[Vwdiesel] Re: Rob's exhaust

[Libbybapa at wmconnect.com]

Good work on the exhaust.  One comment that you made did not make sense to 
me.  You said that you didn't think that the Jetta cast downpipe would be 
particularly constrictive because the gasses were very hot and the velocity high.  
You felt it was more important to be less constrictive when the gasses had 
cooled.  That doesn't jive with my thinking, in fact I would think the reverse.  
Gasses expand when hot and contract when cooler.  I would think that the pipe 
size should be largest where the gasses are hottest and could actually diminish 
in size as they cool without increasing backpressure.  When looking at the 
cast pipe, it seems like the most horrendously constrictive part of the exhaust. 
 Pertinent topic, as I am currently working on fabbing the exhaust on my TD 
vanagon.  I just made a flange out of 1/4" steel and will replace the downpipe 
with 2 1/2" pipe.  Thoughts anyone?
Andrew