Differences between front and rear rotor housings
 

What is the difference between the front and rear rotor housings.

I have 3 good used 13B-REW rotor housings. Of course the best 2 are both rear rotor housings and my only good front is not quite as good.

What are the problems of using a rear rotor housing in the front.

I was concerned about the airpump channels because it would appear the air pump plumbing is only connected to one side of the rotor housing.

Are the cooling jackets identical or are there subtle differences there also?

The only difference is the air pump holes the water jackets are the same .If you arn't using an air pump no problems

Figured as much, and that is a problem for this build. Was planning on keeping everything 100% emissions legal.

if you look Mazda only drilled the hole on one side. on a 12A they drill both sides, so that the housing works front and rear.

its very easy to drill the hole....

I did consider that as an option too. I'm not sure of any possible downsides, surely if there was no downside Mazda would have drilled both sides and just used a common part for both housings.

Mazda proberly did it that way to sell more housings

they did use common parts, except that one drilled passage. they only drilled half as many holes....