Intercooler gpm and IAT2 temp change and coolant capacity

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!

7 thoughts on “Intercooler gpm and IAT2 temp change and coolant capacity

  1. Bruce,

    First, I commend all of your work but there are two caveats that can not be ignored when it comes to IAT.

    First, obviously, is the ambient temperature. If it is 85F or hotter the amount of coolant you have in the tank is going to be of little use as it will still get hot in <10sec of WOT driving. We can argue the valid point that few run at WOT beyond 10 seconds too. However, if you are on an interstate where there are lots of hills as such as we have here then you are on and off boost just maintaining the 70mph (or more) speed and the coolant is going to be quite warm. Here the key is a better air to liquid cooler.

    Conversely, if the ambient is <40 both units, stock and your improved, will be quite efficient as the rush of air will effectively cool either coolant with no problem; we have seen this while data logging via a HP tuner – the stuff just does not get 'hot' at these temps and speeds.

    I do think at anything above 60 degrees your improved unit will yield a better quarter mile ET or a better WOT pass/play result for about 5 seconds but the key is still, as my feeble mind sees it. a better cooler.

    In closing, I commend you for the work.


  2. I agree we are working to stay below an upper limit– so if the ambient temps are low, and or the V is cold anyway it is easier to keep IAT2s below that limit.
    On the dyno the V is pre- heated getting to the dyno shop and of course on boost for the test, and needs to cool rapidly between tests. It strikes me this is also representative of every day driving conditions. So my focus has been on cooling in these challenged conditions.
    Next I would like to run with the 1 gal tank in circuit to see if that confirms a 3sec per gallon coolant circulation time. One might spec the coolant capacity based on intended use — 5 gal for quartermile?
    So perhaps the 2.6 quarts in the stock was viewed as ideal for short boost cycles with rapid cooldown?

  3. I admire your inquisitiveness and your efforts in both cost and time.

    To bad you don’t have a dedicated drag car as you would probably become a great competitor and get every bit of power there is to be had from your car.

    As to the STS-V’s and heat I am sure you will improve markedly upon the OEM arrangement and I wonder how many will copy to obtain your results.

    Ever think of sending some of this stuff to Cadillac?

  4. Howdy, I have really enjoyed following all of your intercooler pump information. In your intercooler GPM blog above I would like you to check the flow rates in conjunction with time, because it makes a huge difference. 1/60 = .016666. So a 5 GPM pump is actually only .1 gallon a second. So in a 10 second quarter mile pass the intercooler actually only sees one gallon of fluid exchange. The stock systems with roughly 3 gallons a minute flow rate would circulate a half a gallon in 10 seconds. 1/60 x GPM x seconds per run = gallons of flow.

    The .42 gallon a second flow rate you referenced above would be a staggering 25.2 gallons a minute.

    Please understand I am in no way being critical, your research is first rate and I have referenced it many times.

  5. I think I understand your question, and I think I agree:

    “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.”

    There appears to be an extra x5 in my thinking here.
    1pm = 1/60 gps = .0167 gps (not 0.083 which would be x5 already)
    5 gpm = 5 x .0167 gps = .083 gps (unit conversion to seconds)
    5 sec run x 0.083 gps = .417 gal over the 5 sec 0-60 mph run
    so during this run, 40% of my intercooler coolant goes through the intercooler, not x5 more as stated in the original article.

    Rather than edit the article the comments will show ‘the rest of the story’. Thank you for pointing this out.

  6. You should also be looking at the ability to recover from a acceleration event and look for better consistency after each run. Gale Banks quoted proper coolant pump speeds for a given temperature drop.

    Also your ecu may reduce torque after a certain IAT2. My 2014 XTS VSport starts to reduce output after IAT2 exceeds ~105F. On my short 8 mile commute I usually see IAT2 at 10+ ambient so 85-90F degree days I usually don’t see a big drop in output.

  7. Yes, the engine’s response to high IAT2 to preclude detonation is an additional barrier to disadvantage of high IAT2 for density. I would like to do more testing on my STS-V/LC3 during the cool weather now. Most of my prior testing was hot water in hot air on hot days.

Please leave a Reply