Converter Stall Speed

When swapping a stock Allison converter behind a Cummins or other low rpm high torque diesel, be prepared to purchase a low stall torque converter, rather than use the Duramax converter. Now, don’t believe anyone who says that a Duramax converter won’t work – that isn’t true, but what those people may mean is it won’t transfer the low rpm torque to the ground very well – when it is not locked up you will notice the transmission will feel quite “slippy”, and what you may especially notice is when it does lock up your engine may drop 800-1000 rpm – a very strong indicator that your low rpm torque is totally wasted and not being put to the ground. If you buy a cheap “low stall” converter on ebay and see this kind of RPM drop after lockup, you were ripped off. Realize with a low rpm engine, that 1000 rpm drop can be a real problem when all you have is 2300-2900 rpm to work with.

Some may argue that locking up in 2nd gear solves the poorly matched stall issue, but I’ll go on record to say it doesn’t and here is why – to begin with, getting a heavy diesel with a trailer in tow moving in 1st gear is where the low stall converter is needed most (visualize gutless diesel pig having trouble going over a speed bump) – and secondly, if you have 1000 rpm of slip with the converter unlocked in 1st that is going to make lockup in 2nd gear rough to violently shocking, even with custom tuning – so don’t skimp in your plans with the converter stall.

For trucks less than 325 hp, an Allison low stall converter is fine (the TC-222 being the lowest stall). These are available from many transmission parts houses – Xcalliber is one worthy of mention.

TC-210,  29538531 or 29543015,  Orange tag
TC-211, 29541293 or 29543003, Green tag
TC-221, 29540484 or 29543017, Black tag
TC-222, 29540520 or 29543016, White tag

If you have over 375hp, I recommend a billet converter from Goerend first, SunCoast, or Precision if you just can’t afford Goerend – they are an investment, at least $1545 or more, but worth it. Most of my typical Cummins customers that buy Goerend have chosen the “X” stall ratio and we have been very pleased with how that performs. One customer would go one step looser (the “G” or the “E”) if he did it again so take some time to consider what your preferences are and what your specific build may benefit best from (rpm requirements for custom turbos, etc).

Tell the other vendors what engine you have, expected rpm range, and so forth and ask them for their recommendation if you choose someone different.