Im curious to know if anyone has put on a long tube header w/Hi flo cats and loss significant power. I have a 2005 Roush Mustang which ran 11:87@121mph in 90degree heat Dynoed at 479rwhp. I have a Vortech V2 supercharger w/intercooler. I put on the new exhaust system and aluminum driveshaft and ran a best 12:47@114mph. That was 6 runs no slower then 12.60 but no faster then 12:47. Somewhere I lost 50-60hp. The last time out the temp was 60degrees and Im wondering if I was running super lean. Any help would be great. Thanks  

yeah I see what you mean did you have it tuned on a dyno after installing headers and cats? I know tire stick better at 90 degrees but not that much ?  

I would assume that you dyno-ed and noticed your HP loss results. If you are attempting to do the math based on your ET vs. HP, you will always be speculative (even if you are using an E.T. calculator). What was your 60ft. time? Tires and pressure,, based on temp. are a huge factor. You can easily lose 1/2 sec. right at the 60 ft. I am guessing you are making up time at 300 ft. I am about 50 hp less rwhp, than you, but I have high 1:50's 60ft's and am in the high 11:90's and slower mph (than you).
The starts are were the race begins and ends. Try some M/T ET's, you'll definitely be mid 11's!
Jeff