How Much Drop From Elbow to Muffler

[Richard Seccombe]

Hi Everyone,


I am replacing the manifolds, risers, and elbows on Mercruiser 8.1S Horizon engines. The reason for the replacement is because the elbow/riser studs continually stripped out of the aluminm manifolds (previous post), and now Mercury has gone back to cast iron manifolds.

The current setup has 6 inch risers which put the elbows very high up. The boat was repowered from 454's and I have no way of knowing why the install used the additional risers, or whether it was just because the 454 install used them.

I would prefer to omit the 6 inch risers and just go from manifold to elbow for a cleaner and stronger install. With the current setup, there seems to be a huge drop from the elbows to the mufflers. I understand that there needs to be some drop to prevent seawater from coming back up. Is there any rule of thumb as to how much drop you should have from the elbow to the muffler?

Thanks very much,
Richard

 

[Don S]

Re: How Much Drop From Elbow to Muffler

The spec is MINIMUM of 15" Measured from the water level in the muffler to the top of the exhaust riser. You can hook a clear hose from the drain fitting in the bottom of the muffler and use it to find the water level.
Note:
This is with the MAXIMUM weight you will have on the back of the boat

 

[Richard Seccombe]

Re: How Much Drop From Elbow to Muffler

Thank You Don.

If there isn't a 6" riser being used, and the ebow is being mounted directly to the top of the mainifold, then would I measure from the top of the manifold or at the beginning of the curve in the elbow?

I guess I am assuming that the 6" "riser" is more of an extension in between the manifold and the elbow, and that the elbow incorporates the actual riser.

I included a photo of a 8.1s that shows the engine without the 6" extension to clarify my attempt at describing it. The photo isn't the best but the assembly can be viewed if you click on the thumbnail.


Thanks,
Richard

 

[HT32BSX115]

Re: How Much Drop From Elbow to Muffler

Richard,

Maybe you have already seen this but check your Install manual for the engine.

If you do not have it then go HERE for the Installation manual and turn to page 15 of 116. Exhaust install info is there.

Cheers,


Rick

 

[Don S]

Re: How Much Drop From Elbow to Muffler

Rick,that info is for a Bravo outdrive and is NOT how his inboard is checked. He MUST check from the water level inside the muffler to the top of the riser on his inboard.

You have a 6" extension. The RISER or ELBOW mounts directly on top of the 6" extension. The 15" (Minimum) dimension is taken from the TOP of the Elbow/Riser.

 

[HT32BSX115]

Re: How Much Drop From Elbow to Muffler

Yeah.


I guess I just assumed that his was a Bravo....he must have mentioned inboard on a previous post....

 

[Don S]

Re: How Much Drop From Elbow to Muffler

That and I knew that an 8.1S was an inboard, plus the fact that he mentioned a huge drop from elbow to MUFFLER......... and Bravo's don't have mufflers

 

[HT32BSX115]

Re: How Much Drop From Elbow to Muffler

Well,


Speaking of mufflers, not to hijack this thread.....Since this is right along these lines I suppose it works to ask here......

My boat had the Corsa Capts Call exhaust diverters and the thru hull's are still there. I haven't hooked them up though....I'm just gonna cap them off for the time being....

Straight pipes just plain obnoxious, illegal, and my wife hated them!! so I never used them with the 460.

Now with the Bravo (I have 3inch risers below the elbows) everything pretty much lines up with where the 460 was so I *could* with a little welding on the SS 4" tubing adapt everything and still use them.

I am hearing that the exhaust tip/mufflers that Corsa has like these are actually bearable and legal....

I get the impresion I'll need to have the same 15" from the top of the elbow to the waterline dimension that you indicated above, correct?


btw, how's the wx over there "on the coast"?

That and I knew that an 8.1S was an inboard, plus the fact that he mentioned a huge drop from elbow to MUFFLER......... and Bravo's don't have mufflers