Smoothing out the 2-1 in automatic cars
Cammed autos sometimes may have an issue going 2-1 coming to a stop. If torque management is engaging on the closed throttle downshift, what happens is your idle will drop way too fast, and then overcompensate back the other direction. Idk about you, but this pisses me off and is extremely annoying.
The first thing you need to do is eliminate the timing pull. I can't speak for all ECMs, but removing limit torque management gets rid of the timing pull for my car and I still get to keep my rev matching. If that doesn't work, you need to turn off CT downshift, which will unfortunately get rid of rev matching. Try the limit tq management ect enable first to see if the timing pull goes away.
Ok now that you have the timing pulled, engage a 2-1 stop. One of two things will happen:
- The car is either going to stop with minimal fluctuation
- The car is not going to dip down below idle, but the RPMS will annoyingly rise 500+ rpm from the lack of timing being pulled.
If you're the first one, congratulations. Normally this will happen if you only had to run minimal timing and airflow for your cam. But if you have a cam with some overlap, you probably have pretty decent spark and airflow values, so you will get a spike.
My "trick" to fix this, and it is a bit of a trick...almost a hack, but it works pretty well, is to use the coastdown spark table as my pseudo torque management downshift table.
What I do is put around 8 degrees in the entire coastdown table. If your car has over/under speed for coast, make sure they are zero'd out completely. That's part 1 of the trick. This is going to guarantee that the car will only see 8 degrees of timing during any coasting downshifts. 8 degrees is about the highest you can go before the RPMs start to flare.
The problem now is that the RPMs are going to drop faster because we have such little spark in the coast table. You can solve this by doing either of these methods or both:
- Base airflow table. Add some air to the cells above your idle. Go 1g at a time, log and retest.
- If that is not enough, subtract from the integral airflow table between the -96 and the -512 cells. Take away 10% at a time and retest.
Once these are set properly, there should be no dip below idle RPM as you let off the throttle.
Another problem with such little coastdown spark is low speed coasting is going to sound like your car is dying. What we need to do is bump the idle speed further out.
Set the adaptive idle MPH to the same value as your 2-1 closed throttle shift MPH. In my case, it is 7.2 mph.
Ok you may be thinking now, if we set the idle mph to the same mph as the 2-1 shift, we won't get the 8 degrees of timing.
That is where the idle adaptive delay comes in. Increase the adaptive over/under delay to hold the idle spark out until the shift is complete. The bigger your idle spark/coast spark disparity, the larger the number will be. My example below is going from 8 to 22 degrees spark and while there is a slight RPM jump, it is vastly improved over before when it was just shifting at the full 22 degrees spark.
Play with the idle MPH and idle adaptive delay until you like how the car is stopping. If you can get it to look like the below chart, it will feel pretty smooth.
One more trick that can help the little under rpm blip....
Give the rolling idle 10-15 mph of lead time. So if your target idle is 700 rpm, set 710 rpm to all the cells over 0mph. Some cars come like this already from the factory.