Virtual Dyno & the ATS-V

I have been working with Tapout Tuning to get my boost up and keep my throttle closed. I ran a session from hptuners scanner to Virtual Dyno to see how things are going.

Virtual Dyno uses the car specifics, such as weight and gearing, and the change in RPM over time to calculate wheel torque and wheel horsepower (whp). Due to the way that the scan was captured, I have limited the rpm range to when the TCC was locked. I applied SAE correction in virtual dyno.

So basically I only needed to focus on the right area in the scanner, export visual, with interpolation, and save off the file. I name the file based on the rpm range of interest as well.

Boost was in the high 17s, again effected by the dynamics of the scan. In this case, I went WOT in third and ran to the top of third, which doesn’t leave as much time for boost to build. I observe that the current tune is building power all the way to the shift point, so good.

A tune-only ATS-V normally has 470-500 WHP, so it looks like we are right in that range.

ATS-V Tune G – Throttle Opening, making torque

Tune G shows more torque production, but throttle opening everywhere.

Changes: AFR (E10 93 oct) 12.5 instead of 12.7. Changes to ramp parameters. Raised overboost limit. Driver demand redone using spreadsheet analysis. Peak torque and Max torque set to 12% over stock.

Conditions: Ambient air 84F; Baro SAE 28.05 Baro 29.23 Weather airport 29.81. Humidity 78F. Correction 1.0214 (29.81), so 480 ft-lbs of torque is 490.2 ft-lbs corrected.

Numbers: Hp 469.2 @ 5357 rpm, torque 480.6 @ 4448 rpm
corrected HP 479 @ 5357 rpm, torque 490.9 @ 4448 rpm.

The throttle closes when boost exceeds desired boost, and closes to the degree those differ. At and example point the throttle closes:

Driver Demand Engine Torque (SAE)109.0 %
Boost Engine Torque Limit472 lb·ft
Final Throttle Torque Req467 lb·ft
Immediate Engine Torque Cmd484 lb·ft
Engine Torque479 lb·ft
Delivered Engine Torque481 lb·ft
Peak Engine Torque561 lb·ft
Maximum Engine Torque472 lb·ft
Predicted Engine Torque Cmd525 lb·ft
torque results when throttle closes

The delivered engine torque of 481 lb ft exceeds the maximum engine torque at that point of 472 lb ft, but not the peak engine torque of 561 lb ft. In the tune, the “Maximum Engine torque limit” table shows 507 lb ft at that point. Max torque for lubrication is 501 ft lbs. So I am unclear why the Max Engine Torque is showing 472 lb ft.

Cadillac ATS-V LF4 Driver Demand Table thoughts and an approach

Gone are the days of pressing the pedal down results in the throttle opening. Now the driver demand table is used to convert driver pedal input to a torque request. The engine management considers the torque request, the predicted torque output, and determines how much throttle is needed.

ATS-V driver demand table, graphs

Yes, the graphs look odd. Part of this oddity is the use of speed for the column values, but the graph also reflects the impact of GEARING across the speed range.

Driver Demand Table, tabular values

This is the same table with values shown. How do we read this table? The left axis is our pedal position, from 0-100%. So if we are at WOT, the bottom row is the row of interest. Note that not all cars have pedal position =100 at WOT. But to keep it simple, as on my ATS-V, WOT gives a 99.6% pedal position so we are operating near the 100 row.

Okay, so what is happening with the columns? The table can be RPM or VSS(speed) based. The axis here goes from 0 to 300, which suggests speed based. When you see huge numbers like these, the table is axle torque. If we saw 0-7200 numbers it would be a RPM table.

Also, conventional wisdom is this is VSS or vehicle speed in Kilometers per hour, not MPH. For an ATS-V with a max speed of 189 mph, the 300 kph table ties out to 186 mph. So that makes sense.

So far so good. Now let’s look at the same table in MPH

Driver Demand in MPH

So we can see we go from 10,113 ft lbs of axle torque requested at 0 mph down to 1,471 ft lbs of axle torque at 186 mph.

Okay, but what about engine torque demand? To get to engine torque, we need to consider the tire diameter, the final drive ratio, and each individual gear ratio.

Driver Demand by gear, RPM, and Engine Torque

So knowing the speed, and the tire diameter, we can calculate wheel RPM. Knowing the wheel RPM, and the transmission gearing (final drive x gear ratio) we can calculate the RPM for each gear. I have ignored torque converter interaction for this purpose.

Now this give us a table with engine torque requests (limits) by RPM range.

What we observe is that in 1st gear, the stock table request is for torque from 778 down to 448 ft lbs near the shift point. In 2nd gear, from 688 down to 502 ft lbs.

Why don’t we just max the whole table out from 0-300? That will result in huge torque delta requests; one oddity of the system is that it tends to respond less rapidly to huge requests, (perhaps fearing that they are in error?) So we want to request close to what we actually need.

It also suggests how the requested torque ends up being numbers we don’t find on individual tables — they are calculated from the driver demand and converted to engine torque.

Building down to minimum requests of 550 ft lbs of torque

In my case I would like my driver demand to be at least 550 ft lbs minimum at any point. So where I see the driver demand for a gear and RPM would fall under 550, I have inserted a 550 in my ‘desired’ area. The final driver demand table 100% row is then a calculated row showing (blue highlights) the cells that need to be increased, as compared to the original table in the row below (marked ‘Original’).

Not every cell needs to be changed. At higher speeds, where one could be in gear 4, 5, or higher, the RPM needs for the LOWEST numerical gear (highest ratio) assure that the resulting axle torque will also exceed the desired engine torque in each higher (lower ratio) gear at the same speed.

Driver Demand G

This is the tune G driver demand table I plan for the next test.

What do you think? Please share your experiences on what has worked well, what has not for ATS-V tuning.