I know this is a rather unusual request, but has anyone had any success with putting a NA 1.8 head on a NB? I have a 95 miata and I am in the position to swap heads with someone with a 99 in exchange for some other work that the engine is going to need. He is fine with the loss of vics and a worse flowing head, I am not looking for an opinion on what I should do, but rather asking if anyone has done it before. I know I will have to swap intake manifolds and almost all of the sensors, and I also know the EGR is different between the two heads. Also, I am going to have to mount the CAS to the front of the 95 head, is that possible with the 99 cam sensor? There is plenty of information about swapping a 99 head to a NA 1.8, but none about the reverse procedure. Any help would be appreciated, I know that there are things that I am probably overlooking. Thanks.

 

I know if you mount a CAS on a '99 head, it goes on the drivers side rear. As far as putting a '95 head on a '99, I'm pretty sure it'll bolt right up to the block. I think you pretty much listed everything that would differ.

 

I've never done it but theoretically I don't see why it wouldn't work.

You would need to use the 99 valve cover so the cam sensor would have a place to mount, you probably need to verify that the cam gears are the same so the sensor is seeing what it's looking for.

Use the 95 intake manifold and 99 throttle body. I think you're going to end up with a throttle cable that's about an inch too short but it shouldn't be too difficult to come up with a different mount to move it a little bit or if you're lucky there might be enough adjustment room to make it work without modification.

 

VVT head swap, new take on the old question - MX-5 Miata Forum