It takes on average 20 hp to gain 1 MPH, at best a crossover will give you 5 HP. For a twin engine boat thats 10 HP. So that equates to .5 MPH gain in a twin engine boat. Do not do it if you think you will pick up measurable speed, because you won't. Unless your running a blower or have clearance issues there is just no need!

i agree,i have 2 twin engine boats,both with crossovers,but they are blown engines,i dump some water overboard before it gets to the engine,thats how i control my water pressure,i like 12 to 15 lbs at wot.bye the way,in 80 degree water,my water temp is 120 degreese.i take my reading from the front of the cylinder head.as i said in an earlier post,most na engines do not require a crossover,but it does clean up the appearance of that pretty big block.

The Merc 525SC's had cir pumps.

yep,but didn,t make a lot of hp,or heat,i know because i had a boat with a pair of sc525s,good reliable engines.

****, you know everything, wow now I know who to ask how when i need to check my oil!

not everything,but i have been doing this for a lot of years,and i have learned a lot.

its comments like this that prove what a jerk you are,what are you,my guess is about 12

jj,what kind of boat does your dad have?

eye eye matey

Ive ran crossovers for a long time, and never had any water psi issues.

I dont truly believe that a circulating pump will solve water psi issues. I had a friend who had bone stock 502 mag MPI engines, that had 35psi of water psi. He needed to install psi reliefs.

I look at the cooling system as one big tube. In order for the system pressure to not build excessive pressure, it needs to be able to exit water, somewhat as quickly as it is pumping water into the engine. The merc sea pumps can move ALOT of water. If your exhaust manifolds have restrictive fittings, clogged with rust/silt, etc, you will build alot of psi in the block. The water just cant get out fast enough. To help remedy this, you can install, and i recommend, running dumps off the rear of the intake manifolds water jackets. You can play with line/fitting size until you get your pressure dialed in. As for relief valves, while they do serve a similar purpose, I think they should be more for blowing off psi spikes, such as in a very fast boat or re-entry spikes, where the sea pump isnt making the psi, the force feeding of the pickup is.

I personally like the look of a crossover setup, and the simplicity of it.