So I keep seeing these little metal fins in my exhaust ports as I work on rebuilding my engine and I have to wonder, what the hell are they for?

I was talking to a second gen guy the other day and he told me to just take them out because it'll increase power or something. When I asked him how it would affect emissions, he just shrugged.


So here's the question, what are they for and what benefits do you get from removing them?

 

If I recall Icemark said they're to reduce noise and the only benefit possible from removing them would be.... less restrictive exhaust outlet?

haha

Oh I think he said they're "exhaust inserts"

 

I don't think you should remove them. I remember reading somewhere that if you do, it kills the flow.

 

I read somewhere that it's also supposed to reduce the high pitch rotary noise.

From a training manual:

Here's how exhaust gases flow through them

 

The turbo applications don't have them also, it's a N/A thing

 

i was thinking that if you port the exhaust you take them out.

 

So what exactly do they mean by smoother flow?

So far, we still don't understand what they are supposed to do exactly other than restrict exhaust in a "two stage" manner...

 

First I've seen of those drawings or the 2 stage idea, sounds reasonable. Looks like I need to dl the Training Manual and read it, lol. They do quiet the exhaust conciderably. The turbos don't need them because the fins of the exhaust wheel break up the sound better than the insert ever could. Inserts do not need to be removed for porting, but it does help.

 

I see, so removing them will not really yield any performance improvements, but give you a better Brap Brap?

 

...Or a louder Ping Ping...

 

brats would be okay, but i don't want my car to play pingpong. that's what my gf's for

 

I've been wondering about these too. When I bought my 12A housings new they didn't have these inserts. Nor have I ever seen them on a 12A. Is this a 13B thing?

 

i think it was an fc thing

 

Wow, seriously???? Those are commonly known as difusers and their only purpose is to quiet the exhaust. They were only used in 86-91 NA 13B's. Get rid of them for a louder faster car. Search the 2nd gen section for more info... They are cast as part of the insert, switch to turbo inserts or gslse ones. OR you can grind them out if you have 24 hours and a die grinder.

 

^ exactly.

 

Plasma cutter did the trick for me.
Drill out the roll pins with a diamond tip, its easier to work with in a vice.

 

FWIW, I don't have experience taking them out, but I can't imagine that they'll restrict flow noticibly.

 

they reduce noise about 3db, and power about 3hp.

considering what a bitch they are to take out, i'd just leave it

 

Is that 3dB relative?

 

If all they do is quiet the exhaust how do they increase performance substantially?
Almost all the second gen guys keep saying that same line over an over again. But when I ask HOW they can't really answer it.

As for searching? under the terms, "Exhaust Diffuser" I found only 3/33 threads on the entire fourm that were worthwhile in reading, yet they had little technical information to explain how these things work exactly.

Sorry to sound ungrateful, but the diversity of and the amount of conflicting answers tends to make me want to know more about how it works.

 

http://www.wankel.net/~krwright/cars...%20Manual.html

section 1 and section 4....

 

Thank you very much for that it was very interesting to read.