![\"VD](\"http:\/\/caddyinfo.com\/wordpress\/wp-content\/uploads\/2015\/08\/VD-XLR-Comparison-Premium-Top-Up.png\")
<\/a><\/p>\n[click to zoom in, back to return here] [This chart was based on incorrect tire diameter — see replacement chart below]<\/p>\n
The Red line is the previous, Top-down test at 256\/239 whp\/lb-ft.\u00a0 Tonight’s comparable run from the exact same location is the Green line at 245\/259 whp\/lb-ft.\u00a0 The Blue line is another run tonight at a separate test location at 235\/247 whp\/lb-ft.\u00a0 Tonight’s runs were lower HP, higher Torque.<\/p>\n
With the top up or down, the variance is in CD, or coefficient of drag.\u00a0 In my previous setup I wrote that I modeled the top-down impairment as a 0.05 CD adder.\u00a0 For today’s test I have left that delta alone, but I have revised the base CD to the 0.31 that Cadillac marketing materials said for the XLR, instead of the 0.35 one of the early magazine reports quoted.\u00a0 So Top-Up CD is modeled at 0.31, and top-down at 0.36.<\/p>\n
I am using ‘absolute pressure’ from the dew point calculation for baro pressure for the virtual dyno calc.\u00a0 This takes<\/a> altitude and local barometric pressure into account.\u00a0 Thanks to Richard Shelquist!<\/p>\n My conclusions are that tonight’s runs were lower results than the previous baseline.\u00a0 This may be normal day-to-day test-to-test variance (unknowns not accounted for), or it may suggest that the top-down drag disadvantage for the XLR is not as great as 0.05.<\/p>\n I enjoyed the XLR all day, and it was out in the sun prior to the tests.\u00a0 The important thing is to capture sufficient baseline data and to establish a baseline, and eliminate test to test variability.\u00a0 I may have to either only run tests first thing in the morning to avoid heat soak, or only run tests with the car heat soaked (!)<\/p>\n Update:\u00a0 the previous Virtual Dyno setup used 27.73 as a tire diameter, and I see from the calibration file it should be 27.24.\u00a0 This changes the results to following table:<\/p>\n Which is less than expected.\u00a0 I am including both charts for now to document my confusion, and to assist in analysis.\u00a0 Yes, tire size has a significant impact on calculated results.\u00a0 With SAE adjustments for conditions the 320 hp rated LH2 should make approximately 256 whp; I am uncertain why today’s results are 226-236 whp.<\/p>\n <\/p>\n","protected":false},"excerpt":{"rendered":" This evening I ran some top-up comparison tests to help calibrate and establish a baseline.\u00a0 Previously I had tested with the XLR top down, enjoying the convertible.\u00a0 I was focused on monitoring calculated hp\/torque, so aero wasn’t a factor.\u00a0 However, … Continue reading <\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n