So your saying you picked up 150+ HP just by changing the heads, intake and carb. And now your going to put in Madera rollers. How much do you think a 2 bolt cast bottom end can take? All Mercs 370 HP and up use 4 bolt mains and all forged internals along with retangular port open chamber heads. Sounds like your going to have an awsome holeshot with all that torque but run out of breath upstairs, that is if the bottom end and outdrives hold up.

I used to have a 10:1 solid cam engine that had studded 2 bolt mains that turned 5500 - 6000 all summer long. Now it is in a Mud Truck somewhere in Kansas. Don't underestimate the potential of a 2 bolt block.

Depending on the year most 330HP BBC had the 4 bolt main block. The bad thing is the cast crank, pistons & rods.

Yes my motors do have 4 bolt mains, Although it is a cast crank, I am not trying to make 500 HP. This original question was about oval port heads making affordable power. When you can make 475+ HP with just heads,intake,carb,& cam and all can be bought used if you want. I would say a cast crank in a mercruiser motor can last many of hours when it is run sensible, and with the stock ign. with the rev limiter. I can say you could get 330's to 425 HP for under $1500 a motor with "some" used parts.If a stock peanut port head motor can run @ 5000 rpm, Then why couldn't a ported large oval head motor run@ the same rpm?

Your key factor is the exhaust. Make sure yo umake that decision before yo udecide on a camshaft.

I have hand ported & port matched imco powerflow's

That's cool. Your on the right track then
'

I can honestly say I have put 330 bottome ends to the test. Ran them hard at over 480hp for years. Good balancing is important in my opinion. The inexpensive HP is what I am amazed with. That's awesome.

Yep and it has seen 6500 a few times

we raced a 2 bolt cast crank & rods for 2 years, running to 6500 every run..never had a issue..so yes that stuff holds up fine !!! valve train failures are more of a concern...Rob