Category Archives: Intercooler

Insulating intercooler piping

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The intercooler plumbing on the Cadillac STS-V heads into the intercooler itself through a pair of pipes above the snout of the supercharger.  These pipes are exposed to the heat of the engine compartment, and are not insulated in any way.  For example, when I went out to verify their size to shop for some insulated sleeves, they were too hot to touch and I feared that my tape measure would melt before I got them sized.  That can’t be helpful for keeping the coolant inside these pipes cold.

Cadillac STS-V Intercooler in/out piping above Spectre intake

One of my next minor projects will be to either add some insulated sheathing to these pipes, or to wrap them with insulated wrap. Yes, the intercooler coolant only rushes through those in and out of the intercooler, but one fewer heat source would be great.

STS-V LC3 Intercooler Flow path & Parts

Update:

Here is the initial insulated piping shot.  I like the look of the sheathing but I need to get it squeezed in to cover the pipe better.

Intercooler HX Testing: Changes in Ambient Temp vs IAT2

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In a water to air heat exchanger cooling system as used on the Cadillac STS-V and CTS-V, ambient air coming into the front of the Cadillac is used to cool the intercooler coolant.  The coolant is then pumped through the actual intercooler to cool the air charge entering the manifold.  Intuitively we expect changes in ambient air to change the equilibrium point of the intercooler cooling system.  This is because the colder the ambient air over the heat exchanger, the better the heat exchanger works and so the lower the expected intercooler temps will be.  Today’s test explores to what degree ambient temp changes impact IAT2s.

The test today and the prior data shown are both for the current intercooler setup:  Updated intercooler hoses, retest hot S3TC heat exchanger

OEM Heat Exchanger + S3TC additional heat exchanger and hoses.  Fluid capacity ~4.6 quarts.

I experimented with the Mityvac system and repulled a vacuum on the intercooler coolant, pulling coolant along with the vacuum, and refilled it.  But the hardware is unchanged.  The test is a 20 minute loop at highway speeds, with one or more acceleration runs along the way to demonstrate intercooler heat up and cool down times.  These show as spikes on the graph.

 

The graph shows IAT2 temps, which is the incoming air temperature after the supercharger, on a prior test day that averaged 69F ambient temp, and today with 84F ambient temp, or 15F higher.  There are 4 lines on this graph.  The dark blue is IAT2 today, and the light blue is IAT1, or air coming into the engine intake, today.  Dark red is IAT2 on the cooler day, and salmon (pink) is IAT1 on the cooler day.

What the comparison appears to show is that when ambient temps are 15.3F warmer (avg 84.8F vs 69.5F), air coming into the engine (IAT1) is 15F warmer (avg 94.2F vs 79.2F), and air out of the intercooler is 11.2F warmer (avg 124.7F vs 113.5F).  Knowing that ambient temps flow into the intake as IAT1 and on through the supercharger to become IAT2, we might have predicted that a 15F ambient delta would resolve to a 11.2F IAT2 delta.  However, that’s why we test, to find out what happens.  In general an increase of 1F ambient leads to 1F IAT2 leads to 0.8F IAT2.

I also note that IAT1 averages 10F above ambient, and IAT2 tends to be 30-32F above IAT1

Same trend for this dataset of about 3 sec after acceleration starts to IAT2 begins to rise.

Let’s think about that for a bit —

Item Qty Units
Pipe ID 0.75 pipe diameter in inches
System loop: 4.00 OEM HX To S3TC
4.00 S3TC to OEM hookup
2.00 width of OEM HX
2.17 Width of S3TC HX
0.67 hose to factory pipe
2.50 Factory Piping
2.50 Factory Piping
Total System Loop: 17.83 Feet long
Obs Circuit 3.20 sec
Result Velocity 5.6 feet/second
GPM 7.7 gpm

That if the coolant is doing a 3.2 sec loop through the system, and the system is ~18 feet long, then the fluid must be moving at 5.6 feet/second, and that the pump must be putting out 7.7 gpm.  The pump is rated at 8 gpm against no pressure, so that seems hard to believe. Intercooler cooling system pressure & flow

Intercooler gpm and IAT2 temp change and coolant capacity

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I am thinking more about this graph of IAT2 over time as the Cadillac STS-V accelerates:

Let’s consider the stock, OEM Bosch intercooler pump.  This pump is rated for 8 gallons per minute (gpm) against no resistance, and likely does 5 gpm in the STS-V system.  It is overall a very good pump, and very efficient.

Now, a gpm is 1/60=0.083 gallons per second (gps).  So 5 gpm would be 0.42 gps.  The STS-V can accelerate 0-60 in under 5 seconds.  So on an average 0-60 run, the intercooler pump moves 5 sec x 0.42 gps = 2 gallons of fluid through the intercooler.

Now, keep in mind that the OEM system had 2.6 quarts of fluid, and my new HX added 2 quarts, so now my system has 4.6 quarts or just 1.15 gallons. A small part of the capacity is likely counted in the side fill loop, so we’ll say 1 gallon.

So on an average 0-60 run, the pump can move 2 gallons of fluid through the intercooler, and the system has 1 gallons in the main loop, so the coolant sees the inside of the intercooler twice in that 5 seconds.  Put another way, my current 4 quart capacity system has a circuit time of ~3 seconds — every ~3 seconds the system circulates the entire coolant capacity.

For the intercooler testing I was focused on just getting an acceleration spike and not best time.  But if we look at this graph of speed vs time vs IAT2,

What it appears to show is that the IAT2 temps are near constant for the first 3.27 seconds (looking at the exact figures in the data table), and rise dramatically after that.  Now it is dangerous to read too much into a single sample, but this seems to validate our figures that at 3.27 seconds the intercooler coolant starts a 2nd loop through the system.

From this I conclude that a system with a 2 gallon capacity of coolant would have fresh, cool fluid in the intercooler for the first 6 seconds.  Now 0-60 mph is not the end all and be all of performance.  To keep uncirculated coolant in the intercooler for a dyno run one might need 10 seconds of fluid or 3 gallons — as a thumbrule think 1 gal per 3 seconds.

Also, if you speed up the pump, you’ll need more system capacity to offset the faster circuit time.

What do you think?  Am I missing the boat?  Do you agree?  Hit the comments please!