Cadillac XLR Virtual Dyno Testing 2015-08-28 #Motorama

I have been testing my 2007 Cadillac XLR with the LH2 4.6L DOHC V8 engine to establish a baseline prior to any mods or tuning.

Today the air was a bit cooler, although not as much as I had hoped.  HPTuners VCM Scanner recorded a 97F intake air temp, and 29.83 barometer during the test.  For safety, testing is done in 2nd gear which is not optimal — it should be done in a 1:1 ratio or as close as possible.  I am using Virtual Dyno to convert captured export data from hptuners to a on-road dyno result.

XLR cooler day 2015-08-28 2 run comparison

[click to zoom in, back to return]

The red and blue runs are both from today, and run within 6 minutes of one another on our 2-test area cycle.  I was hoping to see a bit more whp in the cooler air, but I suppose 97F not all that cooler than 104F from the prior tests.

XLR cooler day 2015-08-28 4 run comparison

This second chart shows today’s 2 runs in yellow and green vs prior runs in red and blue.  Corrected for temp and gas, the results seem fairly consistent at least.

All runs are using current method, which is drive to a known point with transmission manually selected to 2nd gear, then wide open throttle until fuel stop at redline.  Rinse, repeat.

Info Video about this type of testing

xlr cooler day 2015-08-28

Calculated hp/torque for the LH2 in this test peaks 308 hp @ 6635 rpm, and 296 lb ft at 4503 rpm.

Today’s tests appear to be consistent with prior tests.


Cadillac XLR validating frontal area calculation

2009 Cadillac XLR

2009 Cadillac XLR

I did a bit more work on frontal area, which appears to support the short-cut we took earlier.

From a thread on Virtual Dyno on HpTuners, The quick way to calculate frontal area is (((w*h)(0.85))/12)/12 = Frontal Area.

For the 2007 base XLR, W=72.3in,  H=50.4in so for a first approximation (((72.3*50.4)*.85)/12/12)= 21.5 ft2.

The question then is the 0.85 factor.  To test that, I downloaded a diagram of the 2007 Cadillac XLR from and pulled just the frontal area into a photo editor.

cadillac-xlr-2007 frontal

Next, I selected the parts of the diagram that were NOT XLR

xlr outline of not xlr

Then I used the photo editor (GIMP) to tell me how many pixels were shaded (20,668) of the total pixels size (149,464) which resolves to 20668/149464 = 13.8%, or 86.2% for the XLR.

That makes the frontal area for the 2007 base XLR, (((72.3*50.4)*.862)/12/12)= 21.8 ft2.  In this case the approximation was good, but I will update my Virtual Dyno XLR profile to 21.8 ft2.

More Cadillac XLR baseline Virtual Dyno runs

XLR Retest Sunday 3 way Comparison

Couple of quick runs today to gain more data to see what consistent results look like.  The red and blue runs are both done today, from two different test locations.  The green run is run 3 from yesterday at the same location as the blue run.

I altered my test method to lock the XLR into 2nd gear for the test, so that we get a longer look at the torque curve and so that we see how the hp falls off or sustains from 6000-6700 rpm.  XLR retest sunday flat blue

For today’s test Engine Coolant Temp stayed at 199F so out of ECT retard, and the advance was a healthy 25.5 degrees at 6558.  Piston protection kicks in at 6000 RPM and the engine adds 0.5 air fuel ratio AFR to command 12.0 as shown.  The LH2 appears to like a bit more rich, so that’s something to look at another day.

XLR sunday retest calc hp

This chart shows the XLR PCM’s calculated HP and Torque values, not corrected for conditions, and not smoothed.  This graph corresponds to the blue line on the Virtual Dyno chart.  I am including it here as another point of comparison for what the XLR calculates is happening during the run.

My conclusion is that today’s runs are consistent within a range of yesterday’s run.  I prefer today’s method of locking the gear so that we get higher RPM info.