Exhaust Elbow Riser ?

[Meames1]

I have a 1990 Larson DC190. Originally came with a 4.3 , during my rebuild I replaced the broken V6 with a 5.7 V8. An approximate additional weight of 125lbs. I'm running through drive exhaust. The original setup did not use any exhaust riser spacers, just the elbow direct to manifold.

I've measured the exhaust height from the "no-load" water level to the top of the elbows as directed by the Mercruiser manual. The manual states a minumum of 13 inches is needed at full load, which is approximately 1,700lbs on my boat. Mine measured 13 1/2" with 4 people on board and 3/4 of a tank of fuel....best guess around 850 lbs including fuel & gear.

So, my questions.

1. Is the 13 1/2" that I measured "too close for comfort" considering I'm not at full load...or am I simply guessing by not having a full load ?
2. If the full load measurement was right at the 13" minimum would I still risk water backing into the engine when larger guys such as myself are climbing up the ladder, or am I over-thinking this?
3. If I were to add 3" extension blocks (I have room under my engine cover) , but I do not have the extended length connectors, would it be OK to simply get 3" longer 4" rubber bellows ?
4. I may just add the extensions for piece of mind....but again, am I over thinking ?

Thanks in advance for the advice.

As a sidebar:
As this may come up. My original to the boat capacity decal stated 12 persons or 1,865 lbs. I had a new decal made stating 10 persons or 1700 lbs due to the added weight of the 5.7. I realize this isn't scientific, but that's where I came up with the 1,700 lb capacity.

 

[Scott06]

Don’t think you are over thinking it given those measurements. My sea ray 200 with a 4.3 had no riser, with a 5.0 used a riser.

Id add a riser and some have use exhaust hose to stretch the down elbow in similar cases

i wouldn't worry about changing the capacity decal. Factory would use the same load rating with v6 and v8 power

 

[Paintman1960]

^This !

 

[tpenfield]

I am glad you asked this question, having just gone through the riser extension process myself on my 7.4L engines. I added an extended swim platform (2 years ago) and was concerned about the added weight that could be at the stern.

I measured the riser height on my boat with no load and came up with 15 inches. Based on some observations with a normal load of people, I figured that my boat sits about 4" lower in the water with a 'full' load. So the riser height would be only 11 inches with full load vs. the spec. of 13 inches.

I was 2" UNDER spec and used the boat for 2 years with no issues. But . . . this year, and in honor of Murphy's Law, I added the extension blocks bring my no-load measurement up to 18 inches and the full load measurement to 14 inches.

If you are at 13-1/2" with a partial load, you will probably be a smidge under the 13" spec with a full load. . . maybe 12-1/2". It is a judgment call on your part as to adding the extension blocks. Keep in mind that the spec is designed to provide enough height for a certain/reasonable range of conditions.

If it is a matter for sleeping well at night, go ahead and add the riser extension blocks and you will be about 2" above the spec.

As for the 'down elbows' needing to mate to the y-pipe, that is where I had troubles. I believe the 5.7 and 7.4 use similar/same sized exhaust. There are special down elbows that you can buy that have the extra 3" of extension, but they are about $400/pair. If you go with just some exhaust hose to couple the existing down elbows to the Y-pipe, take very careful measurements of the down elbow and y-pipe circumferences (not diameter), since they are oval shaped.

I found that the down elbow and Y-pipe openings needed a 3-3/4" flexible wet exhaust hose, which is an odd size. The more common sizes are 4" and 3-1/2", but neither fit properly. I also made the mistake of installing the extension and riser elbows first, which made the installation of the down elbows and exhaust tube nearly impossible.

If you add the extensions, do all the necessary measurements and get all the parts first, then rebuild the exhaust starting at the Y-Pipe on up to the riser elbow and then onto the extension block. Make sure to use the OEM style gaskets.

 

[Meames1]

Thanks for the replies. Ordered a Barr replacement 3" riser kit today. Luckily my rubber connectors are 4" on both ends, I ordered a sierra marine 4" hose 24" long. I will make a bracket to mount the shift bracket in the stock-ish location.
Piece of mind.

 

[Scott06]

Thanks for the replies. Ordered a Barr replacement 3" riser kit today. Luckily my rubber connectors are 4" on both ends, I ordered a sierra marine 4" hose 24" long. I will make a bracket to mount the shift bracket in the stock-ish location.
Piece of mind.

The shift bracket should move up on the riser just fine no need fir a bracket

 

[Meames1]

The shift bracket should move up on the riser just fine no need fir a bracket

I have a rear header that the shifter cable is 1" from now. I have plenty of room to raise the elbows, but the not the cable. Easy fix though. Thanks

 

[tpenfield]

Thanks for the replies. Ordered a Barr replacement 3" riser kit today. Luckily my rubber connectors are 4" on both ends, I ordered a sierra marine 4" hose 24" long. I will make a bracket to mount the shift bracket in the stock-ish location.
Piece of mind.

Did you measure the circumference of the Y-pipe and the oval end of the down elbow?

 

[Meames1]

Did you measure the circumference of the Y-pipe and the oval end of the down elbow?

Sorry, I missed your question until now.
I did not yet measure the Y-pipe. However, I did replace one hose when installing the V8 as one I had was cut. I ordered and installed a 4" hose and it fit perfect, just like the original on the opposite side.
I've ordered and received a 24" long Shields 4" soft-wall exhaust hose. I also received my Barr extension kit...nice quality.
For piece of mind, I'll double check the Y-pipe measurement before tearing it all apart. Thanks for the heads up.