Taking into account this was done on a turbocharged 3.2-liter inline six running 10 psi and no oil cooler, a high-capacity radiator was the perfect move. We'll report back with our oil and water temps when this PWR-equipped Supra hits the track.
The engine itself has had an easier time staying cool but the underhood temperatures still left something to be desired. On the road, Supras emit an enormous amount of heat under the hood, sometimes closing in on 200 degrees, which doesn't help our intake temperatures with an open element cone air filter.
To help alleviate the problem we went looking for a vented hood. Searching for the right hood we wanted one that would be most importantly functional, and look tastefully aggressive at the same time. Enter MVP Motorsports, an authorized distributor for Top Secret products.
MVP sells a wide selection of performance parts from many different manufacturers, enabling the company to offer products in more of an unbiased manner. MVP has all sorts of high-quality hoods and body components available for the JZ80 (not to mention other imports), but the Top Secret hood was our number one choice. With six louvers and a seventh one that would sit behind the turbocharger, this design looked to be fairly efficient in getting some heat out.
When the composite (also available in carbon fiber) hood arrived the first thing we did was weigh it. At just 8.5 pounds it was a good start with an 18.5-pound savings over stock. With three louvers per side in the design, we found it odd that only four of the six were functional. The ones on each side closest to the radiator were mysteriously blocked off.
As it was, the hood was installed and tested at the California Speedway during a road course event. Still, the underhood temperature was reaching the 170 degree mark after a few laps. It appeared the hood helped in decreasing the rate of temperature rise during both on-track and everyday street driving, but the underhood temp still soared when given enough time. What it needed was to allow more cold air in.
Fortunately, the same gentleman who painted our hood in the factory white paint is also a body man. Lucio Serrano of L&S Custom Products added an air duct to the hood in front of the turbo location to draw cold air into that hot, exhaust side of the engine bay. He also opened up the front two louvers to further release radiant heat from the radiator.
The car hasn't returned to the track with these mods yet but what this did for the underhood temperature on the street was magnificent. The underhood temperature dropped by 45 degrees during cruising and the intake temperature, monitored by an Auto Meter two-channel intake gauge, reading from inside the very back of the intake manifold, was registering just over 10 degrees above ambient once the car was rolling (we'll talk gauges in a later installment).
Driving around town is usually where a car's underhood temperature really picks up. With the factory hood, even on a mild, 80-degree day, the Supra's intake temperature would quickly soar to near cylinder head and radiator temperatures (around 200 degrees!) after being parked for a short grocery-getting stint-as most other cars would. Even after several minutes of driving the temp would stay over 150 degrees. Eventually, it would come down to about 130 degrees, but not getting any cold air in or evacuating hot air out kept it from dropping much lower.
After the installation of our duct-modified Top Secret hood the intake temp rarely exceed 130 degrees after being parked for a short while. Thanks to the six open louvers the addition air allowed in dropped the intake temperature to near ambient within a couple of minutes of driving, which will definitely prolong the life of the rubber and plastic pieces in the engine bay.
There's a rule of thumb that states, "A ten-degree drop in temperature equals a 1 percent horsepower increase." If this holds true, at our current power level we're talking about gaining over 20 whp with this Top Secret hood!
Special thanks to Champion Toyota in Houston, Texas, for supplying us with another oil pump, and to Under Pressure Fabrication and Distribution for getting our car underway so quickly.