In today's video I show a time lapse of how easy it really is to 13B swap a 1st gen RX-7 equipped with a 12a. It quite literally is the easiest engine swap one can do in their driveway on a Saturday afternoon with minimal effort.
In the video the 12A engine removed from my car was sold to a friend for $500 that needed it for his car (that engine is still running today which doesn't surprise me as it's a rock solid motor). The 13B installed was built very cheaply using parts I had laying around my garage and storage and the $400 spent building it was just in parts I didn't already have on hand. It was built specifically for this reason on top of me just wanting to do it for fun. The only things that were needed to install this 13B going from a 12A were the intake manifold, header and front engine mount. Everything else was retained and even the carburetor only needed minor adjustments after initial start where it was already idling fine within seconds.
Of course my setup is very simplified and not as difficult to do as taking a bone stock 12a car and 13B swapping it as there are many emissions related and/or AC & power steering accessories & components that take more time and work to remove, install and setup again. Mine doesn't have anything but what's needed to operate the engine which makes this significantly easier. But that doesn't mean it can't still be done easily. If you have a bone stock 12A car and want to keep all of your current stuff in it you can either take a 74-78 4 port 13B or rebuild your 12A as a 13B and get a 12a intake to 4 port 13B adapter, 1st gen 13B to stock exhaust header and 13B front engine mount and you'll be able to install the 13B with all your current stuff as the old school 13Bs are just big boy 12As
This $400 1/2 ass motor consist of the following:
76-78 R5 12A/13B front plate, RX-7 Y cast tall port center iron, 84-85 12A rear iron all ported to RRR killer bee spec, 76-78 RX-5 cosmo 13B housings with massive prolapsed butthole exhaust ports. Series 5 NA rotating assembly.
Seals: Used oem Mazda apex seals measuring between 7.4mm-7.7mm (new is 8.5mm), used oem side seals each clearanced to .002 (one side seal is new due to one slot being long as hell), used AtkinsRotary solid recessed corner seals, used lightly worn oil control rings, all new oem Mazda seal springs.
Mileage on motor since assembly: 2,000ish