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I´ve read about unavailability of 12A housings. Lots of you did or heard about milling 13B GSL-SE to 12A width and water seal grooves cut in. Did anybody modify them for 79-80 thermal reactor? My aim is to keep the car as stock as possible (out of some safety mods as oil p/t gauges etc..) Is in the housing enough "meat" in the bottom part for drilling the hole for TR air supply without compromising consistency of the walls? I know most of you would reccommend me throw away the TR, but aim is historical fidelity, reliability, low noise.. Thank you in advance!
I've never heard of anyone doing this, but it is possible.
Creating the Thermal Reactor Air Injection Port
Once the housing width is exactly 70mm, you can replicate the 1979-specific air injection passage.
Mapping the Path: The air injection port does not travel straight through the housing wall. It is a dual-angle passage. Air enters from a port on the face of the intermediate/side iron plate, travels horizontally into the side face of the rotor housing, and then angles inward to exit directly into the floor of the exhaust pocket.
Replicating the Angle: You will need a junked, original 1979 12A housing to serve as a physical blueprint. Secure the donor housing on a 3-axis mill or CNC table. Use a dial indicator or probe to calculate the exact entry coordinates on the housing side-face, the exit coordinate in the exhaust runner, and the drilling angle.
Drilling Strategy: Secure your newly milled housing at the verified angle. Use a rigid carbide drill bit to drill the passage from the side face until it breaks through into the bottom floor of the exhaust pocket.
Avoid the Water Jacket: The air injection passage passes remarkably close to the internal coolant cavities. Precision casting lookup is vital. If your drilled angle deviates by even a fraction of a degree, you will breach the internal water jacket, destroying the housing. [
KansasCityREPU thanks for sharing your experience and videos. I´m wondering if anybody did that, because it seems to me doable, but I´m also aware of water jacket passages. At the first I need to source new 13B housings and than I will compare how much material should left after drilling. If it is too close I will refuse the idea of thermal reactor and switch to "modern" header.
You mentioned that the inlet port is not direct hole (but two angled), even the air goes throught intermediate/side plates and what I´ve seen I can´t agree with that for 79/80 thermal reactor. Maybe some other similar version? In my 79 the warmed up air from heat exchanger goes through pipe connected to the bottom of TR. In TR the way is splited to two ducts which are directly connected to housings inlet ports. Inlet ports are straight holes directed steeply up approximately to the center of the exhaust port. Between exhaust sleeve and inlet port sleeve is a gap, which allows flowing between them. The hole in the exhaust sleeve doesn´t follow up directly to inlet port sleeve. I suppose that is due to possibility of making same exhaust sleeve for both rear and front housings.. Bellow I´ve added few of my photos. Straight look in axis of inlet port. On the other side you can see exhaust sleeve and partly the hole in it..
