Rotary Midget project by Dutch 1960

4 minute(s) of a 97 minute read

We have been trying to figure out the radiator and oil cooler. The outlet at the bottom right on the Mazda radiator is going to collide with the steering rack, and where to mount the oil cooler?

We are going to punt on the radiator, as making up some modified piece is not worth it. The Gerard's Garage page notes that the 1985 Audi 5000 radiator is a drop in, and it looks like it is. About $200 aftermarket new. This is an arrangement where the lower right outlet is mounted up from the bottom corner, so it will clear the steering rack. We may need to modify the Mazda water pump housing lower outlet, but we will cross that bridge later.

For the oil cooler, since this is a street car, we can go junkyard diving and get the oil cooler assembly that mounts on the upper rear of the engine, where the oil filter sits. This is from the 1984-85 12A engine car. This piece is frowned upon in racing situations, but for street driving with the occasionally redlined engine, it should work fine, easily clearing the steering shaft, and also the hood (bonnet). This will save us from running the oil cooler lines and mounting an auxiliary cooler. It is a bolt-on assembly, without modification, to any RX7 12A engine from 1979. We will need to run heater hose lines, as the factory Mazda arrangement uses the coolant in the heater system to cool the oil. Another reason to keep the heater in the car. The standard MG Midget oil cooler mounting location is in front of the radiator, but we will probably want as much unimpeded air flow as possible entering the radiator, so this proposal solves that problem, too.

Speaking of engine part heights and clearing the hood, the water pump housing and alternator should just make it. Not so sure about the tall electronic distributor. That one is going to be close. As a Plan B, we can use the shorter points distributor from a 1979 RX7. But rotaries and point sets are not a pleasant combination, and one motivation for the swap is to eliminate as many areas of regular maintenance as possible. The factory carburetor and intake manifold may not clear the hood so well, either. The factory air cleaner will almost certainly need to be exchanged for something low profile. Race cars deal with this all the time, so a foray into the Jegs or Summit catalogues may be in the offing. We really want to stay with the factory carb and manifold. The side draft Weber, and the manifold that does a 180 to wrap around the top of the engine block, are very cool assemblies, but they will really blow our budget. The factory set up is just fine for the street, but it may take some creativity to make it fit, without going for a bulge in the hood.

We have started the front engine mount, by modeling the part in cardboard. We will not drill the front mounting holes yet, and will make sure there is extra material in the vertical, so we can try various slightly different engine heights, to make sure everything clears, at the top and at the bottom.

Time for a quick review. At this point, we are looking at three cuts into the body shell, in the trans tunnel for the shifter, in the heater shelf for the bell housing and clutch clearance, and the radiator posts (which we gave not gotten into yet, but it looks like there is no avoiding it). We are looking at narrowing the Mazda rear axle, and shortening the Mazda driveshaft. These are the two jobs to be farmed out. Fabricated parts include the front engine mount, the exhaust system, the ducting under the relocated heater, and the battery relocation. We will be running new fuel, clutch, and brake hard lines, too. Sourced outside parts include the Audi radiator, the earlier model Midget heater box, and the later model Mazda filter mounted oil cooler. All in all, less hassle and expense than we were afraid of, so far (knock on wood).