Header clearance

[derekf]

LSx conversion in my 69 El Camino, with homebrew engine mounts to put the engine as far back and down as I can.

Bought a set of 98-02 F-body headers (Hedman 68534). Driver's side fits well enough, but on the passenger side the headers come too far out from the engine and hit the frame near the rear LCA mount. The "hit" is very close; I'm still able to bolt them up to the engine completely but there is definitely contact there (sorry, I've taken a dozen pictures and in none of them can you see what I'm talking about)

I'd figured I'd cut and reweld the tubes to give just a little more clearance. I know that there's a limit on how close to the engine they can go, lest I get heat issues with the starter, so I don't want to adjust them too much... but how much clearance do I need between the headers and the frame with stock rubber mounts?

Does the question even make sense or do I need to go try more pics?

[derekf]

Pictures always help, except when they don't.

Here you can see where the headers just barely kiss the frame (circled)
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So my thought was to cut almost all the way through all the way across (similar to the line here) and flex the headers in just a little... but I need to know how far.
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[IMPALA MAN]

You might try moving the tubes farther into the flanges. I can't tell how much you need to move the tubes but it doesn't look like you need much. Before you start cutting, see how much you can move the tubes in without causing spark plug wire interference. If you have enough room, here is how you do it.
1. Remove the welds holding in the tubes. You will have to do all four tubes. These welds may be inside the tube. In your case it may be easier to just cut he tubes where the tubes go into the flange.

2. Clean out the port so you can slide the tubes into the flange.

3. Slide the tubes in and tack weld the to the flange to hold them into location. You can do this on the outside of the flange so you can test fit the header befor doing the complete weld job.

4. Expand the tubes to fit nicely in the ports. They may fit perfectly without any expansion.

5. Weld the tubes in on the cylinder head side of the flange.

6. Surface the cylinder head side of the flange. The closer you can get the gasket surface to be smooth like the gasket surface of an exhaust manifold, the less header leak issues you will have. A gasket between two FLAT surfaces always seals best. Do you ever have to retighten head bolts, water pump bolts, exhaust manifold bolts? The reason being is that both have flat surfaces.

[derekf]

That's actually a really good idea, better than my initial plan, thank you.

I come back to the same question though -- how much clearance do I really need between the headers and the frame?

[IMPALA MAN]

5/8" will usually do it. You want to make sure you have enough room that if (no when) the engine torques, ad the tubes move as the engie moves, no contact is made. Regarding heat, if you want to get them ceramic coated, it wouldn't hurt. Aside from that, 1.00" should give you enough gap that even the heat won't be an issue. Worst case you just heat up the frame, now Ida fuel or oil line is close to it......different story.


Best of luck.