I know the 20B -> RX-7 conversion costs a fortune and is very difficult, but what I'm wondering is whether the difficulties are more with the engine itself or getting it to work with that chassis/electrical system.

I'm looking long term, down the road, putting one in a B2200 pickup, and I know a lot of the problems with FCs and FDs involve interference with various bits under the hood. I would think that in a B2200 this might not happen due to different suspension and steering, as well as a much higher hood line giving good clearance.

I also hear it's hard to get the motor to run, even with a stock ECU. Why is that?

 

Both.

Yes, the thermostat housing on the 20B is too high to fit under a raked sportscar hood, and the oil pan interferes with the steering rack and/or front sway bar. The B2200 may not have these problems due to the larger hood area, but I'm not sure because I don't own a B2200.

It's hard to get the motor to run, especially with the stock JC Cosmo ECU. The main problem is that the stock JC Cosmo ECU looks for inputs from ALL of its sensors, including such things as the variable exhaust and automatic transmission. Since most 20B conversions will not include a lot of these Cosmo parts, the ECU must be fooled into thinking that the parts are still there and functioning correctly, or it will not work or will go into limp-home mode.

 

You might want to talk to Marco Acosta from MVA Motorsports. I am pretty sure he has put a 4-rotor into a B2200 as a pro-class drag truck. Even if he hasn't done it, he can probably answer the questions you have.

 

a friend of mine is doing a 20b- b2600 swap and the big problem looks like its gonna be that the engine bay is short, the 20b is the same length as the 2600 engine but we need to somehow cram a giant radiator, fans and an ic in there

mike