So I'm getting ready to order motor kits and the 355s were 10.14 static/7.56 dynamic.
The 383s will be 10.85/8.13 is this safe to run on 87 no eth?

On the water 93 is not always available

Steel or aluminum heads?

go up a size in head gasket to take the sting out of that ratio... its a tad high for a marine app, aluminum heads or not... IMPO

I ran 10.3 on my 383 aluminum headed engine . 5000lb. boat and no problems but that is riding the edge for 93 . For 87 octane 9.3 max . My blue HP500 was designed to run 87 octane with steel heads and 8.7cr . 10.8 on 87 octane is a recipe for destruction imho .

exactly!!! thats why I suggested a thicker gasket, to drop the ratio down to an acceptible limit

Sound wisdom my friend !

better to be safe than stuck with a busteda$$ boat!! lmao and the gains from the increased compression are so insignificant, better to spend $$$ on headwork that will yeild much greater returns!!!

They are ported world sportsman heads steel. Ill look into thicker gaskets. The motors run cool with the stainless marine crossovers
What is a good rule of thumb on max dynamic comp?

Ill be running twins in 5800-6000# boat

I'm not sure too many look at dynamic C/R, but I could be mistaken.

My motor is an iron head with 9.45:1 and I can use 87/89, but prefer 91+.

Thanks for the info

Here's my problem static compression is just that. What the volume of the cylinder,piston,head gasket, chamber and valve will compress to on a given amount in a stroke. Dynamic compression takes into consideration the points of the cam values.

I'm not a pro motor builder and haven't built marine motors at all. im trying to learn what will run from people that have done this type of thing so we can have some stout small blocks that will run dependable. I have no clue what a marine small block will take and live.

I have built a few single cylinder race motors. I can tell you that a 13.5 piston running with a stock type cam will build more cylinder pressure than 93oct can handle and will need race gas to survive. the other end of that add a cam with a lot of overlap and compression is bled off so cylinder pressure is not a problem for pump gas and will make more power with a less stable fuel.

In your motors if you can run 87oct your saving money and making more power than with the higher oct fuel. the flame front travels faster gives a more complete burn and should raise the cylinder pressure. We have spent quite a few hours on the dyno playing with many types of fuel from 87pump to 116 and custom oxy or nitro blends when there were no fuel restrictions

This is a simplified run down on what is going on but I'm just looking for a rule of thumb kind of thing to get me in the ballpark.