See a lot of misinformation out there. This should clarify how the PCM and TCMs work together, a lot of guys know this but may not have mentioned it formally.
The PCM has two rpm limits, and they are 100% engine rpm limits.
RPM Limit Drive - this is how far the engine can rev before fuel and spark cutout will happen. If you have your settings right (read on) you WILL NOT go into limp mode for hitting this limit, you will simply feel the engine nose over and stop making power
RPM Limit P/N - like it says, engine rpm limit when not in gear. Dodge liked the idea of not letting 16 year olds free rev the motor to a valve bending RPM. I like to keep this stock or maybe mid 4,000s rpms.
Now, this is where it gets wacky. There is also a TCM rev limit, completely outside the PCM, that is the absolute max the transmission and motor are allowed to go. If you get to this point, YOU WILL GO INTO LIMP MODE and throw a few codes. Transmission will likely be locked to just second gear until you park, cycle the key on and off, or clear the codes with a scanner. Think of this limit as the end game limit, there is no soft limiter, no fuel cut, no spark cut, just a pure "no more transmission at all" limit, literally throws the trans into neutral at the instant you hit this limit.
The only way as of today to get a higher than stock TCM Rev limit (limits layed out below) is to buy an aftermarket one or get your stock one reprogrammed by the few who have cracked the code.
Factory TCM (5.7/SRT8) - commands shifts at 5800 or so, Rev limit is 6700
Mopar TCM - commands shifts at 6200, rev limit stock at 6700
Programmers - Paramount, Eurocharged, AJ Hemituner (google him and you will find his info) - they can program any shift/rev limit combo you want.
Diablo - has figured most of this out, except raising the TCM rev limit. They offer "raised" shift points option that adds about 200rpms to whatever TCM you have, but I have hit the MTCM 6700 limit and gone into limp mode, so beware.
Here is how it all meshes together, you ALWAYS want your shifts to be completed around 100-150rpms BEFORE the TCM rev limit, and should have your PCM RPM Limit in Drive set here (6600 for a factory or MTCM, or like me I have a 7200 limit Paramount and have my RPM Limit in Drive set to 7,000). You want to hit the PCM rev limit before you hit the TCM rev limit to avoid limp mode. Moderate powered cars with a factory-ish transmission will complete shifts within 250-350 rpms, so for example the MTCM tends to finish up shifts around 6450-6500 rpms when it starts the commanded 6200 shift on a factory transmission. My Paramount TCM + SHR transmission even at 800whp commands a 6500 shift and its done before 6600, so I have room to play.
Basic formula for the not so gifted after reading the above:
Decide your TCM rev limit based on the above(either 6700 or something you had made custom); set your RPM Limit in Drive 100rpms before this.
Where this plays into the new Hellcat RPM limit everyone was hammering about at 6200, was a PCM based rpm limit, that appears to now have been found.
Hope this helps out a bit.
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Originally Posted by Chris@HPTuners
