Why are alot of high performance engines raw water cooled? Is it because of short life on high performance motors?

Im thinking of building a small block chevy for my boat and was wondering if the merc crusier closed cooling system would keep up with the heat. I would like to include new aluminum exhaust manifolds in the system.

Also any recipe suggestions would be helpful (comp ratios, cam lift/durations) because there is a good deal 350/dart heads (low miles) motor that with a cam/bearing/oil pump change would work nicely but was wondering about exhaust draw back(cam) and aluminum corrosion heads and intake.

The boat is a 18.5 powerplay with 350 and a Alpha ss drive crank mounted raw water pump and thru hull exhaust(in need of mufflers)

Thanx For The Help
Daddio

I don't know the specifics, but I understand that when they increase HP on closed cooling system motors they have to build a bigger heat exchanger. In your case since it is a small block you could possibly use one from a big block and still have sufficient cooling. Hopefully someone here has more info on this subject.

Mark

I have closed cooling on my motor because I leave mine in the water all season. I can't pull it and flush it out after every run. The nice thing about having it beside motor longevity is the temperatures stay much more consistant in the motor. I sit right at 165-175 no matter what the outside water temp is and that seems to be good for overall performance and just good for efficiency too. These motors seem to be happier once they get a little temperature in them. My motor is a 502mpi. I have a half system on my boat so the motor is cooled with coolant and the exhaust is raw water cooled. I took my risers off a couple of weeks ago and everything looked about like it did in the beginning of the season even after running all that salt water through them. I think you can only benefit from having the system on there for the motor though especially if the boat is in all season.

The only drawbacks are additional weight and the limitation on the size of the heat exchanger.

As was mentioned, a big block sized heat exchanger should take care of a healthy smallblock. You'll find that most kits keep the exhaust mans seawater cooled. This is what you'll want to do, as it keeps the heat exchanger capacity dedicated to the engine itself.

If you are making your own kit, there are HUUUUGE heat exchangers available for marine diesel apps. You'll need to size the raw pump to the system requirements. Not sure how much an Alpha pump will flow.

I have closed cooling on 600hp 540 ci motors, works great. I will recomend it!!

/Torbjorn

The main reason Mercruiser installs closed cooling on the new 496's, etc..., is to help the computer control internal engine coolant & oil temperatures. This could not be accomplished with raw water cooling. Everything regarding engine perforformance is now completely controled by the engines computer, just as they are in any new GM car or truck. Ed

Can you tell us some specifics on size of pump and heat exchangers?

The pump in the drive is used as a drive shower with a fitting in the transom just dumping water on the top of the drive.
The crank pump is a full cam pump (big block) which should flow plenty of water thru 1 1/4 transom pickup.
My boat lives in the water which is a nother for wanting to close the cooling system. I have a line on a 300hp small block exchanger but am unsure if it will be big enough for my needs.
Any suggestions on cam ?? I remember seeing a thread once but cant find it now.

Thanx for the help
Daddio

A 300hp exchanger will live a hard life on a 400hp smallblock. I guess it depends on your summer water (as in the ocean or lake water) temps as much as anything.

I have an 18hp marine diesel continuous duty motor with a heat exchanger 3.5" diameter x 16" long.

I have 340 horse Cats with aftercoolers in the coolant loop that have exchangers 7" diam x 30" long.

Xchangers on a 660 Cat are about 14" x 10" x 36" long.
An 800 Cat has basically two of the 660 Cat coolers (they might be a little shorter).

I had a fresh cooled 350hp 454 (Crusader) that had an exchanger about 4" diam by 26" long.

Remember also, that corrosion and scale reduced the heat transfer of an exchanger by about half over time. A larger exchanger will let you go longer between scrubouts.