Question on Head to Manifold mating surface quality on 7.4 454 Mercruiser inboards

[rothfm]

Hi,

(I usually work outboards)
Ok, no pics but I'm helping someone do a twin 7.4 454 Inboard Manifold/spacer/Elbow, Remove and Replace job. Got the old gear off no problem. Inspected the exhaust valve stems for rusting or signs of water...None apparent.

Cleaned up all the head surfaces, and while most look real good, a couple exhaust ports (that mate with the manifold) appear "not-so-flat"....Meaning some slight depressions or pitting...while this is slight, is this a concern? The gasket we are using is OEM, and shiney which indicates its they imbedded coated type. Will this seal ok? As a precaution for this, is it recommended to use something to help seal?

Also we want to put Turbulators in between the manifold and Spacer as a precaution for Resonance Reversion, and the low speed condensation intrusion issues known with big block 454's (as well as Resonators in the Tubes).....Does this metal "Turbulator" take the place of the gasket, or used in conjunction with?

Thanks for any input.

 

[Bt Doctur]

The "turbulator" is used only on the dry joint systems

 

[rothfm]

After extensive research about various means of water intrusion on aggressive Cam/valve designed Big Blocks, We called Mercruiser Support several times to discuss with several people... they support and recommend the use of both Resonators and Turbulators specific to our Serial number engines (7.4 454 inboard), which have only Wet style Manifolds available. So we have forged ahead with the planned maint job with such.

We have the gear in-hand and ready to install. Just wasnt sure of the placement with our without the normal 4 slot gasket.

 

[Scott Danforth]

I thought the number one reason for reversion in big blocks is the boat builder didnt set the riser height correctly at the factory

 

[alldodge]

After extensive research about various means of water intrusion on aggressive Cam/valve designed Big Blocks, We called Mercruiser Support several times to discuss with several people... they support and recommend the use of both Resonators and Turbulators specific to our Serial number engines (7.4 454 inboard), which have only Wet style Manifolds available. So we have forged ahead with the planned maint job with such.

We have the gear in-hand and ready to install. Just wasnt sure of the placement with our without the normal 4 slot gasket.

Don't see an issue with using turbulators with wet exhaust so long as it can flow the cooling water and stay sealed. While they can help slightly with aggressive cams the thing that must be done is increasing the height and the length of the runner before the water mixes with the exhaust

 

[rothfm]

Thanks for the input guys,

Scott D, below is a cut/paste I ended another thread with....it explains 3 means of water intrusion, with certain engines and certain installations.

Like I said im an outboard guy doing maint on Brothers new to him boat.. We knew about 454 water issues, and spent the winter researching, aducating and making calls, prior to doing the mani job.

I have a copy of a scientific write up, found on these forums about the technical details and documented aspects of this.

I can try to attach it when I get home.




Below is post from a prior thread
.....,..........................................................

I've learned a lot more about this I thought I would put it here in case it might help some others.

The documented issue pertains to big blocks in particular the 454 due to the valve overlap design....meaning an intake and exhaust valve is open at the same time for small periods.

So there are 3 areas of water ingestion concern:

1. As stated above by others- lack of riser height, and down angle piping, and the use of in-line straight mufflers.

2. Harmonic Resonance reversion- its proven and documented that some tuned exhausts develop resonance, or sound Harmonics if you will, that causes beads of water in the outgoing exhaust to flow back, thru elbows into engine. Mercruiser had vacuum breaks cast into some risers, then didnt.

In lieu of that cast vac break MC now recommends Resonators post-riser in the exhaust tube, to help stop that Resonance effect. MC has a bulletin about it.

3. Condensation at idle speeds:
More prevelant at low speeds with cool (raw water in manifolds) vs warm (coolant in manifolds) due to the wider temp difference of that cooling water and the hotter riser metal.

Condensation droplets form and drip down into elbow, an issue after "key-off" at the dock. This drip-back affect, runs down to the exhaust valve and over time corrodes it and/or gets into engine.....remember, valve overlap on these blocks means an exhaust port AND intake port can be open at the same time.

This water corrosion/rust messes with the valve seat, eventually bringing big problems.

The fix for this is "Turbulators" between Mani and Elbow. They are like a tray that catches this condensation, and it is burned off with the higher temp of the mani and blown out due to its designed vacuum affect, keeping the condensation from going down the hole. They need to be replaced periodically.


Sorry for long post, lots of research all confirmed with the MC Help line too.

We now have some other things to look at when the job happens.

Remember, the Resonance and Condensation issue can take a long time to Manifest itself....but when it gets to that point, it will be too late

I see posts where people are replacing blocks multiple times , with same results. Im not sure they are truly understanding that there are 3 seperate water intrusion issues on some engines, that need to be understood and looked into.

 

[harleyman1975]

Very interesting!

 

[rothfm]

The 454 and the 8.1 are affected, possibly others

In taking our gear apart, we did not have turbulators, but will be installing them

While I could see the valve stems and seats looked clean, a couple of the head exhaust ports looked a little flaked/rusted like they may have had more moisture than the others

Regardless, will see if Resonators are in the Tubes soon, and either change them or add them in, and get Turbulators installed. All worth it for safety-sake.

I just wasn't sure if the turbulator went alone or it mayes with the usual riser gasket. apparently the bottom portion is identical to a four slot gasket ,so itself must act as its gasket.