Category Archives: Test Drive

Datalogging the Cadillac STS-V – CANScan

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This could be subtitled, datalogging for dummies.  Today was a regular sort of everything-is-complicated project day.

I wanted to get some datalogs on my 2008 Cadillac STS-V to start to study & understand how it reacts to intake air, temperature, etc.  In order to do that I needed to grab my netbook, my CanScan to connect the netbook to the Cadillac, and maybe a camera, and we’re off!

Well, no.  First I had to spend an hour looking for my netbook, a Dell Mini 9, which I seldom use.  This also makes it perfect for the datalogging project, but means that I spent the first hour finding the netbook, and then there was a delay while getting it recharged and able to operate on battery, researching why the battery was not charging properly, etc.

Luckily while I looked for my netbook I found the CanScan USB in the garage, by Harrison R&D.  The CanScan is a USB to CAN bus interface module.  The Cadillac speaks CAN bus, so with this interface module my netbook, once I found it, using the appropriate software, also from Harrison R&D, could speak to the Cadillac.  I also had not used the CanScan in years but luckily it was on the tool shelves.

In between I found my Flip video camera and worked on getting it charged.  For naught as it turned out, as I didn’t actually take any pics, and by the end realized that my model does not charge on the USB port, but rather takes disposable AA batteries.  Oh good.

Anyway, with the netbook and the software and the interface and the flip camera with new batteries and in the STS-V and remembering how to get it all to play together,  I was able to capture this datalog of a drive around the block:

Click the graph to open a larger version; perhaps right-click and put it in another tab or window then come back.  I’ll wait.

The datalog shows coolant temperature, vehicle speed, ignition advance, intake air temp, air flow, and ambient air temp over time (the y axis is shared, the x axis is time).

The brown spikes are heavy throttle application causing high air flow.  The Red is vehicle speed, which goes up with the high throttle angles.  The yellow squiggle is advance as the PCM juggles timing.

The Green line at the top, Intake Temp, and the light blue line, ambient air temp, are of interest. The darker blue at the very top is the radiator coolant temp, which is less interesting today.  I was not able to find something called Intake Temp 2, which perhaps would be the air after the supercharger.  Ambient air is perhaps the outside air, and Intake Temp is the air entering the supercharger.  So with the temp here around 95F and the Cadillac in the driveway, the hood is hot, the engine is hot, and starting my drive the Intake temp was 160F and decreased slowly as the relatively cooler air of the drive flowed over the engine compartment.  The Ambient Temp was 120F, remaining near there throughout the drive.

I am tempted to think the value shown as IAT is IAT2, since even with heat soak it is hard to think the car would be at 160F at the intake to the Supercharger, but hopefully I can find the right info to ask the gadget to send the IAT2 temperature as well in my next test.

Here is a comparative (and also too crowded) datalog showing IAT falling to near ambient temp when on the highway, then zooming up when in traffic.

Datalog of a run up and down the Highway, then stop for Icecream and stuck in traffic

Improving a tenth at a time…

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100F out today here in Texas, but testing must go on.  Mostly because inquiring minds want to know and my interest is piqued about how this could be simpler and yet any more subtle in execution.

Speed vs Time (red) and Distance Travelled (gray)

 

And the table with comparison to last best run:

Today’s Test
Rollout Previous Test
Speed (mph) Time(s) Dist(f) 0.37 Speed (mph) Time(s) Dist(f)
10 0.93 6.33 0.56 10 0.71 7.13
20 1.71 23.73 1.34 20 1.45 23.53
30 2.53 53.59 2.16 30 2.23 51.94
40 3.43 100.4 3.06 40 3.09 96.6
50 4.45 168.07 4.08 50 4.21 170.2
60 5.66 265.64 5.29 60 5.39 265.8

Conditions: Weather: 95.6F baro 28.85 in Fuel: almost empty (car indicated 100F outside; 96F per the weather underground)

Today I wanted to try accelerating briskly until 20 mph or so then wide open throttle.  My goal was to get to 20 mph as rapidly as possible without wheelspin, figuring that even with full throttle there would be little wheel spin after 20 mph.  I was partially correct.

I also discovered that there is a cusp wherein the 6speed automatic will shift from 1 to 2 early in the low 20s if you are not at wide open throttle, which is bad for acceleration.  Manually shifting the automatic is right out because the redline at 1st comes up too fast for the manual shift to be effective.

Good news is a slightly faster best time, at 5.29 sec 0-60 with rollout.  Remember our goal is 4.9 sec 0-60 with rollout.  Low on fuel so 84 lbs lighter this run, which can also cause this difference in 0-60 times vs the earlier test.  The hotter temps act against acceleration, and 20F hotter is significant.

This simple method did improve my 1 foot acceleration time from 0.59 to 0.37 so there is that.  Also my 60′ time from a dismal 2.8 to 2.66 sec.  A reasonable 60′ time for street car on street tires is under 2.2 sec, so I am off in the first 60 ft and its me not the V.

I do think that this will be a matter of defining an exact technique to get the last few 0.1’s out however — brisk but not tire screeching acceleration up to 18-20 mph then full throttle before the transmission can decide to downshift to 2nd or similar.

In the real world it doesn’t matter much, but learning to drive the car can’t but help.

Intake update: the Spectre intakes are due from Streetsideauto.com in the next week or two, and then we’ll get before and after dyno tests run at True Street Motorsports in McKinney Texas per my  Project Cadillac Tuning Plan

Cadillac STS-V First PerformanceBox Test

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I have a RaceLogic PerformanceBox which can be used to measure vehicle performance in a variety of tests.  The Performancebox is a GPS based meter and data logger.

Unfortunately, I don’t get to use it all the time, so when I do there is a short period of re-familiarization.  For my first tests, no data got written to the memory card.  After I changed the setup to “yes, please write data” things improved dramatically.

Here was the best run written to the card today:

MPH vs Distance shows challenge getting off the line

 

Accel results
Speed(mph)     Time(s)
0-60                   05.4

With 1 ft roll-out details:

Speed(mph) Time(s) Dist(f)
0 0.00 0
10 0.71 7.13
20 1.45 23.53
30 2.23 51.94
40 3.09 96.6
50 4.21 170.2
60 5.39 265.8

Roll-out is a determination for ‘when’ the test time begins.  At a drag strip, there is up to 1 foot of roll-out before the timing lights are tripped, hence the term.  In other words, due to surface quality and wheel-spin it took me 0.59 sec to get 1 foot forward, but at the track that time would not have been included in the results and is not included above.

Weather Conditions: 87F; barometric pressure 29.69 in; humidity 64%.  Fuel: Full

Not sparkling time for the Cadillac STS-V, which Cadillac measured at 4.9 sec 0-60 mph with roll-out.  Most magazine tests ran high 4.x to low 5.x sec.  Road & Track measured 4.7 sec 0-60 mph for the STS-V.

I feel the 2008 STS-V is capable of a better time.  Getting the STS-V off the line involves a great threat of wheel-spin to be avoided.  Of course, my test area is not a sticky well prepared launch spot like at the drag-strip, but it does closely model real world circumstances.

On the bright side, this is a new ‘best’ for my personal vehicle measurements; my previous best was 0-60 in 5.95 sec in my modified CTS 3.6L and was measured on the AP-22 meter in more favorable circumstances.

Stock
STS-V


Mod CTS 3.6L
Speed (mph) Time(s) Dist(f) Time(s) Dist(f)
10 0.71 7.13 0.68 4
20 1.45 23.53 1.40 21
30 2.23 51.94 2.33 55
40 3.09 96.6 3.31 105
50 4.21 170.2 4.55 187
60 5.39 265.8 5.95 301

A line by line comparison — albeit of apples and oranges since different days, different gadgets — echoes the same issue — get the STS-V off the line faster and it would have much better times, and at 60 mph is 35 feet ahead of the CTS.