Why use a Crossover vs. water pump?
 

Does a seapump pump strong enough to cool the engine? What if the seapump goes bad wouldnt keeping a water-pump be a good idea? I noticed reversion issues. what is reversion exactly?

BBC rebuild, use big keitheckeirt cam or buy procharger?
 

Also I need help on trying to figure out on my bbc427 bored .60 over, would i be better to run a big cam and nice big 345cc matching heads, or go smaller cam / heads and just add procharger. I like big lope and want river poker run boat, so what would be best on gas usage also? currently have bravo x drive. Any and all ideas welcome! block is sitting waiting for decisions!

Running just a sea pump is just fine. Many people switch over to the crossover. If you lost the sea water pump your circulation pump will do nothing because no water is being pumped to it.
Reversion is water being sucked back into the cylinders/exhaust due to cam overlap/exhaust pulses. Also depends on exhaust type where it mixes in the water . Dry exhaust can elminate this.
There is a alot of smart people on here, im sure some will chime in to.

Crossovers are more for the clean look. As stated earlier you lose a seapump you have no water any how. And 345's are way to big for a 427. You need port velocity to build torque. If you do a search in this technical section about heads, reversion, crossovers, cams and blowers you will probably be reading for months. A ton of knowledge on this board. And Welcome to OSO

I thought a crossover is to increase the useable HP, since the water pump is removed??

Exactly. Installing a crossover for just the "bling" factor is gay. ;)

Seriously, the idea of the crossover versus the circulation pump was to provide better belt placement for roots-based superchargers on offshore race engines. It's easier to package a seawater pump driven off the side of the engine. There is also an argument for cam-driven mechanical fuel pumps (more so in the jet boat crowd... also big blower users).

TZ

If you go to a crossover, you lose about 25 lbs per engine and you gain about 5 hp. If you are not careful though, you could gain a bunch of high water pressure issues and blow head and intake gaskets. Unless you are supercharged and only boat in warm water, you will need to use a thermostat. That means that you will need a crossover with a bypass and a matching thermostat housing. The bypass has to be 3/4" to 1" I.D. hose to relieve pressure when the thermostat is closed. Drilling a couple of 1/8 holes on the outside edge of the thermostat will allow air pockets to vent and make the therm. operate more smoothly.

I like the look and one less thing to go wrong, like said if you lose seawater pump you are done anyway !!

I have been using the crossover with bypass and thermostat for 5 or 6? years. Do not expect a speed gain. When used with aftermarket exhaust and big oil cooler the temps are very stable. One less moving part to break and it looks better.
Reversion is a whole other topic that has has to do with big cams and exhaust mismatch. I use a performance roller cam with wet exhaust but I have long risers.

Would you happen to have a picture of the t-stat housing and the holes drilled into the t-stat? I know, simple stuff but I want to do it right and I've never seen it.