I have a set of 502 gil/mercury performance risers that look very much like the risers that came on my mercury performance 450hp (454 block with mercury performance exhaust manifolds). The design appears very similar except there is a small valve/opening (maybe 1/4") at about the mid point of the bottom of the 502 riser where it appears water can go somewhere (this does not exist on the 450hp riser? What is this opening for, where would water go/flow? Both use the same gasket/part # so I assume they will bolt up and they appear I can get them into the boots that push the exhaust through the transom.

I am considering this change because I am chasing a hot engine and I am wondering if there is some salt or other damage in the existing risers - how would I test for this?

Thank-you!

If I am correctly picturing your description, the hole on the riser connects to the manifold. Let me see if I can dig up a photo
Ryan






I have a set of risers hat have the hose nipples welded on and another set that has a bung for a hose nipple to thread into.

I was told its to reduce steam pockets.

the 2nd pic listed is like the gil/merc perf risers I am considering installing. the existing risers look like this (sorry the pic doesn't focus on risers).

[ATTACH=CONFIG]557411[/ATTACH]

Correct.

and IMO, it changes nothing related to engine water temp. It just may slightly help the manifold and risers from getting hot spots.