THREE QUESTIONS
#1.where should you put the block-off plate or gasket on top of the manifold or on top of the spacer ?
#2.will a gasket do as a block-off or should you use a ss plate between two gaskets ?
#3 has anyone had any experience experience with ceramic paint using it on your exhaust system inside and out ?
Howdy,
Welcome aboard!
1. The plate should be BETWEEN gaskets on top of the spacer. That will require you to put coolant exit fittings in the spacers but there's 3/4" NPT threads there. If you Block off below the spacer, then you have to port raw water to the spacer so it can exit through the spacer jacket and into the riser. having coolant going through the spacer makes it last as long as the closed cooled manifold (forever!)
If you're working on a Mercruiser, the OEM block-off "gasket is a thin flexible stainless steel "plate" with gasket "material" on both sides.
2. see #1. You could make a block-off plate and make your own gaskets too as long as you "sandwich" the plate between the gaskets.
3. I wouldn't expect it to work since it's nearly impossible to get paint to stick permanently to cast iron.
A better way might be to buy new manifolds and have them ceramic coated by a company such as the following
https://www.performancecoatings.com/exhaust-coating
I had them do a set of truck manifolds but the manifolds were brand new. and they did a beautiful job!
They also told me it wouldn't work on manifolds that have been used for very long.
I didn't ask them about coating manifolds used in a closed cooled marine engine but they mention "marine applications" . I have closed cooling on my 1997 7.4L Mercruiser. It's worked well for more than 14 years and I wouldn't have an I/O without it! (salt or fresh)
If you have a Small Block GM engine or a 496, consider getting "dryjoint" manifolds and risers. They're "blocked-off" right out of the box!
It's more helpful if you post your engine/drive serial numbers. It makes it easier to know what you're working on.
Regards,
Rick
