Ram750

Hey Guys ,

I am dropping an LS motor in my boat were there use to be a BBC with fancy headers , being a broke is the main reason for this swap .... and the main reason why I need help to figure out if I can do what I want to do ! Basically the headers would go up and pretty much parrallel to the sunpad out to the back. I am tempted to buy the marine power manifolds but not to sure how I can use the same exits in the hull since the Marine power risers curved down alot. Please check out below and let me know what you think.

How much angle "downwards" do you need in order not to suck back up water in the combustion chambers ? Not bringing up reversion because I am using the stock LQ4 cam and most say the specs are not problematic for reversion. Can I get away with machining myself a spacer wedge or something like I drew up below ? Would also give me space for provision for an 02 sensor



Engine bay with BBC

minx163

You don't need any down angle on the risers .You should also be able to buy risers with different angles. Make sure you install a windage tray on the main or baffle in the oil pan .

phragle

iTrader: (3)

Have you taken the width into account too??

SB

iTrader: (1)

I have this in my notes that Merc has said on black motors:
for first 18"

Ram750

Thanks for the info, so I guess the light drop is to prevent puddling if you will and drain back into the manifold while engine is shut off for example... The side to side spacing I can deal with having the flex rubber hose to go from riser to diverter to exhaust tips..

About the windage tray, the truck motors already have them.. But il check how baffled the pan is

Zone 5

To tie into SB's response, Mercruiser also calls for the top of the exhaust elbow should be a minimum of 13" above the water line.

2nd that the minimum downward slope should be 6 degrees. This is the overall drop from the risers to the tips. My Merc Bravo instalation guide gives me numbers on top of the 6 degree drop saying the following:

I have always used the 6 degrees and 13" with no issues.

BUP

iTrader: (9)

To set the record straight - Mercruiser currently for the V-8 small blocks and the V - 6 the risers have a 14 degree downward angle. This is from 2002 / 2003 to the current year of producing NON CAT engines using Mercruiser dry joint exhaust - manifold and riser - again non catalyst apps (dry joint exhaust) . Of course everything in this range is all CAT and all MPI currently for the past 5 going on 6 years and coming up on 8 for California. .

Mercruiser BEFORE the dry joint exhaust manifold & riser - the riser was a 7 degree downward angle. This was for all 4 inch exhaust risers ( 4 inch exhaust hose riser). Before that Mercuiser had 3 inch risers (3 inch exhaust hose riser) that riser had a 15 degree downward angle. FYI

The dry joint exhaust riser is taller than the non dry joint exhaust. If you need to raise your waterline depth - you can always add riser height by installing riser extension blocks.

(The riser extension height blocks might help you (maybe) to line up your existing transom holes ???. You would have to do all the measurements beforehand ).

the Marine power exhaust manifold and riser for the 6.0 / 6.2 LS engines ( the riser ) has the correct downward degree angle to be used. Do not lesson the degree of that angle PERIOD. With that said you still can add riser height if needed to maintain the bare min of 13 inches or more waterline height and possible somehow make your existing transom exhaust holes work and hopefully still be able to close the engine hatch. Not sure about all that ???

The width really is not the problem as you could fab up some turn outs after the risers or even a S pipe incorporated turned slightly sideways or more into the mix plus using the correct exhaust water hose and hose clamps to mount all that up.

SB

iTrader: (1)

Good info Bup / Zone.
I believe my info cam from the 8.1's. Each time I saw newer merc drop specs, I'd save that.

To the OP, within reason, more drop is always better. Gravity vs water.

On the more extreme side and why many very high performance Eliminator's can reuse their Eliminator stock factory outlet dimensions is because of how much drop they use. Here is one pic:

Ram750

Thanks for all the great information ,

Let me push the question a little further , I plan on buying a PCM marine manifold like I mentionned but because of the important amount of "down" angle I need to give them to prevent water fighting it's way back into the manifold I have considered making a Riser. Could I keep the riser dry till further back to the transom and get away with less angle ?

Sorry it's in MS paint but like this I drew up at lunch ?

cliff_m_b

The answer to you question, as for as running "dry" you will need to have water to cool the pipe but you can have exit at the end of the pipe along with the exhaust