Category Archives: XLR

Cadillac XLR Virtual Dyno calibration

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Using my initial and second (premium) run data captured from HPTuners, I did some Virtual Dyno Analysis (see my initial Virtual Dyno article here).  First I needed a new custom file for the XLR:

Virtual Dyno XLR data

I had run the test data with the top down (worse aerodynamics), and I used a back-to-back wind tunnel test of a different car (Miata) to model the degradation of top down as .06 CD.  I will want to run virtual dyno tests with top up in the future?

I created a 2nd custom file to model the XLR with top down:

Virtual Dyno XLR Tops Down

I edited the .csv saves from Hptuners to only include the acceleration range desired, and loaded both runs.

VD XLR Setup initial Comparison - CD adjusted +.06 for Top down

[click on image to zoom in, back to return]

I adjusted the SAE conditions for the pressure and temps during the test, 29.1 in/hg baro and 100F.  The car intake air was actually a bit higher.  I am not sure this adjustment is quite right — the reference site suggests a dyno adjustment of 4.5% for test conditions.  The Virtual Dyno not-SAE – to SAE goes from 251 to 259 or a 3.2% increase.  A 4.5% increase would be 262 whp, so not much difference really.

The results, 249 whp for the initial test, and 259 whp for the known-quality premium fuel test, seem consistent with expectations.  259 whp / 0.8 transmission losses = 324 hp.  Cadillac rated the stock XLR LH2 V8 engine at 320 hp.

One might conclude the difference between believed-regular unleaded and known premium unleaded in this test case was 10 whp (13 hp).  This is similar (9 hp) to what the calculated hp values showed.

The calculated engine hp vs virtual dyno:

Initial:  2nd gear 293 calc hp x 1.045 conditions adj = 306 hp
Virtual Dyno 249 whp / .8 trans loss = 311 hp

Premium: 2nd gear 302.3 calc hp x 1.045 conditions adj = 315 hp;
Virtual Dyno 259 whp / .8 trans loss = 324 hp

Or told in the other order:

Initial: 306 adj hp x .8 trans loss = 244 whp
Virtual Dyno: 249 whp

Premium: 315 adj hp x .8 trans loss = 252 whp
Virtual Dyno: 259 whp

Note in both tests 1st gear calculated hp was higher, and for comparison with Virtual Dyno analysis of the same runs I am using 2nd gear hp data.

Virtual Dyno depends on consistent, level test area, weights (with/without fuel for example), and conditions for comparable results.  It has however been tested over and over to be consistent with dynojet results when done with proper care.

My conclusion is that I need to do a few more captures of consistent test data for Virtual Dyno use, but the configuration files I have predict results consistent with my other indicators.

 

Cadillac XLR tuning test 2 – premium fuel

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I am running a string of tests to establish a baseline for my 2007 Cadillac XLR.  The previous test is here: Initial Cadillac XLR Hptuners Scanner setup

That test showed 301 hp at 5734 rpm, 290 lb ft of torque at 4572 rpm.  Temp was 95 F.

Tonight’s test was with premium fuel (newly refilled), and without heat soak.  The XLR was warm, having run a set course during the test.  Temps locally were 95 F, 102 F into the engine, and 141 F in the manifold.  Tonight’s run and previous were with the top down.

xlr premium 2nd test first gear

Tonight’s max hp delivered was 309 hp at around 5700 rpm.  Delivered Torque max was 298 ft-lb at 4700 rpm.  This is slightly better than test 1, and I see by comparing the two that incoming air and manifold air were consistent (I was thinking tonight was cooler). Tonight’s engine coolant temp was lower at 192 F vs 203 F last night — unlikely to be a factor.  I suspected the XLR was delivered with regular unleaded and was hoping to see a bit more power with premium unleaded.

xlr premium 2nd run 1-2 gear

This table shows 1st gear, the 1-2 gear shift, and 2nd gear pull.  2nd gear has slightly lower although equivalent hp to first.  I am assuming these calculations are unaffected by vehicle aerodynamics, but I may be wrong.

Here is the HPtuners scanner shot at max hp:

XLR premium test 2 hptuners

Summary:

Tonight’s test is very consistent with test 1.  With the XLR sitting all day prior to the test and not heat soaked, but with same temp air, the results were slightly (8 hp, 8 ft lb) higher than previous.  In the heat there is almost 2 degrees of retard (lost advance) due to incoming air temp advance (gauge in lower right).

Corrected to SAE standard these readings would be higher:  Note: The relative horsepower calculations are made in accordance with SAE J1349. The standard reference conditions for SAE J1349 are: Air temp 77 deg F (25 deg C), 29.235 Inches- Hg (990 mb) actual pressure and 0% relative humidity.

  
Corrected factor for conditions: 1.045.  Corrected hp: 309 x 1.045 = 323 hp.  298 ft lb x 1.045 = 311 lb ft of torque.  These appear consistent with expected 320 hp & 315 lb ft engine rating from Cadillac.  

I would like to see additional tests with no changes for repeatability, but overall the XLR LH2 appears to be performing as expected.  These tests will form the baseline to compare for tuning or mods.

Convertible Cadillacs – Street Side Classics

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Today I went by Street Side Classics in Fort Worth to see the wide variety of Cadillacs they have on hand — convertibles from the 60s, 70s, 90s, and 00s.

They have main showroom, then a nice warehouse full of interesting cars.  This 2009 XLR Platinum was the first Cadillac we ran across there.

There was an Allante there, I believe an 87 with removable hard top in place:

Next was a set of 68s with a 64 near by:

 

 

 

 

 

We had a great time looking at all the Cadillacs, and other cars.  The shopping trip helped me along in my thinking about what type of Cadillac convertible I want for my weekend car.