Sorry for the long post guys:
Ok, so I got a '75 Tahiti with a 455 Olds, and a Legend pump clearanced at 0.050". I've yanked the 1/4" dished pistons, and added speed-pro flat tops w/ 4cc valve reliefs. I also went with a pretty timid Crane Cams marine cam, it's around 208/216 at 0.050". The heads are GM cast iron heads. And the intake and carb are edelbrock performer. Also, I run an A-2 impeller, so I top at about 4300 RPMs (she's very fuel efficient for a boat).
Shes quick enough considering I run pump gas, but the springs in the Mallory YL are are so worn out that it hits whatever full-advance I have set for at under 2000 rpm. It detonates like hell at low RPMs untill I either retard the timing so far it wont idle, or set the max total advance to be under 25 degrees (which still detonates a tiny bit and leaves nothing on the top end).
Now I have the curve change kit and can set any timing curve I want. In trying to choose a curve I find that boats are funny animals. The engine load increases drastically with RPM. I'm guessing that the small load near 1500 RPMs means I wont want much advance there, since less fuel and air will be in the cylinders than if it was a high-load condition like in a car. That also explains why I've been seeing detonation between near 1500 RPMs. This seems to mean that hop-out curves are right out, since the quick rise at low rpms is exactly what I don't want.
So my question is this... given my setup, what do the guru's think will be a good max total advance (it idles real nice from 10-12 initial by the way), and at what RPM do i want to reach my max total advance? I'm thinking 32-34 degrees at about 3000-3200 RPMs... What do you guys think? Is there anyone who thinks a hop-out curve is a better option for any reason? The max total advance can be changed easily, and I can guess and check that, but its the issue of when I want to hit the max that I'm not sure of.
Also, anyone know (ballpark) what lift the GM springs can handle? I'm thinking about going to adjustable rockers rather than the factory ones, and it would be a good time to up the ratio by a step. My cam's lift is .456/.484, and I'm not sure if the springs can take the extra lift.