Klaw-Performance marine use to make their own popet valve system. It was somewhat simular to Merc's design, but not as evolved. It also costed about the same....

I'd first get on the water, and then address the problem. You may just get lucky and not need them.

Looks simple enough to make and simple in design (Thinking here) ....
any patents? $100 is kind of high in my opinion.

The question remains, what are the connection sizes for Part # 863208A3?

1 1/4" on the input and output and 1" on the relief. Hope to hook mine up this week. Will let everyone know the results after next weekend.

Faster,
You are the man! That is exactly what I wanted to hear.
Placing my order today.
Thanks!
Russ

I got my relief valve plumbed in Friday night and ran all weekend. Before I was pegging the gauge past 35 psi at anything above 55 mph. With the valve I am running between 20 and 25 psi regardless of speed.

Where are they installed on a system? After the sea water pump?

I put mine between the sea water pump and crossover.

Do you think that the direction of water flow, as stated in the instructions, has a bearing on it's performance? I have seen pics on this site where the over pressure discharge is opposite of what's stated in the Mercury instructions.

Here is a picture of the over pressure discharge opposite of the supply flow.
Personally, I don't think it matters due to the fact that when it opens the water will take the path of least resistance, regardless of direction.