water press.
 

what would be excessive water press for a bbc.. wondering what gaskets will take.

Ideally, you would like to keep it below 25psi.

I would be worried if the pressure was over 30 at wot.when I changed drives on a boat one time the pressure was 30 and over.this was due to the fact that the drive had a low water pick-up.this had a ramming affect and bosted the psi.i had to add a relief valve to control the pressure.18-25 psi is what I see now.

Much over 25 is playing with fire with standard head gaskets. If you have MLS head gaskets, then they can take more. However, there is no reason to have that much water pressure. It isn't needed.
Eddie

Probably a dumb question but how do you control the pressure? I have a relief valve on mine, and my guess is that it's relieving all the time. I see 25 all the time on mine, just not sure what to do about it other than hope the relief valve never fails.

-2 imco with LWP

Thanks

You can either have a larger bypass installed or dump some water out of the rear of the intake, or where ever you can. I almost always run a dump from the rear of the intake. This not only dumps off excess water, but it also stop any steam pockets from forming in the rear of the intake and heads.

Where is your bypass installed?
Eddie

Good discussion as I think I might have a problem coming with switching to XR's.

Sorry these pics aren't great, mine is installed just aft of the seawater pump. Dumps off the back where I can't really see it, even with the go-pro. It's worked fine like this for quite some time, just seemed like an expensive potential gamble that the blow off valve keeps operating properly-

http://i47.photobucket.com/albums/f1...ps8164c5a9.jpg

http://i47.photobucket.com/albums/f1...pse3af587c.jpg

How big of a dump is needed? Is it just trial and error?

Another thought I had would be to install a smaller hose fitting say just before the sea strainer. What I mean is take the 1.25 inch hose down to 3/4(as an example) then back into the sea strainer. Reducing the flow should decrease the pressure down stream. Rite? Or is this a bad idea for some other reason I'm not thinking of

Also, where is the pressure sensor normally located?

better pic

http://i47.photobucket.com/albums/f1...ps240f347d.jpg

not sure if you got my pm but im having the same problem with too much pressure. even with the overboard dump system I still have greater than 35 psi at 100mph. at 75mph the dump system looks like a water hose on high, think its 7/8in, but it still cant keep up. I have an imco sc lower lwp on my htm and going to try a reducer on the intake side of sea pump tomorrow. its a machined piece of aluminum that slides into the intake of sea pump. it has a small flange to not go to far into pump and reduces the about 1 inch hole on pump to about 1/2 inch. hopefully this will allow my dump system to be able to keep up with the excess water. even with the smallest crank and largest sea pump pulleys I had 7 psi idleing and around 35 at 90mph and about 37-38 at 102mph. gauge pegs at 35psi. like I said blow off was working but looked to be maxed out at top speed shooting a 7/8 stream past the outdrive at 75mph. I couldn't find a buddy to look at 100mph:) I think it will fix the problem, easier than welding up the intake on lower unit. ill be back! send me your email if you want some pics of the reducer. I have hell posting pics on here.

here lately my forehead but for the motor, mines on the front top where the thermostat would normally be. on the housing that sends water to each side of exhaust.

posting reducer pic for la/stryker

http://i47.photobucket.com/albums/f1...ps59ec1853.jpg

http://i47.photobucket.com/albums/f1...ps10062503.jpg

How about just a dump instead of a relief valve?

I put a restrictor in the in let of the water pump today. I'll see if it takes care of my pressure problem tomorrow. If it doesn't I am going to add a .375 dump out of my exhaust manifolds. I used a 3/4" pipe to 3/8" pipe bushing.

Id be cautious about limiting my flow into the pump, it may take the pump longer to prime. Aka, eat impellers faster.

I believe chocking the supply hose down will increase the pressure and decrease the volume. Not a good idea in my mind.

The orifice is about equal to an XR lower.

As far as increasing the pressure? Physically impossible. However, the velocity can increase through a smaller orifice.

doesn't a 496 run some sort of high pressure like 40-43. why are they different if this is correct

496 is closed cooling. That is only pressure to the heat exchanger.

Do what you have to do limit the pressure . Limiting the volume to kill the pressure is not a good idea . You need that volume to carry away the heat . Overboard dumps or dumping from the rear of the intake to the headers is more viable in my humble opinion .

Ran it today and I have no volume issues. I also added a pressure relief valve along with the restrictor...I still blew another water pump gasket. When the imco intake is AT LEAST 4 times bigger than an XR I dont see a problem with trying to get it back to where it was.

Try 3M weatherstrip adhesive for that waterpump gasket.

I sugest that because RTV is probably letting you down.

Then again, I've never had to replace a factory waterpumps housing gasket.

Side note to go along with the thread:

I had an engine on the dyno that went 40+psi water psi (I think it spiked to 60) and the motor leaked water thru head gasket and intake gasket.

The issue for the high psi was a t-stat was left in the housing on a crossover system with no bypass.

Bypass was added, a few small holes drilled in t-stat, and a Merc water psi regulator was added. Replaced gaskets and problem solved.

I had to stack 2 gaskets, I used permatex between them and glued them with gasket spray adhesive on the mating surfaces.

I have pick ups I`ve been trimming down to get the pressure to where I want it, I also have 2 -4AN dumps on the back of the intakes and a 15psi -8AN pressure relief valve . I`ve finally gotten to below 20psi @ wot.
12ish cruising.


Nice thing about a relief valve is that you wont lose pressure down in the lower rpm range.

I have reduced discharge EMI tails so I think the dumps might work well.

OK, I added two 1/2" dump lines, one out of each manifold. I have the relief valve right before the oil cooler. I removed the restrictor before the water pump. Took for a test drive and water pressure went over 35psi at 50mph. Put the restrictor back in and it put me right where I needed to be at ~25psi. I still could not believe the amount that pumps out the dumps at idle even with the 1/2" restrictor.

I have 5/8 and 3/4 lines and fittings to try but atleast I know I can go boating without blowing out gaskets.

JRider

Why do the pressures get so high?

Well, I think the main cause is the size of the inlet on the imco lower. It is like 1/2" x 4" slot. Though I am wondering if there is something goofy with the pulley sizes.