Diesel Rx7??
 

Is it possible to fit a 6.6 liter duramax engine into an 87 rx7??

Well it could be possible I guess if you had the fabrication skils, money & the time to try, but why would you want to? Not sure what the dimensions of that motor are, but that would be a start, then figuring out if the trade off in weight is worth it. Decide what the car is being used for & determine if the motor will best choice for the car.

I have seen diesel swapped RX7's, but if I reacall they were 4 cylinder diesels.