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Originally Posted by djcwardog  Anyway, for your question, I think I am with you on this. I would want to tweak out the stock 425 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.
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. |
UPDATE - I bought a 1977 CDV just a few weeks ago. I had true duals bent and installed - which required me to jet the stock Rochester carb up two sizes - from 72 mains to 74 main jets. I cleaned up the primary (seem to read as "62b" rods... and appear to be the newer style) and secondary metering rods and replaced both the choke pull-offs (primary and secondary). Already the car is faster than it was when I got it. I put on the offset MTS chrome 14" air cleaner to clear the stock a/c compressor. On hand is a pair of 500 exhaust manifolds and a 472/500 intake (with EGR - which I will not use). I also have the MTS-3 cam and lifters ready to go. I plan to remove the valve from inside the RHS exhaust manifiold and seal the holes so the gases flow better - no need for the heat riser/EFE warm-up here! Marty at MTS is sending me the 500 a/c brackets I need to go with the 500 intake. I'll post up results as I progress in this build-up. Maybe the 425 will do all I need until the block lets go. Of course, now I have all the parts needed to adapt a 500 short block (with the 425 heads and holes drilled in the 500 block for steam), or a 500 long block if I use the 500 heads... I know a guy who said his 77 CDV went 425,000 miles on the stock motor and ran fine when he sold it!