i don't know if i am using the proper terminology, but it replaces the circ pump on a big block chevy w/ stainless steel piping- what is to be gained?? is it worthwhile to replace the stock circ pump? what will i gain for the money????

Not worth the trouble on a basically stock engine.

Do a search on it, they seem to have more problems than they are worth. It's a hard system to set up properly. Unless you are running a blower motor without a thermostat I wouldn't waste my time.

Nothing ... except a major PITA!

I have posted this question before, so i,ll try again . I bought a crossover for a stock carb. 365 magnum . I totally agree with everyone PITA not worth the trouble But why do the companies that make and sell them say just bolt on and ride . Nothing is ever said about water pressure relief valves or any of the other 25 problems that arise as opposed to a stock set up. That must be why merc has them on their motors.

JUST DON"T DO IT!!!! I have seen many problems with circulation & overheating with crossovers. The very small if any performance gain you may see is NOT worth the troubles.

I've never seen the claim of "bolt on and ride". I have seen claims of 10hp which isn't even worth the money.

I have had my ups and downs with crossover systems. I presently use one with excellent results. I also use a Mercury Racing Oil T-Stat filter mount to control oil temps and a Mercury Racing Water Pressure relief valve.
I run a 142* Water T-Stat with (3) 3/16" holes drilled in it. Crossover also has a bypass with a 3/8" orifice installed in the 5/8" hose. I have no problems with temps or pressures.
There are many variables to consider when designing a water or oil system.
I agree, it is not a bolt on system. Use what works for you.

If your set on getting one, just make sure you have a pressure relief valve and you will be all right.

I've been running crossovers for years and never had a problem with them. However, if you're going to use a thermostat, you have to get the kind of crossover with a bypass hose to supply the exhaust with water when the thermostat is closed. This also relieves some of the water pressure. Drilling 3 3/16 holes around the perimeter of the themostat will even out the temperature fluctuations some people experience. In some cases, people use a pressure relief valve but I've never had to.