Let me start with the caution that while the rotary is simple the $s start adding up as you add more air and fuel.
My transmission solution is not inexpensive but it is stout, and provides significant gearing advantages. While I offer for sale the adapter plate, the other items will need to be acquired independently and there is a modest amount of machine shop time.
So why go through all the effort and expense?
The FD arrived on the showroom floor producing 184 rear wheel foot pounds of torque.
500 rwhp FDs produce 400 foot pounds and lots of stripped 3rd gear teeth and twisted mainshafts. If you really crank up the boost and are drag racing you will be replacing trans as often as changing your oil.
Then there's the gearing
A 3.483 first gear? Great for pulling stumps. not great for doing anything but getting into second. and second? What's w a 42% drop in revs?, third a 31% drop and then the really long drop to 5th which is pretty much an economy run gear.
Plainly stated, the gearing sucks for anything but casual driving.
Practical alternative trans options offering perfect gear spacing and adequate torque capacity do not abound. Delete all racing transmissions as they do not have syncros and after living w that type of box in my real race car for 6 seasons, trust me, you don't want to be anywhere near one for the street. They are also really expensive. and you will eat up interior pieces and get to know the nice people at the trans shop far too well.
I zeroed in on the Tremec T56. Absolutely perfect ratios, perfect! Adequate torque capacity. Sign me up.
Modern engineering, available at a junk yard near you for between $800-$2000 or in an uprated form as the "Magnum", a bargain around 3K... wider gear faces, better syncros, easier shifting. For an encore to the awesome Magnum, Tremec recently introduced another home run, the T56 F. Same killer Magnum internals in a T56 configuration. I will be looking into the T56 F as a potential no brainer swap for my car...
The T56 is often found in F body Camaros/Firebirds and later in a somewhat uprated version in the LS GTO. The F body variant has better ratios and the GTO has better syncros. I did my swap in 2010 and purposely chose a 50,000 mile '99 F body to see if it would shift at higher revs. There was lots of talk about it getting balky at higher RPM shifts. Counterbalancing that "talk" were numerous drag racing Camaros shifting at 10,000.
I found it works perfectly at 9000. At the Oct 2013 Texas Mile i shifted out of first at 9000, second at 8800 as well as third and fourth. Zero problem for this old junkyard dog.
I am in debt to Jered Olson for much of the engineering on the project. The T56 is just a touch too wide to clear the starter so he figured, by using the auto bell housing, the starter would point forward and clear the trans. One smart solution from a very smart guy.
Tremec 6 speed to rotary
Automatic rear iron. necessary to re-position the starter so it faces forward. The manual starter faces rearward which interferes with the wider transmission case.
Automatic FD bellhousing. Machine .25 of an inch off the rear face to move the input shaft further into the stock pilot bearing. Machine a small opening on the driver's side for the 2 dash 3 hydraulic clutch actuator bearing lines.
i had a 3/8 thick adapter plate made so as to mate the Mazda bellhousing to the front of the transmission. (available from CPR).
This is my initial setup running a Quartermaster double disc and QM hydraulic clutch release bearing. There are around 20 drilled and tapped bolt holes on the adapter plate and the alignment has to be perfect to center. I had a highly accredited outfit do the design.
In order to complete the hydraulics you will need to swap in a "short" clutch master cylinder. .75 piston. Wilwood, Tilton, AP take your pick.
Whether you use an F body or GTO box you will need to get the GTO linkage assembly which locates the shifter rearward 2.5 inches, exactly in the center of the Mazda rectangular shifter hole.
You will need a rear trans mount. i spent some time on this as I didn't like anything i saw. Since I want nothing sticking down underneath my car all trans mounts that bolted across the tunnel were out. i ended up w a very short (9 inches or so) mount that sits under the tailshaft and angles upward on the passenger side to clear the exhaust. Do not use the tunnel stiffener anchor plates as they have been known to separate from the tunnel which would be catastrophic.
The FD driveshaft has always been a source of irritation as the U joints are not replaceable. FD driveshafts have U joints that are 37 years old so you get a win win when you swap in a new driveshaft. I had Quartermaster make me an aluminum shaft. Reasonably priced, well constructed good for 1000 hp, 3 pounds lighter and replaceable joints.
It is just way too easy (thank you 21st century turbos and our free flowing rotary engine) to make crazy FD power. After making the switch to single turbo our dual purpose FDs make between 300 and 600 rear wheel power... up from 216. Torque is often approximately 100 behind peak horsepower so a 500 rwhp FD generates just a bit over 400 foot pounds of rear wheel torque.
Mazda, being the Japanese equivalent of Lotus, loves to keep everything LIGHT.
LIGHT is GOOD, actually near Godliness, when you want to go fast, stop fast or corner fast.
When looking at the driveline and 400 foot pounds of torque rather than 184, light is NOT GOOD. This doesn't mean the entire driveline needs to be scrapped... some items need to be swapped and others modded. this section will deal with the entire driveline... first up, the transmission.
A hydraulic clutch actuator bearing (GM style) bolts to the face of the Tremec 6 speed. It will need to be adjustable as to height. From experience i can tell you there is only ONE actuator to use with the Mcleod clutch: the Tilton 6000.
Ready to bolt in. Mazda automatic bellhousing, adapter plate and the GTO external shifter that situates the lever exactly in the same position as OE.
Since the rotary has a small block it has a small flywheel. This presents a large problem. Clutch/clamp physics is easy. The reality for the rotary isn't good. Since a small flywheel presents small frictional area more spring pressure is needed to avoid a slipping clutch. Higher spring pressure is not fun on the leg and greatly decreases "feather." Feather is what allows you to drive your car in traffic. Simply put, drive a few miles in traffic with an in or out clutch and you will HATE your car. The solution to small frictional area is of course a double (area) disc clutch. I had been running an Exedy double disc with my stock transmission and of course it was a "pull" type clutch. I called Exedy and they had no interest in making something that would work with my new setup so I ended up with Quartermaster. They had made all my clutches when i was racing. i ended up with something really neat. I used the Mazda automatic transmission flex plate (3 pounds) and QM made a small button flywheel that bolted to their 8.5 inch "Rally" clutch.
I ran the QM clutch for four years. It was always a challenge as to feather. I was discussing it with Luke at Beyond Redline and he suggested I take a drive in a 3 rotor the shop had just finished that had a Magnum with a Mcleod RST double disc. I couldn't believe the pedal pressure... the same as a stock clutch as was the feather. Mcleod swears their RST will hold 800 foot pounds. I called them the same day and have now run the clutch for a few years. I can say that it holds 575 rwhp with no problems. I recently sent the flywheel back to them to lighten as it was pretty heavy. It is now 13 pounds. Totally LOVE it.
I am extremely happy w my Power Plant Frame solution. After looking at all kinds of torque arms etc i decided i wanted none of them as they were bulky, heavy and stressing things i didn't want further stressed, especially the transmission tailshaft. I called Justin Samberg and he had exactly what I wanted. Justin delivered his usual masterpiece on time and on quote. Problem solved and it installed in 30 minutes. i also hear from the FDV8 guys that the Samberg subframe hooks up (launch not love) significantly better than the torque arm options. The Mazda PPF weighs 4 pounds more than the Samberg subframe.
A Dakota Digital convertor box will zero in the speedometer and you will want to fixture a reverse lock out switch.
While many find the increased torque capacity of the T56/Magnum the primary draw I really go a little nuts over the gear ratios/spacing. Every time i pull away from a stop i LOVE the longer first gear.
A longer first creates closer following gears and the turbo'd rotary needs close ratios:
Let's compare the FD transmission to the T56 F body at an 8800 shift point:
.............................FD................T56 F body
second gear at.5104.................. ..5896
who do you think wins the race?
Horsepower under the curve wins races, and the T56 gearing places the rotary in a much meatier part of the powerband.
Whether you swap a used T56, Magnum, or a new T56 F here are the ratios you want:
I have loved my T56 for 9 years, especially with my Mcleod RST clutch. There may be other ways of mating the Tremec 6 speed to the rotary which could work for you but I do love the combo and recommend it.
I will be addressing the rear end, bushings and half shafts soon.
184 foot pounds rear wheel torque.