I must have been posting at the same time as you on my last reply.
Let's look at your question about cat-backs.
If part A gets 10 more hp and 15 more ft-lbs of torque and part b gets 10 more hp and 12 more ft-lbs of torque, how could this happen? Realize that you have left out one of the variables, namely rpm's.
Both parts could give a 10 hp increase but a different torque increase, but these numbers would be rated at different rpm's. To fully analyze these gains, keep in mind that you need to know all 3 variables; hp, torque, and rpm's.
Sorry if I am not explaing this too well. I wish we could sit down together with a dyno chart in front of us.....that would make things much easier

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