Do those numbers indicate a breathing problem? Wondering if 2.5” exhaust was a huge compromise
I recently put my 69 Mustang on a chassis dyno and lost 23% at the wheels as compared to a SuperFlow engine dyno. I had open headers on the engine dyno and full 3" Magnaflow exhaust on the chassis dyno. All I can say is that 2.5" exhaust will be more restrictive than 3" but it might not matter until an engine is over a certain HP. I have seen/heard many opinions on the benefit threshold from 2.5" to 3". Most say above 500hp. My personal thought is that your engine might put down a bit more HP with 3" but the installation hassle, drone, and extra decibels may not be worth it until 3" will provide a sizeable gain. By the way, my car is very LOUD even with full 3" exhaust. It would be quieter with 2.5"
Regarding drivetrain loss, I have automatic which probably doesn't help. Maybe it's no worse than the TKO600. Hard to know. I will always dyno the car at the same location so I can compare when I make changes. The place I went to mostly does Toyota's so an FE set on kill was a new experience for them. Ha!
I was on a new DynoJet 424xLC. Just curious what brand you were on?
-John