What can be made to aŽ 220 HP vortec 2 barrel 305 cui mercruiser from 2003. I need easy 30-40 Hp to go up 2" in prop size.

4 barrel intake? cam?

Its aŽtwin installation in a larger boat

Is it 2 barrel throttle body?

Yes, 2 barrel Vortec intake

what he is asking, is it fuel injected or carbed?

Its Carb.

Read this-

http://www.offshoreonly.com/forums/s...d.php?t=192533

I read an article(in Trailer Boats I believe)a few years back where they swapped out the intake and carb to a four-barrel set-up and picked up like 2-3 mph. I was surprised they got that much.

I did a 2 to 4 install on a buddy's Crownline and picked up 2-3 mph. Used an Edelbrock air gap intake and Edelbrock carb.

I have a 5.0 Volvo Penta vortex setup and swapped it to Holley spread-bore and picked up 3 mph. The VP stuff actually has a 4 barrel manifold and an adapter plate for the factory 2 barrel, so it was no brainier.