So You’ve Decided to Go Turbo–Now What? (Part 2 – Intercooling)

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In Part 1 we learned about installation of turbo systems. This section will cover intercooling and making connections. Be sure to brush up on Part 1 if you haven’t read it already!

 

Intercooling

Intercooling lowers the temperature of the charge air mixture flowing into your vehicle’s engine. This not only lowers your engine’s potential for detonation, but also increases air density for greater potential horsepower. Engines running methanol typically don’t run intercoolers because they don’t have the high inlet temperatures that gasoline applications do. That’s an advantage not only because of the resulting extra horsepower, but also because of the weight savings and the elimination of a restriction such as the intercooler that can cause pressure drop.  Gasoline applications almost always run an intercooler of some type, usually either an air-to-air or a liquid-to-air configuration.

Turbo System

This mock-up of a single turbo kit for a 1987-93 5L Mustang comes with an air-to-air intercooler. The piping highlighted in red represents the hot air charge coming from the turbo, while the blue piping shows the cooler air flowing from the intercooler back into the engine.

Air-to-air intercoolers are more typically found on street cars. Looking much like a radiator core, they are placed in between the compressor outlet of the turbocharger and the engine inlet, almost as an open inlet on the nose of the car. Here, custom-formed end tanks direct the air through the intercooler, which intersects with on-rushing air entering from the outside while the vehicle is at speed. Thin, corrugated aluminum fins are the point of contact where the heat transfer actually takes place.

Intercoolers made of bar and plate construction are much less susceptible to damage from road debris and don’t tend to “balloon” under high boost pressures as the cheaper tube-and-fin design are prone to do.

air intercoolers

Liquid-to-air intercoolers are often installed in the place of the passenger seat. This presents a challenge for the driver, should he need to exit from this direction. Another issue involves potential injury in case a backfire results in an explosion, which could be minimized by adding ballistic blankets or a blow-off valve to the intercooler itself.

Although light and relatively inexpensive, the downside is that aluminum is actually a poor conductor of thermal heat transfer. Designers compensate for this by increasing surface area by adding more fins per inch. The resulting high-density design greatly increases overall efficiency. Copper, as found in early automobile radiators, does the job much more quickly, but at a much higher cost. Even so, an air-to-air intercooler will never get the air charge going into the engine any cooler than the ambient outside temperature. As a compromise, some racers will actually blow nitrous at the intercooler to enhance the cooling effect, but that comes at the cost of carrying extra weight.

For the drag racer, liquid-to-air intercoolers are much preferred because they can get inlet temperatures down as low as 40°F―or even cooler―depending on the efficiency of the core. These intercoolers, however, come with their own unique set of problems. They require an ice-filled reservoir and sometimes an electric circulating pump to move the melted water through the intercooler core. Mounting locations for the liquid-to-air intercooler reservoir on drag cars can be found in the trunk, the passenger seat and even at the front of the car. While these are almost always custom made to a particular race car, caution should be taken when welding so that there are no pressure leaks. In addition, a containment blanket or a blow-off valve might be a consideration to avoid injury should a backfire cause the intercooler to explode.  Don’t forget to look into getting a small freezer for your trailer, too, in case the track concession stand doesn’t have ice to sell.

Brad Personett’s twin-turbo ‘68

After two years of development, Brad Personett’s twin-turbo ‘68 Camaro proved that turbocharging could succeed in Big Show racing with victories at Indy and Vegas NHRA Pro Mod competition.

 

Making Connections

Should your car land hard after a wheelstand or if there is an interruption and/or contamination in your oil supply, more often than not you’re going to have to look at changing the turbo between rounds.

V-band clamp connectors

With large volumes and high boost levels, the inlets and outlets on many of the larger turbocharger housings use weld flanges and V-band clamp connectors. This provides secure connections and quick access should a turbocharger need replacement.

That’s why race turbos often use quick-disconnect V-band clamps to connect to the external wastegate, blow-off valve, intercooler piping and throttle body, as well. Use of these requires a matching weld flange.  Even with this, however, some racers have been known to externally bolt their connections together, too.

Utilization of this device helps alleviate compressor surge and saves engine damage.

ProCharger’s top-of-the-line blow-off valve (BOV) is popular on both centrifugal blower and turbocharged race applications. Utilization of this device helps alleviate compressor surge and saves engine damage.

An installation is also going to require tubing to route the air charge from the turbo, then the intercooler, and lastly, into the engine. While lightweight, mandrel-bent aluminum tubing is most preferred, it’s not uncommon to see tubing sections that have been meticulously welded together, most often in 4-inch and even larger diameters. Routing all of this plumbing is going to take some engineering and fabrication, but it’s important to keep in mind that flowing gases don’t like 45-degree bends, just like water.

Reservoirs for liquid-to-air intercoolers

Reservoirs for liquid-to-air intercoolers are often mounted in the trunk, allowing racers easy access to fill with ice between rounds. It’s not uncommon to see these also mounted in the interior, and sometimes even on the front. It can also serve as a convenient cooler once the day is done.

Four-ply silicone hoses are not only used to connect tubing, they also provide a certain degree of flex within the system in order to avoid side-loading on acceleration. Don’t cut corners here by using something from your local auto parts store. Those hoses aren’t designed for high-pressure applications. Do not use hose clamps, either. T-bolt clamps always provide much greater clamping force so you won’t blow off an intercooler tube or hose.

 

Stay tuned for Part 3 which will discuss Boost Control!

Text and Photos by Rod Short

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