Originally Posted by
Jet Black
I'll try to explain this in the simplest terms possible.
First off lets begin with a simple lesson in English by defining the word substantiate.
The competent evidence (or more accurately, empirical evidence) in question was the act itself of swapping out the dumptube. By switiching to a non-ribbed tube of similiar dimensions, the problem was fixed in it's entirety. Simple deduction is enough to prove his assesment. This conclusion is made all the easier when you consider that nothing else was changed (ceteris paribus), so therefore the only remaining suspect is the ribs or pockets. While he may not have explicity made the claim that the dimensions remained the same, I'm assuming that he's not a total dumbass, and therefore can make such a connection between using a different ID piping and fixing the boost problems (which he would have pointed out). Furthermore just exactly how is he supposed to fit on a larger dumptube with the existing wastegate? Do you even know what an external wastegate looks like? The ID of the outlet port cannot be changed. Therefore you cannot simply use a significantly larger dumptube coming from the flange. Of course it is possible that he went out and bought a reducer pipe for the dumptube. But I don't think he smokes crack, so I highly doubt he did that.
Coming back to the point, the ID of the tube can be assumed to be equal to whatever the ID of the wastegate flange was. The wastegate (and in turn, the flange) was choosen based on that paticular application. So if he was using the dump tube with the ID of the wastegate flange, he shouldn't have had any problems. And certainly not a boost spike to more than twice his set pressure level. But instead what he was using was a dumptube that had numerous pockets in it. Pockets can quite easily cause a substantial increase in pressure (much more so when they are located in such a critical point along the system where maximum pressure is achieved...in the bends). They cause a considerable disturbance in the flow characteristics of the gasses, and in turn slow them down (slow exit velocity is also synonymous with increased pressure). On a device whose sole responicibility is to control boost pressure through evacuation of the excess gasses, any back pressure within the evacuation device (...the dump tube) will translate directly into higher pressure. This problem becomes increasingly compounded with increased pressure. That is by far the simplest explanation available.
Oh, and there is the whole empirical evidence thing that I went over...
Understand?
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