Mod Progression and Tips for Success

I’ve owned FD RX7s off and on since 1995 - The first one I bought was an engine burn car which was one of the infamous fire cars that led to the Fuel line recall. I had MazMart in Houston replace my fire damaged engine with one from a crashed FD. Drove it 70k miles trouble free, only changed oil and tires. The only mod I had was a K&N air filter. This car never ever broke down over 5 years of daily driving.

I bought an 8k mile FD in 1999 and had it modified in the early 2000’s by Rotary Performance who took it to 315 WHP dyno’d with the stock twins. Drove that one about 10k miles trouble free and then moved on to a 911 Turbo so I could have a back seat for the kiddos. I’ve purchased numerous FDs over the years and one of my favorite configurations is a modified stock twins car. It has better spool up than any single turbo I’ve ridden in.

Here are some suggested set of mods that work well together for various levels. There are many options out there, and I’m just sharing what’s worked for me and what are relatively safe sets of mods.

Stage 0 - The USDM FD RX7 with 255 HP at the flywheel / around 220 WHP.

Stage 1 - Here’s what you can do with the stock ECU that won’t get too lean and risk damaging the motor. Free flowing intake and exhaust adds around 35-40 WHP and increases the engine sound output. (255-260 WHP)

• Stock Twin turbocharger assembly (93-95)

• Stock ECU

• Stock injectors 550cc Primary, 850cc Secondary

• Stock airbox. An aftermarket air intake system might lean the motor out with the rest of the mods.

• Stock Intercooler

• Rotary Performance Downpipe (#1 mod for any FD outside of CA is to remove the damaging pre-cat that causes the turbo manifold to retain heat and crack). If they are out of stock, then Pettit or Veilside from Japan are great options.

• Rotary Performance Hi Flow Cat (replace the restricted OEM main cat, but DO NOT RUN A MIDPIPE WITH THE STOCK ECU. YOU WILL blow your motor Apex seals by leaning out it out due to boost creep with a midpipe and the stock ECU. The stock ECU will not deliver enough fuel to keep you safely rich if you install a test pipe / mid pipe.). Magnaflow makes a hi flow cat which bolts on. It’s not just the cat, it’s a full replacement for the main cat 4’ long piece. Alternatively, Rotary Performance can take their midpipe and weld in a restrictor plate so it flows the same as the Hi-flow cat. You need to limit the flow or the car over-boosts and leans out and the Apex seal will blow.

• Catback Exhaust system - Many to choose from (HKS is a good one, Racing Beat offers a twin outlet quieter one)

• Efini Y Pipe - Replaces the plastic cross over tube and one rubber coupler on the charge pipe feeding the intercooler

• Boost Gauge - Keep an eye on your boost pattern to make sure your secondary turbo is working right

• Wideband AFR gauge - Keep an eye on the AFR under boost on long pulls. If it leans out the Apex seal will blow.

• Drakes steering column 52mm gauge pod or A pillar gauge.

• <DO NOT DELETE THE AIR PUMP, AND DO NOT GET A MIDPIPE WITH THE STOCK ECU - Motor damage will likely occur from boost creep>

• Reliability / Safety mods

  • Run Idemitsu premix even with the oil metering pump. Add 1/2 ounce per gallon of gas at every fillup. I keep a funnel in a ziploc bag and my Idemitsu in a ziploc bag in one of my rear bins on all my cars. This improves lubrication in the engine and pro-longs your engine life.

  • Suggest replacing the laughably thin OEM single row radiator with a Koyo or Koyo N-Flow radiator for cooling. Heat kills rotaries. Get the heat out.

  • Suggest a dual oil cooler upgrade if your car only has the left side oil cooler. Sakebomb sells a great kit that can work with the factory hard lines (front iron line and rear iron line) or if you have the motor out or cut off the rear line, you can use AN lines all the way. Be sure to ask them which core to get that supports 20W-50W oil. I’ve been told the Kraken core doesn’t support 20W-50W, and these turbo cars need to run 20W-50W. I believe the Setrab cores are what you need for the 13B-REW. JP3 seems to be adding a kit as well.

• Suggest redoing the rats nest with new vacuum lines, new one way check valves, new solenoid valves for the turbo related solenoids (Turbo control vacuum and pressure side, charge relief, charge control, wastegate & pre-control dual solenoid valve). These are still available new but might not be soon, so replace yours now for another 20 years of trouble free vacuum control.

• Suggest refreshing all external O-rings, gaskets, hoses, radiator cap, AST cap, accessory belts - again to give you the best chance of trouble free miles.

• Check your compression using a proper rotary engine compression tester while at operating temperature with the gas pedal depressed and the ECU relay pulled (prevents spark and fuel). Here’s a rough rule of thumb interpretation of the results:

  • > 100 PSI on all six measurements corrected for altitude - Congratulations, excellent motor. I get around 105 PSI out of my original motor low mileage cars that I own now or sold recently like my 9k, 12k, and 15k mile cars. Claims of much higher compression numbers that you see might have been from an invalid testing method where they ran it on a cold motor which gives higher but false values.

  • > 90 PSI - Good motor, should get you around for years of driving, check it again every year.

  • > 80 PSI - You might be giving up some power, start thinking about a rebuild within the next 10k miles. Upper 80s is better than lower 80s.

  • > 70-80 PSI - Not good, Time for a rebuild if it’s mid to low 70s

  • < 70 PSI - Be careful trying to cross 3 lanes of traffic turning left, you’re car is so slow you’re gonna get hit (almost happened to me on a 65 PSI car). Hot starting becomes an issue here too. Drive the car and maybe it seems OK, but then let it sit for an hour (will still be hot), then try to hot start it. Does it take a long time to start or turn over slowly? Motor is tired and needs a rebuild. The good news is you can probably re-use your major components and just need new rotor seals to get the compression back up.

  • < 10 PSI on any of the six measurements means blow seal - Must rebuild. Probably runs like a lawnmower because it’s running on one rotor. You have a bad seal and probably damage to one rotor housing and maybe or both irons that it faces.

  • Starts up rough in the morning for 10-20 seconds and then clears out? Having to refill your coolant at the top of the water pump to avoid the low coolant tone of death every couple of drives? You probably have a bad coolant seal inside the motor. If the motor is original even a lower mileage motor can blow out a coolant seal due to age of the rubber seal. To test for a bad coolant seal, get it up to operating temperature, then shut it down for the night. Check the spark plugs in the morning. If any are wet and taste like anti-freeze, you’ve got a bad coolant seal and it’s rebuild time. Contrary to popular belief, you can have a bad coolant seal without any white smoke out the exhaust. I just rebuilt my Montego Blue car with a 35k mile original motor due to a blown coolant seal and cracked front iron, and the other ones were crispy with carbon across them.

• Suggest replacing the plastic factory AST tank with the Billet one from Pettit available in milled finish or black powder coat or go nuts and get the polished one for more $$. Also suggest replacing any old Pettit designs with the rounded top as they don’t seal after 20 years. The newer design with the flat top is excellent. The factory one can split at the seam and leak very slowly and trigger the low coolant tone of death.

• Understand your coolant temperatures and how the fans operate and improve the fan control dramatically if you have the stock ECU. The Power FC provides a way to lower when the fan turns on under ECU control, but stock ECUs need this because heat kills rotaries.

  • #1 - Test to ensure both fans still work. Turn the key to accessory mode where the radio is working. Press the A/C button and turn the fan speed to any speed other than off. Go outside and both fans should be working. If they aren’t then then a fan is bad.

  • #2 - Replace the factory fan thermoswitch located in the water pump housing with the “Pettit Racing 185°F Fan Switch for Mazda RX-7 FD 1992-2002”. With this mod, the fans will at least turn on to low speed while you’re still well within safe operating temperature (up to 95C). And if you have the A/C on it will go to medium speed which is pretty good. Without this mod, your fans only turn on when the engine hits 99C and turn on an additional speed when the engine is destroying itself at 105C. An unmodified FD is running scary coolant temperatures. And to make it even worse, the coolant gauge isn’t linear so it only goes above halfway mark while you’re cooking your motor.

  • Here’s how the fans work with the OEM ECU: The thermostat opens at 81C. Safe operating temperature in my opinion is up to 95C. Higher than that and we have a problem. Higher than 105C and you need to turn your car off since you are literally cooking your motor and wearing it out rapidly.

    • In stock configuration, turning on A/C adds one fan speed. So if nothing else is triggering the fans it goes to low.

    • When the OEM thermoswitch in the water pump housing sees 99C / 210F (Too hot), then it adds a speed. If A/C is off, it goes to low, if A/C is on, it goes to medium. Mazda chose 99C as the trigger strictly for emissions reasons since rotaries also pollute a lot.

    • When the CPU sees ridiculously high 105C / 221F (Way way too hot), then it adds another speed, but really your engine is toasting itself by this point..

  Stage 2 - Here’s what you can do with maxed out stock twins if you add an after market ECU (Power FC), larger secondary injectors, and go to a catless midpipe without an air pump. This is a list of mods from one of my Montego Blue FDs that I’ve been driving this summer 2023 that dyno’d at 315WHP when it was 108 degrees ambient air temperature in the dyno shop. It’s nearly 50% more power over stock and the car is completely transformed. With some great coilovers, anti-sway bars, new brake pads and rotors it’s very well balanced. (315 WHP)

• Fresh Vacuum lines and solenoid test / remove any ancient original LIM/UIM/Throttle body paper gaskets if still present.

• Mazda Stock Twin turbocharger assembly (93-95) with ported wastegate to support midpipe - If you don’t port the wastegate you will get boost creep with a midpipe and possibly blow your motor.

• Premix - 1/2 ounce per gallon with Oil Metering Pump

• Apexi Power FC with OLED commander Dyno tuned by Rotary Performance to 0.95 bar. Stock twins needs a Power FC to control them, although I’ve been told Haltech supports twins too.

• Rotary Performance Downpipe

• Rotary Performance midpipe

• Peter Farrell Supercars (PFS) Catback Exhaust

• Rotary Performance fuel rail with Bosch 2200cc Secondary Injectors, OEM primary 550cc injectors

• HKS Racing Suction Air Intake Filter Kit for Mazda RX-7 FD, part no. 70020-AZ101

• Pettit Racing Intercooler

• Pettit Racing Intercooler Duct Cool Charge

• Efini Y Pipe - Replaces the plastic cross over tube and one rubber coupler on the charge pipe feeding the intercooler

• Banzai Racing Air Pump removal pulley (FFE FD Idler Pulley Kit)

• Banzai Racing chrome pulley kit with appropriate length belt

• GM Wideband 3 bar map sensor

• Banzai Racing 3 bar map sensor bracket

• AEM AVM-30-4110 Gauge, Wideband UEGO, Digital, Air/Fuel Ratio, Lean/Rich, 52mm

• Boost Gauge - Keep an eye on your boost pattern to make sure you’re getting full power

• Drakes steering column 52mm gauge pod

• Fortune Auto 510 Coilovers

• Racing Beat Sway Bar set front and rear

• Cross drilled / slotted rotors with after market brade pads

Stage 3 - Small to Medium Single Turbo with Street Port (350-400 WHP)

• Ported motor with 3mm Mazda Apex Seals by Rotary Performance

• Premix - 1/2 ounce per gallon with Oil Metering Pump

• HKS Special Setup turbo kit with GTIII-4R turbo (good to about 440 WHP)

• Greddy V Mount kit for FD version 2 with Intercooler and Radiator

• Link ECU (or equivalent) tuned by Rotary Performance

• Tomei Titanium Midpipe

• Tomei Titanium Catback Exhaust

• Rotary Performance fuel rail with Bosch 2200cc Secondary Injectors, OEM primary 550cc injectors

• Banzai Racing Air Pump removal pulley (FFE FD Idler Pulley Kit)

• Banzai Racing chrome pulley kit with appropriate length belt

• GM Wideband 3 bar map sensor

• Banzai Racing 3 bar map sensor bracket

• AEM AVM-30-4110 Gauge, Wideband UEGO, Digital, Air/Fuel Ratio, Lean/Rich, 52mm

• Boost Gauge

• Drakes steering column 52mm gauge pod

Stage 4 - Single Turbo Semi-Peripheral Port (Semi-PP) (450-550 WHP)

• Turblown twin scroll dual wastegate Internal wastegate or External wastegate turbo kit.

• If you go over 500 WHP, you’re gonna damage 3rd gear on long pulls. So at some point you need to go to the Tremec T-56 transmission.

• Around 500-550 WHP you’re gonna blow the rear differential and need to go Ford 9” rear diff.

• Your car is now a science project at or above 550 WHP.

• BRAP BRAP Sound - Idle is rougher than stock. You might blow your A/C compressor if you run it at idle while idle is bouncing all around.

• Bridge port - Don’t even do it. The corner seals wear quickly over the bridge. Semi-PP beats bridge port in every category.