Cadillac STS-V Performance Modeling

Cadillac STS-V performance can be modeled, as with any other vehicle, using software similar to the CarTest 2000.  Simulators don’t always give perfect exact real-world predictions of exact performance, but they offer a ready way to test our assumptions and to model and understand the results we do find.

The 2006-2009 Cadillac STS-V has a supercharged DOHC, VVT Northstar rated at 469 hp and 439 lb ft of torque.  Originally GM estimated that the engine would produce 440 hp, but in the final SAE certification some assumptions changed — such as normal supercharger coolant temps instead of worst case — and the final rating was 469 hp.

2008 Cadillac STS-V Cartest Stats

2008 Cadillac STS-V Cartest Stats [click to zoom, back to return]

This screen shows Cartest stats for the car.  With peak hp and torque at their RPMs the software can make assumptions on the power curves.  Knowing the other stats — weight, gearing, tires — the software can estimate vehicle performance.

Cartest Car Specific Parameters

Cartest Car Specific Parameters

Cartest also allows the user to specify car specific parameters.  This is helpful in matching real-world conditions.  For example, driver weight, altitude, and atmospheric conditions all change the expected acceleration result.

STS-V Comparison Analysis

STS-V Comparison Analysis

Cartest allows the user to run a variety of tests; this shot shows some portions of a side by side comparison test of a stock STS-V, a car modified to 500 hp with no change in torque similar to my current mods, and a car with a 10% supercharger pulley — modeled here as an increase of +25 hp / +50 torque.  Tim Coeling offers a 2.55″ modified upper pulley for the STS-V.

What we see is that opening up the top end breathing from car 1 to car 2 added +30 hp, as my intake and exhaust mods have, it makes little difference in the estimated performance, 0.1 sec by 60 mph and 0.4 sec by 100 mph.  On the other hand, increasing the torque by over driving the supercharger makes more difference to the acceleration.  Not surprising since acceleration depends on torque and not hp.

A beauty of the software is that it allows side by side comparison with target models.  For example, how does the Cadillac STS-V performance compare to a 2011 BMW M3 track car with 4L, 414 hp V8 screaming at 8300 rpm redline?  For this test I have renamed the M3 as “Cadillac STS-V 2008 A Challenger …” for ease of selecting it from the car list:

2011 BMW M3 vs 2008 STS-V

2011 BMW M3 vs 2008 STS-V

What we see here is the 3600 lb M3 makes use of its 7 speed sequential gear box and 600 lb weight advantage to stay ahead of a modified 500 hp STS-V, and match a pulleyed 525 hp STS-V.

When can more power be slower?

It is good to mention that in cases, more power can actually slow a car down.  For example, in our analysis above if we take the same STS-V but increase the power to 550 hp with the same torque, it is slower in 0-60 mph, but faster in 0-100 mph.

More Power, slower 0-60

More Power, slower 0-60

I believe that the simulator in this case is anticipating more wheel spin at the 1-2 gear shift due to the increased power.  To take advantage of the new power curve the shift points would need to be altered.

Cadillac STS-V Performance

The Cadillac STS-V Performance sedan uses a custom Eaton M122 supercharger.  It uses a 2.1:1 ratio, so that the blower as it arrives is spinning x2.1 engine rpm, or 14K+ RPM for the supercharger at 6700 rpm for the engine.  [More discussion in my post – Adding Boost Pressure to the LC3] That is also the top range of efficiency for the M122 — past that speed the supercharger starts to make more heat than pressure.

However, because a smaller pulley increases the boost pressure at lower RPMs, and thus the torque, it can have a larger impact on the acceleration of the STS-V than on the peak HP.   I will also need to address adding more fuel; the model assumes that I am taking care of how to make the power.

Virtual Dyno by Brad Barnhill Review

Virtual Dyno by Brad Barnhill is a stand-alone software program that analyzes and presents data captures in the form of a virtual dyno graph.  It can work with a variety of datalogging formats.

I have been interested in Virtual Dyno and have read a bit about it.  Today made a good day to grab several data runs, slice them up, and compare.

Virtual Dyno data capture

I used my normal 20 minute test drive route.  I ensured that I added several 2nd gear pulls from 30 mph to 60+ mph, as I wanted to check that range at the top of 2nd gear.  I am unfortunately far from Mexico, where all true internet speed captures are done (lol), so a true 4th gear pull to 144+ mph is not in the cards today.

Virtual Dyno data preparation

To capture the data, I used HP Tuners VCM Scanner.  I exported the data file with all runs to a .csv comma delimited file.  I used VCM Scanner gauge review to find the 0-60 runs and noted the sample range for each run.  Then I used Open Office Calc to edit the .csv file, creating new .csv files with only the acceleration run of interest in the .csv file.  I renumbered the sample for each run from 1..n within that file, and named the file by the sample file name and sample range.

Although Virtual Dyno includes a file for the STS-V, it treats them as if the weight were constant for all model years, although it was not. The correct weights are 4,343 lb in 2006, 4,295 lbs in 2007, and 4,233 lbs in 08/09.  I created a custom file in the app data section for the 08 STS-V.

in addition, my STS-V has an extra inline intercooler tank (12 lb with coolant) and a ZZP front mounted heat exchanger (6.4 lbs). So my curb weight would be 4,251.

Today my car was at 1/2 fuel, so 9×6=54 lbs of fuel missing; 4251-53=4199 lbs.

Virtual Dyno screen shot

Virtual Dyno Screen Shot [click to zoom, back to return]

Virtual Dyno includes a few different dyno settings and adjustments.  Since my actual dyno was done on a dynojet I selected it.

Virtual Dyno Screen Shot

This screen capture shows Virtual Dyno crunching 3 different datalog runs from the same day. The data run file info is shown to the left, and the data runs are graphed to the right.

I wanted to compare them side by side to decide repeatability.  With many modern cars this in itself is troublesome — my 2008 Cadillac STS-V will tend to run quite differently from one run to the next.  So determining what variability is due to the software and what variability is due to the vehicle performance is tricky.

Virtual Dyno Graph

Virtual Dyno Summary

Virtual Dyno exports the graphic output into an image file, which makes it easy to use and reference.  What my runs seem to show is that the first run, while the STS-V was up to temperature, but still relatively cool, the V made the most power at 485 whp.

The other 2 runs had relatively more wheelspin, and made relatively less power, at 363 and 349 whp, although within a relatively close range of each other.

Here is the HPTuners Gauge output for the max hp run:

Virtual Dyno comparative HPTuners Gauge Output

Virtual Dyno comparative HPTuners Gauge Output [click to zoom, back to return]

Hot on the dyno before the cooling additions my STS-V made 394 whp on a dynojet dyno in 4th gear.  Assuming the virtual dyno is setup properly and interpreting the data presented, what we may see here is that there is a lot of variability in the power the STS-V produces.  Even with traction off, a lot of wheelspin in 1 causes early shift to 2nd and a longer pull with the intake temps heating up, and power reduced.

HPTuners Gauge snapshot for the lower HP [blue] run:

Virtual Dyno HP Tuners Snapshot

Virtual Dyno HP Tuners Snapshot [click to zoom in, back to return]

Virtual Dyno Smoothing 3

Virtual Dyno Smoothing 3

Virtual Dyno Smoothing

Virtual Dyno offers a range of smoothing.  Smoothing is averaging of the values relative to their surrounding values.  It has the effect of better showing average or trend information out of relatively bumpy real life data.  A smoothing choice that shows smooth data trend lines but no more than needed seems best — and consistent from run to run and day-to-day.  The upper graph has smoothing 4; the lower graph has smoothing 3.  I plan to stick with Smoothing 3.

Virtual Dyno — What does it all mean?

Virtual Dyno gives you another input to try to measure how your vehicle is performing.  It has the advantage that you can use it on the street at your leisure.  It has the disadvantage that you have to exercise more care to isolate and eliminate variables in your test method.  Otherwise you won’t have comparable tests from one day to the next.  As software I find Virtual Dyno easy to use and pretty consistent.    It is another tool in my toolbox of car metrics.  I will continue to work on repeatability.

Meziere 55 gpm intercooler pump?

Meziere 55 gpm intercooler pump sounds even more pumped up than the Jabsco 29 gpm pump.  Torq has a kit for the Camaro ZL1 with the pump mounted to a bracket and ready to bolt in for that app.  They have been doing test and just announced the kit on Camaro5.

Meziere 55 gpm pump

Meziere 55 gpm pump with bracket and wiring

After getting my Jabsco pump experiment together I appreciate that Torq is offering a complete ready to install kit for the ZL1.

The Meziere 55 gpm intercooler pump would be a remote mounted 12v pump like the Meziere Enterprises WP365S.

Meziere 55 gpm intercooler pump

Meziere WP365S

I have emailed Meziere to ask for a pump performance curve, not having found one on their website.  The pump performance curve shows measured output of the pump at various system resistance points.  Considering the curve versus the system resistance curve would let us estimate how the pump would flow in an actual intercooler system.

Assuming that the Meziere 55 gpm intercooler pump has a higher shutoff pressure than the Jabsco pump, and a similar pump curve, it should have higher flow.  Lots too many ifs until we can get a pump performance curve, but if I had to guess I would say that it might do 8-9 gpm in a system.  So with my 2 heat exchanger system, and an inline tank, the OEM 8 gpm pump does 3.5 gpm, the Jabsco 29 gpm pump does 4.5 gpm, and the Meziere 55 gpm intercooler pump might do 8-9 gpm.

Keep in mind that as the flow goes up, the pressure goes up more.  These are centrifugal pumps, so as the pressure goes up they have less flow.  By comparing the system curve and the pump curves we can predict the spot where the pump will work, once we have the pump curve.  I’ll update if Meziere shares that spec.

Summary — Meziere 55 gpm intercooler pump

Torq, in concert with Meziere, is offering an intercooler pump upgrade ready-to-install kit for the Camaro ZL1.   In their bench tests the kit was advantageous.   The kit could be modified to work with the Cadillac STS-V or CTS-V.  I have not tested the Meziere 55 gpm intercooler pump to determine exactly how it would flow in our systems.  This is a more expensive pump, although I have not seen a price quote from Torq yet.

Torq main website