DDK - Die Deutschen Klassiker

We must be getting old! I'd like to reduce the level of the induction noise from the Weber 40 IDF carbs on the 356. They are fitted with K&N chrome air filters. Does anyone know of an air filter, or air box that would significantly reduce the induction noise that gets through to the cabin? Without hampering performance (not THAT old....) W

Bog standard factory parts should fix it?

The carbs aren't standard factory carbs, it would have had Solexes....

You can use the standard air filters with air filter adapter plates.

Winston, a thicker gauge of metal for the top of the filter might help stop some resonance.

Any chance the chrome tops are loose and adding to the noise or the air filters has lost their stiffness?

I don't have much noise from my webers. Mostly from the exhaust.

Sent from my M2004J19C using Tapatalk

Thanks for the suggestions it's not a mechanical noise it's the classic throaty roar of a Weber breathing. I think the idea of a thicker top plate or even a cast Ali airbox may go somewhere to helping..

How about some Knecht 356/912 air filters? They can be easily adapted to fit on webers.

Try sitting further away from them

Got plenty of acoustic insulation on the firewall?

I believe that having a single air intake which is then split to the 4 throttles would be less intrusive. Changes the frequency of the sound. Not seen any on the market though.

Bruce M wrote: ↑Wed Apr 19, 2023 10:24 pmI believe that having a single air intake which is then split to the 4 throttles would be less intrusive. Changes the frequency of the sound. Not seen any on the market though.

These systems are available although a bit £,£££!





https://www.ahnendorp.com/Beetle-typ-1- ... anguage=en

Think the noise must be generated by turbulent air flow at the carb intakes. Turbulence also increases pressure drop which you don't want. Anything you can do to slow down the air i.e. increase diameter, reduce bends and sharp edges should lead to more laminar flow and less noise. Using radiused velocity stacks within the filter housing should also help. Sorry, not a very straight answer but interesting to know what's going on. Other than that, probably intake air box is the way forward ... https://www.torquecars.com/tuning/smoothed-airbox.php

Cheers

Good point. Do you have velocity stacks? I recently bought 4 printed ones off eBay that would help

Sent from my M2004J19C using Tapatalk

If you want it to be quieter just fit the standard air filters it makes a massive difference! You can use weber to solex air filter adapter plates or just modify the filter bases.
They come up for sale regularly.

Late 912s had air silencers and better filters than the earlier Knecht.

I’d track some down and see if you can adapt them.

I agree on noise. 356s are very noisy, I’ve been meaning to do the same for mine.