I have a SBC with 11.25:1 heads and 38 degrees of total advance. What do you think is the lowest octane level I can safely run?

100+

I don't know if I would even run that in a boat. If you do roll back that timing to around 32.

You're gonna have to be a lot more specific about your mods. What cam specs? head design, are the chambers polished? If properly tuned the degrees of advance will actually have less to do with octane than cam & head design.

Roby

I ran 110 with 10.8:1, Gonna be running 110 again with my new setup of 12.6:1.

Wette vette's dad runs a small block which i believe is 11.25:1 and iron heads he runs 110 octane.

This is the boat that belonged to Wette Vette's dad. It just seems like 110 is a little overkill for 11.25:1.

better safe then sorry in my book

Need a lot more information to answer that question. Try to calculate the DCR rather than look at the SCR, depending on your camshaft, you may find that you are lot safer then you think on pump gas.

We ran it using Travis's "better safe than sorry" attitude. It helped that we have a supply for 110 octane near our lake. I believe 38 degrees works so well with this motor for 2 reasons. One is the domed pistons require a little more advance than flat tops or dished pistons that are typically in marine engines. The other is 110 octane is slightly overkill for that motor combo. If the timing is backed off to 34 or 36 there is a noticable loss in power and running the 110 octane we never had any signs of detonation at 38*. I am sure some mixture of 93 and 110 will work just fine, but some timing adjustments may be required. The problem is there is no real set formula as to what mixture and what timing should be used. Careful experimentation is the only real way to find out. I haven't been a big fan of octane boosters, but does anyone know of any that work? That could be another option, but again be careful!!

Toluene & Marvel Mystery Oil.