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I am the proud owner of a rebuild-required beat up 1988 RX-7 Convertible! And I also happen to run a carbon fiber and fiberglass custom body shop. Last year, I had the privilege of participating in Roadkill Garage’s $3K Hooptie Challenge, an annual drag race competition here in Arizona where people race cars worth less than $3K. I was kinda disappointed in all honesty to see a lack of rotary representation, and 95% of all cars there were LS-swapped beaters.
So, back to my story:
A few months back I picked up this ‘vert as a barn find, it’s relatively complete and clean, other than some body work. Unfortunately, it “runs” on one rotor, and definitely needs a rebuild as there is no compression on one rotor.
As a bit of an armchair exercise, and getting advice for this build, I’d like to see what y’all think the best way to rebuild/swap/power this thing for a drag car that’s reasonably competitive (ie, not a 17 sec car). I was leaning toward a turbo swap with a port, but in all fairness I’m not an expert on rotaries, and would like to see what different options y’all might suggest! If I can get some reasonable responses and input, I’ll be filming a build log, and hopefully contributing more to the rotary community!
The lazy way is to LS swap, just like everything else. Since it sounds like you are looking to keep the rotary, obviously the solution is to turbocharge it. The proper way to do this would be with a full j-spec swap, but that rapidly blows your budget. Short answer - rebuild the engine as cheaply as possible, throw on a cheap used turbo, figure out how to control the fuel, replaced the transmission and probably rear end.
To start, I would pull the motor and disassemble to see what you are working with. That rotor and housing are probably shot, but the rest is likely usable.
First, what is your experience with rotaries? They are relatively simple engines, you just have to pay attention to details. There's lots of writeups around.
Since you are just looking for a drag strip beater, you can get away with a lot more than most. You can find OK-quality parts for reasonable prices if you look around. For example, as long as the seal openings are good, rotors are pretty forgiving. Rotor housings with chrome flaking will have lower compression, but you can throw in a little more boost if all you are looking for is straight line speed. Side housings with extra step wear could case problems in a motor you are looking to keep, but who cares if its mostly going down a drag strip. Obviously none of this is recommended techniques, but it will build you a running motor.
FYI - keep like for like when replacing parts. Always match s4 (86-88) or s5 (89-91) for rotors and rotor housings (side housings are basically the same). Always match turbo or non-turbo for rotors and housings (both side and rotor).
For apex seals, I'd go for something unbreakable. Again, who cares about long term wear, at this point you are looking to prevent more broken apex seals. You can occasionally find used ones around to save money.
Now to the important part: power. Option 1 would be to source a turbo intake, turbo manifold, and turbo, possibly even a hybrid turbo.
Option 2 is a different turbo. E-bay t4 manifold plus a spacer to clear the NA manifold is the easiest/cheapest way, and you can find any number of used t4 turbos out there.
Fuel. If you swap in a full turbo ecu, harness, and sensors, you can make it work as long as you add a way to control fuel (Rtek or piggyback).
The other way is a megasquirt. MS2 with a zeal daughterboard will do it. Quick search shows it will run about $500 for what you need to run a rotary, which probably isn't a whole lot more than all of the parts to get all of the turbo parts. It will run a lot better, but is obviously a lot more work. Really depends on what you are going for with the project, and how comfortable you are with wiring. I personally, love it, but its a deal breaker for many. For injectors, there's a specific type of 1680 injectors used in fords for their natural gas vehicles that fit and can be found pretty cheaply. Threw them in the secondaries if you have the megasquirt, otherwise whatever the rtek requires.
Finally, drivetrain. Many people keep the NA drivetrain when they turbo their car, but the transmissions are notorious for breaking if you are rough with them. From everything I've seen, they wouldn't last long at a drag strip, so that means either playing russian roulette every time you launch or looking for a Turbo drivetrain. I think the rear ends are better, but still questionable depending on power and stickiness of tires.
You sir are the best! Most of the write ups focus on the “proper” way to do things, and you’ve though out of the box and written it up in one neat package! Thanks!
To answer your question, as far as rebuilds go, this is going to be my first rotary, but I have worked on cars all my life, and I currently daily drive an RX-8 that’s been modded with bolt-ons.
I was leaning towards turbo on this, like you suggested, but is there any reason I should look at an N/A build? I know most ports wont make much usable power at low rpm, but what would the advantage be if any? Or would it be better to both port and turbo?
Given this caveat, allow me to play devils advocate. You've started with the heaviest, and thus,slowest, of all possible second gen models. Since you run a body shop and can produce carbon fiber parts, why not concentrate on your areas of expertise and take the dreaded "easy way out", which eliminates all the turbo nonsense in favor of quick and easy. You'll have more power at every RPM and more torque (quite useful at the drag strip) with the V-8, reliability and aftermarket are far better and I'd bet the project completion time would even be shorter.
A couple of reasons have me leaning away from the V8, although you raise a fair point. Number one, I did an LS swap on a 1947 *****’s recently, and am frankly looking for something a little different. Also, the uniqueness and fun of doing the rotary means I’m willing to sacrifice some performance if necessary to go ahead and do something out there and different! Looking for a different challenge I suppose, and I figure it will be good practice for rebuilding my 8 with the Hybrid exhausts in a few years.
07-27-19, 08:56 PM
