another thread about injector diffusers
 

In typical fashion I can find only threads that relate to questions I don't have but share keywords with my question.
I am rebuilding a '90 N/A, should I do anything with the injector diffusers, they're probably original and have about 90k on them.
Do the o-rings need replaced, they're pretty hard but I don't know what they're supposed to be like.
These are the secondary ones, haven't touched the primaries and they look fine.

If you can avoid taking them out, i would avoid it. After 30+ years, that plastic gets brittle, and they don't like being removed. But, if you have a steady hand and some patience, and you're confident you won't break them, it'd be a good idea to replace the o rings

I replaced the center iron, right now they are out and need installed into the new engine I guess I’ll order the rings from atkins and see if I can break things trying to put them in:)

yeah if you can get them out, you should change the o rings
9954-10-1252 is the part number

if you have to buy new diffusers, the S5 ones are probably a small upgrade

This is an s5, it has the ones with like an angled plate. Thanks for the part number!

are these even necessary if you run more modern pattern aftermarket injectors?

people seem to think its not, but i'm skeptical

I’ve searched quite a few diffuser threads and never found a clear answer to my question, but I found a lot of people saying they’re not necessary but you need a spacer in there to keep a seal. I don’t know any modern car that has anything like that. I am running stock everything and supposedly it’ll idle like crap without them.

Here's the rundown:

- You 100% need the upper part of the diffuser. The ring shaped plastic thing that holds the o-rings. I'll call it the "sleeve" from here on out.

- You do not "need" the small legs with the diffuser screen. You do, however, WANT this part to help atomization. It will probably be most noticeable at idle and low throttle.

If you try to use the factory injectors without ANY of the above parts, they won't seal right. The bottom injector o-ring is sized to fit into the sleeve, and is too small to fit into the bore without it.

When people break the diffusers, usually the legs are what snaps off. So they just have the sleeve part. That's why people say you can run "without" the diffuser. But what they really mean is that if you break off the remaining legs, the injector will fit and seal with just the sleeve part.

No diffuser at all is not an option.

im not talking the oem injectors. they have a crappy spray pattern. im talking a more modern injector with a better spray pattern.

Better injector spray pattern is great.

Will be even better injecting into that pocket of turbulent air the injector diffuser creates- you just have to decide what is good enough for you.

We dont have to meet cold start emissions as consumers so we feel like the car works perfectly without a precat, without acceletated warm-up high rpm cold idle, without injector diffusers, with air pump directly into high flow cat (no acv/port air), etc.

Car works perfectly, gets same mpg or better than stock but would not meet requirements Mazda had to meet to sell the car.

Well then you can get away without the bottom screen, but depending on the injector I think you would still need the brown sleeve part.

It looks like some injectors use a big donut shaped seal instead of an o-ring for this specific type of situation: https://www.rx7club.com/single-turbo...-guide-920186/

I highly recommend having the full diffuser on the primaries, The relatively low air flow at idle needs the "air bleeds" built into these diffusers to help atomize the fuel as it is injected into the air stream. Stable idle and smooth acceleration off idle.

What do you think?