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Intercooler performance

aaronc7

Autocross Champion
Location
USA
Car(s)
17 S3
Interesting. thanks.

much larger IAT vs Ambient gap than expected, also surprised the starting IAT was so high

You have to factor in the high altitude too. This car hits 28psi boost relative to sea level pressure. At sea level that is a pressure ratio of 2.9.... for me that is a pressure ratio of 3.4. If you take inlet/ambient temp of 70.... at sea level the compressor outlet temp = 337F, for me it's 385F (assuming compressor efficiency of 70%). PLUS, the cooling airmass thru the other side of the intercooler is about 15% less air density, so cooling efficiency is reduced.

From that info I can't tell you exactly how much worse off I am vs a similar Stage 2 IS38 car at seal level....but high altitude cars, intercooler are less efficient and have to deal with more heat--it's a double whammy.

Which is why I listed my elevation in the data...and also why again it makes it so hard to compare these things I think. As a single data point, it's kinda like APR is pretty meh, but it is what it is, just single data point. Most guys are at or near sea level, so that data is probably most useful for comparison sake.

As far as IAT vs ambient gap, I was running the AC prior to the pull, I probably shut it off about 30 seconds before the pull if I had to guess. Need mah AC!
 

DallasDub94

Go Kart Newbie
Location
DFW
Car(s)
18 GTI S
I see this thread has been busy on my four day weekend.



My offering to the IAT gods awaits one local Golf R willing to spend a few hours hanging out for development so this puppy can make its way its owners DBV2/MPI Mk7.5R in NJ.

BTW it’s 30% larger than its Vibrant counterpart
What size core?
 

Gvazquez

Go Kart Champion
Location
North Carolina
I see this thread has been busy on my four day weekend.



My offering to the IAT gods awaits one local Golf R willing to spend a few hours hanging out for development so this puppy can make its way its owners DBV2/MPI Mk7.5R in NJ.

BTW it’s 30% larger than its Vibrant counterpart
Will an A3 help you with your development?
 

GTI Jake

Autocross Champion
Location
Charlotte, NC
Will an A3 help you with your development?

Not for the R, I have one coming Thursday.

I believe the A3 & S3 both have an aluminum bumper rebar which appears to be much larger than the steel version and that’ll limit what can be done without my next step in the puzzle which will be a high clearance DOM tubular bumper rebar and the triple pass radiator that occupies the entire volume of the OEM radiator & intercooler.

On a side note, anyone wanna buy me a plasma table & a tubing bender? Lol
 

fredygump

Passed Driver's Ed
Location
55992
Yeah it's kinda pointless. A bigger turbo setup running more boost will have higher temps and a greater air mass flow-- both of which put greater strain on the intercooler and you'd expect higher IATs. Intercooler performance has so many variables it's hard to get real accurate data or comparisons. The best we can probably realistically do amongst ourselves is maybe compare 60-130 runs, IAT rise for a given setup etc.

One way to get an actual comparison of intercoolers would be to run a vehicle at a steady rate/power output and graph the intake temps. The better intercooler would give lower temps, which would allow for lower boost pressure. This would simplify the question.

The issue I see with typical testing is that it is all about the short pulls. This confuses the subject. Is the intercooler cooling by just absorbing heat, or is the heat being transferred to ambient air? In a short test, you don't really know which it is.

If it was(is?) possible to set up an experiment where you cycled boost on and off at a controlled rate, the IAT would roughly follow the boost, but with a delayed response. The delay is due to the mass of the intercooler, but it isn't very important. (I believe the engineers would call this delay hysteresis...) What matters is the rate the temp changes, not how much of a delay there is. I think the delay is shorter than most of us would expect.

----

I'm processing the replies on the "heat soak" discussion from last week, and I still don't believe that the problem being observed is charge air getting the intercooler so hot that it can't cool down. It could be true, but it doesn't quite make sense to me. As was pointed out, the stock IC doesn't have much mass, so it can't hold much heat. It should cool quickly when boost levels drop.

But the phenomenon described as "heat soak" is still a thing that shows up in test data....

So I'm wondering about the effect of heat from the radiator? I'm thinking about radiant heat, since we know the intercooler is in front of the radiator... In the tests that APR published results for, they show 6 (?) pulls, with one every 30 seconds. And the IAT temps gradually increased with each pull.

One interesting observation from their test of their intercooler is that on the first pull, the IAT is lowest at the middle of the run. I didn't understand why the temp would drop, but it makes sense that the intercooler is being heated by radiant heat from the radiator when the car is at idle.

In the following tests, the IAT's gradually increase with each successive pull, but there was a theme of the temps dropping slightly at the beginning of a pull, and then climbing a little at the end...

Anyway, it is easier for me to accept that the IC is getting pre-heated from radiant heat from the radiator, than it is to accept that the intercooler is just heating up like a thermal battery and can't cool down.
 

aaronc7

Autocross Champion
Location
USA
Car(s)
17 S3
One way to get an actual comparison of intercoolers would be to run a vehicle at a steady rate/power output and graph the intake temps. The better intercooler would give lower temps, which would allow for lower boost pressure. This would simplify the question.

The issue I see with typical testing is that it is all about the short pulls. This confuses the subject. Is the intercooler cooling by just absorbing heat, or is the heat being transferred to ambient air? In a short test, you don't really know which it is.

If it was(is?) possible to set up an experiment where you cycled boost on and off at a controlled rate, the IAT would roughly follow the boost, but with a delayed response. The delay is due to the mass of the intercooler, but it isn't very important. (I believe the engineers would call this delay hysteresis...) What matters is the rate the temp changes, not how much of a delay there is. I think the delay is shorter than most of us would expect.

----

I'm processing the replies on the "heat soak" discussion from last week, and I still don't believe that the problem being observed is charge air getting the intercooler so hot that it can't cool down. It could be true, but it doesn't quite make sense to me. As was pointed out, the stock IC doesn't have much mass, so it can't hold much heat. It should cool quickly when boost levels drop.

But the phenomenon described as "heat soak" is still a thing that shows up in test data....

So I'm wondering about the effect of heat from the radiator? I'm thinking about radiant heat, since we know the intercooler is in front of the radiator... In the tests that APR published results for, they show 6 (?) pulls, with one every 30 seconds. And the IAT temps gradually increased with each pull.

One interesting observation from their test of their intercooler is that on the first pull, the IAT is lowest at the middle of the run. I didn't understand why the temp would drop, but it makes sense that the intercooler is being heated by radiant heat from the radiator when the car is at idle.

In the following tests, the IAT's gradually increase with each successive pull, but there was a theme of the temps dropping slightly at the beginning of a pull, and then climbing a little at the end...

Anyway, it is easier for me to accept that the IC is getting pre-heated from radiant heat from the radiator, than it is to accept that the intercooler is just heating up like a thermal battery and can't cool down.

I believe the momentary drop in temp is due to how the IAT works. At low airflow/load, the sensor gets radiant heating from the surrounding material and makes it read a little artificially high. Then once you go WOT and airflow increases significantly...the radiant heat becomes negligible and the airflow cools the sensor slightly, before it starts to rise again of course due to actual heat in the charge air.

If I'm going 55mph steady state and then increase speed to say 65mph, the IAT will dip a little bit too as I accelerate.

This is just my theory though based on tuning a few setups and dealing with IAT radiant heat issues/hot start issues etc!

I mentioned the 60-130 thing because that was something that at least puts a decent load on the intercooler and makes comparison easy. What you're talking about is great for the engineer designing the thing on a dyno in a controlled environment...but good luck getting any kind of real data like that from the forums ha. A single pull scenario definitely gives the heavier bar and plate intercooler an advantage though.
 

fredygump

Passed Driver's Ed
Location
55992
I believe the momentary drop in temp is due to how the IAT works. At low airflow/load, the sensor gets radiant heating from the surrounding material and makes it read a little artificially high. Then once you go WOT and airflow increases significantly...the radiant heat becomes negligible and the airflow cools the sensor slightly, before it starts to rise again of course due to actual heat in the charge air.

If I'm going 55mph steady state and then increase speed to say 65mph, the IAT will dip a little bit too as I accelerate.

This is just my theory though based on tuning a few setups and dealing with IAT radiant heat issues/hot start issues etc!

I mentioned the 60-130 thing because that was something that at least puts a decent load on the intercooler and makes comparison easy. What you're talking about is great for the engineer designing the thing on a dyno in a controlled environment...but good luck getting any kind of real data like that from the forums ha. A single pull scenario definitely gives the heavier bar and plate intercooler an advantage though.

That does make sense about heat from the engine components throwing off air temp readings.


Also, I took another look at the data from APR, since it is the only "real" data I have seen.... They did 6 consecutive runs, with 30 second intervals.

Their data shows that IAT temps with their intercooler barely change. From beginning of the first run to the end of the 6th run, temp increases by 7 degrees (C)

The crazy part is that this temp increase over the 6 pulls does not happen during the run. It happens in the 30 sec interval between the pulls!


With the stock IC, temps jump significantly during the pull...which is what we would expect.

I'm including a simple spreadsheet...One detail that stuck out to me is that the stock IC cools down 22 degrees (C) in the 30 second interval between runs. But the first run gained 28 degrees. If a longer interval was used, the results would be more favorable for the stock intercooler.

So based on this data, "heat soak" is only a thing if you are doing full pulls every 30 seconds or less. That is quite a lovely piece of data, isn't it? :)


In this data, "heat soak" accounted for 17 degrees (C) temp increase on the 6th run. But there was another 25 degree temp increase due to compressing the intake air. So 40% is heat soak, and 60% is compressing the air. Again, with a longer interval, that heat soak contribution would be essentially zero.


Now, for some math! First run. Assuming PSI numbers that are easy to work with...

43 degree (C) air @ 14psi (absolute) = 1.06363 kg/m^3
71 degree air @ 28psi = 1.9542

Intake Air density at 28psi is 1.83x

41 degrees @14psi = 1.0704
41 degrees @28psi = 2.1408

Intake air density at 28 psi is 2.00x

On the first run, the stock IC lost 17% air density compared to the APR (at the same PSI...). That is losing something like ~14% HP.

On the final run, the APR IC has 11% higher air density than the stock IC.

And their data shows a 9% gain in HP on the last run, which is surprisingly close to the 11% difference in air density I casually/haphazardly calculated..


And...another topic for discussion...it looks to me like the APR Stage 2 dyno charts are only possible with their intercooler. (I wanted to ask, but never did...) They do not say anywhere that the IC is required to reach the 304hp peak power number. And the tuner I went to didn't think the IC was a big deal, saying he would rather ad turbo noises than do the IC...

But if their IC data I'm playing with is correct, showing a peak of 298hp after a 3% loss in air density (due to 9 degree temp increase)...that means the advertised 304hp is only possible with their IC...That means I'm not getting anywhere close to 300hp...more like 260!

Grrrrr..... I love the new clutch I just got, but with the DP and tune it doesn't really feel like a lot more power than I had before....I guess now I know why it doesn't feel like 304hp!
 

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MonkeyMD

Autocross Champion

aaronc7

Autocross Champion
Location
USA
Car(s)
17 S3
That does make sense about heat from the engine components throwing off air temp readings.


Also, I took another look at the data from APR, since it is the only "real" data I have seen.... They did 6 consecutive runs, with 30 second intervals.

Their data shows that IAT temps with their intercooler barely change. From beginning of the first run to the end of the 6th run, temp increases by 7 degrees (C)

The crazy part is that this temp increase over the 6 pulls does not happen during the run. It happens in the 30 sec interval between the pulls!


With the stock IC, temps jump significantly during the pull...which is what we would expect.

I'm including a simple spreadsheet...One detail that stuck out to me is that the stock IC cools down 22 degrees (C) in the 30 second interval between runs. But the first run gained 28 degrees. If a longer interval was used, the results would be more favorable for the stock intercooler.

So based on this data, "heat soak" is only a thing if you are doing full pulls every 30 seconds or less. That is quite a lovely piece of data, isn't it? :)


In this data, "heat soak" accounted for 17 degrees (C) temp increase on the 6th run. But there was another 25 degree temp increase due to compressing the intake air. So 40% is heat soak, and 60% is compressing the air. Again, with a longer interval, that heat soak contribution would be essentially zero.


Now, for some math! First run. Assuming PSI numbers that are easy to work with...

43 degree (C) air @ 14psi (absolute) = 1.06363 kg/m^3
71 degree air @ 28psi = 1.9542

Intake Air density at 28psi is 1.83x

41 degrees @14psi = 1.0704
41 degrees @28psi = 2.1408

Intake air density at 28 psi is 2.00x

On the first run, the stock IC lost 17% air density compared to the APR (at the same PSI...). That is losing something like ~14% HP.

On the final run, the APR IC has 11% higher air density than the stock IC.

And their data shows a 9% gain in HP on the last run, which is surprisingly close to the 11% difference in air density I casually/haphazardly calculated..


And...another topic for discussion...it looks to me like the APR Stage 2 dyno charts are only possible with their intercooler. (I wanted to ask, but never did...) They do not say anywhere that the IC is required to reach the 304hp peak power number. And the tuner I went to didn't think the IC was a big deal, saying he would rather ad turbo noises than do the IC...

But if their IC data I'm playing with is correct, showing a peak of 298hp after a 3% loss in air density (due to 9 degree temp increase)...that means the advertised 304hp is only possible with their IC...That means I'm not getting anywhere close to 300hp...more like 260!

Grrrrr..... I love the new clutch I just got, but with the DP and tune it doesn't really feel like a lot more power than I had before....I guess now I know why it doesn't feel like 304hp!

100% with you on the importance of intercooler on these cars. I think a few pages back I threw out the air density loss comparison as well. Plus the ECU is pulling quite a bit of ign timing with high IATs. Double whammy of a power killer.
 
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