Totally agreed that butt dynos don't disprove butt dynos.That's not really proving. That's just your mind telling you that the truck doesn't sound like it's working that hard (because of the lack of noise) and it's moving just as quick. Unless you can prove the truck is slower with numbers, the difference is negligible. That is unless the exhaust was really messed up.
That being said, after watching dozens if not hundreds of cars get on and off a dyno, I can say there are *very* few cars that benefit from an intake and exhaust nowadays (beyond ditching weight from the exhaust) because modern ECU's target engine load - even my 18 year old BMW. On top of that, modern engines are pretty well maximized compared to 90's Mustangs.
I used to work at a company that made aftermarket tuners, etc. and I've seen the way cars from about 8 brands make power (or lack thereof). The only way to make more power is to find a component that's in bad shape (clogged air filter, etc.) or make a meaningful improvement (like cams or headers) and TUNE THE ECU. Generally intakes and cat-backs are going to give you about plus (or minus) 5hp on a Naturally Aspirated engine without any sort of tune.. but keep in mind my personal car made 5hp between the first and third dyno pull. I think the most recent vehicle I ever saw that had an intake system that *needed* improvement based on the pressure differential was from ~2008.
Load based tuning means that the ECU is approximating torque based on airflow, RPM, and some scaling. This way, the automakers can target a torque that's within the specs and reliability requirements for the transmission, driveline, etc. If your particular engine is capable of making 450 lb-ft of torque on a cold morning at low altitude.. it doesn't matter if the ECU is targeting 410. Modern vehicles are designed to perform *consistently* regardless of atmospheric conditions. No intake restriction? Open exhaust flow? Cool.. Engine is still going to crank out 410 though.
In the event you're able to change the airflow model enough for it to matter (again, usually this means cams and headers for an NA car) you really need a tune for the engine to run right, which FCA made particularly difficult with an encrypted ECU - which is why you have to trade it in to tune it. If you're coupling the exhaust with GOOD (i.e. Kooks, etc.) headers and a cam, then yeah you stand to make ~10-15% more power... but if you're just bolting on a cat-back and an intake, I'd expect 5 hp and be reasonably surprised if you managed 10.
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