351W intake interchangeability through the years?

[Ken Blythen]

The 2-barrel intake on my 351W has some corrosion pitting around the water ports & possibly a crack; it has a casting # D9DE-9425-CB.

I have access to an earlier intake with the casting # C90E-9425-F (apparently a cast iron Mustang/Mercury Cougar intake).

Can anyone tell me if these two intakes will swap satisfactorily? I'm not worried about the early intake being non-EGR.

On RockAuto, the gaskets listed for '69 & '79 have different part numbers.

Thanks

[Ken Blythen]

Just discovered (thanks to Conanski) that the '69-'74 heads & intakes have different bolthole patterns around the cooling ports.

[Gary Lewis]

That would answer the question.  Glad you found that.

[85lebaront2]

From what I remember from the original Muscle Parts catalog, the later intake would work on the early heads (improved head for 289/302 was to use the 351 head as this was a 1969 catalog) difference was 4 more manifold bolts on the 69-74 heads, anything that covered those would work, but using an early manifold with bolt holes there would result in a massive water leak.

A thought, if everything except the extra holes fits, tap and plug the holes.

[PetesPonies]

THere were extra holes added...BUT all will still fit. Now you're in my wheel house  :)

[Ken Blythen]

Thanks for the replies.

If I did adapt this early manifold to fit, are there any downsides (other than weight).......like flow, height,  etc?

[Gary Lewis]

I wish I knew.  But it is pre-EGR I assume.  Is that an issue for you?

[Ken Blythen]

No, we have no emissions testing; I've already removed the EGR. The early intake would be slightly tidier, not having the EGR ports & a block off plate.

[Ken Blythen]

Ex-Mustang cast iron intake installed!  (It's a heavy sucker)

I drilled, tapped & plugged the extra four bolt holes as per Bill's suggestion, & it fitted perfectly using gaskets for the later heads. This will be the end of the aluminium intake's corrosion/seeping problem.

Thanks for the help!

[PetesPonies]

When installing an intake manifold, aluminum or cast iron . . . .  always wipe both surfaces and both sides of the gasket with RTV at the water ports. I used the word "wipe" because you don'r want a lot, but you want enough to make a seal. You must break the surface tension of the cleaned manifold and gasket. You put on RTV and move it around until you see that it is attaching to the surface. Then you must assemble quickly. This is easier seen that explained, but I never have leakage problems do it this way.

[Gary Lewis]

That's a good approach.  However, a lot of the problem that people have with the aluminum manifolds is not due to inadequate sealing, but electrolysis.  You have two dissimilar metals that have a liquid on them, and unless that liquid has the proper corrosion inhibitors in it electrolysis will occur at the junction of the two metals.  To put it simply, if the coolant isn't replaced frequently aluminum will be removed from the manifold and plated on the cast iron.  

[PetesPonies]

I fully understand the metallurgy happenings. But I haven't ever had one leak, down the road.. . .  meaning after lots of usage. When the two objects are bolted together, there isn't iron touching aluminum.The RTV will keep the coolant from the mating surface. You may eat holes elsewhere . .  :) but not at that junction. You get rusting at the water ports with iron and iron. The RTV will seal those pits, so no leakage can happen. Adding a thin layer is good assembly procedure IMO . . but I have seen people use too much, way too often  :) And when it is thin, you have to be careful of it skinning too quickly. Anyway, just passing this on.