[Formulajones]

Okay long post but, As far as power differences go, it's seems to be reliant on how efficient the rest of the system is and whether it's sufficient for the engine. I have several examples, I'll just list a few.

My sons Vega with a nice little 500hp 327, has long tube headers and the exhaust is a 2 1/2" transverse kit for an F-body that I shrunk down to fit the Vega. I ran this same system on my Firebird decades ago and kept it knowing it would go on another project one day. It went on his vega. I installed a pair of Quick Time cutouts about 20" behind the header collectors. Through the exhaust it ran a best 12.77 at 107 mph. The very next pass without a cool down he opened the cutouts and it went 12.40 at 112 mph. The MPH is the telling part. https://youtu.be/M-5PPMnodzQ

My sons mustang has a full 2 1/2" Dynomax kit on it with a BBK "X" Dynomax mufflers and factory looking 2 1/2" tails. On the chassis dyno the stock 302 made 230 HP to the tires, with the cutouts open it made 232 HP to the tires. Not a huge difference so the exhaust is doing a pretty good job on a stock 302.

My 69 Z/28 with it's stock 302 is running Pypes transverse system with an "X" and I installed cutouts on this one. On the chassis dyno it made 277 hp and with the cutouts open it made 284. Not a huge difference.

My Chevelle with a 598, a 3 1/2" exhaust into and out of the X, into a pair of 3" dynomax ultraflow mufflers and 3" torque tech tailpipes. I positioned the cutouts straight back from the header collectors before the bend into the "X" and are about 20 inches from the header collectors, It ran a 10.90 at 123 through the exhaust, I opened the cutouts and it ran a 10.90 at 123 LOL
So that exhaust system is working excellent for that engine.

That's not to say I wouldn't put cutouts on a car even if the performance is marginally the same. They are a hell of a lot of fun on the street, I use them all the time. They are great when a loud mustang or hemi comes up with that awful cackle obnoxious exhaust and I hit the switch and can't hear them anymore