Early air filter housings - Noise, compatibility, jetting

[Tremelune]

I have a 1970 911 with a mostly stock 2.2L. The car came with an air filter housing that was plastic and mangled, so I replaced it with K&N hats when I rebuilt the Webers (with stock jetting).

The car runs well at various temps and altitudes, but at WOT near redline the sound goes from exhilarating to hurting my ears. I'm thinking about replacing them with a new housing to bring sound levels down. I have some questions:

1) Will an enclosed housing be noticeably quieter than my open air filters with hats? Any difference between metal and plastic?

2) Am I correct that all years of these housing (plastic and metal) fit all carbs if you have the base? Do any bases interchange if I have to mix and match?

3) Would the change have the car running any richer or leaner?

4) Could these be called plenums?

[Tremelune]

Well it looks like they changed these a lot from '69-72...

https://www.early911sregistry.org/forums/showthread.php?75913-Correct-air-cleaners-for-various-MFI-years

I think all my various breathers are just vented to atmosphere at this point...I guess the real question would be, which housing do I want?

[Hi_Fi_Guy]

Try some searching. Someone did a write up on modifying the base plates of of the 2.2 air box to adapt to PMO carbs. The process to fit them to Weber should be similar.

The owner also replaced the snorkel with one large Venturi to enhance airflow but the snorkel may be quieter.

If memory serves the air box can reduce HP on the top end but may boost low end torque slightly.

One would guess the air box would cause the carbs to run a bit rich. A before and after Dyno comparison would be useful.

[stownsen914]

The airbox will be quieter. It is a plenum technically - though whether Porsche tuned its volume to give that benefit, I am not sure.

I believe the bases are the same for MFI and Webers. Not sure about Zeniths, someone will chime in to confirm.

The bases for the plastic airboxes are definitely different from ones for the metal airboxes. A metal airbox is correct for a '70 for what it's worth. I've seen people replace the long snorkel with a short later style one, and I've seen a large venturi to replace the snorkel. I've not heard about how this or a different filter affects the noise. I'd guess it might be a little louder, but that the airbox and filter still suppress a lot of the noise.

[gamin]

My experience on a 70 2.2 with both systems. The plastic air box is quieter and the rain hats are noisier. But, seat of the pants, it seemed that the rain hats gave more power. It was noticeable. I have a 3.0 in the car now and I use the rain hats. I remove my hearing aids and wear hearing protection to mute the noise. Also, with the rain hats you have much better access to the top of the engine. The car left the factory on 5/70 and had the plastic air box if that piece of info is of any use to anyone.

[rowingone]

They do make insulation pads for the rear deck area right above the engine, I know my 72 came with one from the factory . . that will make more difference I think than the air box.

[targa72e]

The airbox will be less noisy but will cost HP. I recently did some Dyno testing on my car. I was using Zeniths with stock buckets and plastic cover. You can see details at link below.

https://forums.pelicanparts.com/porsche-911-technical-forum/1151593-dyno-summary-testing-early-2-4l-2-5l.html

john