I've been looking into 425 cars lately, I like the DeVilles alot from this era. I read the whole "cheap 425 power upgrades" thread, but didn't get a great answer on just how much power removing the cat from a 425 car frees up. It seems like the 472/500 manifold and removing the cat are the two biggies as far as cheap upgrades, am I correct? What is a stock 425 rated at, HP and torque?
Automobile(s): 1995 ETC, 75 Deville, Cad500 powered 73 Apollo, 94 Mark VIII
Re: Removing the cat
Stock 425 4bbl is rated at 180hp/320ft.lbs. A center-cut 472/500 intake manifold might be worth anywhere from 10-20ish. Gutting the cat I'd say would be worth similar gains or better. Doing a nice true dual system would be the best of course.