Difference in rotor housings?
 

So I started to teardown my '88 T2 because it had low compression on the rear rotor and I found out why. Long story short I need a new rear rotor housing. I see 2 different housings (front / rear) listed on the parts sites. What is the Difference between them, are they not interchangeable?

On the same topic, the front rotor housing is in very good condition. Should I look for a used housing of similar condition or is it ok to run 1 used housing and 1 new housing?

My searches weren't very fruitful. Thanks! :)

I'll be nice for once. The different part numbers are because for emissions, they run passages through the housings for EGR. If you install them backwards, the ports don't go anywhere, so no EGR.

It's better to run 2 new housings, or 2 comparable housings. Unless your good housing is perfect, then get a used housing.

You CAN NOT mix S4 and S5 housings. The spark plug holes are in different spots.

Use the google for your searches next time. This topic has been covered extensively.

https://www.rx7club.com/2nd-generati...rences-988148/

There are further links in that thread that link to other threads about this topic.

Thanks so much! :) For some reason the search wasn't turning up info. Appreciate it!

its actually the air pump air, but yes, if you swap rotor housings front to rear, it blocks the ACV, and it will never ever pass smog ever.

back in the day there was this semi famous yellow FD that pettit built, and since they have never seen a smog machine they swapped the housings F and R. well the new owner was in CA, and was not very thrilled when his expensive car with a new engine needed to have the engine rebuilt because the engine was built wrong.

My mistake. I don't have emissions testing where I live. I have a set of housings on the bench at work that I'm cleaning up and just followed the passages with my eyes and guessed that they were EGR. Nonetheless, still emissions related.

yep, but even in that case they likely handed the engine off to one of their new and less experienced builders. even a total tool would eventually ask what the F and R stood for, a person with a 50 IQ would probably figure it out after a few engines.

no idea, this was like 1997-98

You must have super tough smog tests if you cant pass without acv....mine did pass without acv, egr, all of the rats nest and the airpump blowing into a dummy cat...i was in the mid of the allowed pollution scale.
Had rtek 1.7 at the time i think if it mathers

california has some of the strictest emissions tests, no way you could pass with a dummy cat, you're allowed 110HC and 1% CO iirc.

Oh my...thats tough! 4.5% co is all i need to pass and i had 2.3 hehe

the amount you're allowed depends on the weight of the car, so it varies, its usually under 90 HC's and about 400 nox's. not sure about CO, i've never failed for that

i believe that is for the enhanced dyno test, non enhanced idle unloaded gives a tiny bit more room.

So in theory, if all the emissions stuff is no longer on the motor and it doesn't ever need to get emissions tested; it would be perfectly fine to run (for example) 2 front housings or 2 rear?

Yes, you can mix and match front and rear housings, provided they are from the same series and engine.

yes, if you plan to NEVER need to run it through an emissions test. never can be a long time.

I passed for 2 years running a Magnaflow car specific cat. Dinky and small compared to the stock cat. I bought the car with a non functional pre-cat.

In Texas, you have to do a 15mph and 25mph smog sniffer test on cars younger than 25 years. If I remember correctly, the stock and Magnaflow cat did like 30ppm HC, below 4% CO, less than 5% percent oxygen dilution and basically unregistered NOx. Of course the ACV and stuff is still intact and functional.

I still have the ACV, but the cat is gone (by the way makes a huge difference on an NA). Fortunately, Texas considers mine as a classic vehicle now. Just has to get special tags but it doesn't have driving restrictions.

Or drill two new holes, the Mazda hole is drilled after casting.

In Wisconsin the only emissions test performed is an OBD2 scan, so anything older than ~1997 doesn't get emissions tested. :icon_tup:

well, people move and sometimes don't think about these issues until they have to deal with them.

the sparkplug holes differ between s4 and s5 n/a housings i think and only in the us. turbo should be the same.