The factory intercooler leaves little to be desired with regards to both pressure drop and cooling effectiveness. When we ran our first dyno tests on the Supra (TURBO Jan '87) we thought the restriction at higher boost pressures was actually in the turbo, but in conferring with Cartech, Spearco and HKS it was found that the stock intercooler itself was a major contributor to the problem. Testing at Cartech showed the stock intercooler to have a 3 psi pressure drop a 6.8 psi and a whopping 4.3 psi pressure drop at 9 psi. In other words, the turbo had to do the same work and therefore, produce heat as if it was run at 13.3 pounds of boost, while the engine itself was only seeing 9 pounds of boost.
All of these intercoolers are similar in size except that the Spearco unit also employs slightly larger diameter tubing in some locations going to and from the intercooler.
The only intercooler we were able do to an actual before and after test with on our own car was one of the units from Cartech. At stock boost pressure we found an 11-horsepower gain between the stock and Cartech intercooler. While this gain was actually measured at the stock (8 psi w/exhaust) boost pressure, it should be noted that intercooler efficiencies are best tested in a real world or street environment with actual air flow across the core. Previous testing on the Cartech intercooler showed a 7/10 psi drop at 6.8 psi and 1.10 psi at 14 psi which basically agreed with our dyno runs. In addition to actual pressure drop, Cartech testing of the intercooler showed 89% efficiency vs. 68% on the factory unit. With the similarity in intercooler upgrades, it would be safe to say that any one of these would be an almost mandatory option if you are starting to go for serious boost.
