I had quite a bit of "fun" getting the LS3 in my Miata to drive smoothly at low load and low rpm (which describes 99% of street driving in a car like this). Even the stock tune that came in the GMPP controller I bought for my LS376/480 crate engine was a **** show under these conditions. And that was with a heavy 52# LS7 flywheel and clutch setup.

The engine currently is 11.8:1 CR, with a 227/232 114+1 camshaft in it. It's got a very light RPS BC2 clutch on an aluminum flywheel ... 25# total. Also long tube headers.

After quite a bit of tweaking, I finally have it running very smooth. I thought I'd attach my tune here so people fighting the same issues could have a look.

The things that I believe contributed to getting this running smoothly, which you can see in the tune...

-- Reducing ignition advance at light load, low rpm, i.e. parking lots and my neighborhood. This car is so light, and the engine so powerful, that cruise is at .18-.20 cyl air on the highway, and as soon as you're off throttle, you drop to ~.08-.12 cyl. air
-- Setting up the O2 sensor proportional gain table and O2 mode vs. Airflow table ... long tubes like different than stock settings due to the signal delay compared to the stock manifolds.
-- Set up the O2 switching voltages vs. Airflow mode to be lean at cruise and richer as load is added.
-- End of injection timing (EOIT) is later.
-- Idle minimum airflow can't be **too** low in the areas above actual idle. I noticed the car would start bucking when I closed the throttle in my neighborhood or a parking lot. When I adjusted the tune for more idle air at those rpms, that stopped.
-- Lowered main throttle mapping in 'Airflow/Electronic throttle'
-- Lowered throttle follower step up/down to 50% of original ... this was a big help

In order to be able to run more coastdown spark on the highway (for fuel economy) at my cruise rpm of 1200-1600 rpm, I use the adaptive idle all the way up to 35 mph. This means that in a parking lot or trying to creep through my neighborhood, I'm running as low as 1.5 degrees of advance off throttle ... that smooths the car out a lot, and gives a nice crackle on decel.

There is a fair amount of trial and error involved in getting the off throttle behavior to be smooth. Too much idle air or spark and you get "cruise control". Too little spark and fuel mileage might suffer. Too little air above actual idle speed, and it can be rough off throttle in parking lots. Play around...

Obviously, the MAF calibration, the injector calibration (I’m running GTP36 injectors), and most of the spark calibration, may not be suited to your engine.

Hopes this gives others a leg up

LAST UPDATE OF ATTACHED TUNE ... 1/31/23

KEYWORDS FOR SEARCH: bucking jerking surging trailer hitching

 

Odd you have such a huge gap in timing between the idle tables and main spark tables around idle. I usually make base and low/high tables about the same spark in the idle region so you dont end up with bucking transitioning from a stop/low speed.

 

Just off idle is cruise in 6th ... so I want a lot more timing there than I do at 1200 rpm with the car stationary. It actually pulls away from a stop pretty smoothly. The car cruises at .16-.20 cyl. air in most situations, so the operational area is maybe more compressed than it would be in a heavier car. Not sure.

 

Very true on the weight. That makes a huge difference, but that flywheel/clutch combo is tougher to tune as well so they probably offset each other.

 

Updated the tune file attached to the original post. The car is perfectly acceptable and streetable to drive at this point.

Areas I found to be most productive in addressing poor driveability with this very light M6 car with a very light flywheel are addressed in the original post