Ok standard big blocks
I was wondering whom has tried these bypass tubes
(they go in place of the "water pump" on the front of the engine eliminating the drag on the engine and the sea pump is then what circulates the water into the engine.
I want to know your results from using them and what you have found - pro's and con's
Also, where the heck did you get them?
Let me know
thanks!

It's called a crossover.
There are several different versions: with/without thermostat, preheat, etc.
Rex, CP, Stainless Marine, and others sell them.
If you're using it to gain hp, forget it. It's not worth the money. The merc cooling system works fine at maintaining correct engine temp.
My $0.02
Gary

I've had by- passes on a number of boats and things SEEMED to work out ok. Having said that, I will be re-installing circulating pumps back on motors at my next opportunity. As a good freind who is very conversant in marine cooling systems says "just because your water temp gauge read OK and you made it back to the dock does NOT mean that everything is peachy in your engine". - Good luck - Jeff

i put them on my motors for the simple fact that they sit so far forward in the engine bay i would hve to pull the dayum motor if i ever had a problem. My opinion is it is one less thing to worry about going bad also it cleans up a motor quite abit.

You need to be very carefull as they can increase your water preasure quite a bit.

I run the setup with out a problem so far , it does clean up the front of the motor , it DOES NOT give you a noticable increase in performance
i run it w/o a thermostat for cooling water , but with a thermostat at the oil cooler , your oil HAS to get up to 220 or so to burn off condensation
my water temp ranges between 115 and 135 depending on how hard i'm running , and oil between 200 and 220
aside from all that , only thing that the kits dont give you is updated belts , i had to measure and go to my local car parts store and buy belts that fit correctly after removing the water pump

Can someone explain why this can be the case? The circulation pump itself is passive, (compared to the raw water pump).

I am looking to ditch my circ pumps, DON'T want to cause any issues on fresh rebuilds though.....

Simply put guys, look at the most successful and plentiful performance motor to date: Merc Racing HP500
Merc saw fit to have that motor (and it's bigger brother the HP525) with a recir pump. When you look at the reasons why, you will have answered your own questions. Consistency.

I can agree with that train of thought. That is also pretty much what I am reading here an on the other forums at this point.

I guess, why mess with a system that works, right?

If you are looking for a pump that out performs the stock unit, rebuildable and looks great, here ya go.
http://www.meziere.com/ps-1211-1179-wp400up.aspx