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R/T and SRT drivetrain differences

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White Elemant

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Discussion starter · #1 ·
I need something to throw my money at. Prolly gonna be a Jeep GC or a Durango, so:

Are Durango R/T and SRT drivetrains the same: Transmission, transfercase, axles, hubs, whatnot?

I'm asking this to determine the extent of part swaps when tuning. R/T's are surpricingly affordable here in europe, but SRT's are not, so it would make sense (or actually it would be less stupid) to buy a high mileage R/T, and swap a built 6.4 in it rather that buy an SRT and mod that. That is, if the R/T drivetrain can handle it.
 
#3 ·
shelbymopar89 said:
I am not super knowledgeable on this but I do know one difference for you. The R/T’s have a two speed transfer case with Hi/Low range. The SRT’s have a single speed transfer case. That’s about all I can help!
Click to expand...
Not all R/T's have the two-speed transfer case. Only the R/T's with the factory tow group (non-TnG) have the 2 speed box.
 
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#5 ·
The R/T can also be had in rear wheel drive only, which is what I have. The SRT is all wheel drive only, and to me that is a negative. I know plenty of people like AWD (and I get why it appeals to them), but to me its unnecessary weight and complexity. I probably would have shopped SRT when I was looking if it came in a RWD option. On the other hand, the delta between the SRT and R/T was huge and past the point of diminishing returns.
 
#8 ·
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#9 ·
See if you can find a R/T which has the "Tow N Go" Package"; not to be confused with the standard tow package.

A R/T with the Tow & Go package is essentially a SRT 392 vehicle, except it has the 5.7L motor and 3.09 differential gearing. Everything else (transmission, AWD transfer case, differentials, brembo brakes, bilstein suspension, track/sport/snow/tow drive modes, etc, etc ...) is the same as the SRT. It even gets the fender flares and black rear valence. And the exhaust setup is just perfection as it is.

If you can find one of these, you may be able to get it for a decent price considering most dealers (and individuals) don't really understand the package. If ordered new, it is a $6k upcharge from the factory, and it'll show up on the window sticker as "Tow N Go Package".

Here's what it looks like on my window sticker:

Image



and here's a video demonstrating the OEM exhaust sound from my Tow N Go (this was before any mods):



If you can find one of these, then the drivetrain can already handle at least the power of the SRT's 6.4, since all the driveline components are the same. As an added bonus, you get the stopping power of the 6 piston Brembo SRT brakes and the handling of the electronic Bilstein adaptive suspension.

This is what I did ... bought a 2023 R/T with Tow N Go, then added a Whipple 3.0L supercharger to up the power :)

I debated on how to add the additional power, and you can read about that decision process here: https://www.dodgedurango.net/thread.../threads/10k-to-bring-r-t-tng-up-to-or-over-392-srt-power-levels.87532/#replies

After I decided on the Whipple, I then documented the install of that here: https://www.dodgedurango.net/threads/3-0l-whipple-install-on-2023-r-t-t-g.88875/
 
#11 ·
The R/T and the SRT both use the same transmission, and it's the ZF8HP70 ... which is rated to handle up to 700Nm (or 516 ft/lb)

The Hellcat uses the ZF8HP95 transmission, which is technically rated to handle up to 950Nm (or 700 ft/lb) even though the engine is spec'ed for 707 ft/lb with standard fuel and 727 ft/lb with high octane fuel.

So the components and torque converter are different in the HP95, and much stronger than the HP70

bigchad4200 said:
Transmission on the Hellcat is almost the same, Tuned better an upgraded stronger parts.
Click to expand...
What do you mean by "tuned better"? I've been tweaking the tune on my Supercharged R/T and am curious what is done to make the Hellcat trans a better tune.
 
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#12 ·
stoopalini said:
The R/T and the SRT both use the same transmission, and it's the ZF8HP70 ... which is rated to handle up to 700Nm (or 516 ft/lb)

The Hellcat uses the ZF8HP95 transmission, which is technically rated to handle up to 950Nm (or 700 ft/lb) even though the engine is spec'ed for 707 ft/lb with standard fuel and 727 ft/lb with high octane fuel.

So the components and torque converter are different in the HP95, and much stronger than the HP70



What do you mean by "tuned better"? I've been tweaking the tune on my Supercharged R/T and am curious what is done to make the Hellcat trans a better tune.
Click to expand...
I'm not exactly sure but the what Dodge engineer told me that.
 
Discussion starter · #13 ·
I would not call 8HP70 and 8HP95 "the same transmission".

I couldn't locate the source quickly, but I recall reading that they are not directly interchangeable, even though the "crust" is the same. For example the TCUs have different capabilities.
 
#14 ·
White Elemant said:
... the TCUs have different capabilities.
Click to expand...
Interesting ... do you know what the different capabilities are?

I've been studying TCM reads from R/T's, SRT's and Hellcats for a while now, as I learn and make changes to my transmission tuning.

I haven't come across anything available in the 8HP95's TCM which I'm not also finding in the 8HP70's TCM
 
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Discussion starter · #15 ·
stoopalini said:
Interesting ... do you know what the different capabilities are?

I've been studying TCM reads from R/T's, SRT's and Hellcats for a while now, as I learn and make changes to my transmission tuning.

I haven't come across anything available in the 8HP95's TCM which I'm not also finding in the 8HP70's TCM
Click to expand...
I think I read somewhere on www.cherokeesrt8.com forum that 8HP95 TCM has capability for more agressive shift strategies for example. That does sound odd, since it's just a computer, and it would seem logical that the actual differences are in valve body...

What tool are you using to study the TCMs?
 
#16 ·
I'm using HP Tuners' VCM Suite software.

The TCM's all have the same shift strategy capabilities, but how the capabilities are configured can be different based on the different models and features.

Shift scheduling has "patterns", and a lot of them:

Image



Then there are tables which allow mapping of driving situations and driver aggression type to those patterns. This is why you can drive aggressively and the tans will shift different for a while, until you go back to driving normally again.

Image



Image



As an example, here is pattern 5 .... which is the standard shift pattern for auto drive mode and a low aggression driver type. The cells in these shift pattern tables hold tail shaft output speed, not engine RPM:

Image



Then when looking at the various clutch control tables (ie: like pressures), there are different shift modes ... Normal (auto mode), Perf (Sport mode), Sport (Track mode), and Max.

Image


Then there are additional control tables which direct the TCM to use a particular mode based on other parameters; mainy which drive mode is selected by the driver. Normal and Perf are available on all HP70 and HP95, Sport (and most likely Max too) are only available on vehicles which have drive modes (R/T with TnG, SRT and Hellcat). But that's really only because the driver has no way to select Sport or Max, not becuase the TCM is any different.

So from the factory, the Hellcat's HP95 may be setup differently to use various modes under different circumstances, or be setup for different shift pattern RPMs and scenario mapping, but the overall TCM capabilities and approaches are the same across the transmissions ... at least, that's been my findings thus far as I learn this.
 
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Discussion starter · #17 ·
stoopalini said:
...
So from the factory, the Hellcat's HP95 may be setup differently to use various modes under different circumstances, or be setup for different shift pattern RPMs and scenario mapping, but the overall TCM capabilities and approaches are the same across the transmissions ... at least, that's been my findings thus far as I learn this.
Click to expand...
Nice! One must, however, keep in mind that the HPTuners' mapping of the 8HP variant is probably not exhaustive. But again, it would be weird to have differing TCU HW and SW (other than settings) for trannies that are of the same family.
 
#18 ·
Yeah, sometimes HP Tuners gets some mapping incorrect and has gaps. I definitely experienced this with the operating system which came in my 2023 R/T TnG. It took a while to get HP Tuners to acknowledge it and fix it for me. Thy not only fixed some table mappings I knew were wrong, but they also added a couple hundered new mappings which were not included when they initially added support for my OS.

That said, the ZF8 transmissions are widely used across manufacturers and seems to be pretty complete in VCM. I did run across one table which seems to have strange values in it, but HP Tuners support insists it's accurate and correct.

Another interesting thing is the TCM is actually part of the valve body, which makes sense since it's all electronically controlled. The PCM does have some transmission control components in it, and the TCM also has some engine control components in it (ie: TQ mgmt, etc ...), but in general, the TCM mappings seem to be pretty solid.

By comparing my OEM R/T calibrations to those of a stock SRT 392 and to those of a stock 6.2L Hellcat setup, as well as comparing them to what Whipple changed them to in their canned tune ..... I've been able to make mine shift very nicely with the Whipple supercharger installed.

My last adjustment to it was a couple of days ago, and the very next day the wife texted me while she was out running errands to tell me "The transmission is shifting like butter!" She doesn't know when I make changes, but obviously this time she recognized the improvement and appreciated it :)

Don't get me wrong, it is a very complex setup (bot the PCM and TCM), and I've been working on it since April ... when I did the Whipple install. I went through 3 different tuners, who are all skilled ... who tried to get this right ... but in the end, I just needed to learn it myself if I wanted it to drive like a factory Hellcat does. And dare I say, I've now achieved that :)
 
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#20 ·
Haha, sure! Happy to share what has worked for me!
 
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