Jana,
Thanks. It seems the 500's don't have the problem, which still makes me suspect the thermostat housing on the later 502's and 454's. My water pressure at idle is about 2-3 lbs.

Dan

2k 29' 500HP EFI 25#+ Wide open ... Low water pickup Bravo.

Sea Dated,
I spoke with Gary @ Grimes Auto Marine in GA who makes the water pressure relief system that MIKEHTMSR24 and RumRunner were speaking of. A very knowledgeable person with race boats. He was evolved with Don Johnson's race boat. That boat had a dump system because of high pressure.

He believes my restriction might be in my tail pipes, not the number of holes in them but the amount of room between the two-jacketed tubes. To confirm this he wants me to tee off the thermostat the hoses that run to the manifolds. I am supposed to put a gate valve in line and have the end of the hoses run over the side. He wants me to run the boat up to 3500 and check the water pressure. Then both valves are to be opened evenly till my pressure drops to 20 lbs. then I am supposed to take it to WOT and repeat to get the pressure to 20lbs. During this time I need to monitor the engine temperature to make sure there is no fluctuation.

The next step is to leave the valves open and bring the boat back to idle. I need to keep an eye on the engine temperature, pressure and riser temperature. If every thing stays the same I can run a dump system without a pressure valve otherwise I need some sort of valve to keep the system with some pressure. The numbers we want for optimal performance is 18- 24. Anything under 16 lbs. at WOT can cause hot spots in the heads. Anything over 24 can cause gasket failure.

I plan to try this set up next week and will make a decision on what to do. The other option would be new exhaust. My current exhaust is mercury/Gill manifolds with Rex Marine power flow tail pipes.

Dan

candyman, mine is also the Merc/Gil exhaust. The clearance between the two pipes is more than enough to flow whatever your pump can pump. There is around a 3/16" space all the way around between the 2 pipes. If the exhaust is the restriction, it has to be the 3 holes that are drilled in the end of the pipes. Possibly they are plugged up some?????? Don't you have 2 hoses going to each exhaust? 1 to bottom of manifold, 1 to the tee at the manifold/riser bypass hose. It would seem the easiest check would be to simply run one of the hoses at that tee overboard. If your pressure comes in check, that would mean your problem is in the riser itself, and not the stat housing or the ex. manifold. If the risers do prove to be the restriction, open the holes up some with a dremel.

US1 Fountain,
There is only one hose on the newer 454's and 502's. The hose goes to the exhaust manifold. The water flow then goes through a by-pass hose to the riser. I was thinking of going to the two hose system with the tee at the riser. But after speaking with Gill and Rex that shouldn't be the problem. The risers are not from Gill they are from Rex Marine.

I like the relief system you came up with for your motor with the crossover.

I can't wait to hear some more numbers from members with 454's and 502's in single, twin or triple’s.

Thanks for the responses,
Dan

Dan, your right. Whether there are 1 or 2 hoses really makes no difference. It all still has to flow thru the risers.

Hey, I got an idea. Run without the risers, That'll say if they are the culprit.

Good Luck
Jerry

US1 Fountain,

When I saw your name I thought you were going to post 0 lbs.
Hopefully it's something cheap and stupid. I have been paying 70.00 for the Seawater rebuild kits. I hate paying list prices.

Dan

i had the big 0 psi today. i forgot to swtich my valves and burned up my impeller. damn damn damn.

Good one!

Yeah, it was something stupid, but never cheap! Damn muffs!

where is the best place to get the sea water rebuild kits?