Exhaust Risers 4.3 L V6 carburated

[ANGEL RONDON]

The spacer 3 inch on my 1997 Bayliner has elongated holes on all 4 sides. But the gasket has elongated holes on two sides and the other two the gasket has a small hole on two sides instead of the elongated cut out. Can anyone tell me what is the purpose of the two holes in the gasket, since the remove spacer was heavily clogged and carbonize where those holes are. Is there a reason for restricting the exhaust in that manner on the mercruiser engine. You would think the gasket would match the spacer. Any responses would be appreciated since I am tempted to cut out the restraining portion of the gasket to match the spacer. /s/ Angel

 

[Scott06]

I think merc used the restrictor gasket with the warm manifold cooling setup. If you have a cooling hose feeding the bottom of the manifold and a separate cooling hose feeding the elbows, the restrictor gasket is used. If you have the cold manifolds where the constant flow of cooling water where one hose feeds the manifold with out a separate feed to the elbows the water goes through the manifold to the elbows , you use the full port open gaskets.
The warm manifolds use hot cooling water that comes off the thermostat after it opens, vs a constant flow of incoming cold water. The idea was that if the manifolds were warm like the block and heads they wouldnt get condensation in them. Both systems work.

 

[achris]

He's talking wet-joint exhaust manifold/elbow gaskets. The small holes are to relieve air from being trapped as a pocket under the gasket. The reason the holes on the sides are small is so the majority of water flow goes the way the designer of the system wants it to, without too much going where it isn't wanted.

 

[nola mike]

Any good write ups on the exhaust system workings? I've seen all the flow diagrams and am still baffled at all the hoses from the tstat housing, why I have separate lines to the manifolds and elbows, where the tstat diverts the flow (seems like not just block/radiator like a car), etc. I probably should have paid more attention to the housing and stat when I put it together. Scott's is the first I've seen that makes some sense (but Chris is saying that's only for dry joint exhaust?)

 

[Scott06]

this may help some https://www.perfprotech.com/blog/articles/warm-manifold-cooling-tips

I wrote I belive cause I wasnt 100% sure...

 

[ANGEL RONDON]

I think merc used the restrictor gasket with the warm manifold cooling setup. If you have a cooling hose feeding the bottom of the manifold and a separate cooling hose feeding the elbows, the restrictor gasket is used. If you have the cold manifolds where the constant flow of cooling water where one hose feeds the manifold with out a separate feed to the elbows the water goes through the manifold to the elbows , you use the full port open gaskets.
The warm manifolds use hot cooling water that comes off the thermostat after it opens, vs a constant flow of incoming cold water. The idea was that if the manifolds were warm like the block and heads they wouldnt get condensation in them. Both systems work.

Thanks to everyone who answered my inquiry. You response was right on the money as to the way my set up is. I guess I wont be cutting the gasket.
Again Thanks a million Scott06
/s/ Angel

 

[ANGEL RONDON]

He's talking wet-joint exhaust manifold/elbow gaskets. The small holes are to relieve air from being trapped as a pocket under the gasket. The reason the holes on the sides are small is so the majority of water flow goes the way the designer of the system wants it to, without too much going where it isn't wanted.

Thank you for your timely response. /s/ Angel

 

[ANGEL RONDON]

this may help some https://www.perfprotech.com/blog/articles/warm-manifold-cooling-tips

I wrote I belive cause I wasnt 100% sure...

Great article. thank you for taking out the time to research this. /s/ Angel