I've never used the copper (I'm too tight) gaskets, just the Mr Gasket composition ones. I found out one thing the hard way: The square port gaskets don't work so well with round header ports, such as the Dynomax headers. I had a leak with new square port gaskets, switched to round port Mr Gasket gaskets like what came with the headers, and no leak. The weld bead on the header that seals the header to the head is round. The gasket must match the header sealing bead. Just tighten the bolts after each of the first few cool downs and everything is hunky dory.
von '69 300 Dlx SS TC #15 ACES #1575 My '69 SS
Also have Dynomax headers on my SBC350. After much trial and tribulation, I bought NAPA stock SBC gaskets for $7 8 months ago. So far so good. Even iff they fail I can simply loosen the header bolts and drop new ones in. About a ten minute job per side. The key, I believe is to do like Von said , tighten them cold after a few hot/cold sessions and do the same once a month or so after that.
Well, the reason I'm so worried about leaks is, my left side header almost touches the frame crossmember and the header wont move away from the head without lifting the engine a little bit. I've had headers on other cars using the composition gaskets and had leaking problems from time to time, just trying to avoid a problem before it becomes one.
Where I work we get a lot of people coming in who have used copper header gaskets that leak. The only way to guarantee they won't seal is if the flange on the header has no welded bead such as the Doug Thorley or Sanderson.
If you look at a copper gasket it has a raised bead around each port, in order to be effective the bead on the gasket must match the bead on the header. That is why they really only work well on certain headers.
The only gaskets I would use are the Mr. Gasket Ultra Seals header gaskets. I would also tighten the bolts after the first heat cycle, then every couple of days until they remained tight.
ToCool-If your header almost touches something when just sitting there, engine torque and or movement may cause them to hit the frame and cause your leaks. You may have to ding the headers to provide clearance. Not an uncommon problem.
Greg, I think you just pointed out my problem. It's not the frame, but the rigidity of the exhaust pipe putting the header in a bind.
I actually have to put a floor jack under my exhaust pipe to get the rear bolt in once I've started the front bolt.
Tomorrow I'm gonna cut the pipe and put a coupling in there to ease the stress.
After putting the locking bolts on the header with the cheap Mr Gasket round gasket, my header leak is worse than before.
I think once I cut the pipe, install the coupling, and use some copper-seal on the gasket I'll be in good shape.
If I still have leaks I'm gonna go for the copper gaskets as a last resort.
I really like the Stage 8 locking header bolts. The ability to use either a hex key or wrench makes installing the header bolts much easier. But the stainless looks too good against my rusty old headers.
Ive dont use copper on my chevelles but when I used to race jet skis professionally we used to use copper head gaskets with a gasket sealer called 1211. We would run the compression on those little motors well over 200 pounds of compression. Worked great on our exhaust gaskets too.
Driver's side always had a header leak. After reading the suggestions above I decided to give it another shot.
I have the short water pump setup with the F-bracket for the alternator. The other bracket uses the front two header bolts, so I thought this might be part of the problem. I don't think it was.
First I replaced the gasket with yet another Mr. Gasket part #150 (1.5" round port). Tightened down with the Stage 8 fasteners. Leaks everywhere after about 10 minutes, even after attempting to re-torque. Black with soot were the ceramics on all four plugs as well as the plug wire boots.
I cut the tailpipe from the header with my torch (yeah, it was welded because I got sick of replacing collector gaskets). Removed header from engine. Cleaned surfaces really well and checked for distortion with straight edge. Found no distortions. Also found that the drop in of the #150 gasket failed because of some old gasket left on bottom edge of surfaces while trying to scrape gasket from headers attached to tailpipe.
Used Mr. Gasket #5902 gasket (1.63" round ports). I noticed that this gasket fits the header and the port very well. None of the port is covered by gasket as with the 1.5". Put "Mega-Copper" high temp silicone gasket on sealing surfaces of gasket. Re-installed header with Stage 8 stainless locking fasteners. Re-welded pipe to header. No leaks! This is the best this thing has sounded in years! I finally got rid of the "tick-tick-tick" of the header leak.
Now I can do a better job of tuning the engine because I'll be able to hear a ping rather than an exhaust leak.
I hope this helps someone.
Edit: BTW, this is with 6 year old Hedman shorty headers. They're still in great shape!
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