Riser Extension Blocks - Full Closed Cooling ???

[tpenfield]

Greetings,

I have been wanting to add 3" riser extension blocks to my Mercruiser 7.4L engines exhaust, because the current setup is slightly below spec (1-2" low). Since I added an extended swim platform, the odds of sinking the stern lower with people is greater than before.

Anyway - the engines are full closed cooling - so coolant goes from the engine block out to the exhaust manifolds and back to the H.E. Currently, the setup is what you would call 'standard' with the elbows directly on top of the exhaust manifold - no riser block - and the block-off gasket is between the manifold and the elbow.

In my search for extension blocks, I have come across a few types in the 93320A part number series, which I assume is the right extension blocks for the manifolds (center rise type)

However, and my question is . . . there are 2 types of extension blocks that I have found . . .

Straight riser blocks
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Which would NOT be a good choice for the closed cooling setup - IMO.

Then there are these . . .
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Which have small channels molded in between the 4 coolant ducts surrounding the exhaust duct. My thinking is that this will allow greater flow from around the extension block.
.

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My plan for adding the extension block is diagrammed below . . .


I want the extension block to be part of the 'coolant' flow through the exhaust manifold, leaving just the elbow to have raw water (salt water in my case), as it is now.

I have seen part numbers of 93320A03, 93320A13 and a few other variants. The websites seem to use these numbers interchangeably, but my application would dictate a specific type.

My questions are:

1) Is my assumption correct that the extension block with the 'channels' are the correct ones for my application? or is there yet a third style of extension block to use with full closed cooling?

2) What would be the correct part number for the 2 styles of extension block? 'A03'or 'A13' ? or something else?

TIA for any guidance on this before I go buying parts . . .

 

[Lou C]

What about the gaskets for the ones with the 4 channels connecting the larger water ports? I'm thinking they might be more prone to leak which is always a concern with wet exhaust joints.

 

[alldodge]

I would use the first type riser (old style) because the newer style may create a slight restriction. Any change in flow may cause the need to change other things

Agree with flow diagram to make the riser part of the closed system

 

[tpenfield]

My take is the straight riser (first one shown) will only flow through 1 of the 4 channels. The other 3 channels have no way of passing water to the outlet fitting on the side of the riser block since there will be the block-of gasket at the top of the riser. Shown in red on my last picture.

Unless there is some internal passageways connecting the 4 channels within the riser block, which I sort of doubt.

I just don't want to buy the 4 riser blocks needed and have a mess on my hands. I'm thinking the flow will look like this with the solid block (first) riser . . .

 

[alldodge]

Your right and looking at Merc manual 16, 23 and 37 (dry joint) the riser should be part of the raw water cooled side. Only the mans should be part of the closed cool

Edit: but I would still stick with the old style unless someone can show how the new would work better

 

[tpenfield]

You're right and looking at Merc manual 16, 23 and 37 (dry joint) the riser should be part of the raw water cooled side. Only the mans should be part of the closed cool

I was thinking that, but still water would only go in the one channel and then up to the elbow.

Ideally, I'd like the riser block to be part of the closed side, since the elbow is stainless steel. If I can't get the riser blocks with the ducts connecting the channels, then I probably would do a little machining on the straight blocks to make them that way . . .

 

[alldodge]

Thinking out loud
Using any kind of restriction to the closed side on the mans may increase the heat. The circulation pump has next to no pressure, so any restriction may cause the mans to get hotter.

This is why I first thought about not restricting the riser.
Also wouldn't want to restrict the raw side because you want as much water flow as you can get most times

 

[tpenfield]

I'm thinking that I'll be buying a 3/16" end mill bit . . .

 

[tpenfield]

I’m going to try to get the second kind that allows flow between the channels and see if I can router the ducts between the channels to be a little deeper than they are originally.

To your point, AD I want to have the most flow through these parts.

 

[Scott Danforth]

most of your restriction will come from your fittings.

either riser will be OK

could just get the taller 8.1 liter stainless elbows and be done with it.

few sets on fleabay

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[tpenfield]

Hi Scott, How much taller are the 8.1 elbows? I'm thinking I need about 3" of additional 'rise' to put things above spec.

 

[Scott Danforth]

from memory about 2.5" However that was me playing with them at Marine Surplus a few years back before I even build the motor I did.

I am sure google will have an answer. let me see if I can find it.

 

[Scott Danforth]

Ted, check this out

How to Measure Riser height for 8.1L 496

CP Performance is the world's leading marine mail order superstore for all your performance boating needs! We carry the finest selection of Performance Marine Parts, as well as a large library of technical information to help you get your boat working in the finest order!

www.cpperformance.com

 

[tpenfield]

You're right and looking at Merc manual 16, 23 and 37 (dry joint) the riser should be part of the raw water cooled side. Only the mans should be part of the closed cool

Edit: but I would still stick with the old style unless someone can show how the new would work better

I found the information in my Merc manual (#16).



It does show that the riser would be part of the sea water flow, but . . .

I'm thinking it would be better to separate the iron (riser) and the stainless steel (elbow) for longevity. So, I probably will go with the 'second' style riser that I showed and put the block-off plate between riser and elbow.

 

[tpenfield]

Ted, check this out

How to Measure Riser height for 8.1L 496

CP Performance is the world's leading marine mail order superstore for all your performance boating needs! We carry the finest selection of Performance Marine Parts, as well as a large library of technical information to help you get your boat working in the finest order!

www.cpperformance.com

Thanks for the info, Scott. It looks like those are dry-joint style, but my manifolds are old school wet-joint.

 

[tpenfield]

I'd prefer to do something like this, but I'll be taking a look at the boat first to make sure about all of the bits and pieces.



On thing I am realizing is that the shift linkage and electrical box may have to mount to the riser instead of the elbow ???

Not sure if they will raise the 3" with the elbows, or if I need to consider mounting them to the riser ??? I suppose they could remain attached to the elbows if the lower shift cable (starboard side) and the MEFI wiring harness (port side) have enough slack.

I noticed that plain/straight style of risers is not tapped for mounting studs, whereas the 'free flow' style seems to have locations for mounting studs on the sides.

 

[tpenfield]

After some search, I have found only a couple of parts like the one I prefer that look like this. . .



an HGE 3320-APR which is an aluminum part - not my first choice, and XME 43320 which is in short supply.

I'll see what I can get . . .

 

[Greg_E]

As long as you can get sufficient coolant flow through the 3" riser, it should work.
I have the dry joint exhaust and have it configured similarly to your first diagram. In the Dry Joint Manual refer to the closed cooled warm riser diagram in the back. The riser is positioned with the outlet at the top same as you have shown. The gaskets are positioned as you have shown. The manifold coolant outlet hose barb is removed and placed in the spacer outlet port and the manifold plugged. I had to get a longer hose for the repositioned outlet.
Your method looks like a much less expensive way to go and looks like it will achieve the same result. The dry joint system is quite a bit more than the older style. One possible downside may be the gaskets used. The dry joint gaskets are SS with silicone bonded gaskets on the water ports. I'm not familiar with your system or what is available for it. Good luck. Let us know how it works out.

 

[tpenfield]

I've ordered parts, so I'll see what arrives. I plan on digging into the exhaust over the next couple of weeks. . . adding the extension blocks, new flappers, etc.

 

[tpenfield]

The parts have arrived . . . Looks good. Here they are, showing both top and bottom surfaces.



One nice surprise is that the extension blocks have openings between the 4 main ducts as evidenced by the twist ties I inserted through one of the passageways. So . . . these extension blocks should support plenty of flow for the closed cooling side.

I'm not sure why there is the small surface channels between the main coolant ducts, given that there are already 4 passageways molded in.

Anyway, I'll be tearing down the exhaust this weekend to install new flappers and these extension blocks.

I got a set of full open gaskets for the manifold/extension block joints, and I have some full separator gaskets (somewhere) leftover from previous work.