They say it is 3/8 but I'm not sure about the primary tube thickness, as for separating the flange, I think I could cut it after building the header?

http://www.summitracing.com/parts/HOK-11654HKR/

Things I learned:
never use any gaskets
logs make power, but wont last
never use any gaskets
use thick flanges, machine them straight when done
never use any gaskets
use heavy wall stainless
never use any gaskets
add as many fastening points as possible
never use any gaskets
use a backing gas when welding tubes
never use any gaskets
Decide if you want to do it once and spend big cash, or repair leaks and cracks every two weeks.
never use any gaskets

another

one more

TRENDZ: what material did you use? I m seriously thinking about a set of cast manifolds as mine is going into a truck with a plate so they might work just not sure how well they would hold up and stay sealed.

I made those out of 321 stainless.
If you end up using manifolds, open up the hole diameter on the end ports for the bolts(front and rear). Also use much longer bolts or studs. Add at least an inch longer fasteners, and make spacers to make up the differance in length. This allows for some stretch in the bolt,and prevents breakage. Manifolds or logs have to float on the head surface. The shape of them wont allow for thermal expansion without movement. This is another reason not to use gaskets... You'll just scrub the gaskets away, and warp the manifold/log.I also strongly suggest using grade 5 bolts or lower, and never use stainless bolts with stainless nuts. Tighten the center bolts as you normally would, and just snug up the bolts on the outer ports.

I've had no problems using copper gaskets yet....

Ours are mild steel,made out of a regular Hedman header kit. Except the flanges, they are self made out of 1/2" flat and common flange, milled flat after welding. No Gaskets, just RTV, no problems whatsoever. My plan was to keep the primaries smallish and short and since the turbos have devided flange it required some routing to keep the pulses as far of each other as possible. After ready they were ceramic coated, and they are supported to teh frame from the flanges. Don't have very good pics, but here is a couple:

These OEM manifolds fit upside down in the car and allow spark plugs

The 62-65 B body logs that exit out the complete rear also can fit depending on what car and if you have manual steering. They don't fit in my Fury but they do fit in my 69 Coronet.

In a cbody with ps and a/c there's still issues however....

Furious, are those truck manifolds? I'd sure hate to hang a turbo off one of them and hope the two bolt flange holds it together.

My best guess is they came on 1 side of van chassis RV's. Not sure how/if they will work yet and how the turbos will mount. There is technically just enough room for them to sit up there, but even with milling the flange down and making an adapter, it's probably going to bump or cook the hood.

I thought the general agreement on those is that they curl in too much when upside down and put the turbo into the valve cover? I suppose it depends on how big of a unit, if it has an internal WG, etc.

If you could get a set of cast iron manifolds that would fit right and work how well do you think they would hold up? Also would you have them milled to use a v band for the piping to the turbo? DO think they would stay sealed with RTV?

Thanks

It's always been my findings that headers, whether tubular or log style, generally only break due to poor fabrication or welding process.

If you use stainless steel weld-els (schedule 10 is PLENTY) such as the ones posted from grainger, or www.acestainless.com, you can cobble something together without having it break quite easily.

And a tubular header will for certain have more power potential than a log manifold on a turbo engine in the end, regardless of cylinder count.