After removing my injectors for rebuilding, we noticed that there are diffusers in the sockets where the injectors fit. When I was cleaning my upper intake manifold, one of the diffusers fell right out, basically unprovoked (I gently put a cloth in the opening of the manifold and the diffuser just crumbled out.)

I do have a spare upper intake manifold with nice, intact diffusers. However, I'm becoming concerned about the possibility of even these "new" ones crumbling while the engine is running and getting sucked into the combustion chamber.

I've read a few threads and there seems to be conflicting data about how necessary the diffusers are. There seems to be a general consensus that they assist in atomization, but that they are not strictly necessary. Some people say remove them to protect your engine, others say make sure they are installed. One post seemed to indicate his engine ran "like crap" without them, and great with them. Also, there seem to be conflicting reports as frequently the people asking are not running stock injectors.

Basically, what I need to know is if removing my diffusers (ideally all four) will cause any damage to the engine or driveability. I am not concerned in with emissions (I am not e-tested anyways) or fuel economy. It makes no sense to risk an engine for a few cents of gasoline. I am running stock injectors, and the engine is also bone-stock (to my knowledge, as this is not the original engine and it seems to have been rebuilt). I am inclined to think that Mazda put them there for a reason, but if that reason is purely emissions or economy related, I will not hesitate to remove them.

Thank you.

EDIT: N/A, 1986

 

they're there to help atomize the fuel better and not let it hit the walls of the intake. It'll run better without them. that being said, most people with newer "EV14" type injectors don't run them and replace them with FFE adapters.

If you're running stock (EV1) injectors then I would run them. especially since you won't be able to get the injectors to seal without them (this is probably why their engine "ran like crap".) If you're really that concerned about it just buy a new set from mazda. they've lasted this long (30 years)

 

I would replace them with new ones from Mazda. They do make the engine run better, especially at idle and low loads. I have never seen personally, or seen anyone report, of one breaking and wiping out an engine.
The people that remove these are also usually the types that remove the BAC and thermowax, and live with a 1000 rpm idle, and say that's how it's supposed to run.

The Renesis has diffusers, and it runs newer style injectors, so that must stand for something.

 

Pretty sure that was a typo.
Would think he meant "run better with them"

 

I have read of some guys that just remove the Diffuser part on the plastic ..and leave the sleeve/o ring in the manifold/keg..whatever.But this is with newer injectors.
The diffuser is just a 'screen like surface" that the gas hits and atomizes fuel from the injector.
The injector already sprays fuel but the diffuser breaks it up a bit more.It would not be noticeable to run without them.Guys often find them gone and sucked into oblivion anyways.

 

Primarys are 50 $ and secondarys 30 $. (S4 NA) Add shipping and customs to that and you are at roughly 200 $. I am not going to spend that much ...

I thought to bring an example of each air bleed to my local machinist to replicate a set of these out of aluminium without the actual diffusor part, just the upper stuff so you can pop two o rings in there and use it to install your injectors as usual. Much cheaper and will last the life of the car.
Turning them on a lathe must be like 30 minutes ...

Mine are so brittle I cant even cut the diffusor part of and install it, it will fall to pieces when I torque the fuel rail down ... The injectors are serviced and got all new o rings, grommets, caps, filters and connectors.

I like this idea.

 

Thank you for all the replies

It seems the general consensus is that they will help the engine run better, and the risk of the engine inhaling a diffuser is negligible. So I'll just put them back in then (provided they aren't so brittle as to break off again in my hand).

 

It's already been done by several companies, most popularly by FFE.

 

I put in a set of EV14 injectors for primaries and old EV1's for secondaries. For the primaries I cut the screen and the "legs" off a set of primary diffusers and just used the o-ring part for a "spacer". For the Secondaries, I left the screens in place.

My understanding is the old injectors don't have a good enough spray pattern on their own, they kind of pour/dribble fuel in, while new style injectors sort of "mist" or "spray" it in, hence the screens with the old style injectors.

 

it may be spray pattern influenced ..but I'm guessing it's to keep more atomized fuel from hitting the inner manifold wall and pooling fuel ...hence more atomized fuel in the airflow.

 

Even new injectors need them when firing straight down into the runners. Look at the air bleed setup on the RX-8. Very engineered.

 

you need the primary diffusers, can live without secondarys

 

i just replaced my primary OEM 550 injectors with ID 1000. Now running 2x ID1000 x 2x ID2000 in my S4.

I removed all the OEM diffusers and replaced the Primaries with ID spacers and double donut'd the secondary's to compensate for the space of the diffuser removal.

Several street tunes later, I can say I cannot see a down side to diffuser removal.

The engine starts better and idles smoother. The secondary transition is seamless. Low rpm cruise has improved greatly, although I did changed to a rotational TPS rather then the old plunger TPS at the same time.

The idle vacuum also went up, which I must attribute to fixing a small vacuum leak.

Fuel mileage yet to be determined.

 

ONLY the FD diffusers are prone to failure since they have 2 long needle like legs. the only ones similar are the secondaries on the FC, which have 3 long legs, but if you don't fiddle with them then they won't break.

the airflow through the manifold alone isn't enough to break good functional diffusers on the FC engines.

i have never seen them break in a running FC engine, the only instance i have run into anything similar was when i have pulled apart FD engines and found one broken for whatever reason, to which i can't say they weren't broken during some previous work. i have worked on many many many FC engines and the fact i haven't ever seen this as a problem with them should tell you that the worry isn't founded. even with the FD theories, all they are is theories, i can't even guess whether a diffuser could damage a rotor side seal or not... the port opening is like a blender on steroids when the engine is running and only about .050" of the side seal protrudes where 95% of it is buried in the rotor.

if you're curious, pull them out and inspect them for cracks.

 

It can depend a lot on the injector. I tuned and FD where the diffusers had been eliminated on the primaries and Accell (disk style I think) 550CC injectors used as primaries, about 40 PSI static fuel pressure. Never could get a very good idle out of it because even though PW stayed constant to load, the port runners would load up with fuel so the ratio would gradually richen until the engine stumbled a bit and the BAC opened to compensate, increasing airflow. Which would suck some of the fuel of the walls, leaning it out, causing it to stumble, then the BAC would close and the whole cycle would repeat. The ONLY difference between this engine and any of the similar setups I've dealt with (nothing exotic, street port, single turbo) was the lack of diffusers and air bleeds.