by "uofime-2" (uofime-2)
Published 09/12/2017 at 16:02
by "uofime-2" (uofime-2)
Published 09/12/2017 at 16:02
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STARS: 1
Often times you’ll hear or read in car and car part reviews how much of a problem heat soak can be for turbo cars, expecially modern ones with small turbos, double expecially if the car has a top mounted intercooler!
In order to study the validity of such claims, you’d need to collect some real world data from a car instrumented to record post intercooler temperatures over time while the vehicle is being used in a manner such that it would produce a great deal of heat.
Well as it turns out I tool my 2015 WRX to a track day this past weekend and it happens to have an Accessport which is capable of datalogging ECU parameters and an engine that utilizes a manifold air temperature sensor (intake temperature manifold) in addition to a pre-turbo inlet air temperature sensor.
The above plot is what that looks like on the latter 700 second half of a 20 minute track session. The red line is ITM, it does of course oscillate with boost pressure, but never does go over 126 degrees. Sure we’d love to have that a whole lot closer to ambient, which can roughly be approximated as 82 degrees, from the intake air temperatures, but at no point during 11 minutes and 40 seconds of track track use does it spiral out of control, lead to massive power loss and engine death...
Any questions?
"cmill189 - sans Volvo" (cmill189)
09/12/2017 at 16:18, STARS: 0
82 F seems too low of an ambient temperature to worry about heatsoak. You should see if you can retest it when it’s for reals hot outside. That’s when I notice it the most. It’s always when the ambient is above 90 and the intercooler has been getting little airflow, pavement could cook eggs, A/C on...
"DipodomysDeserti" (dipodomysdeserti)
09/12/2017 at 16:28, STARS: 0
I have an app that lets me read all the sensors on my BMW with a front mounted intercooler and a small twin scroll turbo. Out ambient temp is 109F today. I’ll see if I can get some reading while doing run of the mill city driving.
"Aaron M - MasoFiST" (amarks563)
09/12/2017 at 16:30, STARS: 0
My WRX had heatsoak problems before I replaced the intercooler...in traffic. Even for people with heatsoak problems during use the issues tend to come up during stationary use, like drag racing. Hot turbo, car no longer moving, you cook your intercooler.
Incidentally, there is a documented heatsoak issue with 08-14 WRXes and STIs and it is due to the scoop design...without the same protrusion that the 02-07 cars had, the amount of heat transfer was suboptimal. I have no idea if the same issue exists on the 15+ cars, though 126 degrees is not great for post-cooler temps...it should be below 120, and if your intercooler is working well it should be maybe 10-20 above ambient. Soo...you may have shown us that you’re running with 20 degrees F of heat soak.
"uofime-2" (uofime-2)
09/12/2017 at 16:34, STARS: 0
See, this is the problem people have. What you are describing is not heat soak, though it is none the less a real issue. The only solution is to get the car moving and air through the core.
If I re-did the test at a higher ambient temp I would see the same delta, difference between intake and manifold temps (124-82=42 degrees). This implies that if it was 90 ITM would be 132, if 100 then 142. There is nothing you can do to change this, even the most massive front mounted core cannot defy thermodynamics all it can do is transfer more heat to the surroundings and reduce that delta from 42 degrees to say 20 or 10 degrees. Thus lessening the reduction in power
Heat soak implies that the temperatures never stabilize and reach a max value, instead continuing to climb
"marshknute" (marshknute)
09/12/2017 at 16:38, STARS: 0
I don’t really know what heat soak is, but I do know that my 15' WRX experienced catostrophic overboosting on the track. After 2 laps, it would engage the fuel cutoff on the straights until the turbo spoiled down. It took between 3 and 10 seconds before the gas pedal started working again. The FA-20 is simply unfit for track duty.
I decided to sell it and buy a real track car (Corvette) rather than dick around with an ECU reflash and deal with Subaru’s notoriously awful customer service if I ever tried to get something fixed under warranty.
"uofime-2" (uofime-2)
09/12/2017 at 16:41, STARS: 0
What you are describing is not heat soak. heat soak is temperatures running away, yes I have a somewhat large delta at 42 degrees but it does not increase over time.
Yes if you sit still the core gets warm until you run air through it, this is going to be true no matter what you do with the core.
Front mounting helps not get as much engine heat and you can cheat by pulling air though with the radiator fans at low speed, though it has a laundry list of drawbacks for cars not designed for it.
"uofime-2" (uofime-2)
09/12/2017 at 16:44, STARS: 0
If you want to see heat soak you need to drive it very hard, be in boost a high percentage of the time. Street driving at low or no positive pressure won’t mean much. A single pull won’t show you heat soak either.
"DipodomysDeserti" (dipodomysdeserti)
09/12/2017 at 16:46, STARS: 0
Back when I owned Subies, I always had a very easy time getting stuff fixed when I needed it. There was even a Subaru regional rep on one of the forums who would personally help people out if they ever had issues with a dealership.
If you don’t know what heat soak is, then you probably shouldn’t be tracking turbocharged cars.
"cmill189 - sans Volvo" (cmill189)
09/12/2017 at 16:51, STARS: 0
Garrett seems to think I’m talking about heat soak.
https://www.turbobygarrett.com/turbobygarrett/Intercooler
"uofime-2" (uofime-2)
09/12/2017 at 16:55, STARS: 0
You will hit fuel cut if you’re below half a tank of gas, usually happens during or directly after coming out of a hard right hander, depending on when the air bubble makes its way though.
Easy solution is to not run the car below half a tank. Its an issue on most cars, though somewhat worse on imprezas
Car runs awesome on track, this is something like the 8th day I’ve done with it. The stock brakes wear out super fast though, even with proper pads (XP12s) I go through a set of fronts every 2 days.
Other than that it needs a radiator all the time and an oil cooler is needed for hot days.
"Aaron M - MasoFiST" (amarks563)
09/12/2017 at 16:58, STARS: 3
Heat soak is a state of the intercooler, it does not mean that there’s thermal runaway...if thermal runaway was a thing, non-intercooled turbo cars would simply stop working after a certain amount of time. Complete heat soak merely means that intake temp = turbo outlet temp, i.e. the intercooler is not working. So your IATs would not technically be heat soak, but they’d be something that a person may describe as “heat soak”.
Nonetheless, the bigger point is that the heatsoak issues people saw with Subarus were when they were daily driving them, not tracking them. The reason TMICs are susceptible to heatsoak is that they’re sitting on top of the hot engine while an FMIC is not. While heatsoak caused my car to bog and be unpleasant, it causes the car to run rich rather than lean, so is rarely dangerous to your engine.
"cmill189 - sans Volvo" (cmill189)
09/12/2017 at 17:00, STARS: 0
I think you are the one that is confused about heat soak.
"uofime-2" (uofime-2)
09/12/2017 at 17:20, STARS: 0
and you aparently have a limited grasp of technical language:
Heat soak is when the intercooler can’t dissipate the heat that it absorbs from the turbo fast enough. When an intercooler can’t cool the charge air by removing the heat from it, it loses its effectiveness.
how do we define when heat is not dissipated fast enough?
the easiest way to define that is that it continues to accumulate uncontrollably, run away.
What would that look like graphically? it would look like a line which continues to increase over time.
What do my temperatures do? they oscillate between a defined minimum and maximum value. Depending on boost pressure and vehicle speed.
I suppose if you define your time period as one in which the vehicle is not moving, during which the core continues to heat up, you could say that in a manner of speaking your car heat soaks while sitting in a parking lot. However is that really a usage case that presents an issue?
I will give you that on a drag strip, sitting in in staging lanes, having a high initial core temperature presents a real issue for top mounted cars, because they are going to demand full power with zero air flow over the core. Therefore for turbocharged and intercooled drag cars a front mounted intercooler represents some real benefit.
"DipodomysDeserti" (dipodomysdeserti)
09/12/2017 at 17:22, STARS: 1
I have a twin scroll turbo, so I’m boosting pretty much as soon as my foot touches the accelerator. I doubt I’ll get any heat soak (I have never felt the effects of heat soak in the 50k miles I’ve put on this car), but I think it will be interesting to see what my temps look like on a hot day.
"marshknute" (marshknute)
09/12/2017 at 17:30, STARS: 0
Then my specific WRX must have been fucked, because it overboosted even in the morning when I had a full tank.
And don’t get me started on the damn brakes, lol. The stock pads had 100% brake fade during my first autocross, so I immediately swapped them out for Hawk HP Plus pads, which as you point out, only lasted 2-3 days.
All that experience taught me was you need to go to Corvette, Porsche, BMW ///M, etc if you want an out-of-the-box track car.
"cmill189 - sans Volvo" (cmill189)
09/12/2017 at 17:39, STARS: 0
Dude. The entire turbo community describes what you say isn’t heat soak, as heat soak. Everyone here, too. What your Impreza seems to be experience I would describe as “running as it was intended.”
"Sovande" (sovande)
09/12/2017 at 18:26, STARS: 1
Per Garrett: Heat soak is when the intercooler can’t dissipate the heat that it absorbs from the turbo fast enough. When an intercooler can’t cool the charge air by removing the heat from it, it loses its effectiveness. This explains why turbo cars tend to run slower or have slightly less power when the weather is warm.
There is no reason to make it any more complicated.
"uofime-2" (uofime-2)
09/12/2017 at 18:46, STARS: 0
The factory boost control ant throttle mapping on stick wrxs was a bit of an odd decision I can only assume was made to give entertaining test drives. Leaves a lot to be desired in daily use.
Hp+ Make good autoX pads though they aren’t suitable track pads and they’re God awful on the street
No car really comes from the factory ready for track abuse. Pretty much all need brakes and cooling stuff.
"uofime-2" (uofime-2)
09/12/2017 at 18:48, STARS: 0
Indeed, lots of people like to invent problems so they can justify buying stuff they don’t need and will never fully utilize.