I have a 20 foot Arriva with the 350 Mercruiser, which I am doing a little freshening to over the winter. I'm installing the GM iron highrise, and rebuilding the stock Qjet. I will probably swap to vortec heads next year, but that's out for now (but I would like to choose a cam grind that will run well with the vortec heads in 2005)

-I can tolerate a rough idle.
-I'm running a Houston Prop 24"P Accelerator prop.
-I would like to get the peak HP at or around 5200-5300.
-I need a FLAT cam. I don't want to spend the money on a roller set-up right now.
-I'm going to be using a geardrive (I know, I know... But I like the sound of the quiet ones....)

I hope somebody can suggest a cam that will open this engine up a bit. Anyone?

Pick up a copy of Dennis Moore's book "Small-Block Chevy Marine Performance", HP Books ISBN 1-55788317-3.
His book has all the information you'll need.

If that's an Alpha-equipped boat, be very careful about using 'lumpy' cams that require a higher idle setting.
You will find they are not kind at all to that Alpha's shift-interruptor circuit, and the gear case will suffer when shifting.
Jim

Ditto on Moore's book. Your limit will likely be the max lift on the vortec heads (0.470 max?)

Look at
Comp Cams XE-262
GMPP 12353918
Isky 201264/271-12
GMPP 24502476

The Comp Cam XM-262 might work, but the exhaust lift might be too much.

220BR is correct. There is a limit on lift. The problem is that the valve spring retainer will strike the top of the valve guide as well as coil bind. Machining of the valve guide and new springs are required for higher lift cams. The spring pockets will need to be machined to a larger diameter too if using aftermarket springs.

He said he's not using the Vortec heads right now. If you look in the Com Cams online catalog, there are two Extreme marine flat tappet cams for the SBC. I'm using the second one on the list (Higher lift). Idle is fine not lumpy, and produces good power.

Sorry I forgot to mention that I have 4" through-transom exhaust. I have read Dennis Moore's book three times, and I have the ultimate respect for his advice. I will be calling him soon, as I need to order some gaskets, but I found cam suggestions in his book that went from 10-15 hp increases on stock 350's to 9.0+ comp, modified 383's and larger cam suggestions, with not much in between. I couldn't find anything in his suggestions for a mid-level increase.

Thanks for the tips and the Comp Cam advice, I will check there. What was the Maximum RPM on the second Comp cam you tried?

I beleive the catalog said either 5500 or 6000 rpm. I ran one in a 350, and now in a 383 with good results. Very strong in the mid range. Punching the throttle from a 30mph cruise almost threw people out of the boat!

Just to let everyone know what most people know already- Dennis Moore is probably the nicest guy in this industry. I just got off the phone with him and he gave me a cam recommendation, we chatted about my motor and what I might do with it, and I couldn't be more impressed with what a knowledgable guy he is. I am going to be buying is new aluminum manifolds in a few more weeks!

By the way- his recommendation for my engine - a Comp Cams XE 256H automotive cam. Should get me to 5200 rpm no problem, a healthy power increase, and a good idle. (and he says it will still work well with Vortec heads!)

I don't usually say this, but I am excited for when I need to buy something else from him just so I can get more advice!

Don't know why I thought you had a 383, my bad.

That's the cam I ran in my Merc 5.7L (XE-256-12). I installed the cam, a new cast iron hi-rise and beefed up the Q-jet. I gained between 600 and 800 rpm and the low end was much better as well.

I'm currently using that cam in my 383 (the old 5.7), but will be upgrading to a roller this winter. It works fine in the 383 -- smooth idle, 18" idle vacuum. Vacuum in the 350 was around 13-14.