Hey guys, I need help. Rebuilt HP500 last year. Added AFR heads, Keith Eickert cast aluminum headers and 3'' oil cooler. Other parts too but nothing that would mess with water pressure. Still using the recirculation pump. I have tried a bypass valve with 1/2 id hose just after the sea water pump. helped but not enough. Tried diverting water off the top hose on the manifolds, before the tips with 1/2 id hoses. Not much improvement. 30 psi at 4000, 35 + psi at 5000. I see others using the Merc bypass vavle. It looks like it uses a 1'' or larger hose. I was going to use 3/4 id hoses off the top of the manifolds and use the bypass valve next . Drive has the dual water inlets. Any thoughts or ideas?

Is this WP higher than it was? Still using the stock sea water pump? If the answer to both is yes, it sounds like the water exits in the new exhaust may be the place to look for the restriction.
Another thought, is the WP at a new MPH level?

The Merc water relief valve assy uses a 1" hose as the discharge line. Part #863208A 3 Yeah Yeah Yeah, I read those posts about those homemade valves. Here is some advice: Leave the "homemade" to pie making. When it comes to performance boat parts of this caliber, stick with Merc Racing. How do you like your KE's?

Thanks for the replies. Yes water pressure is higher than before rebuild and exhaust system change. Factory style sea water pump.

KE's are great so far. Looks could be better but no worries about developing leaks like stainless steel. I talked to Keith Eickert the other day and it does not sound like the manifolds could be causing the problem. The tips on the other hand may not be able to let the water exit well enough. I am re plumbing the hoses to 3/4'' off the top of the exhaust manifold. Trail and error until I figure out the right combination. Seems like the side of error occurs more often that not.

How does the water exit the tail pipes?

I have tried the 6'' factory tips with rubber coupler to through hull tips. Currently I have dry tips from manifolds to outside of transom. The dry tips don't seem to flow water as well as the 6'' tips. Either setup has too much pressure.