Noise Reduction

[Krank]

I recently picked up an '82 Audi 4000 with a N/A 1.6 to go with my '81 Rabbit 1.6 N/A.

I was struck by the difference in sound volume. The Audi is so quiet that you can hear newer gas powered cars idling beside me at stop lights! It's hard to tell that the engine is running when you're driving down the road, even with the windows open!

I wanted to better understand how they did this, so I've been poking around. There's a plastic panel across the bottom of the engine that probably reduces the amount of noise bouncing off the pavement and back out of the engine compartment, but what I really noticed and suspect may be the most significant design difference was the air intake.

I know that an awful lot of noise is actually coming from my air intake. If I place my hand over the snorkle, (not to smother it or anything), The sound level drops significantly. On the Audi, the snorkle tube is actually a flexible peice of corrogated tubing which they've curved downwards towards the bottom of the engine compartment. I'm not sure where it goes (yet) once it gets down there, but it's most obviously a stock part.

Has anyone ever tried putting this onto a Rabbit? I'm curious, since it would just snap in place to replace the original snorkle that already exists. Does it baffle the noise from internal to the engine as much as I suspect it does? It seems like a very simple muffler that works for the air intake instead of the exhaust!

BTW, if anyone gets a chance to get one of these diesel 4000's, DO IT! They're GREAT! It's basically a very luxerious VW! It gets the same mileage, too!

[viperkepr]

I modified my Rabbit intake---I rigged a vacuum cleaner hose(1" 1/2) to the air cleaner snorkel and routed it between the alternator and the radiator, kinda like a cold air intake. That greatly reduced the noise---I could barely believe it. It also seems to have better response to the throttle----I'm not sure if that is real or perceived...

[VWCaddy]

I too found a slight noise reduction with extending the air intake to the front:

http://www.4crawler.com/Diesel/CheapTri ... dAirIntake

[82vdub]

Ram Air!

[tylernt]

I bet the floorpans and firewall have lots of good soundproofing too.

[Krank]

I can't really say for sure, but I can point out some details that I've never seen on a rabbit.
Between every peice of interior trim in the dash is a hidden strip of felt tape.
Everywhere I've been able to see on the interior seems to be lined with 1/2" thick open cell foam. Sometimes one layer on the inside surface and another on the next surface going outwards, equating more than one layer total.
I took the car to the dealer today to get a couple of minor pieces of plastic that I needed, and by the time I got back to my car a crowd of about 5 employees had gathered to admire the car. They said they hadn't seen anything like that in 20 years! It's in some sort of museum condition, so it's kinda weird in that respect. Someone took great care of her for a long time.

modified my Rabbit intake---I rigged a vacuum cleaner hose(1" 1/2) to the air cleaner snorkel and routed it between the alternator and the radiator, kinda like a cold air intake. That greatly reduced the noise---I could barely believe it. It also seems to have better response to the throttle----I'm not sure if that is real or perceived...

I think it's the corugated shape that has the effect of baffling out the noise. A vacuum cleaner hose would have that exact trait.
I can believe it had a better response... you were drafting in cooler air with more expansion potential during combustion. It seems like cooler engines always have more guts than when they're fully warmed up.