Trying to get all the engine components to work harmoniously and live a long life in a single-turbo Supra can sometimes not be so simple. Shortly after the boost was incrementally turned up our stock-cam car was seeing over 520 whp on 93-octane equivalent fuel on evosport's Dynojet. Our goal from that point was to get a decent baseline with the stock cams, install a set of HKS 272 cams, and retest.
Unfortunately things didn't work out as planned. After evosport's Gary Karamikian installed the HKS cams we went out for a drive to get the timing and air-fuel ratios right. Shortly into the drive-and-tune session the bracket for the timing belt tensioning pulley cracked. It happened over the course of the first couple of boosted pulls over 20 psi. As torque increases, so does the tension on the timing belt and, thus, the force on the tensioner and bracket.
Since evosport didn't have a lift available right away the car was towed a local Turbo-friendly shop, Under Pressure Fabrication and Distribution, where we found that the cracked pulley also chipped a piece off the housing of our new oil pump. To our disgust, replacing the housing requires us to drop the oil pan and subframe to replace it. We ordered a new factory oil pump gear and housing from Champion Toyota in Houston, Texas.
Fortunately the timing belt didn't slip off when the tensioner broke, but it was time to look for a fix regardless. To our rescue came the crew at Sound Performance. After seeing this happen to numerous Supras, Sound Performance recently introduced a billet tensioning bracket to replace the cast O.E. unit. We wish it would have been available sooner-and now you know as well. This billet piece of 4130 chrome-moly is sure to outlast the factory unit.
As long as we were back under the hood we hunted down other parts we felt could possibly fail in the near future. The stock crank damper was one. Apparently many Supra owners have been having problems with these coming apart. To avoid ever going through this we ordered a crank damper from Boost Logic. This machined damper has a steel and press-fit hub to prevent cracking and keyway gouging. The best part is that it weighs only 5.5 pounds (compared to the 7.5-pound stocker), a reduction of over 25 percent in rotating mass.
Since the accessory belts would be coming off anyway it was a good time to take advantage of Boost Logic's accessory lightweight aluminum pulleys as well. We got pulleys for the power steering pump, alternator and water pump.
We didn't have a scale with a higher than 0.5-pound resolution on hand but the stock power steering pump pulley registered 1.0 pound and the new BL aluminum replacement didn't even register. BL pulleys are SFI 18.1 approved and use the factory accessory belt. Although lighter, these pulleys don't under drive the accessories. The engine, however, will love the decrease in weight of the rotating assembly.
A camshaft, crank damper and belt tensioner bracket installation requires the removal of the timing belt and re-timing of the cams to the crankshaft. You'll save a lot of time and money if you do them all at once. It's not a bad idea to go ahead and install a new timing belt while everything is easy to get at.
You may have noticed in the previous installment a few new components that were not mentioned at the time. First off, our previously featured engine rebuild included upgrades to the cooling system in the form of a PWR radiator. The PWR unit is nearly an O.E. replacement-all we had to do was trim a bit off the plastic battery tray to make room for the larger end tanks.
The additional 1.25 quarts of cooling capacity will ensure better management in the temperatures cooler during high-performance driving. As with a turbocharged BMW M3 project I managed for our sister magazine, european car, it should help keep the oil temp down significantly too. With the M3 the oil temp dropped over 35 degrees Fahrenheit after the addition of a high-capacity radiator. The oil temp never exceed 200 degrees on the track!
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.