The Intercooler

The intercooler is one of the key components to making reliable horsepower in turbo car. If you have to skimp on an item, this should not be one of them.

As a rule of thumb, an intercooler should flow 1.5 CFM per horsepower to avoid pressure drop. OEM intercoolers never have an advertised flow rate so it is very difficult to know just how efficient one like the popular Starion or Saab units will be in a setup making more HP than the Starion or Saab. One thing is for certain, very few OEMs design a car intercooler with lots of headroom to support a lot more HP. The Starion intercooler was designed for an engine rated at 164hp, so how efficient is it with 300+hp? Think DSM built in double the capacity? 

As you search for an intercooler, here is one case where size is not everything. Carefully check the flow rating for aftermarket intercoolers and the OEM HP rating if looking for a budget unit. Regardless of your choice, the plumbing should be mandrel-bent.

One OEM intercooler I like and had good success with is from the Isuzu NPR truck. Truck intercoolers, in general, seem to be designed to flow more than those designed for cars. The NPR intercooler, pictured next to a Z radiator for size comparison, is the largest of 3 sizes available. I used it with the previous Nissan 2.8L turbo engine and it supported my current setup up to about 400hp before it encountered major pressure drop. Despite the pressure drop, tests showed it still cooled the charge quite well. 

The NPR was replaced with a custom unit from Cartech, Corky Bell's company. It is 27"x8"x2.75" and has a flow rating of about 850 CFM which means it can support 560+hp before encountering pressure drop. This intercooler was acquired from a friend who upgraded and it worked out perfectly, allowing me to use the existing mandrel-bent, stainless steel plumbing with minor mods.

The intercooler has 2.5" inlet/outlet. On the compressor side, the pipe is 2.25" with a 2"-to-2.25" hose to fit the turbo and expanded on the other end to 2.5" to match the intercooler. On the throttle body side, the pipe is 2.5". Nothing worse than blowing off hoses at high boost, so T-band clamps are used on all connections and pipe ends have a ridge. The plumbing, with quality pipes, hoses and clamps can cost almost as much as the I/C.