In 1989, halfway through its expected build life, the FC RX-7 saw a multitude of small refinements. Rotary engine technology had had continued its advance in the 3 years. The engines themselves used new lighter, higher compression rotors. The combustion recesses on the rotors were fully machined and chromed for heat control. With the machining, the compression ratios of each of the rotor's combustion chambers as well as rotor weight, could be more closely matched. The compression ratio for the normally aspirated models jumped to 9.7 and 9.0 for the turbo respectively (up from the 9.4 and 8.5). For both increased emission restrictions and better engine management the engine computer was speed was doubled.

On the normally aspirated (NA) engines the changes allowed the redline to be increased to 8000 RPM. A rotary valve was added between the intake tracks which started opening at 4500 RPM. This variable dynamic intake (VDI) valve enhanced the DEI (Dynamic Effect Intake) by altering the length of the fuel/air mixture path based on engine speed and load. The airflow meter was also changed from the flapper type to a linear type for reduced air resistance and more precise measurement. The oil metering pump was changed from a mechanical pump to an electronic model for more effective lubrication and reduced oil consumption. These engine modifications raised the output of the NA 13B to 160 HP @ 7000 RPM and 140 lb/ft of torque @ 4000 RPM. The power band was effectively widened, giving more usable power at lower RPMs.

The Turbo II received a new turbocharger. Mazda called it the "Completely Independent Twin Scroll". The impeller was fed directly at the exhaust port. The Mazda press release in 1989 said: “This permits the powerful exhaust pulse generated by the opening of the exhaust port to directly hit the turbine blades without interference from the exhaust from the other rotor." This newer design resulted in reduced turbo lag and increased torque. The new electronically controlled wastegate allowed higher boost pressures and quicker response. The modifications resulted in the peak torque smoothed through the 2000 to 5000 RPM band. The horsepower also climbed another 18 ponies to give the revised Turbo II a Mazda claimed total of 200 horse power @ 6500 RPM and 196 lb-ft of torque at 3500 RPM. The Turbo model also now came standard with anti-lock brakes.

The automatic transmission was now electronically controlled with a "hold" mode that allowed the transmission to be shifted manually in the lower three gears. The Convertible was now available with an optional automatic transmission. Plastic end links and ball joint mountings were used on the sway bars to reduce noise, harshness, and vibration. Vehicle speed sensitive power steering became standard on the Turbo II, but in the GTU models, a less accurate (and cheaper) engine speed sensitive power steering was used. The fuel tank was increased to 18.5 gallons across the line.

Inside the car, leather was used to cover the revised shift ****, steering wheel, and hand brake in all models except the GTU (base) model. The seats were re-contoured for better lateral support. The temperature, fuel, voltage, and oil pressure gauges were placed in round recesses rather than the pie wedges that were used previously and a minor revision was made to the instrument surround. The center console radio, shifter and Logicon (climate control) surrounds were slightly re-contoured with a new rubberized material and the Logicon itself getting updated icons for air direction. A new parcel shelf was added that hid items in the hatch area for GXL and Turbo versions. Controversial motorized seat belts became standard on the coupes in the USA and black became an interior color option with the gray interiors no longer available. The Limited Slip Differential found on the 1986-1988 GXL and 1988 GTU was dropped on the 1989 and 1990 model year versions to save weight and costs.

Exterior cosmetic changes included a newly contoured mid-body trim strip that now matched the car color. The front bumper was slightly reshaped with the nose cap restyled with the word MAZDA embossed rather than the decal found on the '86-'88 models. On the upper level models integrated 55 watt fog lights were placed above the brake vents in the front bumper. The radiator opening was reshaped. A new slightly larger rear spoiler similar to the one found of the Turbo II and GTU in '88 became standard on all coupes. A slightly more rounded version of the Turbo II Aero mirrors also became standard across all models. On the Turbo II a new front spoiler and integrated side skirts replaced the 88 models Aero kit. And finally new tail lights inspired by the Ford brand (that aquired a controlling intrest in Mazda in that year) finished off the exterior body changes.

The GTUs and Turbo II received new 16"x7" wheels which were radically lighter than the previous design and licensed from BBS, while new 15"x 6" 5 lug wheels became standard in the base models and the GXL. The convertible retained its ultra lightweight 11 lb 15"x 6.5" BBS wheels.

The former base model, the GX/SE was updated with 5 lug wheels, and was renamed the GTU. While the former GTU/Sport model became the GTUs with a aluminum hood (from the Convertible) and a new power steering ratio. Similar to the 1986-1987 Sport/GS the GTUs also had reduced insulation and 4 piston front brakes. Originally the the GTUs was to have a normally aspirated 3 rotor engine (the 20B), but pre-production fuel mileage and cooling issues forced Mazda to go another route. Instead Mazda attempted to shorten the 0-60 times with a new 4.3 rear end ratio and .762 top gear. The GTUs was intended to be a more simple and pure version of a the RX-7. A non turbo fast and race ready street car with Air Conditioning and a AM/FM radio the only options. Unfortunately the GTUs flopped in the prime US market with fewer than 2500 sold for its entire sub-model two year production run. North American Mazda dealers unable to understand the light weight, back to basics concept of the car; often had aftermarket glass sunroofs cut in as well as other options bolted on.

s5's have rubberized dash surrounds and center radio surround that dont crack like the s4

s5's have nice black interior thats common,