Is there really a rule of 3 when modifying an Rx-7 ? I was told that if you intend to make 3 upgrades to your car, you need to change the stock ECU to a high performance one as the next step.

Is that true?

 

It depends on what "upgrades" you plan on doing. If you're just going to do worthless mods like an air filter and a catback, without the supporting mods, then no. If you're going to upgrade the headers/turbo(s), run any boost above 10psi, or heavily port the motor, then yes, you may need an upgraded ECU. Most likely, the problem can simply be solved with a fuel cut defencer or upgraded fuel system. Not that an upgraded ECU is a bad thing; most aftermarket ECU's enable you to remove to pretty restrictive devices (haltech, wolf3d, motec, megasquirt, ect...).

The rule of 3 is something that, in my opinion, a clueless person came up with to frighten those who aren't the wiser. I mean, 3 upgrades to what? An air filter, a hi-flow cat, and a catback won't require an ECU upgrade (unless boost is close to 10psi). A whacky body kit, LED windshield washer nozzles, and a big funky muffler won't require an upgrade either. It all depends on what your upgrades DO TO THE CAR. For instance, on my 88 GTU (N/A), a set of headers, a midpipe, cone air filter, and a really large street-port (with no 6port actuators/sleeves installed) didn't require a new ECU or any other mods. However, a TurboII can relatively easily reach 10psi with just a downpipe/midpipe, in which case you'd need either an ECU, a Fuel Cut Defencer, or upgraded fuel/induction system.

An RX-7 is no different than any other car when it comes to modifying. Just support the parts you install with other parts. Just knowing the basics of internal combustion engines is all that is needed. Example: Upgraded turbo now puts out 12psi. Fuel cut engages around 10psi. Install FCD; engine runs lean. Upgrade the injectors/fuel pump/intercooler. Doesn't sound like a "rule of 3" to me.