are two different answers for the two tunes, but I would like your clarification on the matter.

second, and semi-related, will the transmission fully lock in the top gear / low rpm for max economy? or again, is this controlled differently in the two tunes?

also, how do you guys control boost pressure if the vanes are controlled by the vacuum signal? Is their a bleeder type solenoid somewhere in the system?

last question -- what pressure ratio are you guys targeting on the HOT tune? I am hoping for a peak of 3 to really let this thing loose. also, do your fuel timing tables and boost tables have sufficient resolution / range to address higher loads of PR's close to 3? i know you guys are aware but here is the compressor map for others http://www.turbobygarrett.com/turbobygarrett/catelog/Turbochargers/GT20/GT2056_751578_2.htm

Sorry for the rather pointed questions. I come from the open source wrx tuning community and am wondering how many parameters you guys have access to.

Also, if you could provide the PN for the "euro" TC i would appreciate it.
GreenDieselEngineering
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Joined: 10/07/2009 07:25:47
Messages: 361
Location: Southeast Michigan
We cannot change any transmission behavior, but the engine will produce significantly more torque. The TCU is not sending torque signals on our vehicles. The customer can specify if one wants full torque in "lock-up" or just partial torque if using a stock converter.

We modify the code to raise or lower boost setpoint, which drives the vacuum level at the turbo.

For this tune we focused on maximizing the turbo speeds in WOT conditions running close to the surge limit and following to the peak speed line. In normal driving, the turbo is tuned for maximum efficiency zones that provide the best fuel economy. The fueling tables have several breakpoints and cover the full engine operating range. We only change the parts of the code that can be deciphered.

The euro TC part number is: 68037142AA. It is our understanding that this converter can be ordered through a dealer or mopar online (less $$$). The converter is on back order until 13 September at this point in time.
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subgenius

Joined: 06/08/2009 14:53:04
Messages: 4
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i was under the impression that it was the TCU's duty to decide how much to lockup the transmission (how much to let it slip). you make it sound like its the ECU's job. can you only specify full lock for a certain rpm/mph/gear, or is it a table where you can set lock-up points? reason i ask is it would be awesome to lockup in certain gears at certain rpm's in order to help in-town mpg.

can the customer specify what boost he wants? i am thinking more along the lines of setting WOT around a PR of 3 instead of 2.5. i am at a high altitude and would like every last bit i can muster out of the turbo.

i am not sure why you say the best zones for economy. the adiabatic efficiency of the turbo is not proportional to mpg. even if it was, the difference between a PR of 2.5 and 3 is 3%, and from 2.5 to 3.25 is 5%. ok, sure, you might not want to REALLY overdrive the turbo into the PR 3.7 zone in fear of really heating the air up, but certainly the intercooler was designed with a safety factor better than 1. IMO, they had to have oversized it by at least ~10% just for the differences in climates that the liberty would come into contact with.

also, have you guys installed the euro TC? if so, were the results positive?

thanks!
GreenDieselEngineering
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Joined: 10/07/2009 07:25:47
Messages: 361
Location: Southeast Michigan
The TCU is in charge of what engine speed/vehicle speed/pedal position dictates the upshifts/downshifts and when to lockup the torque converter (partial lockup isn't available for this application). However, the engine ECU is in charge of how much torque to allow at those various load points. This is how we can allow either "full torque" while in lockup, or our modified tables which eliminate the shudder while in lockup at the applicable load points.

Regarding the boost, the maps available on the Garrett website are only applicable to the wastegated version of the GT2056 and don't apply to the KJ's VGT version since it has different trims, A/R's, and wheel diameters. For VGT applications (and all turbo families for that matter), it's important to pay respect to three main constraints: compressor outlet temperatures, turbine inlet/outlet temperatures, and rotational speeds. For this application, the wide-open throttle performance is limited by the turbocharger speed - if you exceed the rated speed for too long then the turbo will self-destruct; however, the same goes for the temperature limitations especially in trailer-towing conditions.

The boost setpoint has been optimized at all engine points to provide the best fuel economy, which translates to both the lowest BSFC at each point and the lowest CO2 output. If you raise the boost setpoint too high in normal driving and thus close the vanes too much, then the engine has to work harder to force the air out through the turbine housing and the fuel economy goes down; conversely, if the boost setpoint is too low, there isn't enough air in the cylinder for complete combustion and fuel economy goes down and the engine smokes. Tuning for peak fuel economy isn't as simple as cranking the boost up all the way and going to town, each operating point must be optimized independently.

We spent considerable time in altitude earlier late spring/early summer to maximize the turbocharger performance in altitude. The tradeoff with higher altitude conditions is that with air of lower density, the turbocharger spins faster for a given boost setpoint so we have to pay respect to these limitations when tuning the boost system. At a given altitude, the boost setpoint was adjusted to give the maximum speed permissible so that performance would suffer as little as possible. This is mainly an issue at WOT throttle and load points slightly less, in normal driving we are able to mostly maintain the sealevel performance for boost and fuel economy.

Our tune (regardless of power level) at WOT from sealevel through 12000' is able to maintain a PR between slightly over 3 at sealevel to down to 2.7 at higher altitudes.

We currently have the new torque converter on order but thus far they are on backorder and should be available mid-september.
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subgenius

Joined: 06/08/2009 14:53:04
Messages: 4
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great! i hope these questions aren't coming across as being flippant. hopefully they will be beneficial to other customers as your company grows.

what would you suggest for optimal torque converter stall speed? some have suggested going with a 5.7l hemi TC with a stall speed of ~2400 (IMO far too high for the crd), others have suggested a suncoast TC with user definable stall speed (1500-up), yet still others have suggested the euro unit, which presumably has similar stall speed to the pre-f37 TC.

by the way, do you know the stall speed of the euro tc? i have heard that post f37 stall speed is ~1800, but since peak torque occurs at ~1800rpm, i am guessing it is much later.

thanks again.
GreenDieselEngineering
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Joined: 10/07/2009 07:25:47
Messages: 361
Location: Southeast Michigan
The questions are good, we are here to help in any way possible.

Factory torque converters are rated by K factor. Stall speed is a factor of input torque, so the factory KJ 2006MY converter will have two different stall speeds if it is used with the stock engine cal or the tuned cal from GDE. Since ECO tune has more torque than stock, the stall speed may be 100-200 rpm higher.

The K factor for stock KJ converter and Euro TC is the same as far as we understand. It provides a good balance of transmitting useable torque to the wheels and keeping the rpms in check to have decent fuel economy. If the stall speed is too high, the engine will have to rev at higher rpms to keep the vehicle moving. Typically gas torque converters have higher stall speeds than diesel converters.
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subgenius

Joined: 06/08/2009 14:53:04
Messages: 4
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thanks again. i'd just like to clarify that the 2400rpm stall speed of the "hemi 5.7" that i reported earlier was actually an aftermarket TC. based upon feedback from a knowledgeable/reliable source, it appears the stock stall speed of the 07+ hemi 5.7l TC is in the neighboorhood of 1700-1800rpm. the best estimates by a few people on lostkjs indicates that the stock stall speed (flash stall) is somewhere around 2200rpm.

i guess now the question becomes what would be the best stall speed for the CRD. as you are aware there is a 20+ page thread on lostkjs discussing the issue. just brainstorming on the issue, it would seem that you would want a sufficient amount of "slip" to allow the turbo to spool quick, or have a good compromise between rpm and load in order to spool fast. on the other hand, ideally you would want full lock at peak tq. aftermarket manufacturers blanketly suggest a stall speed 500-700rpm lower than the stock TC for diesel engines. so given the fact that the engine supposedly peaks at 1800rpm (supposedly because we are using reference material from the POS stock TC), we would want full lock at 1800rpm. ergo, the best solution seems to be the hemi 5.7 TC, or the suncoast if you just have to have the billet case.
GreenDieselEngineering
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Joined: 10/07/2009 07:25:47
Messages: 361
Location: Southeast Michigan
The optimum stall speed for the KJ CRD would be in the 1800-2000rpm range, right where peak torque is reached. The multiplication ratio is also important and you may have a hard time finding this type of information, usually only known by manufacturer. Lower stall speeds have a side benefit of reducing transmission fluid temps as there is less slippage in normal driving conditions in unlock mode.

Why would the 07+ hemi 5.7l TC have such a low stall speed? Most gas engines typically use converters with higher stall speeds since the torque peak occurs at higher rpms as compared to a diesel. It could be the multiplication ratio is very low on the hemi 5.7, which may lead to less aggressive launch performance if installed on the KJ CRD.

In our opinion the Euro TC is a good balance between stall speed and multiplication ratio and we are confident in its increased clutch capacity during "lock-up". As soon as these are off backorder we will have a couple of them for validating the hot tune and turbo kit. The hemi converter was designed with an 8-cylinder in mind for the lock-up clutch capacity. The KJ CRD torque is similar to the hemi in overall output, but the torsionals will be substantially higher due to having 4-cylinders. These torsionals are the prime driver in "shudder" and lock-up clutch failures.

Another thing to keep in mind, if using the GDE ECO tune or HOT tune, the torque peak is increased and the torque band is broadened. For comparison, stock KJ CRD torque range at/above 290 ft*lb is between 1600-2600rpm and with the ECO tune at/above 290 ft*lb is between 1400-3200rpm. With this broad torque range, the optimum converter should provide a solid launch, minimal slip for heat rejection and keeping the engine rpm in lower ranges to maximize fuel economy.
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flman
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Joined: 28/08/2009 19:59:32
Messages: 74
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GreenDieselEngineering wrote:

The euro TC part number is: 68037142AA. It is our understanding that this converter can be ordered through a dealer or mopar online (less $$$). The converter is on back order until 13 September at this point in time.


It is pretty cheap, less then $200

http://www.moparonlineparts.com/search.htm

Still Burnin Oil since 1992!
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GDE HOT!! Tuned 2006 CRD LTD Silver, Euro TC, GDE Tuned TCM, B&M Trans drain kit
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ac5501

Joined: 17/07/2009 12:56:11
Messages: 4
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GreenDieselEngineering wrote:The TCU is in charge of what engine speed/vehicle speed/pedal position dictates the upshifts/downshifts and when to lockup the torque converter (partial lockup isn't available for this application). However, the engine ECU is in charge of how much torque to allow at those various load points. This is how we can allow either "full torque" while in lockup, or our modified tables which eliminate the shudder while in lockup at the applicable load points.



Does this mean that if we can somehow "trick" TCU into thinking the vehicle is going faster than it is we could then "lower" our shift points?
GreenDieselEngineering
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Joined: 10/07/2009 07:25:47
Messages: 361
Location: Southeast Michigan
The TCU uses several different signals together to determine the shift points.

Vehicle speed does not seem to be a critical factor, at least changing the revs/mi in the cluster did not have any effects. There are other internal checks in the TCM that are limiting the shift points.
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