So what should the water pressure be on a 502 mag efi with KE headers? I built a new motor over the winter and I just got her going. Well I installed a water guage for the first time. I'm getting close to 5lbs at idle and If I bump it up to 1200rpm I get about 13psi of pressure without even moving the boat. I can actuall free rev it and get 22or23psi. Once I get on plane I'm running about 40psi, and today I ran her up to 5k and got 55psi (aprox 70mph)

Motor specs are as follows
Stock 502 mag bottom end
AFR 315 heads,
Crane 741,
Holley single plane Efi intake,
Keith Eickert headers,
Still runing the Circ pump.
Only thing I changed with the water is I added a Hardin 3"x19" oil cooler, a 2"x12" fuel cooler, changed the T-stat to a 140, and rebuilt the stock water pump with a merc kit. My drive has low water pickup and the regular pickup (bravo 1x)

Anyone got any guesses?

Frank

Frank
I was told that with the low water pickups and higher performance motors you need to install a pressure relief valve and vent the excess water either into the exhaust or out through the hull. We had to do this on my hp 500s this spring.
Don't ask me about specs or the specifics on how to hook it up. I'll be the first to admit that i have to hire mechanics to do that stuff for me. Hope this helps.
Jim

Assuming that the gauge is correct, there is an obstruction some where that is causing the water passage to be semi blocked,(sand, Thermostat not all the way open etc) which is increasing the pressure. The dual pickup drive does increase pressure, but not by that much. My single, low water pickup reads 12 lbs at 5800 RPM. nothing on the hose or ideling, and I have the same system as you, except I have a restrictor instead of teh thermostat.

Where is your gauge reading from?

I'm going to try removing the thermostat tomorrow and see what that does. I backflushed everything yesterday to see if there was some type of obstruction and everything flowed very free.

If the t-stat doesn't work I'm just going to run a 5/8" hose from my intake to my A/C through hull and dump some water overboard, just to see what that does.

I wan't to get this under control before I blow a gasket out. I have cometic head gaskets and felpro intakes.

Frank

Can you post a picture of your water system rigging? Did you change any exit water hoses? What exhaust system did the KE exhaust system replace? Are you measuring water pressure after all the new coolers? Is the WP measured at the intake manifold?
It sounds like maybe the KE exhaust may be restricting the water flow and raising the WP...need more info.

I have my water pressure gauge hooked up to the bottom of the block, and a 2nd guage (oil pressure) hooked to the intake. My water gauge only goes to 30 psi, that's why I added the other one.

Frank

I was thinking along those same lines. I'm wondering if the KE's, since they are so much taller and bigger than the merc manifold, are restricting the flow because I have to push all of that water up the header.

I'm measuring the water pressure both at the bottom of the block and at the intake manifold.

I didn't change any configuration of the stock merc water routing. The KE's have 1 water inlet at the bottom just like the stockers did.

Thanks,
Frank

im currently having the same problem. same drives as you. put duck tape over the LWP holes and reduced pressure from 30 psi at WOT to 20 psi at wot. going to install the relief valve kits. merc #863208A3

The gauge on the block could easiely have junk in it from the block. The intake one is the best place to mount it.

You could have a restriction in your exhaust, as was mentioned, but its not from having to push the water up hill. The stock system has to push a lot of water up hill from cool fuel to the Stat housing. (and from the pump to the back of the motor) BUT you could have some junk in the headers water passage.

A couple of days ago I took the hose off the top and bottom of the headers and ran water from the top down to see if I had any crap in there. They flowed as much water as I could throw at them. I never did try the tail pipes though. But I did backflush from the T-stat housing to the water pump and it was very free flowing.

Thanks,
Frank