When it comes to turbo motors, I think maybe Ben Franklin said it best in his “Poor Richard’s Almanac.”

The honey is sweet but the bee has a sting!

The takeaway from Big Ben’s statement is that we shouldn’t let something good tempt us because there is always a price to pay! 


Okay, so maybe Mr. Franklin was more interested in kite flying than turbo LS motors, but the sticky and the stings are no less relevant today. We all love boost, especially when it comes from a turbo, but there is (as always) a negative side to positive pressure. One of the unfortunate laws of physics is that heat is a natural byproduct of compression. All that wonderful boost causes unwanted heat, and heat is the enemy of both power and longevity. We love the boost but hate the byproduct, so what is an enthusiast to do?

The answer is obviously intercooling, but let’s take a closer look not just at intercooling, but at the actual changes in charge temperatures and power generated during a recent test on intercooling (a de-stroked LS3 no less!).

intercooler housing on a dyno tester
We all know we should include intercooling with boost,, but just how effective are they at lower charge temps? (Image/Richard Holdener)

Understanding How Intercoolers Work

Before getting to the test, we should take a brief look at intercooling. We mentioned that the boost pressure supplied by forced induction heats the inlet air and that heated inlet air is bad for both power and safety. The cure to increased charge temps caused by boost is intercooling. Intercoolers involve running the heated charge air through a heat exchanger.

The two most common types of intercooling include air-to-air and air-to-water heat exchangers. The air-to-air intercoolers rely on increased surface area and ambient airflow through the core to lower the charge temperature, while air-to-water cores rely on water as the cooling medium. This discussion is not about which one is more efficient, as the choice will come down to the specific application.

For our test, we ran an air-to-water core from CX Racing with and without water flowing. As the data will illustrate, the mere fact that we had a core, even with no water flow, meant that some cooling took place, but the system was not nearly as effective as had cooling water been flowing freely.

The Intercooler Test Engine

To test the effect of the cooling water, we had to set up a turbo motor. Luckily we had just such an animal at our disposal in the form of a short stroke LS3 engine.

The LS3 block from Gandrud Chevrolet was stuffed with a 4.8L crank, 6.30 inch Lunati rods and custom JE forged pistons. The LS3 short block was filled with a Stage 2 turbo cam from Brian Tooley Racing then topped with a set of Trick Flow GenX 255 cylinder heads and Holley Hi-Ram induction system.

Airflow came via a FAST 102mm throttle body while fuel was supplied by a set of Holley 83-pound injectors controlled by a Dominator EFI system.

The single turbo system was a homemade affair consisting of a pair of tubular manifolds from DNA Motoring feeding a custom Y-pipe. The T4 turbo flange fed a 76mm Precision turbo controlled by a pair of 45mm Hyper-Gates from Turbosmart (set to seven psi).

The test revolved around an air-to-water intercooler supplied by CX Racing that featured 3.5 inch inlets and outlets. The core relied on a single water inlet and single water outlet, allowing us to manually shut off the supply of 83 degree dyno water to the core. We monitored the air temps both before and after the intercooler as well as with and without the water flow.         

Testing Intercooler Performance

The first test was to turn the turbo motor with the intercooler functioning properly with full water flow through the core. The waste gates were set with seven psi springs, which resulted in a maximum boost level of 7.4 psi. Running 7.4 psi resulted in a rising charge temp exiting the turbo. During the run, the inlet air temp exiting the turbo rose from 109 degrees to 183 degrees.

Using 83 degree dyno water as the cooling medium, the air temps exiting the intercooler never exceeded 98 degrees and actually dropped down to 90 degrees during the run (see graph 3). Even at the relatively low boost of 7.4 psi, the inlet air temp rose to 183 degrees and that was with a steady supply of ambient air to the turbo, which might not be the case under the hood. The intercooler was on the job, reducing the charge temps by almost 90 degrees!

The results were quite different after shutting off the water flow to the core, as the inlet air temps (after the intercooler) started higher at 134 degrees and rose to 144 degrees. This was 46 degrees higher than the air temp with water flow. The result was not just hotter air (which can cause harmful detonation), but a loss in power from 733 hp to 706 hp.

Note: No changes were made to timing based on the IATs (timing remained constant).

These results are proof positive that the best medicine to lower the air temps and make more power is the one and only chill pill!

engine dyno chart 1
This test involved running the short stroke, turbo LS3 with and without water flow to the CX Racing air-to-water intercooler. The test was designed to demonstrate the ability of the water to remove the heat from the charge air. From a power standpoint, it is obvious that water flow is important as the power dropped by 27 hp (from 733 hp to 706 hp) with no water flow. Heat is the enemy of power and air-to-water intercoolers only work with proper water flow. (Dyno Chart/Richard Holdener)
engine dyno chart 2
In addition to the change in power, we also monitored the inlet air temps during each run. Equipped with 83 degree (dyno water) running through the core, the inlet air temps never exceeded 98 degrees and dropped below that point at the end of the run. Without the water, the inlet air temps started at 134 degrees and rose to 144 degrees, an increase of nearly 50 degrees over the functioning intercooler. In addition to the loss in power, the elevated charge temps also increase the likelihood of detonation. It is interesting to note that even without water flow, the intercooler dropped the charge temps compared to the air exiting the turbo. Without water flow the intercooler worked, just not as well (Dyno Chart/Richard Holdener)
engine dyno chart 3
This graph illustrates the difference in the inlet air temp before and after the intercooler. The heated charge air coming out of the turbo (at 7.5 psi) rose from 109 degrees to 183 degrees. After running through the intercooler core, the charge temp never exceeded 98 degrees, dropping down as low as 90 degrees during the run. The intercooler dropped the inlet air temps by roughly 90 degrees using 83 degree water. The upshot of all this data is that intercooling works, even at low boost, so use it! (Dyno Chart/Richard Holdener)
man dropping crankshaft into a v8 engine
The unique LS test motor featured an aluminum LS3 block stuffed with a short 4.8L stroke crank. (Image/Richard Holdener)
JE Piston Rings in box
The custom combo also featured forged flat top (with valve reliefs) JE Pistons for a 4.070 inch bore. (Image/Richard Holdener)
piston and rod assembly on a lunati box
The short stroke combo required custom Lunati forged rods. (Image/Richard Holdener)
camshaft going into a v8 engine
To help the short stroke turbo motor make power, we installed a Brian Tooley Racing Stage 2 turbo cam. The BTR Stage 2 cam offered a 0.605/0.598 lift split, a 226/231 degree duration split and 113 degree LSA. (Image/Richard Holdener)
moroso oil pan on a shop floor
To aid in oil control on this high-rpm de-stroked LS3 (it was run to 8,000 rpm with a different cam combo), we installed this Moroso oil pan. Note the fitting for the turbo oil drain. (Image/Richard Holdener)
installing trick flow heads onto a v8 ls engine
To provide plenty of airflow for the combo, we topped the de-stroked LS3 with a set of TFS GenX 255 (rectangular port) cylinder heads. (Image/Richard Holdener)
intake manifold on an ls engine dyno test
The induction system consisted of a Holley Hi-Ram intake manifold equipped with a single EFI TB lid. (Image/Richard Holdener)
mouth of a FAST throttle body on an ls engine
Feeding the 102mm opening on the Holley Hi-Ram lid was a 102mm Big Mouth throttle body from FAST. (Image/Richard Holdener)
shortly headers on an ls v8 engine
Not technically a turbo kit, the DIY set up started with a set of forward-facing DNA tubular turbo headers. (Image/Richard Holdener)
turbocharged ls engine on dyno
The turbo headers fed a custom Y-pipe equipped with a single T4 turbo flange and provisions for a pair of wastegates. (Image/Richard Holdener)
wastegate on an ls engine dyno test run
For this test, the (dual) 45mm Turbosmart Hyper-gate wastegates were configured with seven psi springs. (Image/Richard Holdener)
sensor installed on an intake manifold
To ensure adequate fuel delivery, the Holley fuel rails fed 83 pound fuel injectors. The turbo testing was run on a mix of 91 and 100 race fuel. (Image/Richard Holdener)
dominator efi manifold on a box
Precise tuning of the AF and timing was supplied by this Holley Dominator EFI system. (Image/Richard Holdener)
intercooler on an ls engine dyno test
The test involved this air-to-water intercooler from CX Racing. The air-to-water core featured 3.5 inch inlet and outlets, and had been used successfully on turbo applications exceeding 1,000 hp. Note the pair of water lines to feed the intercooler core. All we had to do was shut off the water feed line for our test. (Image/Richard Holdener)
ls turbo intercooler engine dyno test setup
Tested on the turbo LS, the effect of shutting off the intercooler water had a sizable effect on power and charge temperature. The inlet air temp increased nearly 50 degrees and power dropped by 26 hp! Not only is an intercooler important to power and safety, so is water flow! (Image/Richard Holdener)

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Richard Holdener is a technical editor with over 25 years of hands-on experience in the automotive industry. He's authored several books on performance engine building and written numerous articles for publications like Hot Rod, Car Craft, Super Chevy, Power & Performance, GM High Tech, and many others.