Manifolds Aluminum or Iron

[RomanRegal]

Hi, I will be replacing my exhaust manifolds this coming Spring. Is there any advantage or disadvantage to aluminum vs iron. <br />1987 Mercruiser 350 s/b 260 HP.<br />Thanks Roman

 

[tfjrc2]

Re: Manifolds Aluminum or Iron

I've heard it is harder on the gaskets when / if dissimilar metals are used.<br />They simply cool at a different rate, which causes stress.<br />Others will comment, and will probably have more experience and technical knowledge, but for my 2 cents, if the block is iron, go with iron exhaust manifolds.

 

[trog100]

Re: Manifolds Aluminum or Iron

i think cast iron is used cos its a cheap method that works well enough.. there are better materials but the extra cost vrs benefit dosnt always work out well..<br /><br />overall i would think (except for weight saving in some special cases) u might as well stick with cast iron..<br /><br />trog100

 

[f_inscreenname]

Re: Manifolds Aluminum or Iron

Cast iron = readily available and cheep. Aluminum = light weight, smaller in size, little better exhaust flow, harder to find and cost big bucks

 

[fireship1]

Re: Manifolds Aluminum or Iron

Hello, Jim is correct. If you mate dissimilar metals together you might have problems down the road with leaks. As the cast iron of the head and the aluminum of the manifold expand and contract it tends to "scrub" the gasket in-between both parts. It will eventually cause gasket failures. Auto manufactures sometimes equip their dissimilar metal mating parts with graphite type gaskets. It lubricates the moving parts and prolongs the seal. I have seen this happen on cars and trucks as well as boats. You either wind up with a vacuum leak or an exhaust leak depending on what side of the head we're talking about. My vote would be to stick with the similar metal. Stick with the cast iron.

 

[Kiekhaeferscurse]

Re: Manifolds Aluminum or Iron

Could always install the aluminum heads that solves the dissimilar metal problem.......course if your married you might have a divorce on your hands when she see's the bill.

 

[trog100]

Re: Manifolds Aluminum or Iron

"Could always install the aluminum heads that solves the dissimilar metal problem.......course if your married you might have a divorce on your hands when she see's the bill."<br /><br />except it would create another "dissimilar metal" situation tween head and cylinder block.. he he<br /><br />when u bear in mind that most cars come with aluminum heads mated to cast iron blocks and are subjected to far more (short trip) hot/cold cycles than a boat engine ever is.. i dont think the "scrubbing" problem is real one..<br /><br />how about going the whole hog and having some bronze ones made.. whoops..<br /><br />only joking..<br /><br />trog100

 

[Buttanic]

Re: Manifolds Aluminum or Iron

I am also considering aluminum exhaust manifolds on a closed cooled engine.<br />Advantages<br />considerable weight saving<br />better heat transfer<br />Disadvantage<br />higher cost<br /><br />I believe the gasket problem can be solved by using the soft copper gaskets available from speed shops.<br /><br />Buttanic

 

[newport dave]

Re: Manifolds Aluminum or Iron

I think that the gasket seal at the manifold/riser joint is more critical than the head/manifold, and should be given some consideration. It does not say that the risers are to be replaced as well as the manifolds, but I would assume that they are. <br /><br />If you decide to go with the aluminum manifolds, will the risers be replaced with aluminum as well? Or will the risers be stainless? <br /><br />Are the manifolds raw or fresh water cooled?<br /><br />As mentioned, there is the issue of dissimilar metals cooling/heating at different rates to stress the gaskets, but there is also temperature variances to be considered. To be specific, a fresh water cooled manifold will be 30 or more degrees hotter than raw water cooled riser bolted to it.<br /><br />I believe that this may be why Merc only offers the "Dry-Joint" exhaust sytem with raw water cooled manifolds. They use an aluminum manifold and a riser of a dissimilar metal (stainless steel). To add the additional stress of having the two metals at different temperatures could create problems.<br /><br />Dave

 

[Chris1956]

Re: Manifolds Aluminum or Iron

Roman, Your post indicates you are from Wisconsin. If you boat in fresh water, the cast iron manifolds and risers will last a very long time (~20yrs). Why bother with the higher price of aluminum?<br /><br />In addition, a marine surveyer (David Pascoe??)wrote a paper on why it is a bad idea to make manifolds and risers out of aluminum. I do not remember the details, but is is likely available on the web.

 

[KaGee]

Re: Manifolds Aluminum or Iron

I would tend to think that if this was a good idea, that you would see them being made more readily available. <br /><br />Now you do see some Stainless Steel out there... they may cost as much as Aluminum, I don't know.

 

[yoced]

Re: Manifolds Aluminum or Iron

Most folks who are thinking of the aluminum manifolds and risers are looking at the Chinese parts from GLM (and others).<br /><br />Quick question: why do you think it is that these folks will warrant the iron parts for three years but the aluminum for only one year?

 

[rwidman]

Re: Manifolds Aluminum or Iron

Then there's the stainless steel manifolds and risers that were featured on Shipshape TV a while back.<br /><br />

 

[Kiekhaeferscurse]

Re: Manifolds Aluminum or Iron

I dont even have an I/O anymore and I cant stop drooling looking at those manifolds, interesting exit to the riser!

 

[KaGee]

Re: Manifolds Aluminum or Iron

The drool will cease once you see the MSRP!<br />You'll need a 2nd mortgage for sure. I couldn't believe how expensive.

 

[Kiekhaeferscurse]

Re: Manifolds Aluminum or Iron

Now I remember why I took the I/O out and hung that OB on the back...money money money