I feel it is important for people to understand the testing and the results I have gotten performance wise (13.3 @ 107.3) were from LONG testing on all sorts of performance stuff from chips to full exhaust.
The Idea was to find the best Dp and exhaust for the money. I wanted to pit stock Dp's modified against the 4 times more expensive aftermarket Dp's offered from Audi performance shops. The Idea was simple the B5 guys are using stock modified Dp's (piggies) and going low 11's why are we spending over 3 times as much to get the same performance. So I decided to see if the extra money was worth any more performance
I have seen people from time to time mention they are looking for the best chip. The best chip for your car is a good set of Dp's and a properly sized and built exhaust for your performance goals.
Chips should be the last thing you think about for the B6/7 not the first thing. There IS TONS of power to be had in the exhaust if done proper. Thus me sharing these results for people to look over and come to there own conclusions.
I feel that my conclusion and results speak for them selves in the performance of my car
This first post dose not include the Dp testing results. That is in the post below so feel free to skip down to that.
This post is to help some of the guys understand some things about exhaust that they might not know or just need to be refreshed on.
This is not a thermal dynamics or fluid dynamics post meant to change the world. IT is a plain as day wording of why parts of my Dp conclusion are important. I am not going to fill the post with terms that will have some searching for the definitions just so I can sound smart. I am not here to try and step on a soap box and show off my Internet engineering degree or try to advance some on line adjective. So for those of you who are going to pick apart any thing because you have nothing better to do remember If you disagree that is fine. This is the best way I could explain things to help bring those up to speed that may need it.
On to some of the back ground information that is important to the testing below
The goal behind changing Dp's it to get more performance out of the motor. All the Dp's tested removed one of the cats from the Dp design. The thought to this is If we remove one of the cats from each Dp we eliminate some of the free flowing restriction on the motor.
The best exhaust for our motor is one that will Give you a pipe diameter wide enough so that there is the least level of back pressure possible whilst achieving the highest exhaust gas velocity.
What dose this mean?
This means you want a exhaust that will allow the air to move as fast as possible without creating turbulence or an obstruction in the flow. Turbulence is an uneven flow of gas that creates a uneven flow pattern that actually slows down and can obstruct the exhaust.
AS AN EXAMPLE:
We see obstructions or turbulence if you turn on your out side water spicket. If you don't have a hose on the end of the spicket you see the water coming out going in several different directions. This causes the water to actually slow down coming out of the spicket. If you put a hose on the spicket you can create a positive alignment of water flow where the water is all now WORKING together to move in a specified direction as quickly and efficiently as possible. There is JUST enough back pressure in the hose to keep all the water moving close enough to quickly move in the same direction. So basically proper alignment and back pressure will corral the water and the exhaust in the proper direction in a much faster more efficient fashion then without.
Why is it so important to move the exhaust as fast as possible?
Well exhaust comes out in pulses (you can see this put your hand over the tail pipe you will be able to feel the pulse) and the thought here is if you can move the first pulse fast enough you create a low pressure area between the first and second pulse. In doing so The low pressure behind the first pulse creates a vacuum to pull on the second pulse and so on with the third exhaust pulse and forth exhaust gas pulse ETC ETC. The faster you can move the pulses the stronger the draw or vacuum you can create between pulses and less power is lost because of improper exhaust flow from the motor.
OK so now that we know what we want from an exhaust why do we want aftermarket Dp's that remove one of the cats.
The basic idea of a catalytic converter is to clean the out going exhaust gases. But for a cat to work proper and strip the chemicals out of the exhaust gas the cat needs to be very hot. To get the cat hot you need to slow the exhaust passing threw it down long enough to bring and keep the temp of the cat up to operating temps. Doing so creates a restriction and adversely effects our wanted end result in the exhaust flow.
Aftermarket company's have found that you can still clean the air with 1 set of cats not 2 ( we have 2 cats per Dp and we have 2 Dp's. One Dp on driver side and one Dp passenger side) as we have on our car. So removing one of the cats from Each Dp will now be LESS restrictive and help us to get closer to our optimal exhaust gas flow range. Thus allowing the motor to make more power threw the added exhaust flow.
On a side note:
Most people have said that adding a cat back with out doing the Dp's results in almost no added power. The biggest changes that come from a cat back usually comes in the form of sound and not performance. This most likely would be from the fact that the cat back exhaust is not the biggest part of the exhaust restriction. HOW Ever the cat back will be more effective after a Dp swap due to the fact one of the biggest restrictions has been removed and in doing so the cat back would benefit from a less restrictive Dp system.
Even with the best set of Dp's you need to asses what your goals are and match the cat back to the Dp configuration. The Dp's are just one part of this equations. If you don't properly match your cat back to your Dp's then you stand to loose power. MANY have seen or "FELT" this. The REAL issue is what Dp's do you have and what it the best solution for that. H pipes are imporntnat and A X pipe is only needed if you go the open route. Then in some cases you don't want a X or H this is all biased off what your doing with the Dp's so lets talk about the Dp's