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I highly doubt you are going to get any quantitative data; I dont think anyone is going to bench test different DPs and no one is going to swap them back to back in the same dyno sessions or anything like that either. While it might be true that you want a smooth transition from the turbo outlet diameter (3.5 or 4 depending on PWG or EWG) to the exhaust diameter to decrease turbulence and increase exhaust velocity, i would expect a negliglbe different in the performance of different catless DP shapes/designs, especially with a stock turbo application. Now if you are pushing say 500+ whp you might start to see some differences, but i would still expect it to be very minor. This is particuarly true because the choke point is most likely going to be the exhaust, so the DP, when catless, is probably not what is determining overall backpressure/exhaust flow resistance.
Also, I would suggest doing an IC even if you are going to stay stage 1. The stock IC is barely up to the task on the stock car, especially if you live in a hot climate like AZ.
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