Rotary Midget project by Dutch 1960

5 minute(s) of a 97 minute read

Yes, the driveline will be all repurposed RX7. One of the attractions of the RX7 engine and driveline is the reliability factor.

I plan to use the exhaust pipe shielding from the RX7. One challenge is that the RX7 maintains a space between the exhaust pipe and the shielding, and between the shielding and the floor of the car. The Midget does not get such a luxury, until it clears the rear axle, at least. Also I will probably bring the two exhaust pipes together as soon as possible, perhaps on the down pipe right after the exit from the engine. Alternatively run long, small diameter primaries, to reduce the heat and aid in ground clearance. I think the exhaust will be the biggest challenge of all, to come up with something that is quiet, reliable, and doesn't burn the thing down.  

A "resonator" designed for a rotary aft of the rear axle on the left side, leading into a muffler mounted across the rear of the car, in the style of the early 70s original MG, is the initial plan. Shielding the muffler from the fuel tank will be critical.

A 70 page manual, wow, that must have quite a bit of good technical info. I hope to keep the "meat" of this conversion to about a dozen postings. Trying to give a real world accounting of what to do to get a street car done, as cheaply and simply as possible.

Stock fuel tank for now, with a stock 12A, mileage should be in the high teens, not great but not horrible. A 12 gallon fuel cell could be added, but it takes things in another direction.

The heater shelf is gone on this one, I just hacked it all away. I am going to measure just how much space is necessary there, to get the engine installed, maybe a reshaping and partial removal of the heater passage under the shelf would be all that is necessary. Perhaps the center section of the passage could be cut out, retaining the shelf, and splitting the heater box output to either side?

2-19-2014

Another possibility is to move the heater back on the shelf a bit, if one is working on the ducting already. The fresh air ducting is a challenge, because the intake is mounted where the FAD goes. Perhaps pull the air from the passenger side footwell through its roof, recirculating interior air. Maybe duct it through the right side block off plate. Super toasty. I am not a fan of drawing air from the engine room itself, for a bunch of obvious reasons.  

The battery for the rotary is much bigger than for the Midget, it takes juice to spin up the rotary's starter. So the battery goes someplace else in any case, unless one eliminates the heater box.


So the heater box/battery shelf is 12 inches front to rear. The first 5 inches need to be removed, as the clutch throw out is higher than the flat upper of the shelf. Also, the bell housing needs to be tipped up into that area as well, for installation. So 5 inches go, leaving 7.

The center 6 inches of the tunnel, right to left, needs to have the heater ducting removed under the shelf, even further back, to leave room for the transmission to swing upwards for installation.  

The factory oblong heater hole in the shelf is 8 inches wide, right to left, by 2 1/2 inches deep, front to rear. The shelf is 13 inches wide about 4 inches forward of the firewall. So two round inlet holes in the shelf, 2 1/2 inches in diameter, with a six inch solid space between them, leaves about one inch of solid shelf on either side. But the outer edges of the two holes are now 11 inches apart, not the 8 inches of the single oblong hole.

The factory 1973 heater box has all sorts of problems for this application, not the least of which, the integrated fan box on the right side comes out to the side about 3 inches up from the shelf, and the right side footwell rises 5 inches up from the shelf at the firewall. The older, smaller, square heater box solves that, as well as allowing a separate fan assembly to be mounted, and is not as tall as the later box either. Which means that a one inch high "splitter" can be placed under the heater box, to split the outflow, and to widen the ducting to meet the spread out holes in the shelf floor. The bottom of inlet on the right side is then 6 inches up from the shelf floor, solving a clearance problem.

Seven inches of shelf is not as good as twelve, and the structure underneath will not be as cleanly and strongly boxed as the factory set up, but we will have heat. A piece of square or rectangular steel stock can be added, side to side under the shelf floor for strength, if it is not too tall.