Intercooler performance

[GTI_Owner]

As the 20 looses steam as RPMs increase you will see the IATs climb is what you are saying?

More boost pressure from the IS38 would cause higher compressor discharge temperatures. The fact that IAT is lower with the IS38 than on the IS20 at lower boost is an indication that the Unitronic IC is cooling better, confirming what you observed.

Peak boost is the same - the IS38 has a higher PR ceiling than the IS20 at the same psi = less heat.

What do you mean by PR ceiling, I'm not familiar with that term as you are applying it?

 

[IanCH]

Pressure is pressure.

In this case P*V = T

If you have a bigger turbo running higher pressure then you have higher temps. My results above with a 8f over ambient delta with my is20 are not comparable to the is38 tigeo posted.

 

[Hollywood0220]

More boost pressure from the IS38 would cause higher compressor discharge temperatures. The fact that IAT is lower with the IS38 than on the IS20 at lower boost is an indication that the Unitronic IC is cooling better, confirming what you observed.



What do you mean by PR ceiling, I'm not familiar with that term as you are applying it?

What I am referring to is the PR of each compressor. The 38 has higher and wider (x/y axis) efficiency islands - it is more efficient. The 38 @20psi is equivalent to the heat signature of a 20 @16psi.
A larger turbo will generate less heat signature at the same psi. However, the boost peaks depicted are the same - thus, less heat.
I am not denouncing the ICs efficiency/cooling - just that the heat signature is not equal to that of the smaller turbo.

 

[GTI_Owner]

What I am referring to is the PR of each compressor. The 38 has higher and wider (x/y axis) efficiency islands - it is more efficient. The 38 @20psi is equivalent to the heat signature of a 20 @16psi.
A larger turbo will generate less heat signature at the same psi. However, the boost peaks depicted are the same - thus, less heat.
I am not denouncing the ICs efficiency/cooling - just that the heat signature is not equal to that of the smaller turbo.

Where have you found compressor maps for these turbos? Can you provide a link or post them here, I've never come across any.

In the example you give if the IS38 efficiency is 75%, the IS20 would have to be 63% to produce an equivalent temperature at lower boost. I'm very skeptical that an IS20 at 16 psi is only operating at 63% efficiency.

 

[oddspyke]

You might be thinking about the curves wrong. There isn't a set efficiency for a given PSI. Variable turbine speed means it's a 3-D curve. With the smaller compressor, the same airflow and pressure require far higher turbine speed. I'm rusty on my pump laws, but I think power required is related to Diameter^5, assuming you hold flow and pressure constant. Any power not used for flow and pressure becomes heat. A little more turbine goes a long way.

 

[Hollywood0220]

Where have you found compressor maps for these turbos? Can you provide a link or post them here, I've never come across any.

In the example you give if the IS38 efficiency is 75%, the IS20 would have to be 63% to produce an equivalent temperature at lower boost. I'm very skeptical that an IS20 at 16 psi is only operating at 63% efficiency.

I wish we had Compressor Maps for our own edification bud...
Allow me to more easily sum this out:
A bigger turbo will move more air thru the compressor with less effort; thus creating less heat. This equals “more efficient”. Especially when cross comparing to the smaller turbo at the same pressure.
Is that understandable m8?

 

[The Dude]

Peak boost is the same - the IS38 has a higher PR ceiling than the IS20 at the same psi = less heat.

Pressure is pressure.

In this case P*V = T

If you have a bigger turbo running higher pressure then you have higher temps. My results above with a 8f over ambient delta with my is20 are not comparable to the is38 tigeo posted.

What I am referring to is the PR of each compressor. The 38 has higher and wider (x/y axis) efficiency islands - it is more efficient. The 38 @20psi is equivalent to the heat signature of a 20 @16psi.
A larger turbo will generate less heat signature at the same psi. However, the boost peaks depicted are the same - thus, less heat.
I am not denouncing the ICs efficiency/cooling - just that the heat signature is not equal to that of the smaller turbo.

so fellas, you're all right. The term you're looking for is adiabatic efficiency. Pv=nrt is the ideal gas law, and adiabatic efficiency in the case of dynamic compression, like a turbo or supercharger, is the lurking variable you're trying to understand. The compressor maps efficiency island has to do with adiabatic efficiency, or the amount of additional heat added to the system by the act of compression. If your compressor is 100% efficient, you will add zero additional heat beyond what's going to be added according to the ideal gas law. If there's any increase in the temperature of the system BEYOND what can be calculated by the ideal gas law, that's due to the lack of adiabatic efficiency of the compressor. The less efficient a compressor is (small wheel turning big boost), the more heat (IAT's) are added to the system, and the more efficient your ability to cool the charge becomes.

So again, you're all correct.

 

[bentin]

So what you're all saying is that it would be stupid not to just buy an IS38? Got it, glad I dropped by.

 

[Ezekiel81923]

It's the age old trade-off.

You could push an is38 to 400whp and it'd be pumping some heat, which you'd have to combat. But you'd have better spool.

Or you could turn down a vortex XL and make the same power with less heat, strain on the turbo, and your IC wouldn't have to work as hard. At the cost of spool time.

Pick your poison.

 

[tigeo]

My aftermarket direct-fit intercooler keeps my IAT cooler vs. stock during WOT, that's the bottom line for me. Any small differences in the turbo size on my setup aren't material.

 

[The Dude]

My aftermarket direct-fit intercooler keeps my IAT cooler vs. stock during WOT, that's the bottom line for me. Any small differences in the turbo size on my setup aren't material.

not true at all. the less heat you add to a system, the less your intercooler has to take out.

 

[GTI_Owner]

I wish we had Compressor Maps for our own edification bud...
Allow me to more easily sum this out:
A bigger turbo will move more air thru the compressor with less effort; thus creating less heat. This equals “more efficient”. Especially when cross comparing to the smaller turbo at the same pressure.
Is that understandable m8?

The heat results from the pressure increase and not being adiabatic (mentioned above by @The Dude ). In this example the IS20 is at lower pressure, so the adiabatic efficiency of the IS20 would have to be a whole lot less, like I mentioned closer to 63%, which is going to occur nearing the surge boundary or choke line, across the middle of the map where it will be operating most of the pull the efficiency will be in the 70-75% range.

A map of a similar size compressor wheel will give a good approximation for the IS20/IS38. I'll try and find a couple later to illustrate.

 

[The Dude]

it's not just the size either, the aerodynamics of the wheel make a big difference. like the G series compressors are super efficient. I'm gonna log temps for the IS20 and stock intercooler and then the G25 with a Majesty, we'll see what's up.

 

[IanCH]

I should note that the heat transfer from the compressor is going to result in a pretty negligible temperature increase or decrease based on efficiency. Some of that heat goes outward too.

My point with my initial post about pv=t is that you shouldn't really even be factoring efficiency it's such a small contributor to the IAT readings.

 

[tigeo]

Had my Unitronic IC installed a few weeks ago at the same time as my IS38 on my 4Motion Sportwagen. Also did the Unitronic charge pipes/hoses. Here is a quick compilation of the data I have collected thus far and before. Yeah, they work. These are the data points from ~redline in a third gear pull starting at 2K rpm so max heat more or less. The car was not heat soaked for any of the runs.