Zex Nitrous Oxide Injection System

[10/4/2001] Reviewed by: Bob McCouch - bob@mccouch.com

Applicable to: '90 - '97 1.8 liter

Basic dry-injection nitrous system which utilizes bottle pressure to determine how much to increase fuel pressure. This fuel pressure boost means more fuel is sprayed at each injector pulse. Only nitrous is directly injected into the intake stream, hence it is a "dry" system. The kit includes nitrous and fuel metering jets for 55, 65, and 75HP levels. The Zex kit works only with 94-97 Miatas, because it requires a 0-5V variable TPS and a return line fuel system. 90-93's have the wrong TPS, and 99+ don't have the return line.

Installation was straight forward, although the instructions are rather generic. I spent nearly a day thinking through placement issues and doing a clean wiring job. The kit included all necessary parts for the installation. The longest and most difficult part of the install was deciding where to fit everything. I mounted the bottle in the trunk, ran the nitrous line under the car, into the engine bay, and across the firewall. Then I ran a wire from the switch through the firewall, tapped the TPS output and two vacuum lines, and installed the nozzle in the intake tube. I "programmed" the Zex unit according to the instructions, which let the unit learn the voltage my TPS sends at WOT. Now, with the bottle open, I just flip the switch in the cockpit and mash the pedal, and I'm off to the races. A Mallory RPM Window switch ensures that if I miss a shift, the nitrous shuts off by 7000 RPM. Overall, I've been very happy with this product. The 55hp jets give the car a nice boost.

Many people think nitrous is out of place on the Miata. I disagree, as the Zex kit offers a surprisingly linear power increase as the juice comes online. It's also nice to be able to have a completely stock (or at least N/A) car when you want, like in the rain or snow. One 10 lb. bottle lasts me about 3-5 weeks of general tooling around. At $30-45 per fill, it can add up, but the buy-in price of around $500 can get you in the Fast Miata Club much sooner than saving up for that turbo will.

Difficult to remove without leaving damage

Back to Product Reviews 16 October, 2001