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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!

Quote:

Originally Posted by endeavour32 (Post 3613495)

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.

Quote:

Originally Posted by US1 Fountain (Post 3613828)

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.

Quote:

Originally Posted by mike tkach (Post 3613236)

blower belt clearance is not an issue on marine engines because of the 3 groove pulley on the crank,because of this,the blower drive snout is longer,and the belt is farther foreward,and can you explain how slowing the flow of water down before it enters the engine,has anything to do with heat transfer inside the engine,and one more thing,mercury did not design the circulating pump,they have been around longer than mercury has been.why post information that is not factuial,all you do is confuse people,like yourself,that dont know the facts.dont take it pearsonal,its just the way it is!

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

:thankyouthankyou:

Quote:

Originally Posted by JJONES (Post 3613880)

****,you know everything, wow:eekdrop:

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

Quote:

Originally Posted by JJONES (Post 3613882)

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

its comments like this that prove what a jerk you are,what are you,my guess is about 12:7160:

jj,what kind of boat does your dad have?

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.