<VV> How to Quiet Down my Spyder

[Steve Brennan]

Since purchasing my 1962  Spyder coupe a year or so ago, I have spent substantial time and money trying to get it as quiet as possible.  (My 17 year old daughter will be driving it, and you know how picky teenage girls can be, even though she loves those cute little buttons on the seats.)  In this effort I "dynamatted" the entire passenger compartment, including the roof, the inner and outer skins of the doors and side panels of the rear seat, and put double layers behind the rear seat (adjacent to the engine compartment).  (With all that extra weight, there goes the gas mileage.)  

While I am sure this has had some positive effect, the car is still noisy.  Tracking the source of the noise down as best I can, I think much of it is entering the passenger compartment through an "passage" that runs unobstructed from the area covered by the rear seat side panels (i.e., where the rear side window mechanism is), up over the rear wheel well and then through a triangular shaped chamber that makes up the upper portion of the body between the passenger compartment and the engine compartment, and then around to the other rear side window area.  (I believe that the walls of this chamber are 1) the back wall of the "storage shelf" behind the rear seat (which I dynamatted and carpeted), 2) the exterior sheet metal between the back window and the hood, and 3) the upper portion of the front of the engine compartment.).  As best I can tell, this triangular chamber acts like a drum, collecting the noise from the engine compartment and then radiating it over the rear wheel wells directly into the body hollows on each side of the rear seat.

So, I have a few of questions.  First, does anyone know what purpose, if any, that the triangular chamber serves, and if there is any good reason not to fill it full of carpenters expanding foam (or some other sound absorbing material)?  There are 2 fairly large "access holes" with removable rubber caps inside the engine compartment that would allow such an experiment.

Second, has anyone ever tried applying the spray-on sound deadener to the front wall of the engine compartment and the underside of the body over the transaxle to create an external barrier from the drivetrain noise?  If so, what were the results?

Lastly, and more generally, is the air cooled engine design just inherently a noisy configuration?  Forget about noise when you are inside driving the car.  Just standing outside next to a Corvair you never have to wonder if it is running.  This is fine by me, cuz I like engine sounds, but others have asked me why it is such a noisy engine, and since all my automotive history is with water pumpers, I don't really have an answer.  Is it that the exposed cylinder "cans," as opposed to a large heavy metal block, allow more detonation noise to escape into the surrounding atmosphere?  In other words, is more noise a necessary side effect of an air cooled engine?  If so, is it true that Porsches, etc., are likewise "noisy" cars?

Thanks,
Steve