Hey guys I'm thinking of putting a bigger cam in my gen4 454mag (365hp). From what I saw in the mercruiser service manual the stock is .224/.224 @ .050. I was wondering what size I could bump it up to on stock exhausts and what size I could bump it up to if I either got the stainless marine hi-torque manifolds and risers or the new Hardin marine seaward series when it comes out. I want to use stock valve springs and valves. dont have the money to get new heads and that's why I'm throwing around the idea of even just getting new aluminum replacement manifolds and keep the stock cam. Heeellpppp please!!!

Stainless marine exhaust, and the crane cam from the 400HP/420/425 series engines, is a nice upgrade for the 365 mag engine. If you're keeping stock exhaust, I really wouldn't bother much doiing a cam change.

I've used the 454/420hp cam with roller rockers with no other changes amd was a noticeable difference over stock 365 mag. Results will vary however this was in an 89 24' challenger. Went from 69 mph bone stock 365 mag to the only two noted changes and went to 72+. I do not recall if I changed springs. If it called for it I would have.

One of the problems I think with the 420hp cam is that I also have a below swim platform exhaust exit. I just looked it up and it said must have a free flowing above water exhaust. It also has a lsa of 114 and mine stock is 112. I don't know much about cams so I don't know if that will make a difference or not.

Didn't know this thread was here but my thoughts exactly haha