CaddyInfo Cadillac Chat 2015-09-17



  • Platform names
  • Cadillac XT5 — Does Cadillac need a high performance Battery electric vehicle Tesla Competitor?
  • Intercooler coolant temperature control
  • Programming VVT on the Cadillac LC3

After the chat I redid the analysis of cd 0.31 vs cd 0.33 and determined only 1 whp delta, but playing with loading different profiles showed me something was wrong with my default profile.  Here is a comparison showing Tune 6F if the XLR was 0.31 vs 0.33 cd:


xlr comparison of different CD 031 vs 033

What we see here is the Tune 6F at 0.31 coefficient of drag in red, and the same data except CD 0.33 in Blue.  The blue is 1 whp better.  All other setting identical.

Note that with the profile fix or re-ordering, Tune 6F is now registering at 252 whp not 241 whp with the previous default profile.  Unfortunately, now that I reloaded the profiles to get the CD test to work, I can’t ‘go back’ to the broken default profile to understand what was different about it.

Additionally, I created this graph to compare Virtual Dyno output to calculated torque & hp:

XLR Tune 6F Compare Calc HP to VDyno Output corr

The blue and red lines are the calculated torque and hp. The high yellow line is the corrected hp for atmospheric conditions.  The orange and light blue lines are the virtual dyno w-torque and whp.  The Green line is the Virtual Dyno line with a factor applied to move it up to the calculated hp.  The green line is a smoothed line (average of averaged of values) but appears to be a good fit for the calculated hp curve.  This surprises me as I was thinking that the virtual dyno and the calculated hp frequently do not follow one another based off of the detailed data.

There is still some additional losses in both sets of data from running the test in 2nd gear instead of a 1:1 gear.  The XLR doesn’t have a perfect 1:1 gear, but testing in 2nd is a trade between smooth data, safe testing, and mechanical losses.


VVT Tuning & Info for the Cadillac STS-V LC3 V8

I plan to update this page with notes on variable valve timing tuning for the LC3 DOHC VVT Supercharged V8 in the STS-V.


HPTuners Table — Intake Cam position


HPTuners table — exhaust cam position

Cam Phasers: [ref]
Intake: Initial timing 133 degrees ATDC with 40 degrees advance authority
Exhaust: Initial timing 117 degrees BTDC with 50 degrees retard authority

Valve Lift: Intake: 10.5mm (.413 inch)
Exhaust: 10.0mm (.394 inch)
Duration @ .050″
Intake: 202 degrees
Exhaust: 214 degrees

One of the key elements in achieving the broad output of the LC3 is the variable valve timing (VVT) system. With VVT, the seemingly opposed objectives of smooth and torquey low-end output, and massive specific output to a peak at 6400 rpm become possible, using individual hydraulically actuated phasers on each of the four camshaft. “Four-cam VVT is an exceptional performance enabler, but also provides the control flexibility needed for highly advanced NVH and emissions characteristics,” said Dave Caldwell, Northstar V-8 SC development and calibration engineer. “The supercharger module and VVT system complement one another, resulting in a genuine luxury and performance engine.”

This system allows the camshaft phasing to be altered in relation to the piston position, as well as in terms of event timing between the intake and exhaust camshafts. The VVT system was introduced last year on the normally aspirated Northstar 4.6 liter V-8, and the system received all-new command strategy optimized for the supercharged 4.4 liter application. The variable valve timing system makes it possible to target optimal idle quality, control cylinder pressure and detonation, and enhance drive-ability, while providing for the high-speed breathing necessary to turn a number at the top of the power band. Another advantage of the system is a reduction in exhaust emissions, which effectively eliminated the need for supplemental emissions equipment in the form of air injection or exhaust-gas recirculation systems while meeting today’s stringent emissions standards.

Simple cam tuning rules for BOOSTED engines: [ref]

  • Advance intake and exhaust => more low-RPM power, less high-RPM power
  • Retard intake and exhaust => more high-RPM power, less low-RPM power
  • Less overlap => lower EGTs, faster turbo spool, less fuel
  • More overlap => higher EGTs, slower turbo spool, more fuel
  • Conclusion: Advance Both at Low RPM, Retard both at High RPM

What is happening in the VVT cam programming for the LC3:

Intake:  From 3200 to 6400 RPM, position set at 20 degrees
Exhaust:  At low RPM position set at 5 degrees, decreasing to 2 degrees at mid and back to 5 degrees at high RPM

The VVT strategy the factory tune is using seems odd — the hope of VVT is to change the position of the valve timing from low (3200) rpm to high (6400) rpm, but the system appears to command a similar intake (20) and exhaust position (5) for both rev ranges.  The conventional wisdom for boosted engines is more advance for both at low RPM and more retard for both at high RPM.


The challenge of tuning a motor with VVT is that every change of the cam timing must have a corresponding change to the ignition timing and fuel tables. In one example, a change to the cam timing caused the PCM to enter a different cell on the spark table, which killed the timing and power in the mid to upper rpm as the result.


What do you think?  Why did the factory take this strategy?

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.