7.4 454 mercruiser exhaust

[Jamie 10017]

I want to install the mercruiser 496 exhaust manifolds on my 454. I have the closed cooling system on these engines and I wanted to find out if anyone on here has done this before? I need to find out how they are plumbed and so forth. Do I use the manifolds with or without the water rails? Any thoughts or ideas will help Thanks Jamie

 

[Fun Times]

Re: 7.4 454 mercruiser exhaust

Hi there, The manifolds that have the rails where the first design when the 496's came out in 2000/01 and as I recall there were/seemed to be a few issues with them though I don't recall exactly what they were.

If possible to find, try to find out what year the engine was when the manifolds were removed for resale as used. For the least amount of issues with the manifold system, your best bet would be to find a set that came off of an engine model that was from 2004 to current (09?). 03 on back was more or less trial errors from what I recall.

For some of your plumbing type questions, be sure to follow/update your threads over on offshoreonly as you are getting some decent responses over there as well. There are a few OSO members that have already done what you would like to do so they should be able to help out as well.

Good luck.

 

[HT32BSX115]

Re: 7.4 454 mercruiser exhaust

I want to install the mercruiser 496 exhaust manifolds on my 454. I have the closed cooling system on these engines and I wanted to find out if anyone on here has done this before? I need to find out how they are plumbed and so forth. Do I use the manifolds with or without the water rails? Any thoughts or ideas will help Thanks Jamie

Howdy,

I have closed cooling too. If your system is a "Full" closed system, the coolant flows through the engine and manifolds.....and there's a "block-off" gasket between the manifolds and risers.

Heat exchanger (raw-water) discharge flows from the heat exchanger directly to the risers and then overboard.

496 manifolds are DRY-JOINT type now-a-days. I would LOVE to use them because that eliminates the need for block off gaskets (that eventually leak and must be replaced)


I don't think you can directly bolt 496 exhaust manifolds on a 454 (I think they'll bolt to the heads but your shift mechanism, will not no longer fit)

Water rails? Are you talking about the tubular/header-type manifolds? If so, you won't have separate risers. you'll essentially be converting to a "half-system" where the heat exchanger raw-water discharge goes to your manifolds......up through the tubes and overboard with the exhaust.


You might need to be a little more specific about what you want

Regards,



Rick

 

[Fun Times]

Re: 7.4 454 mercruiser exhaust

Water rails?

Hey Rick, just to help give you an idea of what he's asking about, Have a look at item number 2, http://www.mercruiserparts.com/Show...UST+MANIFOLD(W/+WATER+RAIL),+ELBOW,+AND+RISER

And here they are without the rails,
http://www.mercruiserparts.com/Show...ST+MANIFOLD(W/O+WATER+RAIL),+ELBOW,+AND+RISER

Here's what one side would look like installed on an engine,
http://www.supernova19.com/11b680e00.jpg

Boatinfo - Mercruiser Service Manual nr. 30 - 1998-Up - 496 CID/8.1L Gasoline Engines

Some of the guys that have done it say the 496 manifold and risers are about 40 lbs lighter each side plus they claim the boat runs a bit quicker all around.

 

[Jamie 10017]

Re: 7.4 454 mercruiser exhaust

Fun Times ,Rick thanks for the response , My boat weights 15000 lbs so the weight savings would be a great thing , my biggest reason to change is to get the dry joint exhaust. I have heard of guys doing this change but have never actually seen a engine that has been done. I want to make sure that it can be done on a closed cooling system I realize it will be a costly changeover that is why I want to make completly sure it will work since I have 2 of them to do . The effiency improvement would be a benefit also. The boat is a inboard with velvet drives so the oil filter and shift linkage is not a issue doing this.

 

[HT32BSX115]

Re: 7.4 454 mercruiser exhaust

Hey Rick, just to help give you an idea of what he's asking about, Have a look at item number 2, http://www.mercruiserparts.com/Show...UST+MANIFOLD(W/+WATER+RAIL),+ELBOW,+AND+RISER

And here they are without the rails,
http://www.mercruiserparts.com/Show...ST+MANIFOLD(W/O+WATER+RAIL),+ELBOW,+AND+RISER

Here's what one side would look like installed on an engine,
http://www.supernova19.com/11b680e00.jpg

Boatinfo - Mercruiser Service Manual nr. 30 - 1998-Up - 496 CID/8.1L Gasoline Engines

Some of the guys that have done it say the 496 manifold and risers are about 40 lbs lighter each side plus they claim the boat runs a bit quicker all around.

Yeah,


I was thinking of the tubular steel "header" type manifolds. I have read a lot over on Offshore Only and haven't found a LOT of people who could tell me if I could directly replace my 454 manifold/riser 's with 496 dry-joints! Even though they'll supposedly bolt to a 454 head, they evidently don't just "fit"

It seems that they're either not the same "width" or height. That would make it harder to match up with an existing Y-pipe or thru-hull.

I would want to talk to someone who has actually bolted one to a 454 before I went out and bought a set.....

They're certainly "better" but if they don't directly bolt on, it might not be an easy replacement.



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