[djcwardog]

I am looking to buy a Deville this summer and the 77-79 cars have my interest, as do the 1980 cars. Both sets have smaller big block engines (425 and 368). If I decide to drop in a 500 (even a junkyard one at first), I'm told that everything bolts across as far as accessories, pulleys, etc. Of course the 1973 and 1975-6 cars also interest me! Tough to choose. 5000 pound car with mongo motor or 4000 pound car with smaller relative of it...

Anyway, for your question, I think I am with you on this. If it were me, and it could very well be this summer, I would want to tweak out the stock 425 (or 368 if I get a 1980 Coupe Deville, that year sure is good looking!) first for not alot of money just to see what it will do. Then if I decide it doesn't do enough, I can go ahead with the 500 option. So - to optimize beathing, first you need to at least port match your intake manifold. If you swap in a 472/500 one check its ports as well. You will not be creating extra work in doing this because you are going to have to remove the manifold anyway to do the one thing that is mandatory for you...

Pitch out that stock cam and put in something like the MTS 3 (for great torque and better mpg) or their MTS-5 or MTS-10, or even a just a stock spec 1973 cam, for better power over what you are getting now. Your stock smogger cam is retarded by design and not at all optimized for much of anything! A new cam with lifters is maybe $200. If you can use your stock rockers and valve springs then you are doing OK. Call MTS and ask them. Cad Co and Potter offer similar stuff as well... Comp Cams lists a few cams for these big block Caddys.

I would also recommend a true dual exhaust system custom bent at your local muffler shop. I like Dynomax Super Turbo mufflers but pick what you want.

Bottom line: short duration/high lift cam, port-matched intake, dual exhaust, and a proper carb setup to go with these mods and you will be at a point where you know whether or not the 425 will do it for you in the long run. If not, pull it and sell on ebay - someone else will want such a carefully prepped motor for their MPG king Caddy! You can then put in a 500.