1990 Mercruiser 5.7 Water to exhaust manifold questions

[ringmaster72]

I have two water hoses going to each exhaust manifold---one to each riser and one underneath each manifold. I am planning on swapping an LT1 (like came in Mastercraft boats in the late 90s) in place of my 5.7, while using my existing manifolds. The Mastercraft LT1 just have one hose going to each manifold and in the riser they basically have hoses for steam vents,

My question is why does my current setup have hoses going to the riser as well as the manifold itself and would I be able to run a hose with the new setup to the bottom of the manifold and just run a smaller "steam hose" to the riser?

 

[alldodge]

Serial numbers are best when trying to ask a question of one system to another to verify. I would post some pics but there is still an issue with iboats and IE11

Sounds like you have the older style which supplies water to the bottom of the manifold and has a thermostat housing which would have 6 ports. The top 2 will have check balls which restrict water a bit going into the risers in order to help keep block and manifolds full.

To go to ones which do not have connections to the risers, you would need to change the thermostat housing to 4 port style. Then also check the gaskets between risers and manifold so there is two slot openings

 

[Bt Doctur]

There are no steam vents on marine motors, Per Dodge it all depends on what thermostat housing you have . Water enters the bottom of the manifold and also the riser

 

[ringmaster72]

The LT1 in the Mastercraft did have steam vents. Hoses went from the front of the cylinder heads to the manifold risers.

 

[ringmaster72]

Correct, mine is the 6 port out of the Tstat housing. I would be going to the 4 port Tstat housing on the LT1.

 

[Scott Danforth]

the LT1 motors have no advantage over a Vortec headed motor. the LT1 combustion chamber is the basis of the vortec combustion chamber. the LT1 does have a reverse cooling system which can be an issue finding marine water pumps as they are a bit more rare since the LT1 (Gen 2 SBC) was available only from 1992-1997. the perceived benefit of reversed cooling really never materialized, so 99% of the boats out there still use the Gen 1 motors

what is driving the conversion over simply finding a 96+ vortec headed motor?

 

[ringmaster72]

I am an LT1 guy. Have a 383 I was going to build for my car, but am going to put it in my boat instead. Using the Mastercraft/Indmar as a blueprint, I believe I have the cooling figured out, other than the routing to the risers. A few posts down you can see the hose form the front of the cylinder head to the riser. https://www.mastercraft.com/teamtalk/showthread.php?t=51459&page=2

 

[ringmaster72]

They just used a basic corvette style water pump, even had the GM part# on it, nothing special marine wise.

 

[ringmaster72]

Only difference is that I will not have the crank driven seawater pump, as I will be using an Alpha drive.

 

[Scott Danforth]

They just used a basic corvette style water pump, even had the GM part# on it, nothing special marine wise.

and the impeller will rust out within a year, and the rear cover within 15 months. there is a reason that marine pumps use brass impellers and a stainless rear cover

there is a reason that the LT1 marine circulating pumps are $550 and the automotive ones are only $140

 

[ringmaster72]

LT1 water pumps dont have a rear cover, it is all aluminum. I will be using a Electric Water pump insert, the impellar is made of billet Aluminum. Again, I am just trying to see what the deal is with the exhaust hose routing.

 

[Scott Danforth]

exhaust hose routing for the LT1 is very specific to the LT1 and Indmar and Ilmor engines because of the reverse cooling and the known problem of building steam and causing engine overheats. the Mastercraft forums have about a dozen threads on the specific topic and include the TSB's on the issue.

 

[Scott Danforth]

here is a start of some reading

http://www.mastercraft.com/teamtalk/showthread.php?t=31626

 

[ringmaster72]

Correct, I am aware the issues. I know about the TSB and the fix. I have the routing figured out, I am just trying to see what the purpose of my existing engine having the second hose on each manifoild going to the risers. I have done some research and see that not all Mercruiser engines ran a second hose to each manifold and that the reason is just for the "overflow" of water that is not being circulated by the engine pump.

The "fix" for the Indmar LT1 was to remove the factory steam crossover on the rear of the heads, and run it in the front cylinder heads connected to the risers.

 

[Bt Doctur]

not to start a pissin contest but dropping in the 330 hp 6.2 might be a better option small block size with BB hp

 

[ringmaster72]

I already have most everything I need to put this 383 LT1 together, and it is going to be more than 330 hp lol.

 

[Scott06]

Feed to riser is a constant flow to cool the exhaust regardless of thermostat being open. When thermostat opens it sends hot water through manifold and out riser. Lets manifold warm up to burn off any condesat inside exhaust, if current set up always flows water to manifold use non restrictor gaskets between manifold and riser and all water can come up through manifold

 

[ringmaster72]

Thank you for your help, that is what I was after.

 

[wca_tim]

I already have most everything I need to put this 383 LT1 together, and it is going to be more than 330 hp lol.

sounds like fun... have you considered just going with a heat exchanged and closed cooling? I'm also curious what you're doing for a marine ignition? lastly, what kind of cam are you running in it? ..just thinking about overlap and the old style factory exhaust...

 

[ringmaster72]

sounds like fun... have you considered just going with a heat exchanged and closed cooling? I'm also curious what you're doing for a marine ignition? lastly, what kind of cam are you running in it? ..just thinking about overlap and the old style factory exhaust...

I would like to go closed cooling, but that isnt in the budget at this time, lol. I had planned on building this motor and running the fuel injection, but my current motor let go so I am doing this sooner than I had anticipated. So, for the time being I am using a carb intake, which has the distributor hole to run my existing ignition setup (mercruiser). LT1s still have the hole for the distributor and the cam has the distributor gear. Stock LT1s have a dummy distributor shaft for the oil pump.

To answer your question regarding the ignition system for when I do go fuel injection, there are two companies that make a conversion kit to allow the LT1 to use the LS pcm and coil per cylinder. It is the 24X kits made by EFI Connections and the newest and simpler setup is made by Torqhead. I have been using the EFI connections kit in my Trans Am for several years now.

I will be running a comp cam Xtreme Marine XM276HR Hydraulic Roller Camshaft
Lift .503"/.510"
Duration 276°/282°
RPM Range 1500-5500