I have a standard 454 marine 330 hp 1990. I am trying to figure out which cam to use. I figure someone on this site has used either one of these. I am looking at a comp cams xm270h vs xm278h. Boat is 20' openbow cruiser. Used mainly for fun family boating. I would like to use the stock short block. Will have 049 mild ported heads with larger valves, performer rpm intake. I would like to use the stock 715 carb. I can't afford headers so my stock / snail riser exhaust will have to do. I am looking for a reliable more than stock motor that will not break the bank. Any of your thoughts would be appreciated.
I have a solidly reliable 454, that was dead stock Indmar 330HP 454 5 years ago, and you already have almost all the work I eventually managed to do (same intake, ported '049 heads). Ran my stock 700CFM 4150 untill just this past summer.
I overhauled the engine in 2004/5, put on the manifold, and was advised by a friend of mine who works performance jets for a living, due to my uses and intentions, I should go with the Isky 280H, bought the full kit, and love it.
It was perhaps a bit big at the time with stock heads, logs, and 700 Carb. It is still a great cam, keeping up just fine as I have managed the rest of the mods (including Lightning jacketed headers).
The springs are pretty mean for a Hyd. Flat cam, put roller rockers on it. My stockers were OK untill I pushed the engine to 5400 RPM, then they started cooking. Friend set me up with a set of Comp Hy-Tech Stainless Steel rollers, used, got them rebuilt by Comp, and still spent less than new Pro Magnums
You'll likely need longer than stock studs for roller rockers too, if you haven't already.
It's a great cam, but your log exhaust will be holding you back pretty heavilly. As soon as you can find $2,000 for Lightnings, I'd put a set on. You'll like the results.
