The Perrin Subaru Intercooler Test

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The Perrin Subaru Intercooler Test

Post by drwrx » Fri Jun 27, 2008 2:48 pm

Go here for the full write-up: (it's worth a read)

If you don't want to read it I'll run it down:
Perrin TMIC made gains of +9.5 lb/ft and +10.4 whp @ 20psi. over stock STi TMIC

Perrin FMIC made gains of +13.8 lb/ft and +17.3 whp @ 20psi. over stock STi TMIC

Stock TMIC vs. PERRIN TMIC at ~17psi
First thing we noticed was the 15WHP changes were gone. Previously we would see pretty large HP swings when we would run the car quickly back to back. Now it would take about 5 runs before the HP really started to drop. This is a great first sign of a better intercooler. Couple other interesting notes is we saw roughly .5PSI more boost from 5000 to redline. This is an important thing to note as the stock STI turbo pretty much can't push more air than 14psi at redline. Adding more boost without changing the boost settings is also very good. The air temps were much more stable from run to run. If we compare the stock IC during the first few runs (while its cool) the PERRIN TMIC outlet temps are very similar. Which means the efficiency of it is about the same. The turbo outlet charge temps were very similar but slightly higher. This could be because the turbo is flowing more air and the turbo is further out of its efficiency range. This shows that the PERRIN TMIC makes power by being less restrictive, and more consistent.

Stock TMIC 17psi PERRIN TMIC 17psi

3000RPM Inlet 171F/ Outlet 97F Inlet 195F/ Outlet 107F

4500RPM Inlet 204F/ Outlet 102F Inlet 228F/ Outlet 119F

6900RPM Inlet 261F/ Outlet 138F Inlet 284F/ Outlet 158F

IC Efficiency 71%-63% at redline 69%-59% at redline.

The constant airflow from the fans you can see that its not quite enough to cool the thicker core. On the road, the PERRIN will start to perform even better. Even with the lower efficiency it made more boost at redline, and it made more power from 5000 to the top.

Stock TMIC 20psi vs PERRIN TMIC at 20psi
With the Stock TMIC pushed to 20psi, we started to see where it really stopped working. Because the Turbo is running more boost, and is running out of its efficiency range, higher pre IC temps were expected. This is also where the stock IC started to show its heat soaking issue. Both IC's were very similar the first run, but the stock IC run after run would heat up a bit. Both IC's from about 6000RPM on ran very similar in efficiency, but at lower RPM's the PERRIN TMIC was more efficient. The charge temps were a little cooler, the EGT's were 50F cooler, and overall the power was a little higher. The above graph shows the HP gained over stock, which is still very good.

The pressure drop difference from stock to the PERRIN TMIC got larger with the higher boost. Especially in the areas where the turbo really starts to kick. 1-1.5psi more boost was seen at lower RPM with the PERRIN TMIC. At lower RPM this results in a steeper sharper boost curve. At 20psi the PERRIN TMIC was good for a few more HP and still that consistency, but not much cooler temps.

This is the intercooler that we had a leak issue with. With the leaks present, we saw an averaged loss in roughly 30WHP, and air temps were about 20 degrees higher, and 1.0-1.5AFR richer. This turned into a 40WHP loss at redline, and that was running the same boost!

Stock TMIC vs PERRIN FMIC at 20psi
This is where we see what an intercooler is good for! We did both 17 and 20psi of peak boost, but 20psi is what the IC was made for! The stock TMIC and PERRIN TMIC work great for certain situations. But neither cool the charge air as good as an intercooler "could". This is where a front mounted intercooler comes into play. Having the intercooler on the front of the car is the most obvious place to put an intercooler. So why didn't Subaru put it there? Lots of reasons (not that I agree with all of them), packaging, installation, costs, responsiveness, insurance claims and not to mention the use of that signature scoop!

All the TMIC's would see hotter and hotter temps as the runs continued. Meaning that if the IC outlet temp peaked at 140 the first run, by the 3rd or 4th run it would be 150F and so on. While our TMIC was still better than the stocker in this situation, it still had room for improvment. There is just not enough ambient air flow for TMIC's to work properly under heavy load. With the PERRIN FMIC installed, we would see intercooler outlet temps peak to 105F and by the 4th run it would peak to 110F. Yes, the highest Intercooler outlet temp we saw was 111F, this is compared to 158F we saw with the PERRIN TMIC. The below data is taken from the 3rd run of both the intercoolers with roughly the same time between runs.

Stock TMIC 17psi PERRIN FMIC 17psi

3000RPM Inlet 171F/ Outlet 97F Inlet 197F/ Outlet 92F

4500RPM Inlet 204F/ Outlet 102F Inlet 248F/ Outlet 91F

6900RPM Inlet 261F/ Outlet 138F Inlet 300F/ Outlet 99F

IC Efficiency 71%-63% at redline 80%-86% at redline.

AT these lower boost levels the turbo works perfect and has no issues keeping up with extra plumbing.

Stock TMIC 20psi PERRIN FMIC 20psi

3000RPM Inlet 218F/ Outlet 110F Inlet 213F/ Outlet 103F

4500RPM Inlet 245F/ Outlet 113F Inlet 274F/ Outlet 103F

6900RPM Inlet 289F/ Outlet 149F Inlet 314F/ Outlet 107F

IC Efficiency 72%-63% at redline 75%-84% at redline

IC efficiency on the stock TMIC changes (compared to the 17psi runs) because the IC gets more and more restrictive as air flow goes up, and in turn needs more ambient air flow to cool it off. With our constant velocity fans, this doesn't happen. But if you look at our FMIC, the efficiency goes up! This is due to the IC being bigger and capturing more the ambient air flow in turn cooling the air better. Remember this is with some simple fans, which do not represent the same type of air flow you see on the road!

So what is the downfall to the PERRIN FMIC. A very slight loss in response. The "fill time" is just barely noticeable compared to the TMIC. Again the IC inlet temps were higher on the FMIC as it was flowing more air putting the turbo further out of its efficiency range. While this might be the case, it still made more power. Besides seeing the turbo outlet temps higher than other runs, the boost was also a little lower (but not more than .5psi) so after a retune, there will be much more than 17WHP and 13 ft-lbs of torque.

The Stock TMIC is ok, for a stock car running stock boost, but when pushed it started to show its faults. Not much else to say there!

The PERRIN TMIC is better than the stock IC. It does make more HP than stock and makes more boost efficiently. But overall the TMIC still has cooling issues, because of where it is placed in the engine and because of the rather small opening for air to reach it. Because the TMIC is not restrictive, and has some issues with cooling, this makes for a perfect intercooler when using Water injection. Our PWI-1 can turn the PERRIN TMIC into a great IC for super responsive autocross guys that can use water injection. But for those who can't, the FMIC stomps the competition!

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Re: The Perrin Subaru Intercooler Test

Post by drwrx » Fri Jun 27, 2008 3:02 pm

I should point out that there is one big issue I have with the test as it was run:
The entire front of the car was removed when the FMIC was tested. That gives the FMIC a huge advantage as the entire surface area is exposed, which it never is under normal driving conditions, and it also allows heat to dissipate more quickly. I am certain that skewed the numbers in the FMICs favor and was an advantage it really didn't need as I am certain it would have outperformed both TMICs. But my guess is the margin would have been not as much. Although 4 lbft and 7 whp over the Perrin TMIC isn't a huge gain.

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