I have a 87 454 mercruiser with closed cooling system I want to change over to the 496 exhaust manifolds and risers , but not sure exactly how to plumb the cooling hoses. Has anyone done this swap before I know its been done with the raw water cooling, I may be over thinking this but I just want to make sure I get it correct.. Thanks Jamie

Anyone ??

Ayuh,.... What BBC exhaust manifolds are you callin' 496 manifolds,..??

Your manifolds now are in the closed loop?
The water supply that cools the closed loop should just run out through the manifolds

Bondo , they are the mercruiser 496 ho manifolds]

Need a picture of your current thermostat housing. It can be done.

Chris

http://www.crowleymarine.com/parts/2...q=22-862210A01

This is what I used in the bottom of the 496 manifolds.

https://www.wholesalemarine.com/ther...FQERaQodPwMLvw

This is what my thermostat housing looks like.

The manifolds and risers are not used as part of the closed cooling system, they get raw water. Next you cannot use that thermostat housing with closed cooling. This is a 496 cooling but note raw water goes in the bottom and comes out the top.

[ATTACH=CONFIG]565449[/ATTACH]

This is my guess of what you want to do. Would need different manifolds

[ATTACH=CONFIG]565450[/ATTACH]

You don't need to use both inlets on the bottom of the 496 manifold. Use the one that points forward and plug the bottom. or change the unit to a 90* fitting

Ayuh,... 'n Hopefully the H/E is big enough to include the manifolds,...