I finally got around to installing this higher stall torque converter (HSTC) that I've been ranting about for a while. What a difference!!! It turns a very sluggish car into one that really scoots!
Before getting to the details, I'll need to rationalize this to the people who will poo-poo me for not going the 5sp manual transmission conversion route. First off, I live in SoCal and driving in heavy traffic with a manual transmission, changing CDs, answering phone calls etc. can be a real pain. It's sometimes nice just to have a automatic transmission as one less thing to worry about when driving. Secondly, unless you have some parts cars lying around, it can be somewhat expensive, like over $1K. Then there's tracking down the appropriate single mass flywheel, which are not easy to find. Lastly, it takes quite a while to perform the swap. I've never done this, but it looks like we're talking one/two weekends minimal for someone who had never dropped the tranny out of their car before. There's some welding that needs to be done as well.
So, our cars are equipped with the ZF4HP22 automatic transmission. They don't have a good reputation because many of them came with a serious design flaw that would burn out the "A" clutch pack if the transmission was rev-ed in Park or Neutral. First off, don't do this and if you get it rebuilt, make sure they update it so it's not susceptible to this anymore. Secondly, you should change the transmission fluid/filter every 30-50K miles......not 100K+ or even never like some of the factory recommendations. Following a good maintenance schedule should allow the transmission to last the life of our TD cars, to 300Kmile+. One last bit of tranny trivia is the ZF4HP22 is rated to 260lbsft of torque, which is more than enough for our cars, even if you do some mild tuning. You can stuff the internals from the ZF4HP24 transmission into our tranny and have up to 350ftlbs capacity!
Okay, so enough of the techical crap. I tried an OEM solution and that simply didn't work. However, I was able to base the higher stall TC on that component and through my custom supplier, I was able to create one that satisfy my needs. First off, the HSTC weighs 10lbs less than the stock torque converter. This makes the M21 actually rev much more freely like a lightweight flywheel has been installed. Secondly, the revs during normal driving stay right in the meat of the M21 powerband, around 2200 to 2700 RPM and the turbo is always ready to go. The responsiveness is very dramatic. But the biggest problem that's been solved is the off of the line performance. Stock, it seems like the turbo takes forever to spool, like around 3-4 seconds. This has been reduced by around 2second with the HSTC. Overall, this HSTC mod alone could give a 5sp conversion a run for its money in a drag race. But it remains very civilized for daily driving......the mileage should stay the same or even increase as the turbo spools up quicker allowing for more complete burn of the diesel fuel and less smoke as well. Lastly, the HSTC can be installed in one day and then even be able to change the tranny fluid/filter as well.
So, my supplier and I are going to offer this HSTC to any interested parties for $390 plus shipping. It comes with all brand new parts and the internals have been strengthened as well. Specifically, OEM torque converter splines have a tendency to strip and this should be mitigated. Let me know if you're interested.
Disclaimer: this HSTC is rated up to 250lbsft of engine torque. It's not intended for racing activities or for high horsepower applications.
Thanks!
Chris H.
