[urq] Why are the L5 Turbo engine sounds different ?

[Huw Powell]

John Cody Forbes wrote:
>> But how can we explain Andrew view, same exhaust but different head
>>  components ? Anyone else has an explanation ? Other examples ? Any
>> musician out there ? J
>> 
>> Louis-Alain
> 
> I think Huw is our resident acoustical expert ;-). C'mon Huw, lets
> hear your idea!
> 
> Think of it this way: The very source of the exhaust note is the bang
> of the combustion explosion inside the cylinder. You only get to hear
> the portion of that explosion that is still hapening when the exhaust
> valve opens. If you open the exhaust valve sooner you get to hear an
> earlier part of the explosion and you hear more of it if the valve
> stays open longer. If you also open that valve more you are going to
> speed up the finishing phases of the combustion process. Then take
> into account that all of these valve timing and lift changes are
> changing the way the pressure pulses move through the header you've
> got a pretty cut and dry explanation.

There is also the sound of the compressed gases "whooshing" out through 
the valve.

The initial explosion and whoosh sounds also overlap to varying amounts 
and affect each other.

And of course, as people have said, from then on there are a series of 
chambers with varying resonances (some of which are different for each 
cylinder), and of course some funky windmill sort of thing (with varying 
resistance to flow) chopping it all up in the middle.  Kinda like making 
sausage...

Not that I know what I'm talking about or anything.

-- 
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/