Originally Posted by larose481

Block has been decked and heads milled. Borgie, these are a factory head 781 castings. They appear to have the same coolant port configuration as an aftermarket head based on the heads I have looked at. So the port that was in question on my original post, I think I am ok. Now as far as the differences on the factory vs. aftermarket for this conversion, I think aftermarket heads do in fact run the same coolant port location as the stock Gen 4 heads but the actual port openings in the casting is smaller on the i.d. to help with any mis alignment of the coolant ports. Also, they look to have more material towards the lifter valley which might aid to this type of conversion. Now, I took the Gen V gaskets that I took off of this which still had the impression of the coolant port outlined in the gasket and then put alignment dowels in the new Gen 4 heads and layed the old gaskets on the heads. I then took a small hammer and tapped around the coolant ports to leave an impression on the gasket. I pulled the gasket off to compare the location on the two coolant ports and both of them were in the same location as far as the amount of material to be clamped on the lifter valley side which is where the issues are. Lastly, the new cometic gaskets lay right to the edge of the block and the head and the heads match or overhang slightly into the lifter valley. I am having a hard time believing that these would not seal the same as the original Gen V heads that were on there as they have the same clamping area. Not sure why some people say they do this conversion all the time and no problems and others say they have never seen it work. I personally have never done it.

Originally Posted by Borgie

Well its the internet, and you never really know if these people had proper machining performed, assembly etc... Everyone that i have spoken with, that have actually done this, have zero issues if 1. block and heads are decked 2. not rusted out like many can be in a marine environment 3. proper gasket is utilized (felpro, cometic) for this Mark 4 Gen V mismatch. And this is regarding a factory Mark 4 head on a Gen V block. The aftermarket heads on Gen V blocks seem to be a non issue entirely.

Oh and one more thing, are you going to use head studs? This will help with clamp as you know, and really is the only way to go, suoerchaged or not. After speaking with several builders here on OSO, I'm convinced that bolts are a stock engine application only hardware.

Originally Posted by Budman II

Keep in mind that studs on a 454 block will go into the coolant passages, so he will need to make sure to use the proper sealant on the threads. There are a number of "flavors" for this, with many claiming success with RTV, Right Stuff, various teflon based thread sealers, etc. I went with old school Permatex #2, the brown stuff in a tube, and is working so far. The almost universal answer I seem to hear is that the ARP thread sealant does not work well for this.