| you are increasing the density of the air flowing through those pipes, which will add to the resistance of airflow. At 15psi, you have ~doubled the mass of air.
At 30psi you have ~tripled the mass of air. I think all other things being equal, taking the same car and upgrading the entire intake system to 2.5" is going to yield better performance. I also think that there will be very little difference in spoolup characteristics of the turbochargers due to the fact that they move an incredible amount of air to start with and the volume increase from 2.0" to 2.5" isn't going to be significant enough to show any spoolup differences. You have to keep in mind that although the pipes are larger in diameter and have larger volume, the turbos are pushing air from the filter to the throttlebody at ~350fps. Last time I checked, there is about 12feet from the filter to the throttlebody. That means that each molecule of air is making its way from the filter to the throttlebody in 0.034s, thirty four thousandths of a second. To increase the boost pressure from 0psi to 15psi within the pipe would require that you do that twice (doubling the amount of air in the pipes) which means you are looking at 0.068s, 68 thousandths of a second. Lets say that you increase the pipes from 2.0" to 2.5". Thats a difference of 350-269 ft/s = 80f/s. So instead of it taking 0.036s to make the run through the pipe, it is going to take 0.044s instead. To double the boost in the pipe will take 0.088s, a difference of 0.020s, or twenty thousandths of a second. Folks, the difference here is marginal.. Blinking your eyes takes about 30 milliseconds (0.030s). It takes you longer to bat an eye than the difference in boost response in going from 2.0" to 2.5" piping. Spoolup characteristics are primarily predicated by the turbo's design. Just look at the gent who put the turbocharger in the back of his car. His dynochart, if you didnt know it, would not appear any different than any other car with the factory piping. This is because the volume of the pipe plays a very small role in terms of spoolup. The pipe's cross sectional area plays the most significant role in terms of its ability to efficiently flow the air. What you are trying to accomplish with the larger pipe is a little bit lower velocities, which is going to reduce the drag of pushing the air through the pipe exponentially. It isn't going to hurt the system by any notable degree - it should only stand to benefit. How much exactly, I dont know, but I just may have some numbers for you within a week during my trip to PA. I have my massive SMICs and a box full of 2.5" mandrel bent pieces to assemble the system. We will be comparing stock piping vs. 2.5" piping, stillen SMIC vs. AshSPEC MASSIVE.. fingers are crossed that we will be able to get all of this done within our timeline.
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18:42:26 06/23/05
