Anyone know how much boost I can put to an MPI3 7.4 without having to do ANY other mods other than bolt on a supercharger (paxton or magnacharger for example)

I believe you can run the Prochargers up to 5psi with proper installation. That would be your safest option.

I ran fine with 5#s on my stock 7.4 mpi: however the block had some time on it and I experienced blow-by (or so I thought). Then I put lots of goodies in and did not up-grade the injectors and then had to re-build again. Now it runs great with an in-boat ecu tune (expensive but well worth it). Net, Net if your rings will hold up, you may have to replace intake and head gaskets and get by with nothing else. If you are like most others on this site you might want just a little more and the blowers help you find the weakest part.

I also recommend head gaskets and studs if the engine has over 100 hrs or so. It's alot easier to do with out all the s/c stuff hanging on it.

thanks for the input gentleman, i was thinking 4 PSI VERY safely but the hours are unknown so i think i better take it apart this winter and check it out before i blow it (literally)

Man... Just reading the title of this tread, I thought I was in the unsensored section!!!

one piece of advice I did not follow but wished I had is to start with a different block. 502 if I had to do it all over again. The 454's and mag's have forged internals, which I now have but more inportantly they have rectangular intake port heads and therefore a different and superior intake/plenum.