offthefront

iTrader: (1)

So ...... remove the heat exchanger ... loose the weight .... 25,000 motor .....

fstboater

You can probably find .233 mph increase after much time and money just run with a 1/2 tank of gas for the same results.You will have a hard time getting your temp up to the level for the efi to work right. Unless you are supercharging leave it alone but the seawater pump will be fine no closed cooling and no circulation pump along with low temps you can get into hi water pressure problems. Lab your props and pick up a couple of mph for less bucks and better results.

Codered

I'm some what confused. With crossovers you talk about dialing in water pressures and temperatures yet all the manufacturers and dealers that sell these setups say bolt it on and ride. Now I realize they are the ones making money off of the sale . But whats the truth ? This has to be the MOST talked about subject on this forum. For the record I put a crossover on a carburated 454 Magnum and was not impressed and it was a top grade crossover

offthefront

iTrader: (1)

you were not impressed ? explain ....

Mudball

Crossovers DON'T work if you want a thermostat out of the box!!
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I just went through the crossover ordeal myself...Finally got it working fine.
1. No thermostat = no temps, good water pressure = too cold running for an N/A motor.
2. Thermostat = good temps, high water pressure = blown hoses, head gaskets or intake gaskets.
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Here's what works, if you want to run a thermostat:
1. Use a crossover with a bypass. You need the bypass for keeping the exhaust cool when the thermostat is closed.
2. Drill 2 to 4 3/16" holes in the thermostat inside the sealing lip. This allows air and steam to escape when the thermostat is closed, and allows some hot water to escape to the top of the thermostat. This also helps equalize the side to side temps somehow.
3. Use a pressure relief valve to control water pressure. The Mercury Racing part is a good one. It goes inline anywhere between the seawater pump and the crossover. A 1" dump goes overboard. Sorry, I don't have the P/N handy. They cost a little over $100, except at Bam, where they doubled the price for some reason recently.

Voila! A fully working crossover system with a thermostat..
Kent

Codered

When I say I was not Impressed I mean I used a thermostat with the holes drilled in it by the supplier also it was the right degree thermostat. It also has a bypass. I noticed a slightly elevated engine temp.And what seemed to be excess steam from the exhaust. Everything else on engine is OK ,riser gaskets, Impeller ect.I have a hard time believing that by removing a circ. pump it increases water pressure ,with all the restrictions in the cooling system . If water pressure is a issue with these systems why don't the manufacturers offer relief valve kits with the systems. I am under the impression the steam could be coming from the fact that without a circ.pump to build pressure in the block steam pockets form.Again this doesn't appear to be as cut and dry a modification as the manufacturers make it out to be or is it

offthefront

iTrader: (1)

Thats pretty much what ever one realizes ....I don't think you can claim better performance ..My 454's had em when I bought the boat ...First thing I did was loose a sea pump and cooked a motor ....If I had a Circulating pump it might have saved the motor by buying me more time. My Merc Mechanic went nuts when he saw them ...I spent alot of $$ converting both motors back over. Water Temp and Oil Pressure alarms had also been removed .... I learned ALOT fast ...($$$$) . It is doable because there are alot of em out there ....but you need to really know what your doing and what to keep tabs on ... Main thing for me is the Clean and cool look .....most will not admit that .... Would I go back ? I might ....but you definitely roll the dice when you do .... I still have mine ...... on the Shelf .....

88Fount33

I went to Crossovers with no bypass, no thermostats on stock 330's. Then installed Oil Temp Thermostats to get some oil heat, with larger (racing) oil coolers. Had heat issues with stbd. motor for water and oil after 10 min WOT. No debris or impeller vanes loose, new seawater pumps did not fix issue of "tired" motor. Drilled 6-1/4" inch holes in Thermos and reinstalled. 10 min WOT now gives 110-120 Water and 190-200 oil. Fuel level and traffic in channel limited longer run.

offthefront

iTrader: (1)

88FOUNT33 .. key to your app is 110-120 water temp .... to me that is TOO cool ....motor shoul be min 150 .... my .02

what temps you run just cruising or slow speed zones ? Motor need to be hot enough to disscourage condensation ...maybe you need to have less holes in Thermo ? This is typical results I have seen ... not being consistant across operating range ...

Mudball

I forgot to mention that if you are running a crossover, you should run a water pressure gauge. This will also tell you if the seawater pump is getting weak. I am running a Gaffrig mechanical with the nylon tube in the block.

I ran the thermostat without the relief valve at first. The water pressure gauge was PEGGED at beyond 35psi at 2,500rpm! It then blew off the hose at the crossover.
A fellow on the 'other' board had his engine milkshake on the dyno from this. Others have had this happen, too.

I believe that the four large holes that 88Fount33 is running likely has the same affect as the bypass. It would be very interesting to see what the water pressure is on that motor....

If you look at how a stock setup works, they just don't have water pressure issues. With a crossover and a closed thermostat, the seawater pump is basically deadheaded. And the thermostat restricts flow, increasing water pressure even when it is open.
Kent