Exhausting Cadillac STS-V options – Corsa

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After reading and re-reading everyone’s experience and advice on exhaust options, and resulting sound files,  I decided to go with the Corsa 14157 axle-back system for my 2008 Cadillac STS-V.

Just ordered the part today, so not installed yet on the V.

I had a Corsa cat-back system for my 2005 Cadillac CTS and enjoyed the system & sound, and I think it makes a nice match for the STS-V.

Corsa stock photo of exhaust on a 05-07 STS

I was sorely tempted to follow my plan as stated, to replace the individual components with the Magnaflow exhaust & cross-flow muffler for the resonator, but the cost with shop support for dyno, adjustments, and testing as a project was similar to getting the Corsa axle-back system.  I will still need to establish a clean before/after test regimen for the exhaust install.

Corsa offers this flow-bench testing to show that the 14157 system out-performs the factory exhaust.

The Corsa 14157 is not advertised to fit the 08 Cadillac STS-V, but rather the 05-07 STS.  There were changes made by Cadillac in 08 for exhaust hanger location, so the system will need some adjustments at the muffler shop during installation.

Re-Establishing the Cadillac STS-V air box heat barrier

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I like the Spectre intake for the Cadillac STS-V.  However, when we put the intake on we discarded the factory engine covers along the front and side. The Spectre intake includes a barrier to direct air away from the intake filter, but it is not closed at the top.

Cadillac STS-V Spectre Intake filter and air dam

I was considering building an insulated cover or box, but it is desirable to me to re-use the factory trim pieces.  Also, there are some functional air blocks built into the trim that I want to recover use of — example the foam air dam below the center front piece, and at the rear of the driver side piece.

Foam on the under side of front middle trim acts to keep air in the radiator flow

The factory piece that would fit over the driver side won’t fit with the Spectre intake in place, so I trimmed the side piece, and the front center piece, to allow them to fit with the Spectre Intake.  I need to get some rubber gasket material to close the gaps, and smooth the edges, but now all the pieces fit.

Trim pieces trimmed and in place

Even though the V was hot I did a test and data run:

Max calculated power for the test run 415 hp in 2nd gear at 6346 RPM for comparative purposes; max torque 377 lb ft at 3324 RPM.

 

Unfortunately I only have a heat-soaked mid-day comparison run for today.  I attended Church this morning, then worked on trimming pieces, then did a test run.

Baseline from August 2011

MPH (Temps in Deg Fahrenheit)
Deltas Item 0 30 45 60 Deltas
Ambient 90 90 90 90 0
23 IAT1 113 117 113 106 -7
5 IAT2 118 120 127 135 17
2 MAT 120 121 136 169 49
Trimmed Trim Mar 2012
75F
Deltas MPH (Temps in Deg Fahrenheit)
Item 0 30 45 60 Deltas
Ambient 75 75 75 75 0
16 IAT1 91 93 93 91 0
33 IAT2 124 122 129 136 12
-2 MAT 122 121 134 163 41

There is a lot to read and try to analyze here, but let’s piece it together.

First, today is cooler than back in August, 75F instead of 90F.  However, my STS-V is heat-soaked today and wasn’t back in August.

IAT1 is 16F above Ambient now and was 23F back in August.   That is what the trim is supposed to help with, so good.  In August the 0-60 run itself cooled the IAT1, while it did not today.

IAT2 was only 2F above IAT1 in August (morning run, not heat soaked); today it was 33F above (heat-soaked).  In August the IAT2 gained 17F during the 0-60 run; today 12F.

MAT in August gained 49F on the run; today 41F.

I am cautiously considering replacement of the trim beneficial — did result in lower delta temps.   I would like to have a non-heat-soaked current run to compare for apples to apples however.  There are still some gaps in the trim fit that will benefit from some gasket material along the edges.

 

Datalog analysis of Cadillac STS-V Ambient vs IAT1 vs IAT2

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I have been planning new data-logging experiments and modifications, so I have been reviewing the datalogs I did last August in the summer temperatures.  For my next datalog I will attempt to capture comparative data to this info:

This screen is an HP Tuners VCM Scanner guage snapshot of parameters after a 0-60 run culminating at 65 mph.

Baseline from August



MPH (Temps in Deg Fahrenheit)

Item 0 30 45 60
Ambient 90 90 90 90
IAT1 113 117 113 106
IAT2 118 120 127 135
MAT 120 121 136 169

What we can see from this table, is that at the beginning of the 0-60 run the Ambient temp is 90F, and stays at 90F through the run.

IAT1: The IAT1, which is incoming air temperature as read in the intake air tubing, starts at 113F.  It has rapidly gone up to this value because the STS-V is stopped.  However, as the V accelerates to 30 mph it rises to 117F.   By 45 mph it has returned to 113F, and by 60 mph due to the incoming 90F air cooling it has resolved to 106F.  Conclusion:  heating of the incoming air at the IAT1 sensor does in fact effect the air temperature, and thus performance.   Conventional wisdom is that the incoming air is not in the intake tube long enough to become heated. Net Rise: -7F

IAT2: The IAT2, which is air after it has been heated by the supercharger and cooled by the intercooler, starts at 118F, a 5F increment over IAT1.  By 30 mph it has risen to 120F.  At 45 mph it has risen further to 127F, and by 60 mph has peaked at 135F.  Net rise: +17F.  Keeping in mind the IAT1 went down 7F in this time.

MAT: The manifold air temperature is a calculated value the engine uses to predict the temperature of air in the manifold.  It tends to go up at a higher rate than IAT2.  The MAT starts the run at 120F, is about the same at 30 mph at 121F, but rises to 136F by 45 mph and on to 169F by 60 mph.  Improvements in the IAT2 should have even greater improvements in the MAT value.  Net rise: +49F.

As a result of the high MAT temp by 65 mph as shown in the image, IAT temps are causing 3.6 degrees of advance to be pulled.  This begins at 59 mph when the IAT2 hits 135F and the MAT is at 157F at -3.2 degrees.
This was a video capture of the dashboard of the 0-60 run from August: