After reading a number of posts about which gasket to use it seems that some guys have good luck using copper r.t.v. and nothing else.It also seems as though they are running heders and not logs. My concern was that the scrubbing of the stainless flange against the aluminum head would gouge up the head after a while and cause more problems. A log is going to expand and contract more than a header flange due to the body of the log growing with the heat. Has anyone ever tried using the cheap factory replacement gaskets in pairs? You know, the ones with stainless on one side,and soft gasket material on the other.I thought if you used r.t.v. or spray Permatex copper on the soft side and stuck it to the head,and stuck the soft side of the other to the log, then put antisieze between the stainless sides it might work. The harder stainless sides could slide against each other to allow movement without harming the heads sealing surface. The flange is split between the end ports and the center pair.I know the manifold grows quite a bit as it had tweaked the studs outward on the center pair of ports even with 9/16" holes around a 3/8' stud.Any thoughts?

I never trusted Permatex to survive 1600+ degree heat. All kinds of gaskets from cheapies to soft copper were used on the hot rod but they always leaked. I never split the flange on these like I did on my last headers.
Spliiting the old header flanges made it harder to install the headers due to the flex and they still leaked.

I think the root of the problem I had was the gaskets. I used the embossed copper,I think Mr. Gasket,and the port shape didn't align perfectly with the "bead" on the gasket.

We have 1/2" flanges that were milled flat, no gaskets, only RTV. I think they might work even without RTV, but anyway, we have experienced no leaks.

My flanges are 1/2" cold rolled steel.

Jyrki, did you cut your flanges between the ports?

I've had good results with RTV only with headers in a NA application. I understand the concern about growing but the RTV will shear and let the parts slide if there is a lot of force... its a lot better than direct metal to metal which might lock the parts up. Since the head is water cooled, temps at the flange surface shouldn't be too extreme despite the high exhaust temps. I'd use the RTV.

I'm assuming you are talking about a big block with the 3/8 exhaust bolt reference. I found these on Summit's website
.http://www.summitracing.com/parts/CGT-C5902-030/
They are MLS exhaust gaskets and that's what Cummins uses on their 5.9 and 6.7 diesels. They seem to hold up very well on those applications, even to the point of the manifolds cracking and falling apart, yet the flanges usually continue to seal up unless the bolts are broken.
I'd give them a try. In fact, I think I'm going to on my 440 with headers. Cheap gaskets included with the headers keep leaking worse and worse.

We have a common flange.

Some are blowing-out soft copper ... and then others having good luck with RTV ......

If you have a 0.001" gap between two particles it's way harder to blow through it than with a .040" gap. And if it really does happen, the .040" gap leaks significantly more than a .001" gap.

www.remflex.com

they are good to 3000 F

I'm a pipefitter by trade and the graphite used in these automotive gaskets is what we use for high heat / high pressure applications without failure.

Well, since it's $30-$40 cheaper,I'm going to try the no gasket route first.I'll probably still try some of the copper spray coat on it too. The offending manifold is at my local machine shop now,and he is going to run it across the head surfacer(giant beltsander)for me to insure a flat surface. We'll see how it goes. Thanks for all the ideas/suggestions.

IF it is TRULY flat .. there should not be a problem. Some are saying and comparing manifolds that are 001 ...and 040 "out-of-wack".

USING a gasket that will "insulate" the manifold from the head can be a major bummer SINCE the heat from the manifold(especially the flange area) ... bleeds-off TO the head.

Machine the flange and use high temp RTV. I hae never had a leak that way but the flange needs to be straight. What most people forget about a turbo application is the fact that there is alot of back pressure in the manifold compared to a N/A app. When I ran my old motor I had 26 psi of back pressure for about 14 psi boost. With the thin layer of RTV and a straight flange the pressure has no gasket or weak area to push out. It just seals.

It's all back together ,machined flat,cleaned both surfaces with brake clean,coated the manifold with copper spray. And the ace-in-the-hole, I added 2 5/16"X24 studs between the center ports on the top and bottom of the flange.(does best Homer Simpson "There,take that.")