Intercooling & Interesting Twists


The point of this argument is: The heat that finds its way through the walls of the tubes to and from the intercooler greatly contributes to the overall effectiveness of the intercooler system. Taking full advantage of that benefit is a must for any designer.

Premise: Never insulate a compressor outlet tube.

Testing my own turbo has produced an interesting set of charge temperature numbers. This was particularly evident with respect to the temperature changes in the tube from the turbo to the intercooler. Rather than produce a bunch of equations, I’ll offer the data and suggest a couple conclusions. The conclusions are rather obvious and have design quality and experience implications way beyond the data presented here.

The basic layout of the system: The turbo is positioned in the same place we originated 15 years ago, just 3.5 inches out from the head and an inch above the port centerline, right between cylinders two and three. One major change is the discharge of the compressor is now downward and out into the wheel well area. The tube goes forward to the intercooler, through the long tube IC core with baffled inlet, then out the opposite side, turns aft and up into the throttle. Pretty straight forward, but clearly not well understood, as evidenced by other designs offered up in the market. This layout was chosen specifically for the purpose of shedding heat wherever possible. For this test, all tubes were made from mild steel.

While seemingly obvious, but obviously not well understood, is the need to let the compressor outlet tube discharge some of the heat from the compressed air exiting the turbo. There is a substantial amount of heat that can be removed from this tube before it gets to the intercooler. EVEN IF THE TUBE STAYS UNDER THE HOOD IT WILL LOSE HEAT, AS THE UNDERHOOD TEMPERATURE IS NOT AS HIGH AS THE TEMPERATURE INSIDE THE TUBE.

We have taken the compressor outlet tube into the ambient air stream as quickly as possible. Hence, downward from the turbo and out into the wheel well.

Repeat:
The design principle: First; The air charge temperature inside the compressor discharge tube is higher than the underhood temperature, and Second, the discharge tube must get quickly out into ambient air temp where it can shed even more heat.

Here is how we tested it:
Data: We measured temps from right at the compressor discharge and at the IC entry. This data was consistent over several days of runs. Forward speed was held to 60 mph in 4th gear by dragging the brake. Boost was 6 psi. Time under boost was held until temps stabilized.... about 20/25 seconds. Tough on brakes, but we needed good data. The tally is an average of 12 measurements, none of which varied more than 3 or 4 degrees.

NOTE: This is a measurement of the temperature drop through the turbo discharge tube only!

Ambient F 95/96 F
Turbo Exit F 189/191 F
Temp Rise F 94/96F
Intercooler Inlet F 169/172 F
Temp Drop F 19/22 F

This data clearly states that approximately 20F is removed from the system through the walls of the tube between the turbo and the intercooler. Cool, eh?

Keep in mind that this data represents only 6 psi boost. At 12 psi, the compressor discharge temps will be approximately 90F higher yet. If so, while assuming the “efficiency” of the tube will remain the same, then the simple tube from the compressor outlet to the intercooler will discharge approximately 40/45F. Downright newsworthy.

General underhood area temps at the compressor discharge were 112/118 F. Temps in the wheel well area were 97/101 F.

This data states three things absolutely clearly:
1. The temperature inside the compressor outlet when under virtually any boost is far higher than the surrounding areas, thus heat exits the tube through the walls.
2. Behavior of the tube: The temperature removed from the system by the compressor outlet tube alone was 19 to 22 degrees F. Approximately equal to the temperature gain accompanying 1.5 psi boost.
3. Temperature out of the Intercooler, is within 5 degrees F of ambient.

Conclusions #1:
Anyone insulating the Compressor Outlet tube is blowing in the wind. That means their concept of the heat flow is backwards. If done so, their “Quality of Design” is subject to serious question.

Conclusion #2:
The compressor outlet tube should be made from a material with a high heat transfer capability, such as aluminum. This is precisely why we introduced the “multi-material tube set” moons ago with just that, an aluminum compressor outlet tube. Perhaps a bit in excess of reason, and not of world shaking proportions, but a maximum effort system should have a compressor discharge tube made from silver. Now, wouldn't that be a hoot? Maybe expensive too...

Conclusion #3: Porsche will one day build either aluminum, copper or silver compressor outlet tubes, and when they do, we will once again be able to claim we plagiarized their design.

Summary: Regardless of where the turbo is located,
NEVER, NEVER (NEVER SQUARED??) INSULATE THE COMPRESSOR OUTLET TUBE.

What is considered insulating a tube?
Wrapping in in fabric or using a heat retaining tube like silicone turbo hose

One more reason why the BEGi “quality of design” is superior to ALL others.

Should any reader like to verify our data, I’ll lend our digital thermometer to anyone for a reasonable deposit. You must use our Intercooler, tube system and duplicate our test conditions.

$100 - a 24" wide intercooler to replace the standard 19" unit. This upgrade is not compatible with air conditioning, and it's also a larger intercooler than the FM II needs on a stock engine. But it looks great and offers a good upgrade potential down the road.