Hemi Exhaust Manifold Questions

[floorit426]

While I have my manifolds off, I noticed a couple of things. The heat riser flap (which I have pinned open), only opens at about 90%. It looks as if it's designed that way, but it seems strange. Secondly, there is a post, adjacent to the heat riser axis pin, that looks to have no function, yet has a groove machined into the top, for a retainer clip. I can't even imagine what would clip to it. Does anyone know, or care to speculate?

[Chryco Psycho]

The extra post is for the other end of the Bi-metallic spring  that closes the flap when cold & releases pressure as it heats up allowing the flap to open up .
I would try to get the flap 90* open or remove it from the shaft  completely as you are not using it , with the shaft in place the manifold is sealed & no one will know the plate is removed

[floorit426]

Okay, that makes sense. I must've lost the spring somewhere along the way. I'll see about getting that flap out of the way, too. Thanks!

[Chryco Psycho]

 

[Cuda_mark]

The extra post is for the other end of the Bi-metallic spring  that closes the flap when cold & releases pressure as it heats up allowing the flap to open up .
I would try to get the flap 90* open or remove it from the shaft  completely as you are not using it , with the shaft in place the manifold is sealed & no one will know the plate is removed

This is exactly what I did to mine.

[fc7cuda]

Or, you could acquire the missing pieces and allow it to function as designed.

[Chryco Psycho]

Yes you could but I don't see many 426 Hemis driven in cold weather anymore &
In the first picture with the flap closed the heat has nowhere to go as port into the tube up to the intake is blocked off !!

[floorit426]

Yeah, I saw that, too. Very good pictures, though. What would be the best way to block those heat tubes off? I was thinking maybe a couple of freeze plugs, or maybe two block off plates, at the intake manifold.

[Cudino]

Yes, a trick used by Roger Gibson on a few of my cars is cutting off the internal baffle (leaving the shaft) like mentioned above and then blocking off the manifold side of the tube internally with a freeze plug.  Externally everything looks like it's working normally, but inside nothing can go wrong.  Or you can install block off plates like one shown in FC7s picture above, and not install the one tube at all.  I think I have a couple extra block off pieces if you want 'em.

Also, not to confuse the two, but this original heat-riser mechanism actually has 2 springs.  One is a bi-metallic spring coiled up under the butterfly mechanism, which you can kind of see it in FC7's picture.  I guess your manifold still has this Bill, and you'll be able to feel the spring coiling as you rotate the butterfly.  The spring on the other side, the one you're missing that goes to the post you mentioned, is just an anti-rattle.

Either way, disabling this feature means no more driving your original Hemicuda in the snow Bill :-)

- Wade

[floorit426]

Okay, what I did was apply a little pressure, with a slot screwdriver, to the tab that bumps up against the stop. It popped over the stop and is now on the other side, stuck in 100% open mode. As for the heat tube block off, would I have to block both, or just the manifold one, as Wade said? I do want to maintain appearance, and the exhaust pipe side has the open nipple on it.

[Cudino]

I don't believe I ever blocked off that other side.  It really doesn't hurt anything because exhaust is supposed to pass through it anyway, and with the front side blocked there won't really be any flow.  So I see no harm in leaving the rear one as original.  Frankly you might as well leave the front unblocked as well.  If it was blocked off (via freeze plug) and somehow your butterfly came off that stop then (when cold) you'd have no flow at all and could cause damage.  In other words I'd only block off that port if the internal baffle was completely removed.  So if you're planning to just clamp the butterfly open I'd leave both of the intake pathways open at least as backup, that's the way the factory expected it to work.

- Wade