There are few sports cars that can compare with the 1993 and later Mazda RX-7. The super-light aluminum body, race-bred suspension and powerful Wankel powerplant makes it a force to be reckoned with on the streets and on the track. From the factory, the 255-hp, 1.3-liter rotary engine is capable of propelling the RX-7 down the quarter mile in just 13 seconds. Besides the excellent performance potential of the RX-7, the Mazda's sleek, seductive bodylines respond well to body tuning. Several aftermarket body kit manufacturers have developed body tuning packages ranging from mild to wild. In this installment of Power Pages, we decided to up the power ante on the 13B-REW powerplant with a combination of simple, bolt-on performance products.
The EngineUnlike most of the import super cars available in the United States that are powered by a six-cylinder powerplant, the Mazda RX-7 relies on a pint-size 1.3-liter (79 cubic inches) rotary engine for horsepower production. However, don't be fooled by its small displacement; the power numbers generated from the 1.3-liter are far from small. The sequential turbo 13B-REW engine yielded an astounding 255 hp and 217 lb-ft of torque in stock trim. Mazda was the first major car manufacturer to utilize the rotary engine; the first one was used in the R-100. Unfortunately, the RX-7 was discontinued in the United States in 1996. Although the rotary powerplant died stateside, it still powers some Mazdas in Japan. The 13B powerplant is very popular for 510 owners and many of the old-school Toyota racers. Some of the more notable racers that rely on the 13B engine are Abel Ibarra, Ray Lochhead and Ari Yallon.
Performance ComponentsOne of the major drawbacks of the rotary engine is its lack of torque. Although the twin-turbo pumps out 217 lb-ft, it doesn't come close to the Supra, 300ZX or 3000GT, all of which produce torque figures in the neighborhood of the high 200s to low 300s. Since most enthusiasts drive their RX-7s daily, we elected to pump up the Mazda with only simple bolt-on components for simplicity's sake.
The beauty of factory turbocharged vehicles is the hidden horsepower of the engine. The easiest way to increase power from a turbocharged engine is by increasing airflow to and away from the heart of the engine. Most factory intake and exhaust systems are rather restrictive and thereby rob the engine of potential horsepower. To remedy the situation, we turned to A'PEXi for some power enhancements.
Dyno TestingPrior to testing any of the products, we performed a routine maintenance on the rotary, changing the oil and the spark plugs. We recommend changing the spark plugs every 15,000 miles on a rotary. Routine checks of the oil level on a rotary engine should also be performed. Even though the oil was changed only 2,000 miles ago, the oil level was already reading one quart low. Instead of adding oil we decided to change it. With the vehicle strapped on the dyno we performed a baseline run. The 7 was only able to muster 201.4 hp and 199.2 lb-ft of torque to the wheels. Even with a 15-percent loss to the wheels, the car should be making around 217 hp. The Mazda was down nearly 16 hp. Instead of proceeding with the bolt-ons, we decided to investigate. Fortunately for us, our dyno shop, XS Engineering, is a rotary performance specialist.
After talking to Koji Arai and Pete Yeung of XS, we were informed that broken vacuum hoses were a common occurrence in the third-generation RX-7. The heat generated by the engine causes the rubber hoses to dry out prematurely, making them very brittle and prone to cracking. If there is a leak in the vacuum lines performance figures would be affected. We performed a pressure test on the entire engine to locate any possible leakage. Immediately after pressurizing the system, we noticed several leaks in the spider web of vacuum lines directly under the intake manifold. In order to replace the vacuum lines, it would require us to remove the upper half of the intake manifold.