Flow is not the end-all be-all
test for intercoolers, but it is VERY important! If your turbo has to make 5
extra psi to hold your desired boost level, you are overheating the air by about
55 degrees, which means your "high efficiency" cooler may become "low
efficiency" in short order. These flow results DO NOT show the cfm flowed; they
show how the coolers were tested for flow IN
RELATIONSHIP TO EACH OTHER.
This relationship is *NOT* LINEAR!
This means that an increase of one inch H2O from 10" to 11" represents a MUCH LARGER gain of backpressure than an increase of one inch H2O from 4" to 5".
Nevertheless, this test tells which cooler outflows which, and allows you to go from there in your selection.
Isuzu NPR Supra
Here are the results of the test, starting with the best flowing cooler, and descending to the worst flowing:
1. SPEARCO intercooler. 32 short thick
wide tubes. 4" H2O
2. TALON intercooler. 42 short thin narrow tubes. 6" H2O
3. Supra intercooler 30 ultra-thin wide tubes 6.75" H2O
3. Isuzu NPR cooler (small version) 16 ultra-thin wide. 8.25" H2O
4. FORD intercooler. 17 short thick wide tubes. 8.5" H2O
5. VOLVO intercooler. 34 long thin narrow tubes. 9" H2O
6. MOPAR intercooler. 10 long thick wide tubes. 9.25" H2O
7. SAAB intercooler. 26 long thin narrow tubes. 10" H2O
results of the NPR cooler were just added. Because of heavier air (cool with
higher barometer) than at the last test, everything was reading ONE psi higher
than last test, so the NPR result was adjusted accordingly. It flowed one full
psi better than our stocker, but has a MUCH better surface area and cross-flow
properties than the stocker.
Here's how the results were derived:
As you can see, the abrupt change from over 3" ID to a 2.5" pipe hampers flow. So we get 2" of backpressure from a simple short straight 2.5" pipe. Therefore backpressure of the coolers is measured in inches of water *above* 2".
NEW!! EXTERNAL FLOW TEST NEW!!
THIS TESTS THE ABILITY OF AMBIENT (OUTSIDE) AIR TO FLOW THROUGH THE CORE OF THE COOLER, INTO THE ENGINE BAY. EACH EXTRA 5 MPH OF AMBIENT AIR FLOW THRU THE CORE MAKES YOUR COOLER MORE EFFICIENT. SPEARCO HAS CHARTS SHOWING DRAMATIC COOLING EFFICIECY IMPROVEMENTS FROM BETTER FLOW.
I have tested only 5 cores so far; here they are in descending order of flow quality:
1. Supra intercooler 30 ultra-thin wide
2. Isuzu NPR cooler (smaller version) 16 ultra-thin wide. 5.75" H2O
3. Spearco intercooler. 11 long thick wide tubes 7" H2O
4. MOPAR intercooler. 10 long thick wide tubes. 9.75" H2O
5. Spearco intercooler. 32 short thick wide tubes. 11" H2O
Surprises? Yes! The NPR tubes are
so thin, that they look like they would not flow well. Apparently the internal
fins are designed for very little resistence, and the cooler actually beats the
stocker by a decent margin in INTERNAL flow, and beats the stocker HANDILY with
The Supra cooler turned out to be just like the NPR cooler. The thin tubes are very deceiving to look at.