Category Archives: Test Gear

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.

Initial Cadillac XLR Hptuners Scanner setup

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Tonight I setup my test laptop with HP Tuners in the 2007 Cadillac XLR to see if it would all play together — with some success.

xlr first test 1 gear max hp

I used the scanner profile that is setup for my 2008 STS-V,  which makes for good comparison but perhaps higher scales than the XLR needs.  The XLR was well heat soaked, and it was warm here in Texas still even though evening time.  Intake air was 95 F outside, 100 F coming into the engine, and 135 F in the manifold.   Plano is at 600 ft elevation above sea level.

What I see in this initial scan is a) it works at all and b) the XLR PCM calculated that the engine output was around 301 hp in 1st gear at 5734 rpm. It stayed around 300 hp from there to when it shifted.   The XLR LH2 V8 is rated at 320 hp at 6400 rpm under ideal test conditions at sea level, 70 F etc.

xlr first test 1 gear max torque

Max first gear calculated torque was 290 lb ft at 4572 RPM.  The LH2 is rated at 315 lb ft of torque at 4400 rpm under SAE test conditions.

320 hp LH2 Rear-wheel Drive Variant

320 hp LH2 Rear-wheel Drive Variant

On first blush, I am pleased that I got the test gear working, and the HP tuners can talk to the XLR,and I can capture data and post it.  Now I can study what it means lol.

XLR first scan

This is a graph created from a data export from hptuners vcm scanner of the delivered torque, and derived calculated hp.

 

Cadillac Supercharger Boost Vs RPM Reprise

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I studied boost vs RPM for the 2008 Cadillac STS-V LC3 engine in this post but I am back on this topic again.

2013-05-25 Boost vs RPM

This graphic shows the Boost from the Supercharger in pounds per square inch (PSI) of pressure in blue, and the incoming air volume through the mass air flow sensor feeding the supercharger in LB/Min in red.

As we have seen before, the supercharger boost is surprisingly spikey.  The supercharger in the STS-V spins at a 2.1:1 ratio to engine RPM, so at 6000 RPM the supercharger is spinning at over 12,000 RPM.  One would think the boost from the supercharger would be pretty constant.

Of course, constant is a relative term.  The blower is spinning up with the engine and the entire graph above is a less than 4 second interval.  The spikes and troughs tend to be 4 samples over 1/10 of a second.

Here is a zoom in on the run from 6400 RPM to 6700 RPM and boost values:

Time Engine RPM (SAE) rpm Boost PSI
13:03.672 6409 9.1
13:03.687 6452 9.1
13:03.719 6452 9.1
13:03.750 6508 8.8
13:03.765 6540 8.8
13:03.781 6540 8.8
13:03.828 6577 8.8
13:03.844 6608 9.6
13:03.859 6608 9.6
13:03.890 6625 10.0
13:03.922 6651 10.0
13:03.937 6651 9.4
13:03.969 6691 9.1

All of which happens in 0.3 seconds (3/10 of a second).

I don’t see a correlation between the surges in the Supercharger boost pressure and surges in demand of air volume via the MAF; the air through the MAF appears to have a pretty constantly increasing slope.  Perhaps as the RPM goes up and the engine has greater demand for air, and the boost is building, we should see a higher MAF slope than we do?  The MAF slope appears to be increasing at 2900-5900 RPM and lower at  RPM above 5900?  The rate of increase in boost psi also flattens at that point, so the blower may have reached its capacity.

I would like to see a boost graphic for an STS-V with an upper pulley for comparison.

Are there things that could be done to help smoothen the boost output of the blower?

 

Update:

Here is a graph comparing IAT2 Temperatures (intake air after the supercharger) with the boost curve.  I see a close relationship here.

kn 2013-05-25 boost vs iat2

As the boost goes up the air is getting compressed into the manifold, and the air temperature goes up, making the air less dense, and eventually causing the engine to start to pull timing via IAT2 advance (retard) on hot days.  On this run the engine stays out of that range, but there is the other range that if the IAT were cold enough the computer would add timing.