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    #1

    Project L33T: 1981 Mazda RX-7 FB

    Project L33T: 1981 RX-7

    After the completion of Project Capella I had a goal of getting this RX-7 running in the first half of 2016. Unfortunately I kind of ran out of time, but I got pretty close.







    The car is an Australian-assembled 1981 RX-7 with a shade over 200,000km on the clock. I first bought this car as a wreck in 1996, sold it in 1998 then tracked it down and bought it back again in 2004. Iíve driven it for about 100,000km all over New Zealand with a combination of standard and bridgeported 12A engines, and various suspension and wheel combinations. You could say Iím attached to it. Here it is before the work:



    Itís been in pieces pretty much since 2004 and Iíve set up various suspension and brake combos on the car in an attempt to modernise it, but nothing really stuck. This is because the stock running gear is prohibitive Ė the suspension and brakes are capable in stock form with a mild power increase, but if youíre staring down the barrel of a good 500 RWHP the factory steering, brakes and suspension arenít up to the task of getting the power to the ground in a safe and effective manner. Thatís about as diplomatic as Iím going to get about recirculating ball steering, live axles and single piston brakes.

    THe first major change was to swap out the entire front subframe for one out of a later model RX-7. The FC3S RX-7 was produced between 1986 and 1992, and has a much more modern front end including large brakes, 5-stud wheels, rack and pinion steering, aluminium lower control arms and an adjustable steering column. So, out with the 60s technology, in with the 80s.



    The main motivation for changing the front subframe was the desire to eventually run slicks on the front, which necessitated thicker stub axles than factory fitted to any FB, and the elimination of the vague steering by fitting the FC rack and pinion. I did go to the trouble and expense of having Wilwood brakes mated to large vented disks and custom hubs for the FB, but changed my mind and sold them on earlier this year. I just couldnít stomach the idea of running slicks on the tiny FB stub axles. Seriously, the FC stub axles are vastly larger than the FB ones, the difference is astonishing.

    Swapping in the 13B out of a series 6 (FD) RX-7 required the creation of custom engine mounts which Iíve welded directly to the FC subframe in order to use the rear mounts on the FD engine. This is a better way of distributing the power of the engine to the mounts compared to the earlier front mount setup, and it also allowed me to move the engine rearward and downward 30mm in each direction for a better centre of gravity.

    The FC gearbox has had the shifter moved forward 104mm too, this is also a fairly common mod.

    The engine has a large extend port, new rotor housings, new seals throughout, a 5kg flywheel and Exedy clutch, itís doweled and has a heap of internal work done to it. The turbo is a Borg Warner S300SX.





    The thing that extended this project out this year was that I really didn't like the performance of the factory live rear axle.

    Yeah, Iím aware that a solid axle can be tweaked. Thereís 3 link, 4 link, better bushes, adjustable spring platforms and a whole heap of aftermarket parts that can help. I looked at them all. You can spend thousands making a live axle easier to live with, and even pull some impressive lateral G figures on a skidpan, but ultimately youíre stuck with a setup that was originally used to save Mazda money in order to allow them to ship more units at a competitive price rather than a suspension designed purely for the sake of performance and comfort.

    Itís not like I didnít try to stick with the live rear axle either. This car in 1981 had an open diff head out of the factory, but even swapping in an expensive aftermarket setup limits you to about 350HP, or even less if you really lean on it. I wasnít happy having such a weak link in the drivetrain, so it had to go anyway.

    As you can see from this pic, I initially replaced the factory Mazda rear axle with a shortened Borg Warner 78 unit out of an EA Ford Falcon, but I was never comfortable with the characteristics of the trailing arm setup.





    It was also a 25 spline axle unit, meaning LSD centres were hard to find and expensive, and the axles werenít even really that strong to begin with anyway. Not to mention the hassles of routing a 3Ē exhaust pipe over a large rear axle and still having room to lower the car to the deck.

    Yeah, I could swap in a 28 spline Ford unit. Hell, I could go set up a Toyota Hilux rear end for a couple of grand, or even a Ford 9Ē if reliability was the only problem. But that kind of stuff Ė beneficial as it is in a straight line Ė wonít help you much on the track, or on some of our winding roads. This is not a car designed to go from traffic light to traffic light on a Friday night; I built it to get into and drive challenging roads in comfort and at speed with solid reliability.

    In reality, Iíd already spent a lot of time and money on a setup that was never going to compete with a half decent IRS.

    I looked around various rotary forums to see what IRS setups had been done in the FB before. From what I can find itís really only MX5 and FC that have been swapped in, and neither really appealed. The MX5 stuff is too weak for the FD engine, and the FC stuff looks archaic with the trailing arms and passive 4WS that people spend good money to delete anyway.

    It occurred to me that there might be a fairly common OEM IRS setup with a similar width to the FB that I could investigate using. Iíve always been a huge fan of early Nissan RWD stuff in general, and upon looking at the hub to hub measurements of the S-chassis and R32 found they were within 5mm of the FB.

    In order to investigate this further, in late 2015 I bought a stripped rear subframe from a R32 GT-R Skyline and took some measurements.



    I saw pretty quickly that the four mounting points would physically fit under the FB and there were no weird angles or design decisions that specifically prevented its use.

    Most importantly however, the rear subframe houses the diff, axles, hubs, sway bar, lower arms, camber arms and toe arms. Itís all entirely self-contained Ė you can literally undo four large nuts (plus brake hoses/cables obviously) and drop the entire rear suspension on the ground. From an engineering perspective, this means no need to set up brackets on the body to house suspension arms. In other words, no difficult and time consuming laser measurements to get each link positioned precisely Ė just make sure the four mounting points are aligned front to rear, left to right, diagonally and vertically and you can guarantee everything else is correct.

    Keen to take this further, myself and my friend picked up an A31 Cefiro from a local wrecker.





    All we needed was the rear of the car. We started by cutting out the entire rear floorpan behind the front seats all the way to the very rear panel. We used cutoff disks, a reciprocating saw and a plasma cutter, and only set fire to it once!







    Once the floor section was extracted, we could take a closer look at the subframe mounting pins to determine how to attach them to the RX-7. It would be extraordinarily difficult to attempt to retrofit the four pins that locate and mount the subframe to the existing RX-7 rear floor, thereís simply too much to chop out and change and youíd never get it millimetre-perfect, which was a prerequisite. At that point it pretty much confirmed our suspicion that the only way to do it was to swap the entire rear floor section.

    Next step then was to chop out the RX-7 floor and make a hole big enough to insert the A31 floorpan in its place, keeping the RX-7 outer guards with the A31 inner guards.







    No going back now! You can see the RX-7 rear floor sitting on top of the A31 floor, and how similar the width is.



    A bar was welded between the Nissan strut towers to keep it rigid, but in reality it was more beneficial as a handle to help lug it in and out of the car a few dozen times when we were measuring it all up.











    Some may have noted by this point that the A31 open differential and axles arenít up to the task of surviving 500HP either. Most of the 4x114.3 PCD RWD Nissan gear is based off the R180 platform, that is, a differential with a 180mm crownwheel and 29 spline axles. These axles are bolted to the diff ears with so-called ď3x2Ē bolts, three sets of two bolts grouped on each of the tripod corners. This is common across S13, S14, R32, R33, C33, C34, A31, basically any 1989-2000ish RWD Nissan with the 4x114.3 PCD.

    But by going to the larger 5x114.3 PCD, you gain 30 spline axles with ď5x1Ē proper CVs, the R200 diff, bigger brakes and better rim choices. In order to do this, we chose the 4.083:1 viscous LSD out of a 300ZX, R33 Skyline turbo axles and hubs, along with vented disks and calipers from a Laurel.



    To change from four lug to five lug, simply bolt in whatever hub you want Ė in this case, R33 Skyline turbo:



    We used BC Racing Gold coilovers all around too Ė FC in the front, S13 in the rear, and topped it off with a BNR33 GT-R rear strut brace (yet to be fitted in the pictures). Good bendix brake pads and braided lines are used all around too.

    In order to get the R200 diff to go into the R180 subframe, we chopped out the back of the (now useless) R32 GT-R subframe and welded it in place of the A31 diff mounting bracket. The GT-R has the HICAS four-wheel-steer system that dynamically changes the toe-in and toe-out characteristics of the Skyline, this is a feature I didnít want to use so we had to make a couple of changes to the toe-arm mounting brackets to swap things over. We could have sourced a R200 non-HICAS subframe to use but theyíre not super common and changing the mounting plate over was a half-hour job.





    Mixing and matching is pretty important Ė you canít use an R33 or S15 rear subframe for example, theyíre too wide. The 300ZX is even wider, as is the Q45 and the J30. But you can use some componentry here and there, which takes a good deal of research along with trial and error. I think I must have spent more than fifty hours researching every component before deciding which would complement each other.



    All that said and done, the rear of the car required I-CAR approved joins to connect the chassis rails. This is a road-legal vehicle so the standard required to modify this car safely is set high. The amount of time required to connect the floor to the rest of the car is immense.






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    #2














    After physically joining both Nissan and Mazda sections, we had assumed we’d be able to use the A31 fuel tank (all set up for EFI) or at the very least, re-use the FB tank (with a swirl tank). Unfortunately neither would be possible – the A31 tank is designed to straddle one rear chassis rail, which was no longer possible. Having removed a good 300mm from the back of the floor, the tank was now so far forward that it was actually within the inner guard on each front corner of the tank.

    The FB tank wouldn’t fit either, it’s too wide to go between the Nissan rails and too long to fit between the back of the new subframe and the rear of the car.

    The only solution was to make up a custom drop tank, so we decided to make it a large one. It’s a shade over 90 litres in capacity, which means it can double as an additional device to add weight over the rear axle if traction turns out to be a problem.









    Also, by chopping out the back of the car to accommodate the tank, we could fabricate new rail ends and rear panels to tidy up the transition between Nissan and Mazda, along with a false floor to hide the top of the main tank, the swirl tank, two fuel pumps and two fuel filters.



    - - - Updated - - -

    All the EFI componentry is contained on the right of the car, meaning the exhaust will exit the car on the left Nissan-style. This is mainly because the rear sway bar has a bend to accommodate the exhaust pipe exiting on the left, and also because how many FB RX-7s have you seen with a single exhaust on the left?

    In doing all this, we added a factory rear bumper back on to the car. During the period of time between 1998 and 2004 when other people owned the car, it had been repainted and the rear bumper removed Ė probably due to a minor rear impact which there is ample evidence of. I never liked this ďshavedĒ look so I was only too happy to cut it all out with a grinder and replace it with a more factory look. I do like however that the side indentations on the car have been filled, it makes it look much newer. I will also add the rear garnish between the lights eventually too.





    Yeah, the purple colour is stupid, it was silver originally and Iíll be painting it gloss black eventually. But thatís a job for the future.

    So having fabricated new floor sections, and finished welding the car back together, we ground everything fairly flush and covered it all liberally with zinc rustproofing and Sika seam sealer. Eventually the floor will be covered with dynamat before the carpet goes on.

    We even managed to reuse the original Nissan hard brake lines, and the 76mm driveshaft has been custom made with new replaceable UJs - Itís good for the task of transferring 500HP between the FC gearbox and the 300ZX diff. The handbrake was easy enough to make out of half Nissan and half Mazda bits and pieces too.

    At this point however I have to leave New Zealand and travel back to Canada for the foreseeable. This means the car goes back into storage and I get to think about the next phase in the build Ė interior and bodywork, most likely. It will be at least two years until I can get back to it.

    Iíve run out of time to get the engine running and actually take it for a drive Ė the car is 95% ready to go, but such is life. If it helps, Iíve towed it down the road a bunch of times and it handles like a lowered skateboard, despite not having a proper wheel alignment and all four wheels pointing in different directions. Itís eternally frustrating that I canít post a video of it powering through a corner, but that will come in a couple of years. I have to remind myself that itís been 12 years since I drove it last, two more wonít be the end of the world.

    In 2018 itíll get a repaint and I wouldnít mind making a completely custom interior. Iíd like to pick up a Haltech ECU to replace the ageing Microtech LT10S too, and some additional Nissan go-faster bits for the rear suspension. Adjustable camber arms and possibly even a clutch-type NISMO LSD out of a GT-R or something, Iíve never been a huge fan of the viscous units, as strong and cheap as they are. Seriously, the Nissan diff cost $100 and came with free axles, itís so refreshing not paying the rotary tax for a change.

    Here are some more pics, but just a note about the crazy rear camber, the coilovers are set about as low as they can possibly go, and the factory camber arms are set to maximum negative - this is not the final configuration, it was just set this way to check clearances and I haven't had a chance to wind it all back out again. It's actually too low to get a trolley jack under the diff like this, and it turned into a tripod going down my steep twisty driveway.

    More to come in the future!













    Summary:

    Vehicle: 1981 FB RX-7
    • Engine: FD3S 13B-REW, large extend port, dowelled, lightened rotors, 3mm apex seals, new rotor housings, high capacity oil pump, windowed bearings, 5Kg flywheel, Gilmer belt drive, FC water pump.
    • Turbo: Borg Warner S300SX 66mm T4 twin-scroll on custom steampipe manifold w/50mm wastegate.
    • Transmission: FC3S 86-88 turbo gearbox with shifter moved forward and short shifter kit. Custom 75mm driveshaft, Exedy solid plate clutch & heavy cover.
    • Suspension: BC Racing Gold coilovers all around, FC3S front, Nissan S13 rear.
    • Brakes: FC3S vented front rotors, FD3S front calipers, Nissan C35 Laurel vented rear rotors & calipers, bendix pads & braided lines, FC3S master & booster, FB pedal box.
    • Differential: Z32 300ZX 4.1:1 R200 viscous LSD with R32 Skyline turbo 5x1 axles, R33 Skyline hubs, A31 Cefiro hub carriers, LCAs, sway bar, camber arms & toe arms, BNR32 GT-R Skyline subframe diff housing, BNR33 GT-R Skyline rear strut brace, HICAS & ABS removed.
    • Steering: FC3S 15:1 de-powered rack, welded quill with FC3S turbo column, aftermarket steering wheel.
    • Fuel system: 90L alloy tank, Holley Black lifter pump, 100 micron pre-filter, 3L surge tank, Walbro 255 high pressure pump, Ford V8 EFI filter, 3/8" solid & flexible EFI lines.
    • Wheels: JDM 16x7" 5x114.3 PCD +45
    • Tyres: 205/50/16 asymmetric front, 225/50/16 directional rear.

  3. Post
    #3
    That's a **** load of work. Good stuff.

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    #4
    Swwwwwwwweeet Jesus....... Well, if you need Nissan bits, let me know

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    #5
    Holy shit it's JvJ!

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    #6
    Just read the rx2 project thread. Just wow! Looking forward to seeing how this comes along

  7. Post
    #7
    Thanks for the comments guys Boo, back in Canada now.

    I posted this up in a bit of a hurry and only really concentrated on the work done to transplant the Nissan IRS. But there's also a lot of work in swapping the front subframe over too, so I wanted to post some pics of that.

    So as previously stated, the factory FB front suspension, steering and brakes are - generally speaking - junk. The steering is recirculating ball, so after a couple of hundred thousand k's the steering wheel moves about 30 degrees before the front wheels budge.

    The brakes are single piston, and whilst vented they look about the size of something you'd run on a tandem
    trailer. From 100kph, you get one good stop, but never two. Around Taupo, I'm guessing half a lap before they melt.

    The suspension is Macpherson Strut, which is adequate, but coilovers to suit are ridiculously expensive, and even adjustable camber plates are pricy. Gotta love that rotary tax.

    I've already stated how thin the stub axles are; there are cases where the stub has broken on the track. I don't know how much this will get tracked, but using factory stub axles just isn't an option, particularly with slicks.

    Initially I addressed the brake concern by purchasing custom hubs and Wilwood 310mm four-piston rotors and calipers. Problem with that was always going to be the lack of adjustability and attempting to get the ride
    height where I wanted it to be with lowered springs. Plus I'd still have to buy camber plates. Annoyingly, the entire lower strut and stub axle are one unit from factory.

    They looked pretty though :/



    Anyway, I sold them on, having lost a small fortune on a gamble I never should have taken and decided to bite the bullet and swap the entire front subframe, suspension, brakes, steering, steering column, sway bar and engine mounts for the setup out of a FC3S (series 4) RX-7.

    Why FC3S? Well, it retains the Macpherson setup, it's roughly the same width (10mm wider each side) the steering column fits without too much drama, you can get a huge range of coilovers and other performance stuff because drift, and parts are cheap and plentiful. For now.

    I started by purchasing all the parts I needed used from the Rotary buy sell and trade Facebook group. You can sit on TM all day and this stuff never comes up, but place one wanted post on FB and you have three people messaging you right away with the stuff you need, it's brilliant.



    I went with series 4 componentry rather than series 5, as the 86-88 front lower control arms have detachable ball joints, rather than the encapsulated, pressed-in ball joints in the series 5 (88-92). Everything was pretty filthy so I spent quite a long time cleaning it, priming it then painting it flat black.











    I started on the car by removing the old FB subframe and measuring up the rails for the transplant. Although the FB subframe sits flush on the straight chassis rails, the FC3S subframe is slightly curved vertically, which meant I needed to weld a spacer plate towards the rear to make up the 15mm or so difference in height. I made this out of 5mm angle so I could then bolt the back of the subframe directly to the old steering box and idler arm mounts.













    Whenever I got frustrated or annoyed with lugging the subframe in and out over and over, I'd jump in this old girl and go for a fang



    In the front, the existing 10mm bolts had to be relocated 25mm rearward to ensure the wheel physically sits in the same place as the FB. To do this, I had to create new crush tubes to be welded into the rails, then drill new holes and make sure they were correct on a vertical and horizontal plane.







    I used two rods to check how parallel the new vs. old hole was:



    I also had to create two engine mount tabs to weld to the FC3S subframe. One quirk with RX-7s is that each generation has a different engine mounting setup. The FB mounts right off the front cover, the FC3S mounts in the middle of the engine, and the FD3S mounts at the rear of the engine.



    Because the engine in this car is out of an FD3S, I need to create mounting points for the rear engine mount to attach to the FC3S subframe bolted to the FB body. Crystal?

    Just need some 5mm steel and a MIG:













    Too hot. Must weld. Sweating it out in Hawke's Bay mid-summer:









    One advantage of using custom mounts is that you can reposition the engine however you like. This is 30mm more rearward and 30mm lower in the car than the factory position.







    As the gearbox is out of an FC3S, the shifter is in the wrong position. I chopped the remote, redrilled the selector linkage and moved the shifter forward 100mm so it sits more or less in the factory FB position.





    The vast majority of FC3S cars made had power-assisted rack & pinion steering in either the 15:1 ratio (S4) or
    17:1 (S5). A very small number of non-turbo low-spec models had manual steering with a 19:1 rack, those are very hard to get a hold of and expensive. I opted instead to have my 15:1 rack professionally de-powered by Mossrax in Wellington, who did a fantastic job. My certifier was happy with their work so it will be easy to sign off when the time comes.



    The FC3S sway bar was added with new mounting points too:




  8. Post
    #8
    The steering column needed a new bracket to be welded to the base to attach near the floor of the firewall, and a new bracket to attach it to the lower dash. One advantage of using the FC3S turbo column is that it's adjustable.

    I also took the time to make a new gearbox crossmember out of a FC3S factory xmember and some more 5mm steel:



    I spent a lot of time trying to get the front struts to work. I cut the FC3S strut housings up and married the lower half to the top half of a FB strut, then tigged it together. By the time it all sat in the car, the strut cartridge had no movement whatsoever, and the car still sat too high.







    I then bought some weld-on coilovers off TM hoping to again get away without having to spend a lot of money on coilovers, but even those weren't able to lower the car enough without running out of suspension travel.



    So yeah, I should have just bought the coilovers to begin with. Sucks trying to save money and ending up wasting money on options that just don't work. Live and learn.



    But I'm happy with the ride height now, and assuming the BC Racing Gold setup isn't too hard for road use, it
    should all work fine.




  9. Post
    #9
    God dam inspiration man!! Well done to you sir!! I plan to do the same to an RX2 when I move to Canada in December!!

  10. Post
    #10
    rb26s13 wrote:
    God dam inspiration man!! Well done to you sir!! I plan to do the same to an RX2 when I move to Canada in December!!
    Thanks! Watch this space, even more crazy stuff in the future. I've already bought another car from the 70s, it's not a Mazda but it will be getting a lot of TLC in a couple of years, I'll put up a new thread about that then.

    I've been living in Ontario for four years now, and the oldest rotary car I've seen would be an FB RX-7. Good luck finding an RX-2, unless you're planning on getting one from the states? Even then, the roads here are total shit, so if you have a nice car with low suspension it will either be pounded to hell and back in no time, or totally rusted to crap within a few years from the salted roads anyway. There's a reason why people love their pickup trucks here

  11. Post
    #11



    Some sweet OEM parts for the project New door rubbers and rear garnish panel, still available new in North America.

    Will be picking this project up in September 2018.

  12. Post
    #12
    For those that are still wanting to follow this project it continues here

    https://www.rx7club.com/build-thread...1101100/page2/

  13. Post
    #13
    The quality of write up in this thread is insane, great read. Awesome car too.