How much is needed to get a 94 Convicor 253 to hit the mid 70's. It has a bravo 1 with 1:50 gears. Me & my dad are having a dispute so please help us settle it. One more thing, are Pro Chargers a good choice for reliable boost.

That's a light hull. I'd say 450hp would do it.
I'd think it would do Mid 70's with a 496ho with CMI's.
I have a friend with a 96ish 253 convincor w/ Merc HP500. It ran 80 on gps when it was newer. Mid 70's now that the motor is getting tired.

I had a 1997 253 with a 415hp 502. The boat would only run 67-68 mph. I've never seen a 253 run in the mid 70's with only 500 hp. A 251 which is narrower will run much faster with less power than a 253. I have a friend who has a 1996 253 with 610 hp 509 and it will run 76-78 depending on load. He has tried everything to get it to 80 but has been unable to get there.