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Group, Found this on the RX7 forum........A long read and a lot that will only pertain to a street driven Rotary but has some suggestions on how to make
a boosted (Turbocharged) rotary live at the higher HP levels that will possibly be of use for our aircraft use since we have several Turbo-ed A/C
already flying and more in the works............Of particular note to me was the opinion that exhaust back pressure was a killer and that a 3 inch
down-pipe after the Turbo was needed plus a quality intercooler.............FWIW
Kelly Troyer
The reliable daily driven FD recipe (for beginners)
The general public and sadly even some of our own RX7 enthusiast feel that the FD is a great car with the exception that the rotary engine is a pile of junk that leads to many reliability problems. However that’s not the case if you follow these FD reliability laws that don't include installing a V8 (that's right I played that card early hehe)
Purchase a nice low mileage unmolested car which will fix 99% of the reliability worries. If you happen to be that lucky or smart depending upon how you want to look at it you don’t need to do anything but add a boost gauge and properly maintain the car fixing things along the way that need addressing so pretend that you did exactly that. You bought a car with say 20k miles on it and it needs nothing.
Here are the things that are bad from the factory and can and will eventually go wrong. You can fix them now or live with any issues the car has.
1) Replace the stock ecu with a pfc and commander. The PFC is great because it fixes the annoying 3k hesitation that every single FD ever made in the USA has. As a bonus you will get 16 to 17mpg (versus the normal 12 to 14), a boost gauge, boost controller and temp gauge via the commander along with many other important engine readings like volts etc…. Most importantly it’s a standalone engine management system so once you’ve set your car up with the mods you prefer you can get your car tuned specifically for those modifications which should be done ASAP after installing the PFC.
2) Even though the PFC has a boost reading buy a boost gauge to make watching the boost and vacuum much easier.
3) Replace the stock precat with a DP (straight 3 inch down pipe) because it will eventually start to clog (probably already has to a degree) causing the exhaust flow to slow down/heat up the engine bay and suffocate your cars power and further cook your engine bay accessories and electronics. Rotaries run really hot giving off tons of carbon etc… that clogs up both the precat and midcat but the precat gets it the worst and was put on because of the strict emissions constraints in the us. In japan the FD didn’t have a precat at all for good reason.
4) Check your AST and the plastic side tanks on the radiator if they are faded/cloudy replace them with quality aluminum parts if not just wait until they are and replace when needed. If you are a worrier replace them now because they will eventually split.
5) You notice a boost problem and it’s the check valve under the pressure tank so you replace it with a viton check valve from Dale or find one on your own. The check valves either split or go bad so you can replace them now or later. Or its a split hose or disconnected dried up vacc hose so you replace all the vacc hose with high temp silicone hose or viton that you source from mcmasters or somewhere else. Get lots a 1/8 and the ¼ ID thick walled hose.
6) You notice slow boost response (laggy turbo) after several hard pulls and discover the midcat is clogged so you either jump up and down with joy because you live in a state that doesn’t test for emissions so you can remove all the emissions BS or pray that replacing it with a HF midcat will allow you to pass emissions.
7) The midpipe is causing the car to run like a raped ape and boost is creeping up to 12 psi, the air intake temps are rising, it’s cutting out/fuel cut in hard left handers and also under acceleration when the tank is getting low and also you notice the clutch is slipping on those cold mornings heading into work .
8) So you take your car to the tuner and he notices your fuel pressure dropping and your duty cycle hitting low 90s, AIT are above 60c, clutch slipping etc… so he recommends a supra TT pump, a nice VMIC (why not lets go all out) and some stock bored out 1200cc injectors that he sent off to RC engineering, ACT SS clutch with HD pressure plate and then he tunes the car up to 14 psi and its making 340 hp and now you can’t stop smiling.
9) Until six months later because 340 just isn’t enough so you come back to the tuner and ask for more power he says you can’t get more power without going single so that’s what you do and boom Sean at Aspec sells you a killer 500r and you go away making 400 hp and are smiling bigger than ever.
10) The turbo was killer alright it killed your motor and now
you’re back at the shop for a port etc because you want 500 hp………
OK the lesson here is if the power hungry guy in you can’t rest then you will never have a reliable FD because frankly this engine, driveline and chassis wasn’t meant to make double its stock HP and remain reliable, FACT, PERIOD, end of story so if this is the road you choose don’t malign the FD because it’s your fault for not starting with a corvette or viper to begin with  I find that most of the reliability issues are poor mods, poor maint or big power.
Another problem this car has is the gadget guy who adds 15 gauges, stereo with big amps and subs, alarms, auto locks, sleak head lights etc…..etc…. 1st don’t do that to this car unless you’re an electric engineer or are very good at faking it because this car doesn’t stomach tampering with the wires because it has electric issue that we call grounding problems, I have no idea what is going on, maybe it’s the small aluminum block iron combo or the thin sheet metal, combined with a monocoque chassis or more than likely it’s simply possessed but whatever it is don’t temp the electric gremlins in this car or they will surely cause you major headaches: trouble starting, gauges malfunctioning, fuel pump problems etc….. ALSO leave the battery in the stock location and if you must relocate it run all wires through the engine bay back through the fire wall up high staying committed to the exact same setup as stock with simply a long positive wire and a ground to one of the thick seat belt holder spots in the back. Most important thing for success and your relocated battery is to keep the wires short and dry.
Speaking of electric issues the engine harness is a major problem on these cars with 100k plus miles because of it’s age and the large number of heat cycles it’s suffered through so look that over because it can cause lots of scratch your head type issues which are always the most frustrating kind or the something is wrong and I can’t figure it out sort.
So in summary here are my top 10 or so mods for fun and reliability:
PFC tuned by a pro
Boost gauge is a must have for any turbo car
Full exhaust for more heat reduction but it also reduces weight by 50lbs or more and increases boost response by increasing exhaust flow so there's nothing better you can do to increase the power on a turbo rotary than opening up the exhaust because as mentioned above it creates LOTS of exhaust/heat so the quicker you get rid of it the faster that turbo will spool and the less time it will sit in the exhaust chamber/manifold creating heat. So with that said go 3 inch front to back with a HF cat if you need to
DON'T give up on the twins because they are the single coolest thing about this car for street driving from the down low response/torque to the super cool feeling that the extra boost of the secondary coming on line provides (priceless stuff and one of the hallmarks/trademarks of this car). I've driven them all and nothing comes close to a really nice twin turbo FD for having fun around town or out in the country/mountains.
Upgrading the intercooler is extremely important because IMO the #1 out of the blue engine killer is pre detonation from hot air intake temps. So buy a SMIC, FMIC, VMIC…….or whatever works to keep your AITs at or below 50c and one that also doesn’t interfere with your radiator air flow or raise your water temps.
Upgrade your fuel pump(supra tt is a direct drop in it has good flow and it is reliable) because the stock pump doesn't flow enough for a 300 HP car which for me is the perfect power level to get the most out of this car and maintain reliability throughout entire car to include; driveline, bushings, PPF, oil pan leaks etc….
Aluminum AST or delete and replace coolant with evans (do a search and make up your mind). The stock AST is made of plastic and after it's baked in the rotary oven (engine bay) thousands of times it become brittle and cracks usually at the worst time causing your precious rotary to overheat (never a good thing search) so unless your tank is nice and dark and not faded and cloudy you will need to replace the AST and the radiator which is also made of plastic.
High quality aluminum radiator which may need custom ducting but your temps should stay below 100c when driving hard and never exceed 110c other than hot starts
Add a second oil cooler if you don't already have one. Rotaries run extra hot because of all the extra air and fuel they need (inefficient engine) which means you need lots of cooling and a second oil cooler is mandatory for your rotary engines long life.
IMPORTANT and probably the most important thing you can do for the longevity of your engine and driveline keep the boost set at 10 to 12 psi (will creep with a mid pipe). The duty cycle will be in the low 90s to even mid 90s so I'd advise upgrading the stock secondaries with 1200 or 1250cc injectors. For some reason when the stock injectors are bored beyond 1250 or at the 1300 limit they can stick and also the spray is less consistant so I recommend 1200 which is all you should need.
At the 300 rwhp level the stock clutch is on the edge of slipping. I like the ACT SS clutch with HD pressure plate and retain the stock fly wheel for better street drivability. The LWFW isn’t worth having more difficult launches, back lash under light throttle etc…..
Once you've done the above mods you will have a super fun car that's very reliable and will keep you smiling each time you drive it but beware of the voices especially the one whispering for the need to increase the boost and power. Listen to the voices that suggest simplifying the car and reducing weight and most importantly the voice commanding you to slow down before you kill yourself, the one that convinces you to go to the track to really learn how to drive etc… 
For those that can’t get rid of the 1st voice that one begging for power hehe:
If you must have more power IMO the power limit for safe reliable street use is 375 and you'll need:
a singe turbo or upgraded twins
Igntion amp (i like the twin power)
Colder plugs (i like NGK 10s)
10mm wires
A spare trans and spare diff LOL
Sure you can go to 400 and up BUT add water or meth injection along with a spare motor to your must have list and lots of patience.
500 plus HP see the drag racer forum where they replace motors, diffs and transmissions like gas and oil so if you need that sort of power that's your best bet for reliability discussions 
Things to have on hand and replace while modding or making repairs especially if your car has 100k plus miles (lots of stuff at the 100k mile mark in the engine bay is damaged by heat and should be replaced):
Variety of oil resitant high quality thick walled silicone hose
Factory water hose kit
Fuel filter and relocate after you change
Low mileage OMP and new OMP factory lines (aftermarket ss lines are a PIA and the factory lines are good for atleast 100k miles if not damaged by you working on the car) or delete it and run premix (1 oz per gallon if you use the cheap stuff at walmart or 1/2 oz per gallon if you use expensive synth stuff like amsoil).
Low mileage good engine harness
Fuel pulsation dampener, fuel hose, engine harness....
MAINT:
Oil every 2500 with cheap castrol GTX or something similar 10w 30 winter 10w 40 summer (this car pollutes the oil with gas really fast so no need for expensive oil as frequent changes are necessary)
Plugs every 15k miles (NGK 9s all around)
Premix 4 onces per tank if it helps you sleep at night and or you daily drive your car and live in a high traffic area (lots of idling)
Every 30k miles: fuel filter, gear oil
Belts when you see cracking (don't over tighten)
Bushings and pillowballs when you can shake any of the wheels or hear clunking etc.... (usually around the 50 to 75k mark)
Coolant hose if bloated and soft
Fuel hose if hard and cracking
In summary don’t get caught up in the power game and or crazy electronic mod game and you’ll have a nice fun relationship with this car otherwise beware.
PS Lots and lots of little things (like popping your hood when you can to let the heat out) I didn't mention but the above is the bare bones top 10 ingredients to make your TT FD a fun reliable DD car. |
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